GB2289076A - Internal screens and partitions - Google Patents

Abstract

A fire-resisting and/or acoustically-insulating glazed internal partition (10) comprises a frame (12) constituted by a number of frame members (30 - 58) joined by dowels and forming a number of apertures each glazed with a glass pane (14 - 28). The frame members (30 - 58) are formed of a man-made material (eg MDF) having a density not less than that of high-density hardwood, and having their exposed surfaces covered with cloaking beads or trim. Intumescent material is incorporated as necessary at the edges of the panes and at the frame joints. The structure is of modular construction and may be assembled on site. <IMAGE>

Description

INTERNAL SCREENS AND PARTITIONS This invention relates to structures for dividing the internal space in a building and which may have fireresisting and/or acoustically-insulating properties.

The term "structure" as used in this Specification includes both partitions, which are defined as having less than 45% of their area glazed (and may be entirely nonglazed), and screens which are defined as having more than 45% of their area glazed.

Architecte, interior designers, epecifiers and the public at large like the mellow appearance of timber and, in particular, that of tropical hardwoods. The depth of grain and colour imply warmth and quality.

Bespoke hardwood joinery glazed screens and partitions, made from solid timber have been produced for many years, are generally produced off-site. They are heavy and cumbersome to transport and manhandle, and are therefore easily damaged during transport to site ard during installation.

Sometiries a local joinery company will produce a fire-resisting timber g'azed screen on site. These are usually not constructed very well; and there is often considerable doubt whether the materials used and the method of construction would be adequate to greet the required fire integrity rating. The architect, specifier or contractor thus ends up with an uncertified construction of indeterminate fire performance.

The Applicant successfully tested a multi-paned screen some while ago. Fire Test Report FR 1265, dated 23 November 1988, provides the detailed observations covering this test, in which a fire integrity rating of 37 minutes was achieved.

Whilst solid hardwood, multi-paned1 60-minute fireresisting screens are produced, no-one has successfully tested one constructed with high density hardwood glazing beads. A small number of companies have obtained letters of assessment from Nanas approved fire test laboratories.

These have been mainly based on Fire Test Reports FR 198A or FR 1503.

30-and 60-minute fire-resisting timber glazed screens and partitions should be made from timber, from managed forests, to meet the environmentalists' criticisms. Some 30-minute elements have been made from softwoods from managed forests, but no-one has successfully tested these elements. (Care must be used when referring to timbers as softwood and hardwood, as there ió no accurate definition of these terms. Softwoods are regarded as tiinbers coming from coniferous trees, and hardwoods as coming from the deciduous species. There are a number of softwoods, which have relatively high densities, up to 600 kg/m3, and behave more like hardwoods than softwoods.There are also many hardwoods which have very low densities and behave more like softwoods. A softwood must therefore be considered as a timber having a density greater than 500 kg/m.l and a char rate of 0.7 mmJminute or more, when subjected to the BS476 PART 20:1987 time/temperature/pressure regime. A suitable high density hardwood is a timber which has a density greater than 650 kg/m3 and a char rate of 0.40.5 mnZntinute. Whilst ash and iroko are regarded as hardwoods, they are not suitable for use in this type of fire-resisting element.) Today, however, environmentalists are decrying the needless and wasteful use of tropical hardwoods.

Moreover, hardwoods and, in particular, tropical hardwoods have increased substantially in price, and there is every indication that this rise in price will continue unabated.

No-one has produced a timber-based, modular selfassembly construction for screens and partitions, which meets the desired level of fire performance, despite the apparent definite need for such a construction.

It has therefore become necessary to find alternative ways to produce dividing structures which meet performance and design criteria, overcome the environmental objections, and yet maintain an aesthetical'y-pleasing appearance.

According to the present invention there is provided a separating structure for dividing internal space in a building, comprising a frame constituted by a number of frame members and defining one or more apertures each occupied by respective panel, and jointing members for securing the frame members together, the frame members being formed of a man-made material having a density and char rate not less than that of high-deneity hardwood, and the arrangement being such that the structure may be assembled on site.

