GB2158478A - A cavity closer and cavity wall construction - Google Patents

Abstract

An extruded plastics cavity closer, for use at the ends of cavity walls, adjacent to an opening for a door or window frame, comprises a strip of water-resistant, moisture- impermeable material, the strip locating on the jamb 16, head or sill of the door or window frame, and having a part which bridges the cavity and provides a hollow structure which when substantially filled with mortar provides a mortar fire barrier which closes substantially the full width of the otherwise open end of the cavity. In one form of the invention, the cavity closer has an outer frame- engaging part which is adapted to fit between an end of the wall and the door or window frame member, and an inner part extending to one side of the outer part but offset from it so as to provide a reveal for the mortar fire barrier. <IMAGE>

Description

SPECIFICATION A cavity closer and cavity wall construction The present invention is concerned with a cavity closer for use in a cavity wall of a building, adjacent to an opening for a door or window frame. Traditionally, the cavity was closed at the end of the wall forming a vertical edge, to a door or window opening by bricks placed across the end of the wall. More recently, special cavity closers have been produced which can be fitted across the end of a cavity at an opening in the wall. In the specifications of United Kingdom Patents Nos: 1 302 694, 1 302 695 and 1 302 696 there are described various forms of cavity closer which perform the functions of closing the end of the cavity, providing a damp-proof course between the two leaves of the wall, providing a damp-proof course between the wall and the window or door frame, and tying the two leaves of the wall together.The ways in which all these functions are performed are fully described in the three patent specifications mentioned above. Since the invention of this type of cavity closer in 1969, there have been various developments in the construction and manner of using such cavity closers.

The present invention provides a cavity closer which is capable of performing at least some of the functions set out above, and which in particular, is capable of meeting stringent fine precautions. More particularly, the invention provides a cavity closer, which in use ensures that there is a minimum thickness of mortar (which throughout this specification is used in a broad sense to cover any mortar-like substance, and including plaster) across the end of the cavity itself. Besides providing a cavity closer, the invention also includes a structural assembly incorporating a cavity closer, and methods of fitting a door or window frame into a cavity wall. The structural assemblies and methods in accordance with the other aspects of this invention, are also intended to provide constructions which will satisfy fire precaution regulations.

Whilst a cavity closer in accordance with the invention is intended to be used with a cavity wall, i.e. a wall with inner and outer leaves, with a space between them, it is to be understood that the two leaves of the wall may themselves by made of any suitable material. Thus, the leaves may both be made of bricks or blocks, or the inner leaf may be a timber frame construction. Further, the invention may be employed in situations where the "cavity" is in fact filled with insulation material.

According to one aspect of this invention, a cavity closer and damp-proof element for use in a cavity wall between the wall and the head, jamb or sill member of a door or window frame or subframe, comprises a strip of water-resistant moisture-impermeable material, the strip having an outer frame-engaging part adapted to fit between an end of the wall and the door or window member and an inner part extending to one side of the outer part and being offset with respect to the outer part to provide a reveal for a mortar or like coat and at least one tie adapted to fit in the reveal of the strip and having securing interengagement with the strip, the tie also having a part which projects from the reveal of the strip for engagement with or in a leaf of the cavity wall.

Preferably, both the outer and inner parts of the strip are substantially flat and parallel with each other, there being a step joining them to provide the reveal on the inner part and the end of the reveal opposite to the step is open, the tie projecting through this open end of the reveal when in position on the strip.

It is further preferred that an undercut recess is formed in the outer part, open in the rear face, that is the face which is intended to face the end of the wall, the undercut recess extending throughout the length of the strip, so that it provides anchorage for wall ties or mortar at any position along the length of the strip. Preferably, the outer part is of substantially constant thickness, so that it has a portion projecting from the front face which faces towards the window or door member, in use, to accommodate the undercut recess, and it is further preferred to provide a lip on one or both longitudinal edges of the outer part, projecting from the front face, this lip or lips projecting by the same distance as the recess projection.

According to another preferred feature of the invention, an undercut recess is formed in the inner part of the strip to receive a key formed on the tie. Where undercut recesses are used, it is preferred that they are of dovetail crosssection and that the formation of the tie which engages in such a recess is correspondingly dovetail shaped. The formation on the tie can be fitted into one end of the strip and the tie slid along the strip to the required location, or the formation on the tie can be fitted into the recess by turning or tilting the tie relatively to the strip, until the formation can be pushed through the open side of the recess and then turning the tie to its working orientation, so that the formation interengages with the recess.

It is further preferred that the tie has one or more perforations so that mortar can extend through the tie. Preferably there is a series of perforations with at least one in the part of the tie which fits in the reveal of the strip.

This preferred feature assists in keying the mortar or the like in the reveal and in the case of the perforation(s) through the part of the tie which engages in the leaf of the wall, it also assists in keying the tie in that leaf.

The tie may be straight, or it can be formed with an angled portion adapted to engage between courses of the inner leaf of the wall.

The angling of the inner end portion of the tie ensures that there is some mortar between that portion of the tie and the end of the wall; this helps to ensure that the tie is firmly anchored in the inner leaf of the wall. Instead of this angling, the portion of the tie which is intended to fit in the reveal of the cavity closer may be tapered, with the wide part at the inner end, and the portion which is adapted to enter the inner leaf made in straight continuation of the rear edge of this tapered portion, but being of substantially constant width, so that its front edge inclines inwardly away from the end of the wall, the part of the cavity closer which bridges the cavity being inclined to fit the inclined rear edge of the tie.

Preferably, the inner part of the strip is provided with a moisture barrier adapted to resist moisture migration across the inner part between the outer and inner leaves of the cavity wall. The moisture barrier may simply take the form of a projection from the rear face of the inner part, which faces into the cavity when the inner part is located across the end of the cavity, with at least one sharp longitudinal edge on the projection. The moisture barrier could take the form of a simple flange with relatively sharp longitudinal edges, or it could be provided by a series of longitudinal grooves (preferably with a sharp longitudinal edge between each adjacent pair of grooves).In the preferred construction however, if this recess is dovetail shape crosssection and the projection to accommodate it is correspondingly shaped, that projection will have very sharp longitudinal edges, and sharp longitudinal grooves at the root of the dovetail, which will provide the required resistance to moisture migration.

According to a second aspect of the invention a cavity closer and damp-proof element for use in a cavity wall between the wall and the head, jamb or sill member of a door or window frame or sub-frame, comprises a strip of water-resistant, moisture impermeable material, the strip having a cavity entering wall adapted to abut the outer face of the inner leaf of the cavity wall inside the cavity and a pair of substantially parallel, but spaced apart cavity bridging walls, extending from the cavity entering wall, these bridging walls being adapted to extend across the cavity in the wall and to provide a space between them for the recpeiton of mortar to form a fire barrier across the cavity, the front cavity bridging wall being adapted to be secured to the head, jamb or sill of the door or window frame or sub-frame.

Preferably the front cavity bridging wall is wider than the rear cavity bridging wall. It is further preferred that an undercut recess is formed in the outer face of the cavity entering wall to receive the root of a wall tie.

According to another preferred feature, a moisture barrier is formed on the rear face of the rear cavity bridging wall.

