GB2594468A

GB2594468A - Method of installing a fire barrier in a wall cavity

Info

Publication number: GB2594468A
Application number: GB2006163.6A
Authority: GB
Inventors: Lewis Roger; Cleveland Craig
Original assignee: R Lewis & Co Uk Ltd
Current assignee: R Lewis & Co Uk Ltd
Priority date: 2020-04-27
Filing date: 2020-04-27
Publication date: 2021-11-03
Also published as: GB202006163D0; WO2021219981A1

Abstract

A method of making a fire barrier in a wall cavity of a building (100) comprises injecting a liquid intumescent sealant into the cavity via an inlet (115A-D) formed in a wall (101) that bounds the cavity (107) to form a fire barrier between an upper region of the wall cavity (107U) and a lower region of the wall cavity (107L). The intumescent may be injected into a preformed envelope or sock which has been inserted into the cavity and is supported within it by pins. The intumescent sealant may be a high expansion water based acrylic sealant containing graphite.

Description

METHOD OF INSTALLING A FIRE BARRIER IN A WALL CAVITY

BACKGROUND OF THE INVENTION

[0001] The present invention concerns fire barriers. More particularly, but not exclusively, this invention relates to methods of making fire barriers in wall cavities of buildings.

[0002] Buildings can comprise outer claddings to improve their aesthetics, to provide weather proofing, heat insulation and/or sound insulation. A building 100 comprising an outer cladding layer 101 is shown in FIG. 1. The building 100 is a three storey building, with the first and second floors formed by concrete slabs 103, 105. The cladding layer 101 is adhesively bonded the building at the slabs 103, 105 using a cement adhesive. FIG. 2 shows the section of the first floor slab 103 and cladding layer 101 at the location labelled "A" in FIG. 1, where the cladding layer 101 is adhesively bonded to the first floor slab 103. As can be seen, the presence of the adhesive between the cladding layer 101 and slab 103 results in the cladding 101 being spaced apart from the slab 103 by a distance X to form a wall cavity 107. In practice, the distance X may be around 50 millimetres. In the event of a fire, it is therefore possible for the wall cavity 107 to act as a chimney that accelerates the spread of the fire. This is especially true where the cladding layer 103 itself is flammable, or where some other flammable material is contained within the cavity 107, for example, a flammable insulating layer. It is therefore important that some form of fire barrier is provided within the cavity 107 to prevent the cavity 107 acting as a chimney in the event of a fire and to mitigate the physical spread of fire.

[0003] FIG.3 corresponds to FIG. 1 but with the cladding layer 101 removed to expose the adhesive that bonds the cladding layer 101 to the slab 103. As can be seen, the "dot and dab" method of application of the adhesive has resulted in discrete patches 109 of adhesive being transversely spaced-apart along the slab 103. While a continuous, unbroken layer of adhesive may provide a fire barrier effect, the gaps 111 between the patches 109 allow air to flow between an upper region 107U and a lower region 107L of the wall cavity 107 and so do not provide an adequate fire barrier function. Where a building has been discovered to have such gaps 111 between the adhesive patches 109, a fire barrier may need to be retrofitted installed to ensure that the building is adequately fire-proofed. Usually this -2 -involves removing and reinstalling the cladding layer 101, which is time consuming and costly.

[0004] In some buildings ventilation within the outer wall cavity is desirable. FIG. 4A shows a cross-section of such a building, with a cavity 207 located between a slab 203 and an outer cladding layer 201. To provide a fire barrier while allowing air flow within the cavity 207 an intumescent strip 213 is fixed to the slab 203. During normal conditions, as shown in FIG. 4A, air is free to flow within the cavity 207. However, during the event of a fire, heat from the fire causes the intumescent strip 213 to expand and block the cavity 207, as show in FIG. 4B. The expanded intumescent strip 213 therefore provides a fire barrier between an upper region 207U and a lower region 207L of the cavity 207.

100051 While ventilation and fire proofing may be desirable in some buildings that have been built without adequate fire proofing, it is not possible to retrofit an intumescent strip as shown in FIG. 4A and FIG. 4B without removal and replacement of the cladding. 100061 The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide improved methods of installing fire barriers within wall cavities in buildings.