The structure according to the invention preferably comprises an outer frame, transoms and mullions, all of which are based on a compsoite construction, having a reconstituted, cellulosic, fibrous material as a core, cloaked on the two opposite minor faces with an aesthetically-acceptable z.arerial, such as a tropical hardwood from managed forests. When assembling into a glazed screen or partition softwood or hardwood glazing or panel retention beads are used, which are wide enough to cover the exposed face of the celluosic core material and to overlap the edges of the timber cloaking beads, providing the appearance of a solid timber structure.

Some preferred forms of construction of the various components of screens and partitions according to the invention will now be described: (i) Frame, including transoms and mullions These components are made of a central core cf reconatituted, fibrous, cellulosic material, for example medium Density Flhreboard, (MflF), including the flameretardant version, of such new materials as Pressed Strip Lumber (PSL), or Laminated Veneer Lumber (LVL). In essence any reconstituted, cellulosic, fibrous material of a density and char rate the same as, or very similar to that of, high density hardwood (ie approximately 0.40.5 mm per minute), with a low volatiles content, relatively stress free and preferably producing only a low level of smoke ernission, may be used in the construction of the present invention.

The core may be formed of one thickness of material or of a laminate of two or more layers to achieve the requisite thickness.

In the case of a 60-minute fire-resisting screen or partition the major faces should be lined with 6 mm thick hardwood (greater than 650 Kgym3), but this is not required for shorter periods of fire resistance.

(ii) Cloaking beads and cover tries The edges of the cellulosic core material, which would be exposed to view in the assembled frame, are preferably covered with cloaking beads or cover trims, to provide an aesthetically-pleasing effect. The beads or trims also provide a degree of fire protection to the cellulosic core material during a real fire.

The cover trims may be selected to match, complement or contrast with the glazing beads to be described later.

In the case of non-fire resisting elements the cover trims may be made from a wide selection of materials, eg, softwood, hardwood or plastic, depending on the desired effect, whereas with fire-resisting elements the cover trim should be of hardwood of a density greater than 650 kg/S.

Alternatively, there may be used a non-combustible material, such as calcium silicate, magnesium oxychioride or gypsum plaster, or any material with a char rate similar to or less than that of high density hardwood, (density greater than 650 kg/u3) when subjected to a BS 476 parts 20/22:1987 test, eg heavily filled GRP materials, which materials should also have a class 0 or 1 spread of flame to BS 476 parts 6 and 7. The materials may be decorated by either timber veneering over, or covering with, a suitable surface-finishing material, such as paint, plastic or thin metal. In the case of plastic, it is desirable to keep the thickness of the plastic as thin as possible, eg, to 0.3 mm or thereabouts. Suitable plastic materials are melamine, PVC and phenolic materials.Where elements of 30-minute fire-resistance or less are concerned, beads should be made from high density hardwood, flame-retardant MDF, or flame-retardant treated softwood, either formed by pressure-impregnation with flame-retardant chemicals or by coating with intumescent varnish or paint.

The cover trim may be secured to non-fire rated units by adhesives or by mechanical means, (including screwing pinning or with the use of concealed clip8 or brackets), whereas in fire-resisting elements the trims should be both glued and screwed or glued and pinned. The cover trims may be used to conceal a channel, rebated into the edge face of the cellulosic core, or into the back of the trim or in both, for use in a cable management system. If this design feature is adopted in fire-rated elements, then an Intumescent seal should be incorporated, behind the cover trim, to seal the channel in the event of a fire.

The cloaking beads may be profiled to produce a variety of pleasing effects; in particular, the edges of the exposed face of the cover trim may be chamfered to make a feature of the butt joints.