According to a third aspect of the invention, a structural assembly in a building at the end of a cavity wall adjacent to the head, jamb or sill of a door or window frame comprises inner and outer leaves of the wall; a frame element of the door or window; a cavity closer and damp-proof course which itself comprises a strip of water-resistant, moisture-impermeable material, the strip locating on the jamb, head or sill of the door or window frame, and having a part which bridges the cavity and provides a hollow structure substantially filled with mortar to provide a mortar fire barrier which closes substantially the full width of the otherwise open end of the cavity.

In one such structural assembly, the strip has an outer frame-engaging part fitted between an end of the wall and the door or window member, and an inner part which extends across the end of the cavity and being offset from the outer part so that it provides a reveal for mortar filling, and at least one tie fitted in the reveal of the strip and having securing interengagement with the strip, the tie also having a part which projects from the reveal of the strip and engages with or in one of the leaves of the cavity wall.

Preferably the mortar or the like is keyed directly or indirectly to the inner part of the cavity closer. For instance, the inner part of the closer may have an undercut recess extending throughout its length and open into the reveal, so that the mortar or the like becomes keyed into this recess direct key.

Alternatively, or in addition, there may be a tie keyed to the inner part and extending across the reveal, the tie having one or more perforations, so that the mortar or the like extends through the perforation(s)--an indirect key.

It will be appreciated that a cavity closer in accordance with the first aspect of the invention may be employed in a structural assembly in accordance with the third aspect, and therefore each of the preferred features of the first aspect may be employed in such a structural assembly.

In another structural assembly in accordance with the third aspect of the invention, the strip has a cavity entering wall abutting one leaf of the wall inside the cavity and a pair of substantially parallel but spaced apart cavity bridging walls extending across the cavity from the cavity entering wall, the space between the two cavity bridging walls being filled with mortar.

Preferably, the rear cavity bridging wall is of approximately the same width as the cavity and the front cavity bridging wall is wider than the cavity and rests on the leaf of the wall other than the leaf which the cavity entering wall abuts.

It is further.preferred that a wall tie extends from the cavity entering wall across the cavity and engages in the leaf other than the leaf on which the cavity entering wall abuts.

Other preferred features of this form of structural assembly will appear from the following specific examples, but it will be appreciated that a cavity closer in accordance with the second aspect of the invention can be used in this form of the third aspect and that therefore each of the preferred features of the second aspect may be employed in this form of structural assembly.

According to a fourth aspect of the invention, a method of fitting a door or window frame into a cavity wall comprises the steps of: securing the outer part of a cavity closer in accordance with the first aspect of the invention, to the stile of the door or window frame; offering up the frame to a partly constructed wall, building up the wall with the inner part of the cavity closer across the end of the cavity; causing the cavity closer to become anchored to the inner leaf of the wall by means of at least one tie and applying a base coat of mortar, plaster or the like in the reveal of the cavity closer.

Preferably the cavity closer is also secured to the outer leaf of the wall during building up of that leaf either by mortar squeezed out from between the courses of the outer leaf engaging in an undercut recess in the outer part of the closer, or by the use of one or more wall ties anchored in said undercut recess or by both these methods in combination.

Other preferred features of the invention will become apparent from the following description of various types of cavity closer and their methods of use given by way of examples only, and with reference to the accompanying drawings, in which: Figure 1 is a horizontal cross-section through the end of a cavity wall adjacent to a window opening, showing a jamb of the window, Figure 2 is a view looking in the direction of arrow II in Figure 1, but with a mortar base coat omitted for clarity, Figure 3 is a view similar to Figure 1, but showing an alternative construction employing a cranked tie, Figure 4 is a view similar to Figure 1, but showing an alternative construction employing an inclined tie, Figure 5 is a cross-section through an alternative construction of cavity closer, Figure 6 is a cross-section through another form of cavity closer, Figure 7 is a view similar to Figure 1, but illustrating a construction employing an inclined and cranked tie, Figure 8 is a plan view of a tie used in the construction shown in Figure 7, Figure 9 is an elevation of the tie shown in Figure 8, Figure 10 is a horizontal cross-section through the end of a cavity wall adjacent to a window opening, showing an alternative construction, Figure 11 is a perspective view of the construction shown in Figure 10, and Figure 12 is a view similar to Figure 10.

but showing an alternative form of cavity closer.

Referring to Figure 1, there is illustrated part of a structural assembly, which occurs at the end of a cavity wall, adjacent to an opening for a window frame. The cavity wall has an outer leaf 10 and an inner leaf 12, with a cavity 14 between them. In this particular construction, it is assumed that both the outer leaf 10 and the inner leaf 12 are built up from blocks secured together by builders' mortar, and in a typical construction, the outer leaf 10 would be made of bricks, and the inner leaf 12 would be made of breeze blocks. It is to be understood however, that alternative constructions such as are now used in the building of cavity walls could be employed.For instance, the inner leaf could be constructed as a timber frame with plaster covering, although for the purposes of this invention, it would be necessary to provide horizontal courses in that frame, as will hereinafter appear. In the particular construction which is being described, it is assumed that the cavity between the two leaves is 75 millimetres in width, although the invention can be employed with narrower cavities.

One jamb 16 of a timber window frame is illustrated, and it will be noted that this is disposed closely adjacent to the end of the outer leaf 10 of the cavity wall. There are alternative positions for the window frame in relation to the thickness of the cavity wall, but builders frequently prefer to fit the frame in the outside leaf of the wall, in the position illustrated in Figure 1. The present invention is intended to locate the window frame in this position.

It will be appreciated that it is always necessary to close the end of the cavity 14 at each opening in the wall for a window or door frame. Traditionally, this was done by laying three-quarter bricks and quarter bricks across the end of the cavity, and using a flat strip of conventional damp-proof course material arranged vertically between the outer leaf of the wall, and the parts of the three-quarter bricks and quarter bricks closing the end of the cavity. This traditional construction is illustrated in Figures 1 and 2 of United Kingdom Patent Specification No: 1 302 694. There are various disadvantages in this traditional construction, not least being that it is time consuming and expensive to produce. For this reason, plastics cavity closers have been devised, as described for example in the specifi cations of United Kingdom Patents Nos: 1 302 694; 1 302 695 and 1 302 696.Such a plastics cavity closer can be manufactured economically, by an extrusion process, which means that its cross-section is constant throughout its length. Providing it is correctly constructed and fitted, a plastics cavity closer can close the end of the cavity; provide a damp-proof course between the two leaves of the cavity wall (traditionally provided by the flat strip of damp-proof course material); provide a damp-proof course between the end of the cavity wall and the door or window frame (not provided by the traditional method) and tie the two leaves of the wall together adjacent to the window or door frame opening (a feature not provided by the traditional method).

Stringent fire regulations in some countries now require that there shall be a layer of mortar (in the general sense previously mentioned) extending across the end of the cavity.

There is no provision for such a layer of mortar when using a cavity closer of the kind illustrated for example in United Kingdom Patent Specification 1 302 694. The present invention has been made, largely in response to the requirement for the provision of such a fire resistant mortar layer. It must be apparent however, that there are problems in attempting to provide such a fire resistant mortar layer, when using a plastics cavity closer, because mortar will not normally adhere to a plastics surface. In seeking to solve this problem however, the invention has also provided a structural assembly, and a method of providing such an assembly, which is superior in several respects, to known structural assemblies incorporating plastics cavity closers.