SUMMARY OF THE INVENTION

[0007] The present invention provides a method of making a fire barrier in a wall cavity of a building, the method comprising the step of injecting an intumescent sealant into the cavity via a first inlet formed in a wall that bounds the cavity to form a first fire barrier portion. The first fire barrier portion serves as a fire barrier between an upper region of the wall cavity and a lower region of the wall cavity.

[0008] The invention provides a method of creating a fire barrier in a wall cavity of a building that is particularly advantageous where the building has been built and then later discovered to have inadequate fire proofing. The method uses an intumescent sealant which has an uncured liquid state so that a fire barrier can be installed via injection of fluid sealant into a wall cavity via relatively small inlet. The sealant cures post-injection to form a fire barrier. Other methods of retrofitting fire barriers in such buildings are more invasive, and may require removal and replacement of sections of wall and/or cladding. This can be time consuming, wasteful, and costly, especially where entirely new cladding must be fitted. [0009] The method may comprise the further step of injecting an intumescent sealant into the cavity via a second inlet formed in a wall that bounds the cavity to form a second fire barrier portion adjacent the first fire barrier portion. The first fire barrier portion and second fire barrier portion may form a fire barrier that extends between the two inlets and serves as a fire barrier between the upper region of the wall cavity and the lower region of the wall cavity.

[0010] The cavity may have a length and a width. The length may be longer than the width. The second inlet may be spaced apart from the first inlet along a length of the wall cavity and the second fire barrier portion may be formed adjacent the first fire barrier portion. The second fire barrier portion may be formed contiguously with the first barrier portion. The first fire barrier portion and second fire barrier portion may form a continuous fire barrier that extends between the two inlets and serves as a fire barrier between the upper region of the wall cavity and the lower region of the wall cavity.

[0011] Alternatively, the first fire barrier portion and the second fire barrier portion may be spaced apart across a width of the wall cavity and located either side of a cavity member. The cavity member may be an insulating board.

[0012] The first fire barrier portion may be spaced apart from the second fire barrier portion such that, when heated in the event of a fire, the sealant of the first and/or second barrier portions expands to close any spacing between the first and second barrier portions. Where the fire barrier portions are separated by a cavity member, the fire barrier portions may expand to substantially crush the cavity member. Alternatively, the second barrier portion may be formed substantially contiguously with the first barrier portion.

100131 The cavity may have a length and a width. The length may be longer than the width. The second inlet may be spaced from the first inlet along a length of the cavity. The first inlet and second inlet may be aligned along a horizontal axis. The method may comprise the steps injecting intumescent sealant into the cavity via a multiplicity of laterally spaced inlets to make a multiplicity of fire barrier portions. The method may comprise the steps of -4 -making holes in the walls that bound the wall cavity, the holes providing the inlet(s) via which intumescent sealant may be injected into the cavity. The holes may be drilled.

[0014] It will be appreciated that the number of fire barrier portions needed to create a fire barrier within a wall cavity will depend on the size of the cavity. For example, for a relatively small cavity, only one fire barrier portion may be needed. Where a wall cavity extends along the outside of a building then several fire barrier portions may be required to create a fire barrier that laterally extends across the entire of the cavity to separate upper and lower regions of the cavity. Furthermore, the volume of sealant required to form each fire barrier portion will in part be determined by the spacing between adjacent inlets. It will be appreciated that a higher volume of intumescent sealant will be required to create contiguous fire barrier portions the further apart the inlets are spaced. The inlets may have a centre-to-centre spacing of, for example, between 100 millimetres and 200 millimetres. The centre-to-centre spacing may be approximately 150 millimetres. The inlets may be formed by holes having a diameter of between 10 and 20 millimetres [0015] The cavity may be an external wall cavity of a building. A wall that bounds the cavity on a first side may be a cladding layer. The first inlet may be formed in the cladding layer. The second inlet may be formed in the cladding layer. The cladding layer may form the outermost layer of the building. The cavity may be defined on a second, opposite side by the edge of a slab forming a floor of a building. One or more fire barrier portions may extend between the edge of the slab and the cladding layer.