(iii) Glazing beads and panel-retaining beads The glazing or panel-retaining beads for fireresisting elements should be made from high density hardwood (density greater than 650 kg/m3, apart from iroko or ash. The former has a high level of in-built stresses and thus readily distorts in a fire; and the latter tends to char more quickly than other tlibers of a similar density and does not produce a stable char. Suitable timbers for 60-minute fire-resisting glazing and panelretaining beade are oak, utile, beech and kapur. The beads should be nominally 15 mm high for 30-minute fireresisting systems, and nominally 25 mm high for 60-minute systems.

The beads must be of sufficient depth to extend back from the glass or intumescent glazing seal, such as Pyrogiaze 30 or 60, to cover the exposed face of the cellulosic core (or hardwood liner to the reveal) and to overlap the top edge of the cover trim, the overall effect being to produce an element of construction that appears to have been made from solid timber. The element thus meets the requirements of the architect and the designer in an economic and environinentally-acceptable manner, whilst achieving the required fire integrity.

The timber beads may be of the same species as selected for the cover trim or of a different species, chosen for its colour and grain structure, to complement or contrast with that of the cover trims. The hardwood timber beads may be plain, untreated timber when used in 30-minute fire-resisting units or in 60-minute fireresisting units utilising fire-resisting insulation glass, or for single pane monolithic glasses or double-glazed acoustic insulation units and for the retention of solid panels. Moreover, in the case of multi-paned fireresiting screens or partitions, it has been found necessary to use high density hardwood beads of density greater than 700 kg/m3, or timber of 650 kg/m3, which has been pressure-impregnated with flame-retardant salts or coated with an intumescent paint or lacquer.

In a similar way to the cover trims, other materials may be used to produce the glazing and panel-retaining beads. The performance required from the beads for monolithic glasses to achieve 60-minute integrity is far greater than that required for use with insulating glasses, panels and cover trims, the beads being exposed to much high levels of radiated, conducted and convected heat. The choice of alternative materials is therefore restricted to non-combustible materials or high density products with a low volatiles content, and preferably low smoke remission, and a surface spread of flame rating of class 0 to BS 476 parts 6 and 7, such as specially formulated fire-retardant glass reinforced resins or heavily filled fire-retardant epoxy resins.Both these materials are well known and have been used and promoted for fire-reoisting glazing beads, as indeed have non cobustible materials such as calcium silicate-based products. These products require some additional surface treatment in order to make them aesthetically acceptable to the architect or designer, unless a basic paint finish is all that is required.

The chamfered face of the beads can be profiled, the profiling being used to considerable effect to give the impression that the bead is smaller and less obtrusive than it actually is.

In the case of non-fire resisting partitions or screens there are few restrictions on materials and bead profiles, except for the obvious requirement that the bead is able to retain the glass or panel within the aperture under normal conditions.

Screens may be constructed using the system according to the invention, in which a door opening is provided to accept a standard size door of the same modular width.

The same glazing bead profile is also used to form the door stop, maintaining the same design theme throughout the screen or partition. The exposed cellulosic core, which forms the rebate of the door frame, is masked by either a thin veneer or a thin timber lipping.

(iv) Glass In the case of non-fire resisting screens and partitions virtually any glass may be used (providing it complies with safety reguletions, such as Part N of The Building Regulations 1992), ranging from standard float glass to irlpact-resistant and safety glasses. In the case cf fire-resisting elements, any fire-resistant glass of proven fire performance in tiinber-based constructions may be used.