Reverting to Figure 1, an extruded plastics cavity closer 18 is employed. Essentially, this closer comprises an outer part 20, an inner part 22, and a step 24 joining the parts 20 and 22, so that the inner part 22 is offset rearwardly from the outer part 20, by the width of the step 24. As illustrated in Figure 1, the outer part 20 is intended to be sandwiched between the end of the outer leaf 10 of the cavity wall and the jamb 16 of the window frame, and in use, it abuts against the end of the outer leaf 10. The step 24 abuts against the inside face of the outer leaf 24, and the corner between the outer part 20 and the step 24 of the cavity closer strip 18 provides a location for the cavity closer 18 on the outer leaf of the cavity wall.Furthermore, because of the offsetting of the inner part 22 with respect to the outer part 20, when the strip 18 is fitted to the end of a cavity wall, the inner part 22 is set back into the end of the cavity 14, and provides a reveal on the inside of the outer leaf 10.

The inner part 22 of the cavity closer strip 18 is of the same width as the nominal cavity width, so that the inside leaf 12 of the cavity wall can abut against the inner end of the inner part 22. However, if the closer 18 is to be used with a narrower cavity, then it is only necessary to cut off part of the inner part 22, to ensure that the remaining inner part is of the same width as the cavity in which the inner part is to fit. Indeed, a line of cut may be pre-marked on the inner part 22, for a 50 millimetres wide cavity.

The outer part 20 of the cavity closer strip is formed with a dovetail-shaped forward protrusion 26, but the thickness of the outer part 20 is constant, so that a dovetailshaped recess 28 is provided in the rear face of the outer part 20. This recess is intended to accommodate the root of a plastics wall tie 30, which is of a known kind, developed for use with extruded plastics cavity closers.

Briefly, the wall tie 30 is a moulded flat member, having an enlarged head 32 through which there is formed a substantially triangular hole 34, and a root portion 36 which is generally dovetail-shaped for fitting into a dovetail-shaped recess such as that formed at 28 in the cavity closer strip 18, but with a notch 38 which will allow some slight deformation of the parts of the root on each side of the notch. Such a tie can be fitted into a recess 28, by first tilting about a longitudinal axis of the tie 30, until the dovetail-shaped root 36 can be pushed through the open narrow rear opening of the recess 28, and then turning the tie about its longitudinal axis until its top and bottom faces are in planes at rightangles to the rear face of the outer part 20, so that the root 36 becomes interengaged with the dovetailshaped recess 28.In practice, the root 36 is made slightly larger than the recess, so that there is some slight compression of the two parts of the root towards each other, thereby ensuring that the tie is firmly anchored in the recess. It will be appreciated, that when this tie is fitted between two courses of the outer leaf 10 of the wall, mortar is able to flow through the opening 34, and that mortar on the front side of the enlarged portion 32 together with that extending through the opening 34, keys the tie to the outer leaf, and prevents it being pulled in a longitudinal direction out at the end of the leaf. The arrangement of the wall tie 30 and the undercut recess 28 provides a means whereby the outer part 20 of the cavity closer strip 18 can be firmly secured to the outside leaf 10. Furthermore, it will be appreciated that since the undercut recess 28 extends throughout the length of the strip 18, it is possible to fit the ties 30 as and where they are required, in order that they match up to the mortar between the courses of bricks forming the outside leaf. Also, mortar is inevitably squeezed out from between the courses as the end bricks are laid, and some of this will engage in the undercut recess 28 between the ties 30, and when this mortar in the recess 28 sets, it forms another key securing the strip 18 to the outer leaf. Indeed, it might be possible to dispense with the wall ties 30, and rely simply on the engagement of the mortar in the recess 28 as a means of securing the outer part 20 of the cavity closer to the outer leaf 10 of the cavity wall.

Lips 40 and 42 are formed on the longitudinal edges of the outer part 20, and in fact the lip 42 forms an extension of the step 24.

These lips 40 and 42 project from the front face of the part 20 by the same depth as the projection 26. Hence, when the front face of the outer part 20 is butted up against the outside face of the jamb 16, contact is established between the jamb 16 and the outer part 20 at three positions across the width of the outer part, namely at the lip 40, at the projection 26 and at the lip 42.

Another lip 44 projects inwardly of the step 24, and forms a short continuation of the outer part 20. The purpose of this lip will appear hereinafter. In addition, a dovetailshaped formation 46 is provided on the inner part 22 of the cavity closer strip 18, this formation 46 being similar to the dovetail formation 26 on the outer part, excepting that it faces in the opposite direction, and provides an undercut recess 48 open on the frontface of the inner part 22.

A special inner tie 50 is provided, and takes the form of a plastics injection moulding. The tie 50 has a flat web portion 52, which takes the form of a straight rectangular strip, and a flange 54, disposed at rightangles to the web 52, but extending along a length of the web 52, which is approximately equivalent to the length of the reveal formed between the inside of the step 24, and the outside of the inner leaf 12, when the cavity closer strip 18 is fitted in position. As illustrated in Figure 2, the flange 54 extends both above and below the web 52.

A dovetail-shaped "root" 56 is formed on the rear edge of the tie 50, and this root 56 is similar to the root 36 formed on one of the wall ties 30 previously described. Its location on the web 52 is such, that it engages in the dovetail-shaped recess 48 of the inner part 22 of the cavity closer, when the outer end of the tie is engaging with the inner face of the step 24. When in this position, the flange 54 extends across substantially the full width of the cavity 14 (see also Figure 2) but part of the tie 50 extends inwardly of the cavity, and has to be fitted between two courses of the inner leaf 12 of the cavity wall. A series of circular holes 58 is formed through the web 52 of the tie 50, and it will be noted that some of these holes 58 are in the part of the web which lies across the cavity, and the others are in the part of the web which extends into the inner leaf 12.

In order to fit one of the ties 50 to the cavity closer 18, it is first necessary to tilt the tie about a transverse axis, until the root 56 can be pushed through the narrow opening of the undercut recess 48, and then the tie is turned back to a horizontal orientation, in which the root 56 engages tightly in the recess 48, in the same way as described above with relation to the wall tie 30. Since the groove 48 extends throughout the length of the cavity closer 18, it will be appreciated that it is possible to fit the special ties 50 at any desired position along the length of the cavity closer. Referring to Figure 2, an arrangement is shown, in which the special ties 50 are fitted at every third horizontal joint of the inner leaf 12.It will also be appreciated, that mortar in the horizontal joints of the inner leaf, flows through the holes 58 which are in the inner leaf, and this provides a very strong means of securing the tie 50 to the inner leaf 12.

It is now possible to describe the method of constructing the cavity wall adjacent to the window frame opening, and building in the window frame.

When the wall has reached the level of the sill, a section of the extruded cavity closer 18 equal to the depth of the window frame is cut from the supply. (It should be mentioned, that it is possible to supply the cavity closer strip in quite long lengths, so that the builder can cut it to required shorter lengths on site.) The outer part 20 of the cut length of cavity closer strip is then butted against the outer face of the jamb 16 as illustrated in Figure 1, and the strip is secured to the timber frame 16 by nails or screws. It will be understood of course, that it is possible to drive the nails or screws through the plastics strip, and this provides a quite adequate method of fastening the strip to the timber frame.The first course of bricks in the outside leaf 10 is then laid, and the window frame can then be offered up to the outer leaf of the cavity wall, with the rear face of the outer part 20 abutting the end of this first course of the outer leaf in line with the window opening. Also, the step 24 is butted against the inner face of the outer leaf 10, so that the window is properly located relatively to the opening. It will of course be understood, that a similar cavity closer strip will be nailed or screwed to the other jamb of the window, and will be similarly located relatively to the first course of the outer leaf on that side of the window opening.

A tie 30 is fitted as previously described, and laid on the first course of the outer leaf 10, so that it will become embedded in the mortar laid on top of that course. It is then possible to start building up the inner leaf 12, with the first course abutting the inner end of the inner part 22 of the cavity closer-that part thereby establishing the width of the cavity at the end of the wall-and as soon as one course of bricks has been laid in the inner leaf 12, one of the special ties 50 can be fitted as previously described, so that part of the tie is laid on top of the first course of the inside leaf. This part will become embedded in the mortar laid on top of the first course of the inner leaf, in order to anchor the tie 50 to the inner leaf.

It is then possible to build up both outer and inner leaves of the wall, but at intervals, ties 30 and 50 will be fitted. When the wall has been built up to the full height of the window opening, the end of the cavity at the opening will be bridged by the inner part 22 of the cavity closer. The dovetail-shaped projection 46 on the inner part 22 provides a moisture barrier to prevent water migrating from the inside face of the outer leaf 10, to the inner leaf of the wall. In damp climatic conditions, the outer leaf 10 of a cavity wall is frequently damp for long periods of time, and in severe wet weather, the inside face of the outer leaf 10 may be actually running with water. This water will attempt to bridge the cavity, and will use any surface inside the cavity for this purpose.Thus, some water will attempt to flow across the rear face of the inner part 22 of the cavity closer, but it will be practically impossible for this water to negotiate the sharp corners provided on the outer edges of the dovetail projection 46.

Hence, the moisture barrier prevents the water travelling across the inner part 22 to the inner leaf 12 of the cavity wall. The window frame 16 is very firmly secured in the outer leaf 10, because of its attachment to the outer part 20 of the cavity closer, and the securing of that outer part to the outer leaf 10 by the mortar which engages in the undercut recess 28, and by the wall ties 30 if they are used. Another advantage of the construction is that the two leaves of the wall are tied together at the end of the wall, whereas in the traditional method of closing the cavity at this point, it is not possible to tie the two leaves together. The outer leaf is tied to the cavity closer by the mortar in the recess 28 and the ties 30, and the inner leaf is tied to the closer by the mortar passing through the holes 58 in the ties 50, and the anchoring of those ties in the recess 48.

When the wall has been built up, a rendered base coat 60 of mortar or rough plaster is applied in the reveal formed by the step 24 and the inner part 22 of the closer. This base coat fills the reveal, and the lip 44 provides a trowel line for the plasterer applying the base coat. A scrim 62 is then applied over the exposed front face of the base coat 60 and the front faces of the flanges 54, some of this scrim 62 extending over the end of the inside leaf 12 of the wall. Finally, plaster is applied over the scrim 64 in the conventional manner.

If required, a timber quadrant 66 can be fitted in the corner between the plaster 64 on the inside of the window opening, and the window frame itself.

Apart from providing the advantages previously mentioned, the construction also provides a mortar base coat 60, across the end of the cavity 14 of substantial thickness. In a practical instance, the thickness may be 19 millimetres. This in effect provides a barrier against flames entering the cavity at the window opening.

One of the important features of the arrangement described above, is the provision for supporting the vertical column of rendered base coat 60. If a plastics cavity closer is fitted across the cavity, it is not possible to apply a base coat of mortar, plaster or the like to the front face of the cavity bridging part of the closer, because the mortar will not adhere to the plastics surface. However, by providing the undercut recess 48 in the inner part 22 of the cavity closer, and by providing the special ties 50, it is ensured that the column of mortar will remain in place. Obviously, some of this column of mortar becomes keyed into the dovetailshaped recess 48, but in addition, shelves are provided at each position where there is one of the ties 50, to support the section of the vertical column above each shelf, and below the next higher shelf.Furthermore, the flanges 54 on the ties 50 help to retain the column of mortar in the reveal formed by the inner part 22, and incidentally, the front faces of these flanges 54 provide a guide for the plasterer applying the base coat.

In the above specific example, the cavity closer 1 8 is used between the jambs 16 of the window frame and the ends of the cavity wall. It should be undertsood however, that a similar arrangement could be employed across the head of the frame, or underneath the sill of the frame. If the arrangement is used across the head of a window frame, then it will be necessary to provide a temporary shuttering under the rendered base coat, until that coat has set and become keyed into the ties 50 and the undercut recess 48. It will be understood, that the window frame may be of any size, and that the same arrangement as that described above, can be used with a door frame. If the window frame is made of metal, then it would be necessary to provide a subframe for attachment to the outer part 20 of the cavity closer, or alternatively, the metal frame should have drilled and tapped holes, for the reception of setscrews screwed passed through holes formed in the outer part 20 of the cavity closer.

The cavity closer strip 18 may be made of any convenient plastics material, which can be extruded into the required shape. It is essential that it shall be moistureresistant, because once in position parts of it will be exposed to water, and the cavity closer must not deteriorate. Further, the cavity closer strip should be moisture-impermeable, because it is required to provide a damp-proof course between the window frame and the outer leaf of the wall.

A suitable grade of polyethylene is preferred for the manufacture of the strip 18. The ties 30 and 50 may be moulded in similar material, although they could also be moulded in other plastics materials such as nylon.

The structural assembly illustrated in Figure 3 is quite similar to that illustrated in Figures 1 and 2, and the same reference numerals are used for euqivalent features.

An extruded plastics cavity closer strip 70 is employed, and this has an outer part 20, an inner part 22 and a step 24, all of which are identical with the equivalent parts of the strip 18 shown in Figure 1. In fact, the only difference between the strip 70 and the strip 18, is that the lip 44 is omitted, and the lip 42 is replaced by a somewhat longer lip 72 in continuation of the step 24. The lip 72 provides a location for the inner face of the jamb 16 of the window frame, and its front edge also provides a trowel line for the plasterer applying the plaster 64 as the last stage of producing the structural assembly.

Wall ties 30 are used as previously described, for securing the strip 70 to the outer leaf of the cavity wall, but instead of the ties 50, an alternative type of tie 74 is employed.

Each tie 74 is made as an injection moulding in plastics material, and generally takes the form of a flat strip, formed with a dovetailshaped "root" 76 for engagement in the undercut recess 48 in the inner part 22 of the strip 70. A flange 78 is also provided on that portion of the tie 74 which in use bridges the cavity 14, and the construction of this flange 78 is the same as that of the flange 54 described with reference to Figures 1 and 2.

Also, a series of holes 80 is formed in the tie 74, or at least in that portion of the tie which bridges the cavity, for the purpose of keying the rendered base coat which is applied in the reveal formed by the inner part 22 and the step 24 as previously described.

However, in this construction, the tie 74 is somewhat shorter than the tie 50, and at its inner end, is formed with a cranked portion 82 of similar shape to the enlarged head 32 of the wall tie 30. A hole 84 of generally triangular shape is formed through the head 82.

The cavity closer strip 70 is built into the structure in the same manner as that described with reference to Figures 1 and 3, excepting that the window frame 16 is located on the lip 40 and the projection 26, and is located by abutment with the lip 72. The head 82 acts in similar fashion to the head 32 formed on the wall tie 30, in that mortar between two horizontal courses of bricks in the inner leaf 12 engages with the edges of the head 82, and extends through the hole 84, to key the tie 70 to the inner leaf. This may be regarded as a better tying method than that illustrated in Figures 1 and 2, in that it provides a substantial amount of mortar in the space between the front edge 86 of the cranked portion and the end of the wall, and in the hole 84.