Examples of such glasses are as follows: Wire-reinforced polished plate glass Wire-reinforced cast glass Wire-reinforced polished plate safety glass "Pyran" reinforced borosilicate glass "Pyroswiss" tempered float glass *Swissflam-lite" partially insulating glass *Firelite" ceramic glass "Pyrocet" coated and tempered float glass "Vetroflam" partially insulating glass "Pyroguard" wire-reinforcement between float glass "Fyreguard" wire-reinforced float glass laminated to wire-reinforced glass "Pyrostop" fire-resisting insulating glass "Contraflam" fire-resisting insulating glass "Pyrobel " " " " Swissflam. " " " " "Pyrodur" partially insulating fire-resisting glass "Pyrobelite" " .0 H (t II "Swiss Flamlite" " H " "* various fire-rated double glazed units The composite element as described above has been fire tested to BS 476 part 22:1987, (Fire Test Report FT10094,l/maw/93); in addition, letters of assessment have been issued covering a range of fire-resisting glasses in multi-paned screens using Mann McGowan's Pyroglaze 30 and 60 systems.These are as follows, the Standard employed being BS 476: part 22: Report/ Sponsor Description Fire Integrity Assessment No of glass (wins) FR 1265 Applicant GWPP 37 FAS 652 " Pyran 37 FAS 92068 " GWPP/CWPPSG 36t FAS 92069 as Pyran 39** FAS 93033 II Firelite 30 FT/10312 " Pyroguard 30 FT/10094 " GWPP 30 FT/10386 " Pyrostop) 30 Pyrobel ) C56298 II Pyrostop 30 WFRC 56298 Pilkington's Pyrostop DGU 60 FAS (D) 950 Castlecomer GWPP 60 Multi-paned screen incorporating a double leaf doorset SE " " " " " single " SE Legend GWPP - Georgian wired polish plate glass GWPPSG -" " " " safety glass DG - Double-glazed unit Wire-reinforced safety glass is considered to be one of the most difficult of the fire-resisting glasses with which to achieve a 60-minute fire integrity rating when testing to BS 476 part 20/22:1987, since the glass loses its ability to support its own weight at around 40 minutes into the fire test. By achieving this fire performance with wire-reinforced safety glass, it generally follows that the same performance can be achieved with other monolithic glasses with higher softening points and of proven fire performance, such as borosilicate glass ("Pyran" glass from Schott Glass), or ceramic glass ("Firelite" from Nippon Electric Glass).Tests have also been successfully carried out on insulating glasses ("Pyrostop from Pilkington Glass and "Pyrobelz from Glaverbel). This is not an exhaustive list and other glasses of proven fire performance in a timber based system can be used. The system according to the invention is therefore able to accommodate a wide range of glasses and still achieve the desired level of fire performance.

Where a fire-resisting glazed screen or partition is required to meet certain acoustic insulation criteria, a double-glazed unit of proven fire and acoustic performance should be employed. If one of the components is a soda lime float glass, care must be taken to ensure that the float glass element is always positioned towards the fire risk side.

Special requirement; sometimes arise where the glazed screen or partition has to meet both acoustic insulation and fire insulation criteria, and the manufacturers of fire-resisting insulating glasses have developed a double glazed unit of insulation glass to meet this need.

(v) Solid fire-resisting panels Fire tests have been successfully conducted using a panel comprising a central core of Mann McGowan's Pyrostrip 210 intumescent material faced on each side with 9 mm thick interior grade plywood. A fire integrity performance of 40 minutes and insulation rating of 36 minutes were achieved; and a central core of 9 mm thick exterior grade plywood faced on each side with Pyrostrip 210 intumescent material and covered with external layers df 9 mm exterior grade plywoocl achieved 60-minute integrity.

(vi) Frame jointing system The jointing system employed for assembly of the screens and partitions is preferably a simple dowel system, in which two or more hardwood dowels are used at each font, to make the joints between the frame, mullions and transoms. The dowels may be of plain round form, but a stronger construction is achieved if grooved dowels are used. This fact is well known and is common practice in the joinery trade. Alternatively, right-angled steel brackets may be used, but should be protected by intumescent strip or coatings.

(vii) Frame size Where a fire-resistant screen is required to have 30minute fire integrity, it has been found that an overall section for the frame, mullions and transoms of 92 mm wide and 50 nun deep is satisfactory, the cellulosic core of the framing detail being 68 mn x 50 mm and made from two layers of 25 mm thick MDF board bonded together. The two cover trims positioned on each side of the MDF were of Brazilian mahogany, 12 mm thick and 50 mm wide. This composite construction may be used for the outer frame, mullions and transoms.