Figure 4 illustrates another arrangement, which is generally similar to the construction shown in Figures 1 and 2, in that there is an outer leaf 10, an inner leaf 12, with a cavity 14 between them, and the jamb of a window frame is shown at 16.

In this construction, a cavity closer and damp-proof course strip 90 is used, which again is made in the form of a plastics extrusion of constant cross-section throughout its length. The strip 90 has an outer portion 20, which is identical with the outer portion 20 illustrated in Figure 3, and includes a lip 92, against which the inside face of the jamb 16 can be abutted for location purposes, the end of this lip 92 also providing a trowel line for the plasterer applying the plaster 64.

The cavity closer 90 has an inner portion 94 offset from the outer portion 20 by a step 96, in order to form a reveal inside the cavity, but in this arrangement, the inner portion 94 is inclined rearwardly and inwardly, so that the outer end of the reveal is narrower than the inner end. In a practical example, the inner end of the reveal may be 12 millimetres wide, whilst the outer end of the reveal is 25 millimetres wide.

A dovetail formation 98 is provided on the inclined inner part 94, and this formation includes an undercut recess 100, similar to the recess 48, excepting that it is inclined with respect to the end of the wall, following the inclination of the inner part 94.

Ties 30 are used for securing the outer part 20 to the outer leaf 10 of the wall, but instead of the ties 50, special ties 102 are utilised. Each of these ties 102 is made as a plastics injection moulding, and has a generally flat web, and a flange 104 which is of the same construction as the flange 54. The web of the tie 102 includes a wedgeshaped part 106 which is adapted to fill the cross-section of the reveal formed by the inclined inner part 94 of the cavity closer strip, that is to say, the portion 106 of the web has a front edge 108 parallel with the end of the cavity wall, and a rear edge 110 parallel with the inclined faces of the inner part 94. A "root" 112 similar to the root formed on the wall ties 30 is engageable in the undercut recess 100 of the cavity closer.

On the inside of the portion 106, the web of the tie 102 has a parallel sided portion 114 in continuation of the rear edge 110 of the web, and the inner end of the tie terminates in an enlarged portion 116 with a hole 118 formed through it, this enlarged portion 11 6, being similar to the enlarged portion 32 formed on the wall tie 30. The inclination of the part of the tie 102 which extends between horizontal courses of the inner leaf 12, ensures that there is a substantial amount of mortar between the front edge of this portion and the end of the wall, besides that which passes through the hole 11 8, for the purpose of entering the tie 102 in the inner leaf of the wall.It will also be noted, that there are holes 120 formed through the web of the tie 102, and whilst the purpose of those holes 120 which are in the cavity is to provide a key for the rendered mortar base coat, one or more of these holes 120 may be provided in the portion which extends into the inner leaf of the wall, for additional keying to that leaf.

In Figure 5, there is illustrated an alternative form of cavity closer strip, which can be used with the tying systems illustrated in any of Figures 1 to 4. The strip 120 is very similar to that illustrated in Figure 3, and essentially comprises an outer part 122, an inner part 124, and a step 126 joining the inner part to the outer part in order to provide the reveal for the rendered base coat. In addition, there is a forwardly projecting lip or flange 128 for locating the inner surface of the window frame as described with reference to Figure 3.

Each of the outer and inner parts has a reversed dovetail section 130 and 132 respectively providing longitudinally extending dovetail-shaped undercut recesses 134 and 136 to accept the ties used for securing the cavity closer 120 to the inner and outer leaves of the cavity wall. In this construction however, in addition to the projection formed by the reverse dovetail section 130, the outer part 122 is formed with a series of four longitudinally extending parallel ribs 138.

each of which protrudes from the outer part 122 by the same depth as the protrusion of the reversed dovetail section 130. Hence, the edges of the ribs 138 are in the same plane as the front surface of the projection 130. The provision of the ribs 138 is of assistance in locating the outer part 122 against the outer edge of the jamb, particularly, where the jamb is provided with a mortar tie groove, which would reduce the area of contact between the jamb and the projection 130. Furthermore, the provision of the ribs 138 generally strengthens the outer part 122, and assists in preventing bending of the outer part, when it is being secured to the jamb of the window frame.

In Figure 6, there is illustrated another form of cavity closer strip, which is formed as a plastics extrusion, in similar manner to the cavity closers previously described. The cavity closer 140 has an outer part 142, and inner part 144, and a step 146 providing an arrangement generally similar to that described with reference to Figure 3. There is also a lip or flange 148 in continuation of the step 146 to provide a location for the inner face of the jamb of the window frame.

In this arrangement however, there is no reversed dovetail formation in the outer part 142 to provide an anchorage for the wall ties 30. Instead, there is a pair of converging ribs 150 protruding from the rear surface of the part 142, and forming a dovetail cross-sectioned longitudinally extending undercut recess 152 between them. It will be appreciated, that this recess is adapted to receive the root of a wall tie 30, in exactly the same manner as the recess 28 described with reference to Figure 1, but because the recess is formed by the converging ribs 150, there is no corresponding dovetail-shaped protrusion on the front surface of the outer part 142.

A reverse dovetail formation 154 is provided on the inner part 144, and this functions in the same manner as the corresponding formation on the previously described cavity closers.

Figure 6 also illustrates the provision of extensive moisture traps on both the inner and outer parts of the cavity closer. On the front surface of the outer part 142, there is formed a series of longitudinally extending parallel grooves 156, each in close juxtaposition to its neighbours, so that a sharp protruding longitudinal edge 158 occurs between each adjacent pair of grooves 1 56. It will be appreciated, that it is virtually impossible for water even when driven by a wind, to travel across the surface formed by this array of longitudinal edges 158. Similar groove arrangements 160 and 162 are formed on the rear face of the inner part 144, on each side of the reversed dovetail formation 154. The moisture traps provided by the grooves 160 and 162, and their sharp edges, prevent the migration of water across the cavity from the outer leaf to the inner leaf.

In Figure 7, there is illustrated a structural assembly similar to that shown in Figure 1, and including an outer leaf 170 and an inner leaf 172 of a cavity wall, with a cavity 174 between them. Here again, there is an extruded plastics cavity closer 176, used to close the end of the cavity, to provide a moisture barrier across the cavity, to provide a moisture barrier between the window frame and the outer leaf 170, and to assist in tying the inner leaf 172 to the outer leaf 170. The cavity closer 176 includes features derived from some of the other cavity closers already described. It has an outer part 178, formed with converging ribs 180 on the rear face, for the reception of the root of a wall tie 30. In addition, a rib 182 is formed on the outer end of the outer part 178, this rib protruding from the outer part by the same depth as the converging ribs 180, so that when the outer part is butted up against the end of the outer leaf 170, there is engagement with the outer leaf along three longitudinal edges, provided by the edges of the ribs 180 and 182. The front face of the outer part 178 has a series of grooves 184 to provide a moisture barrier, as described with reference to Figure 6. Figure 7 illustrates a jamb 186 of a window frame, and nails 188, passing through the outer part 178, and entering the jamb 186, to secure the outer part to the window frame. It will also be noted, that the cavity closer 176 includes a flange 190 to provide a location for the inner face of the jamb 186.

The cavity closer also includes an inner part 192 having a reversed dovetail formation 194, and moisture barriers formed by longitudinally extending sets of parallel grooves 196 and 198. A step portion 200 joins the outer part 178 to the inner part 192, in order to form the reveal for the reception of the rendered base coat, but in this construction, the inner part 192 is inclined in similar fashion to the inner part illustrated in Figure 4. Again, in this specific example, the reveal formed in the cavity at the outer side thereof is approximately 12 millimetres in width, whereas at the inner side of the cavity, the reveal has a width of approximately 19 millimetres.

An injection moulded plastics tie 202 is used for securing the inner part of the cavity closer to the inner leaf 172 of the wall. This tie 202, has a web, part of which is shaped to fill the tapering width reveal, and is fitted with a root formation 204 of the kind previously described, for fitting in the reverse dovetail formation 194 of the inner part of the cavity closer. This part of the web of the tie is also provided with a flange 206, for retaining the mortar base coat in the reveal as previously described.

The part of the web of the tie 202 which enters the inner leaf of the wall when the tie is fitted, includes a parallel sided portion which is a straight continuation of the rear edge of that portion which fills the reveal (i.e.

it is inclined with respect to the end of the cavity wall) and a cranked head portion 208, with a hole 210 formed therethrough, this cranked head portion being similar to that illustrated at 82 in Figure 3.

The assembly illustrated in Figure 7, is built up in the same way as that described with reference to Figures 1 and 2, but there is a better adhesion to the inner leaf, because of the mortar which will occupy the space between the front edge of the part of the tie which enters the cavity, and the end of the cavity wall.

The tie 202 is more clearly illustrated in Figures 8 and 9. It is to be noted in particular, that the root 204 which enters the undercut recess in the inner part of the cavity closer essentially comprises a pair of diverging ribs, and that there is a deep V-shaped notch 212, permitting some distortion of the diverging ribs 204, whereby the root can be made slightly larger than the undercut recess into which it is to fit, to provide a tight interference fit when the tie is in position. It will also be noted, that the outer end of the flange 206 is rounded. This is to enable the tie 202 to be tilted when the outer edge is in engagement with the inside of the step 200, in order to allow the root 204 to pass through the narrow entrance to the undercut recess, before the tie is turned back to a horizontal position, in which the root 204 completely fills the undercut recess.

In Figures 10 and 11 there is shown a somewhat different form of cavity closer which ensures the provision of a flame barrier at the end of the cavity adjacent to a door or window opening. The outer leaf of a cavity wall is indicated at 300 and the inner leaf at 302, with a cavity 304 between them. In this construction, the outer leaf is made of building blocks and the inner leaf is a timber frame clad on the inside with plaster board. This is typical of the so-called timber frame type of house construction in which the timber framed inner leaves of the building (which are often prefabricated off site) are erected first, and then the outer leaves are erected around the inner leaves.A problem with this type of construction is that of shrinkage of the inner leaf of a wall after completion of the building-indeed parts of the inner leaf may move downwardly by as much as 25 millimetres due to shrinkage. Hence, there has to be provision for relative vertical movement between the inner and outer leaves.

An extruded plastics cavity closer and damp-proof course 306 is provided at the end of the cavity wall adjacent to a window opening and one jamb of the window frame is shown at 308. The cavity closer 306 comprises a cavity entering wall 310, front and rear cavity-bridging walls 312 and 314. and flanges 316 and 318. The cavity entering wall 310 is adapted to engage with the outer face of the inner leaf 302 as shown in Figure 10, but its own inner face is preferably formed as shown, with a series of shallow parallel grooves 320 in close juxtaposition to each other, so that a longitudinally extending sharp edge is formed between each adjacent pair of grooves 320. This formation provides an effective moisture trap to prevent moisture migrating along the inner face of the cavity entering wall 310.

The front cavity bridging wall 312 projects at right angles to the cavity entering wall 310 and is wider than the cavity for which the cavity closer is designed. In the specific embodiment illustrated, it is assumed that the cavity 304 is 50 millimetres wide and the jamb 308 is 70 millimetres wide. Thus, with the cavity entering wall 310 abutted against the outer face of the inner leaf, the wall 312 extends across the full width of the cavity 304, and part of it rests on the front end of the outer leaf 300. It is intended that the wall 312 shall be sandwiched between the end of the wall and the jamb 308, and its front face is formed with a series of shallow grooves 322 similar to the grooves 320 on the cavity entering wall 310. The grooves 322 prevent moisture migrating along the interface between the jamb 308 and the cavity-bridging wall 312.The rear cavity-bridging wall 314 also extends at right angles to the cavity entering wall 310 and is only as wide as the cavity to be bridged. This wall 314 is spaced rearwardly (i.e. into the cavity) from the wall 312, and on its rear face is formed with a series of shallow grooves 324 similar to the grooves 320 and acting to prevent moisture migrating across the rear face of the wall 314 from the outer leaf 300 to the inner leaf 302.

The flange 316 is in effect an inner continuation of the front cavity bridging wall 312, whilst the short flange 318 is in effect a continuation of the cavity entering wall 310.

Thus, a right-angled corner is formed between the cavity entering wall 310 and the flange 316 and this enables the cavity closer 306 to be located on the corner of the inner leaf 302 during building construction. It will be noted that the rear face of the flange 316 may also have a moisture barrier formed by a series of shallow grooves 326. A diagonally opposite corner is formed by the front cavity bridging wall 312 and the short flange 318 and this enables the cavity closer 306 to be properly located on the jamb 308.

Finally, a pair of inclined ribs 328 is formed on the outer face of the cavity entering wall 310 on the rear side of the cavity bridging wall 314. The ribs 328 form a dovetail crosssection recess 330 extending along the length of the closer 306 in which the root of a plastics wall tie 30 can be received. The dovetail-shaped recess 330 therefore performs the same function as the dovetail-shaped recess 28 described with reference to Figure 1.

During the construction of the building the inner leaves are erected first, and then cladding by building the outer leaf 300 commences. When the outer leaf reaches the bottom of the window opening, a length of the cavity closer strip 302 is cut off from the supply and fitted on to the jamb 308 of the window frame, taking care to locate the jamb in the corner between the wall 312 and the flange 318. Nails 332 and 334 are then driven respectively through the wall 310 and the flange 318 and into the jamb 308 to secure the cavity closer 306 to the window frame. It will be appreciated that the closer 306 is secured very firmly to the jamb because the two sets of nails are approximately at right angles to each other. At this stage, the outer end of the space 336 between the two walls 312 and 314 is open.

The window frame is then offered up to to inner timber framed wall, and the cavity closer 306 located on the corner of the inner leaf 302. Nails 338 and 340 are then driven respectively through the wall 310 (inside the recess 336) and the flange 316 into the inner leaf 302 to secure the cavity closer 306 to the inner leaf. Thus the window frame is firmly secured to the inner leaf, and incidentally, if there is subsequent movement of the inner leaf, the window frame will move with it.

At this stage, it is necessary to close the bottom end of the space 336. For this purpose, a special plastics closer (not shown) may be provided, which extends across the bottom of the space 336 and into one of the courses between blocks of the outer leaf 300.

In fact, this type of closer may be similar to the ties 50 or 74, but without holes or root formations. As an alternative to fitting a special bottom closer, a block of timber may be nailed to the outer face of the inner leaf 302 to close the bottom end of the space 336.