Where 60-minute fire integrity is required, it has been found necessary to increase the MDF core to 76 mm x 38 mm with 6 mm thick Brazilian mahogany cover trims on the main faces, and 12 mm thick trims on each side of the minor faces, providing a composite section having overall dimensions of 100 mm x 50 mm.Alternatively, a core of 50 mm thick MDF faced on each minor face with 12 mm thick lippings of hardwood and provided with a central groove in the main face of the MDF to incorporate a 38 mm or wider intumescent strip, for example Mann McGowan's Pyrostrip lOOEC which is an edge-coated intumescent material of 100 grade based on hydrated sodium silicate; other types of intumescent materials, such as ammonium monophosphate, ammonium polyphosphate, or graphite-based intumescent materials may be used. This intumescent seal should run the full length of the frame, transoms and mullions, so that when assembled the intumescent seal lines out the glazing and panel apertures.It should also run through the jointing system, so that it expands during fire and seals any gaps which might develop due to shrinkage of the MDF during fire exposure, thereby protecting the joints.

Alternatively, where the intumescent strip lines out the reveal of the glazed and panel apertures it may be replaced with a layer of calcium silicate board or similar non-combustible material, the intumescent strip being used only at the joint positions to seal any gaps that develop due to the shrinkage of the MDF.

The purpose of the intumescent strip or the calcium silicate board is to isolate the glass from the reconstituted cellulosic core and prevent erosion of the glazing channel under the glass. It also forms a barrier to hot combustible gases which may form in the cellulosic core, preventing them from penetrating around the glass and thus reducing the chances of failure due to the loss of fire integrity, (viii) Adhesives In non-fire resisting structures and elements requiring only 30-minute fire integrity, a pva adhesive is satisfactory for bonding the dowelled joints and the cover trims Longer periods of fire resistance required the use of a thermoset adhesive to achieve the desired fire performance, suitable thermoset adhesive being a phenol/resorcinol formaldehyde resin.

(ix) Intumescent glazing detail Modified versions of Mann McGowan1s Pyroglaze 30 and 60 fire seals for t7mber-based glazing systems (based on adhesive pvc sleeved intumescent strips) systems were used as the intumescent glazing seals. In the half-hour fireresisting system the Pyroglaze 30 system was modified by increasing the intumescent seals on each side of the glass to 15 mm x 3 ma lOOPSA (self-adhesive), and for the onehour fire-resisting system the intumescent glazing system incorporated an intumescent seal (38 mm x 2 mm Pyrostrip EC - edge coated) in a groove formed in the MDF directly under the glass.

Pyroglaze 60 comprises Pyrostrip 25 mm x 3 mm SOOPSA intumescent seal set on each side of the glass, between the glass and the hardwood glazing bead.

In accordance with good glazing practice the glass was supported on 5 mm, thick high density hardwood setting blocks and spaced away from the mullions.

The beads used for the half-hour fire-resistant screen were secured using 32 mm long, lost-head pins, set at an angle to the normal face of the bead and at nominal 150 mn centres. Opposed pins were staggered and the fixings at each end of the beads positioned so that they were not more than 30 mm from the ends of the beads.

The glazing beads for the 60-minute screen/partition may be 57 mm or longer, lost-head pins or brass cup steel screws set at an angle to pass under the glass, and penetrate beyond the centre line of the screen, with the ends of the fixings securely located in the other side of the frame under the opposite glazing bead.

The screws are positioned at 150 mm centres, whilst pins are at 100 mm centres. Opposed screws and pins should be staggered so that they do not contact each other under the glass. End fixings should be within 30 mm of the ends of the beads.

(x) Fixing of the cover trims The cover trims for non-fire resisting and for fireresisting screens of up to 30-minute fire-resistance may be bonded with almost any type of thermoplastic or thermoset adhesive.

A screen was tested for 30-minute fire integrity, the cover trims having been bonded on to the cellulosic core using a pva adhesive. The cover trim was also pinned using 25 mm long lost-head pins at 250 =n centres.

In non-f ire resisting elements the trims can be glued, pinned or screwed; it is not necessary to use two fixing methods together. In 60-minute fire-resisting screens the adhesive plays a far more important role, having to hold the cover trim in position for the maximum period of tè. The protective char formed by the degradation of the cover trims serves to insulate and protect the cellulosic core from the full effects of the fire. The use of a thermoplastic adhesive, such as pva, is therefore unsuitable and a thermoset adhesive such as urea formaldehyde, phenol formaldehyde, phenol resorcinol formaldehyde or resorcinol formaldehyde, is required, combined with pinning the cover trim with 25 mm lost-head pins at 400 mm centres in the middle ar.d 150 mm centres at the ends.

It will be appreciated that screens and partitions constructed according to the invention may conveniently be of nodular construction and can be assembled on- or offsite, and be easily adjusted to size during assembly.

Because the construction is composite it may be easily packaged for protection against damage during transport when supplied in kit form.

Moreover, screens and partitions constructed according to the invention are inevitably cheaper to produce than a bespoke construction, particularly one formed of solid hardwood; moreover, structures according to the invention are immune from criticism on environmental grounds.

A construction according to the invention has been fire tested to BS 476 part 20/22:1987 at a Namas approved laboratory and achieved fire integrity ratings of 42 minutes and 55 minutes and subsequently assessed for 1 hour fire-reeistance. The products can therefore be offered to architects, specifying authorities and contractors, as a fully tested, assessed and certificated system.

An em.bodinent of the invention will now be described, by way of example, with reference to the accompanying drawings in which Figure 1 is a side elevation of a glazed screen according to the invention; Figure 2 is a section on the line II-II in Fig.

1; Figure 2A is a similar secTion through a modified construction; Figure 3 is detail of the bottom right hand corner of the screen of Fig. 1; and Figure 4 is a section on the line IV-IV in Fig.

1.

As shown in Fig. 1 a glazed screen 10 2720 mm wide and 2400 rnxti high comprises a frame 12 defining eight apertures each glazed with 6 mm thick polished plate wirereinforced safety glass panel 14 - 28, the dimensions of the panels being as follows: Reference Number Width (=u) Height (mm) 14,20,24 830 238 16,26 830 942 18,28 830 940 22 830 1942 The frame 30 comprises two outer frame members 30,32 and two mullions 34,36 joined at the bottom by bottom rails 38,40,42 and at the top by head rails 44,46,48, the fran:e being completed by transoms 50,52,54,56,58. All the rails and transoms were 840 mm long.

The constituents of the frame 12 were each formed (sce Fig. 2) of a central core 60 of MDF 50 mm thick and 68 mm wide comprising two layers 62,64 of 25 mm thick MDF board laminated together with urea formaldehyde adhesive 66 and flanked by cover trim 68,70 of 12 mm thick by 50 mm wide Brazilian mahogany bonded by pva adhesive and pinned by 25 mm long lost-head pins (not shown) at 250 mm centres, to its respective lateral faces.

The three bottom rails 38-42 were of similar construction but 100 mm deep.

The jointing of the frame 12 was accomplished as follows. The outer frame members 30,32 and mullions 34,36 were drilled (as shown in Figs. 3 and 4) through their entire thickness with pairs of holes 12 mm in diameter, at 20 mm centres each side of the central plane of the frame 12, and the bottom rails 38-40, head rails 44-48 and transoms 50-58 correspondingly drilled. High density hardwood dowels 72 (12 mm diameter and 45 mm long) were then inserted into the drillinys to assemble the frame 12.

The dowels 72 inserted from either side into one of the mullions 34,36 shared between transoms 50,52 and 52,54, respectively were of insufficient length to contact each other. The intervening space was therefore filled, or partially filled, with Proms gunnable intumescent sealant; the voids behind the remaining dowels were similarly filled, as shown for example at 73 in Fig. 4.

The glass panels 14-28 were mounted on 5 mm thick high density hardwood setting blocks (not shown) in accordance with good glazing practice, and held in place by high density hardwood glazing beads 74 15 mm high and 32 mm deep, fixed in position with 38 mm long lost-head pins (not shown) at 200 mm centres.