The outer leaf 300 is then built up, and at intervals, ties 30 are fitted as previously described. The outer leaf closes the outer end of the space 336 which thus becomes an opentopped box. Mortar is dropped into this space 336 by the bricklayer and hence a mortar fire barrier bridging the end of the cavity is built up between the walls 312 and 314. Theties 30 tie the cavity closer 306 to the outer leaf 300 but whenever there is shrinkage of the inner leaf, the ties permit relative movement between the inner and outer leaves either by flexing or by allowing the ribs 328 to move relatively to the root portions of the ties.

It will be clear that this form of the invention provides all the requirements of a cavity closer. It provides a damp-proof course between the two leaves of the wall because moisture cannot travel across the wall 31 4-and even if it did, it would not be able to negotiate the ribs 328. It provides a moisture barrier between the wall and the window frame, and by virtue of the nails 338 and 340 and the ties 30, it ties the two leaves together adjacent to the window opening. Moreover, because of the mortar filling of the space 336, it provides a fire barrier at the end of the cavity 304.In practice, the mortar filling the space 336 will adhere to the blocks of the outer leaf of the cavity wall, and even if one or both of the cavity bridging walls 312 and 314 were to be destroyed by fire, that would still leave the mortar bridge extending substantially across the full width of the end of the cavity.

Turning now to Figure 1 2, there is shown a timber framed wall having an outer leaf 400, an inner leaf 402 and a cavity 404. The jamb 406 of a window frame is illustrated, and an extruded plastics cavity closer and damp-proof course 408 is also shown. The cavity closer 408 is very similar to that shown in Figures 10 and 11 (and the same reference numerals are used for identical features) but instead of the inclined ribs 328, there is a dovetail formation 410 on the rear cavity bridging wall 314 to provide a dovetail cross-section recess 412 as described in previous examples. A special wall tie 420 is provided and in con struction this is similar to the wall ties 50, 74 and 202 previously described, but the vertical flange 54 is not required. The tie 420 has a web 422 which extends across the cavity and fills the cross-section of the space 336.Holes 424 are formed through this web 422 and there is also a root portion 426 which fits in the recess 412. The tie 420 has a head 428 cranked rearwardly with respect to the part which enters to space 336 and formed in similar fashion to the head 32 on the tie 30 (Figure 1).

The wall is built up as described with reference to Figures 10 and 11, excepting that when the window is offered up to the end of the cavity wall, one of the ties 420 is fitted, and a short strip of timber or card is placed on the web inside the space 336 to provide a "floor" for that space blocking the holes 424 through the bottom tie. Afterwards, the space 336 is filled with mortar, but ties 420 are fitted at vertically spaced positions without blocking the holes through those ties. In this arrangement, the bottom tie 420 provides one of the ties holding the cavity closer 408 and the window to the wall and also provides the "floor" for the fire resistant mortar in the space 336.

Claims (51)

1. A structural assembly in a building at the end of a cavity wall adjacent to the head, jamb or sill of a door or window frame comprising inner and outer leaves of the wall; a frame element of the door or window; a cavity closer and damp-proof course which itself comprises a strip of water-resistant, moistureimpermeable material, the strip locating on the jamb, head or sill of the door or window frame, and having a part which bridges the cavity and provides a hollow structure substantially filled with mortar to provide a mortar fire barrier which closes substantially the full width of the otherwise open end of the cavity.

2. A structural assembly as claimed in Claim 1, in which the strip has an outer frame-engaging part fitted between an end of the wall and the door or window member and an inner part which extends across the end of the cavity and is offset from the outer part so that it provides a reveal for a mortar filling and at least one tie fitted into the reveal of the strip and having securing interengagement with the strip, the tie also having a part which projects from the reveal of the strip and engages with or in one of the leaves of the cavity wall.

3 A structural assembly as claimed in Claim 2, in which both the outer and inner parts of the strip are substantially flat and parallel with each other, there being a step joining them to provide the reveal on the inner part, the end of the reveal opposite to the step being open and the tie projecting through this open end of the reveal.

4. A structural assembly as claimed in either of Claims 2 and 3, in which an undercut recess is formed in the outer part, open in the rear face, that is the face which faces the end of the wall, the undercut recess extending throughout the length of the strip, so that it provides anchorage for wall ties or mortar at any position along the length of the strip.

5. A structural assembly as claimed in Claim 4, in which the outer part is of substantially constant thickness, so that it has a portion projecting from the front face which faces towards the window or door member to accommodate the undercut recess.

6. A structural assembly as claimed in Claim 5, in which a lip is provided on one or both longitudinal edges of the outer part, projecting from the front face, this lip or lips projecting by the same distance as the recess projection.

7. A structural assembly as claimed in any one of Claims 2 to 6, in which an undercut recess is formed in the inner part of the strip to receive a key formed on the tie.

8. A structural assembly as claimed in Claim 7, wherein the undercut recess formed in the inner part of the strip is dovetail crosssection and the formation of the tie which engages in the recess is correspondingly dovetail shaped.

9. A structural assembly as claimed in any one of Claims 2 to 7, in which the tie has one or more perforations so that mortar extends through the tie.

10. A structural assembly as claimed in Claim 9, in which there is a series of perforations with at least one such perforation in the part of the tie which fits in the reveal of the strip.

11. A structural assembly as claimed in any one of Claims 2 to 10, in which the tie is straight.

12. A structural assembly as claimed in any one of Claims 2 to 10, in which the tie is formed with an angled portion which engages between courses of the inner leaf of the wall.

13. A structural assembly as claimed in any one of Claims 2 to 10, in which the portion of the tie which fits in the reveal of the cavity closer is tapered, with the wide part at the inner end, and the portion which enters the inner leaf made in straight continuation of the rear edge of this tapered portion, but being of substantially constant width, so that its front edge inclines inwardly away from the end of the wall, the part of the cavity closer which bridges the cavity being inclined to fit the inclined rear edge of the tie.

14. A structural assembly as claimed in any one of Claims 2 to 13, in which the inner part of the strip is provided with a moisture barrier adapted to resist moisture migration across the inner part between the outer and inner leaves of the cavity wall.

15. A structural assembly as claimed in Claim 14, in which the moisture barrier takes the form of a projection from the rear face of the inner part, which faces into the cavity with at least one sharp longitudinal edge on the projection.

16. A structural assembly as claimed in Claim 15, in which the moisture barrier takes the form of a simple flange with relatively sharp longitudinal edges.

17. A structural assembly as claimed in Claim 14, in which the moisture barrier is provided by a series of longitudinal grooves.

18. A structural assembly as claimed in any one of Claims 2 to 17, in which the mortar or the like is keyed directly or indirectly to the inner part of the cavity closer.

19. A structural assembly as claimed in Claim 18, in which the inner part of the closer has an undercut recess extending throughout its length and open into the reveal, so that the mortar or the like becomes keyed into this recess.

20. A structural assembly as claimed in Claim 1, in which the strip has a cavity entering wall abutting one leaf of the wall inside the cavity and a pair of substantially parallel but spaced apart cavity bridging walls extending across the cavity from the cavity entering wall, the space between the two cavity bridging walls being filled with mortar.

21. A structural assembly as claimed in Claim 20, in which the rear cavity bridging wall is of approximately the same width as the cavity and the front cavity bridging wall is wider than the cavity and rests on the leaf of the wall other than the leaf which the cavity entering wall abuts.