The pins were driven in at an angle to the chamfered face of the glazing bead, so as to pass under the glass panels 14-28 and through the central plane of the frame 12. The surface of each bead 74 was profiled in steps 76,78 (see Fig. 2) maintaining a ininimum 10 chamfer in a direction normal to the glass panel, (ll0 to the vertical plane of the glass).

Fire sealing was effected by using a modified version of Pyroglaze 30, intumescent strip 80 having a core 82 of intumescent material surrounded by a pvc sleeve 84 having adhesive faces; the intumescent strip 80 measured 15 irm x 3 mm in section and was positioned on each side of each of the respective glass panels 14-28, between the glass and the vertical face of the timber glazing bead 74. Strips 86,88 of intumescent material were also recessed into the upper surface of the layer 64 and under surface of the layer 62.

Fig. 2A shows a simpler construction of a transom in which similar parts are designated by the previously-used reference numerals. In the Fiy. 2A construction the core is formed of a single element 90 of MDF 50 mm thick and 68 mm wide, flanked by cover trim 68,70 of 12 mm thick by 50 mm and it will be noted that the stepping of the beads 74 is simplified.

The screen 10 was fire tested at SGS United Kingdom Ltd, Yarsley Technical Services, Trowers Way, Redhill, Surrey (now Warrington Fire Research) to BS 476 part 20t22:1987 and achieved 42 minutes integrity, Screens and partitions according to the invention may easily be fabricated so that a complete construction can be offered from stock, with special finishes being available to order. This availability is unique in the market into which the products will be sold.

Claims (20)

CLAIMS:

1. A separating structure for dividing internal space in a building, comprising e frame constituted by a number of frame m.exiber6 and defining one or more apertures each occupied by respective panel, and jointing members for securing the frame members together, the frame members being formed of a man-made material having a density and char rate not less than that of high-density hardwood, and the arrangement being such that the structure may be assembled on site.

2. A structure as claimed in claim 1, in which the exposed faces of the frame members are covered with cloaking beads or cover trim.

3. A structure as claimed in claim 1 or 2, in which the man-made material is a reconstituted, fibrous, cellulosic material.

4. A structure as claimed in claim 3, in which the manmade material has a low volatiles content, is relatively stress-free, and has a low level of smoke emission on combustion.

5. A structure as claimed in claim 3 or 4, in which the men-made material is medium density fibreboard, pressed stripped lumber or laminated veneer lumber.

6. A structure as claimed in any preceding clam, in which the jointing meens comprise dowels insertable into holes drilled in the frarne members or metal brackets.

7. A structure as claimed in any preceding claim, in which at least one of the panels is of glass.

8. A structure as claimed in any preceding claim, in which at least one of said panels is of solid, opaque material.

9. A structure as claimed in any preceding claim, in which the or each panel has acoustically-insulating properties.

10. A structure as claimed in ary preceding claim, in which at least one of the panels is retained in respective aperture by hardwood beads secured to the frame.

11. A structure as claimed in claim 9, in which the or each bead is secured to the frame by fasteners which extend into the frame beyond the medial plane of the panel.

12. A structure as claimed in any preceding claim, in which the frame and the or each panel have fire-resistng properties.

13. P structure as claimed in claim 12 and additionally com.prisìny intumescent material arranged, in the event of fire, to seal any gap between the or each pane and the frame and between the frame members.

14. A structure as claimed in any preceding claim and being of modular construction.

15. A structure as claimed in any preceding claim and arranged to be demountable.

16. A structure as claimed in any one of claims 1 to 14 arranged to be free-standing.

17. A structure as claimed in claim 1 and substantially as hereinbefore described.

18. A separating structure substantially as hereinbefore described with reference to Figs. 1, 2 or 2a, 3 or 4 of the accompanying drawings.

19. A kit of parts for forming a structure as claimed in any preceding claim.

20. The features herein described, or their equivalents, in any patentable, novel selection.