22. A structural assembly as claimed in Claim 20 or Claim 21, in which a wall tie extends from the cavity entering wall across the cavity and engages in the leaf other than the leaf on which the cavity entering wall abuts.

23. A structural assembly as claimed in Claim 22, in which the cavity entering wall is formed with an undercut recess to receive a root portion of the tie.

24. A structural assembly as claimed in Claim 23, in which part of the tie extends across the space between the two cavity bridging walls and substantially fills the horizontal cross-section of that space.

25. A structural assembly as claimed in any one of Claims 20 to 24, in which a moisture barrier is formed on the rear face of the rear cavity bridging wall.

26. A cavity closer and damp-proof element for use in a cavity wall between the wall and the head, jamb or sill member of a door or window frame or sub-frame, comprising a strip of water-resistant, moisture-impermeable material, the strip having an outer frameengaging part adapted to fit between an end of the wall and the door or window member and an inner part extending to one side of the outer part and being offset with respect to the outer part to provide a reveal for a mortar or like coat and at least one tie adapted to fit in the reveal of the strip and having securing interengagement with the strip, the tie also having a part which projects from the reveal of the strip for engagement with or in a leaf of the cavity wall.

27. A cavity closer and damp-proof element as claimed in Claim 26, in which both the outer and inner parts of the strip are substantially flat and parallel with each other, there being a step joining them to the reveal on the inner part and the end of the reveal opposite to the step is open, the tie projecting through this open end of the reveal when in position on the strip.

28. A cavity closer and damp-proof element as claimed in Claim 26 or Claim 27, in which an undercut recess is formed in the outer part, open in the rear face, that is the face which is intended to face the end of the wall, the undercut recess extending throughout the length of the strip, so that it provides anchorage for wall ties or mortar at any position along the length of the strip.

29. A cavity closer and damp-proof element as claimed in Claim 28, in which the outer part is of substantially constant thickness, so that it has a portion projection from the front face which faces towards the window or door member in use, to accommodate the undercut recess.

30. A cavity closer and damp-proof element as claimed in Claim 29, in which a lip is provided on one or both longitudinal edges of the outer part, projecting from the front face, this lip or lips projecting by the same distance as the recess projection.

31. A cavity closer and damp-proof element as claimed in any one of Claims 26 to 30, in which an undercut recess is formed in the inner part of the strip to receive a key formed on the tie.

32. A cavity closer and damp-proof element as claimed in Claim 31, wherein the undercut recess formed in the inner part of the strip is of dovetail cross-section and the formation of the tie which engages in the recess is correspondingly dovetail-shaped.

33. A cavity closer and damp-proof element as claimed in any one of Claims 26 to 32, in which the tie has one or more perforations so that mortar can extend through the tie.

34. A cavity closer and damp-proof element as claimed in Claim 33, in which there is a series of perforations with at least one such perforation in the part of the tie which fits in the reveal of the strip.

35. A cavity closer and damp-proof element as claimed in any one of Claims 26 to 34, in which the tie is straight.

36. A cavity closer and damp-proof element as claimed in any one of Claims 26 to 34, in which the tie is formed with an angled portion adapted to engage between courses of the inner leaf of the wall.

37. A cavity closer and damp-proof element as claimed in any one of Claims 26 to 34, in which the portion of the tie which is intended to fit in the reveal of the cavity closer is tapered, with the wide part at the inner end, and the portion which is adapted to enter the inner leaf made in straight continuation of the rear edge of this tapered portion, but being of substantially constant width, so that its front edge inclines inwardly away from the end of the wall, the part of the cavity closer which bridges the cavity being inclined to fit the inclined rear edge of the tie.

38. A cavity closer and damp-proof element according to any one of Claims 26 to 37, in which the inner part of the strip is provided with a moisture barrier adapted to resist moisture migration across the inner part between the outer and inner leaves of the cavity wall.

39. A cavity closer and damp-proof element as claimed in Claim 38, in which the moisture barrier takes the form of a projection from the rear face of the inner part, which faces into the cavity when the inner part is located across the end of the cavity, with at least one sharp longitudinal edge on the projection.

40. A cavity closer and damp-proof element as claimed in Claim 39, in which the moisture barrier takes the form of a simple flange with relatively sharp longitudinal edges.

41. A cavity closer and damp-proof element as claimed in Claim 38, in which the moisture barrier is provided by a series of longitudinal grooves.

42. A cavity closer and damp-proof element for use in a cavity wall between the wall and the head, jamb or sill member of a door or window frame or sub-frame, comprising a strip of water-resistant, moisture-impermeable material, the strip having a cavity entering wall adapted to abut the outer face of the inner leaf of the cavity wall inside the cavity and a pair of substantially parallel but spaced apart cavity bridging walls extending from the cavity entering wall, these bridging walls being adapted to extend across the cavity in the wall and to provide a space between them for the reception of mortar to form a fire barrier across the cavity, the front cavity bridging wall being adapted to be secured to the head, jamb or sill of the door or window frame or sub-frame.

43. A cavity closer as claimed in Claim 42, in which the front cavity bridging wall is wider than the rear cavity bridging wall.

44. A cavity closer as claimed in Claim 42 or Claim 43, in which an undercut recess is formed on the outer face of the cavity entering wall to receive the root of a wall tie.

45. A cavity closer as claimed in any one of Claims 42 to 44, in which a moisture barrier is formed on the rear face of the rear cavity bridging wall.

46. A method of fitting a door or window frame into a cavity wall comprising the steps of: securing the outer part of a cavity closer in accordance with any one of Claims 26 to 41 to the stile of the door or window frame; offering up the frame to a partly constructed wall, building up the wall with the inner part of the cavity closer across the end of the cavity; causing the cavity closer to become anchored to the inner leaf of the wall by means of at least one tie and applying a base coat of mortar, plaster or the like in the reveal of the cavity closer.

47. A method of fitting a door or window frame into a cavity wall as claimed in Claim 46, in which the cavity closer is also secured to the outer leaf of the wall during building up of that leaf either by mortar squeezed out from between the courses of the outer leaf engaging in an undercut recess in the outer part of the closer, or by the use of one or more wall ties anchored in said undercut recess or by both these methods in combination.

48. A method of fitting a door or window frame into a cavity wall comprising the steps of: securing the front cavity bridging wall of a cavity closer in accordance with any one of Claims 42 to 45 to the stile of the door or window frame; offering up the frame to the inner leaf of a partly constructed wall with the cavity entering wall abutting the inner leaf; building up the outer leaf of the wall with the rear cavity bridging wall inside the cavity and extending across the cavity; causing the cavity closer to become anchored to the outer leaf of the wall by means of at least one tie, and filling the space between the two cavity bridging walls with mortar.

49. A cavity closer and damp-proof element for use in a cavity wall constructed and arranged substantially as herein described with reference to Figures 1 and 2, Figures 3 and 5, Figure 4, Figure 6, Figures 7, 8 and 9, Figures 10 and 11 or Figure 12 of the accompanying drawings.

50. A structural assembly in a building at the end of a cavity wall substantially as herein described with reference to Figures 1 and 2, or Figure 3, or Figure 4, or Figure 7, or Figure 10 or Figure 12 of the accompanying drawings.

51. A method of fitting a door or window frame into a cavity wall substantially as herein described with reference to Figures 1 and 2, or Figure 3, or Figure 4, or Figure 7, or Figure 10 or Figure 12 of the accompanying drawings.