[0016] The method may comprise the step of determining the location of an adhesive used to bond the cladding layer to the edge of the slab. The method may comprise the step of making the first inlet and, optionally, second inlet in the cladding layer. The first and second inlets may be made vertically above the adhesive.

100171 Intumescent sealant may be injected via the first inlet into a preformed envelope to inflate the preformed envelope. The inflated preformed envelope may form the first fire barrier portion. The preformed envelope may be configured to control the shape and size of the first fire barrier portion. Intumescent sealant may be injected via the second inlet into a second preformed envelope to form a second fire barrier portion. It will be appreciated that a multiplicity of preformed envelopes could be used to make a multiplicity of fire barrier portions.

[0018] The preformed envelope may be defined by an outer wall and there may be a plurality of apertures formed in the outer wall. In this particularly advantageous arrangement of the preformed envelope, intumescent sealant is pushed out of the envelope via the apertures during inflation of the envelope. The sealant located upon the outer surface of the envelope can then adhere to a retaining surface within the cavity to ensure that the first fire barrier portion is held in place within the cavity. The retaining surface may be, for example, one of the walls of the cavity, one or more fire barrier portions within the cavity, and/or a layer of insulation contained within the cavity. The envelope may be formed by a mesh. The envelope may be formed by a mesh sock. The plurality of apertures may be provided by the mesh. The envelope may be formed by a fabric or net. The envelope may be made from a plastic, metal, or from any other suitable material. The envelope may be formed by a high-density polyethylene netting. The envelope may be made of a fire retardant material.

[0019] The first fire barrier portion may be supported by one or more supporting members within the wall cavity. One or more supporting members may be placed within the cavity to support and position the first fire barrier portion formed by the preformed envelope. The supporting members may be, for example, pins that span the width of the cavity between an outer cladding layer and an inner slab edge. There may be a plurality of supporting members within the cavity. The supporting members may be aligned along a horizontal axis. The method may comprise the additional steps of inserting a plurality of supporting members into the cavity. The pins may be inserted through an outer cladding layer of the building into the cavity. The outer cladding layer may be a layer of bricks and mortar. The pins may be inserted through the mortar.

100201 Prior to inflation, the preformed envelope may be laid across one or more supporting members positioned within the cavity. The preformed envelope may be elongate and form an elongate first fire barrier portion that runs along a length of the cavity when inflated with intumescent sealant. The elongate preformed envelope may be up to 1 metre long. The elongate preformed envelope may be up to 2 metres long.

[0021] The inflated envelope may define one or more ventilation ducts therethrough. The first fire barrier portion may therefore be formed with ventilation ducts configured to allow the flow of gases between the upper region of the wall cavity and the lower region of the wall cavity via the ventilation apertures. The ventilation ducts may be between 25 and 100 mm in diameter. In this particularly advantageous embodiment of the invention, a ventilated fire barrier can be provided by using an envelope having preformed ventilation ducts.

100221 The uncured intumescent sealant may be a high expansion water based acrylic sealant containing graphite.

DESCRIPTION OF THE DRAWINGS

100231 Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: FIG. 1 is a schematic drawing of a building; FIG. 2 corresponds to a section of the building contained within the box labelled "A" in FIG. 1 and shows a wall cavity between the slab edge and outer cladding of the building; and FIG. 3 corresponds to FIG. 2 but with the outer cladding layer removed; FIG. 4A shows a cross-sectional view of a wall cavity of a building comprising a fire barrier in the form of an intumescent strips that is arranged to allow ventilation within the wall cavity; FIG. 4B corresponds to FIG. 4A but with the intumescent strip in an expanded state; FIG. 5, shows the section of FIG. 2 during a process of installing a fire barrier in the wall according to the first example of the invention; FIG. 6. Corresponds to FIG. 3 after installation of the fire barrier; FIG. 7. Corresponds to FIG. 5 after the process of installing the fire barrier has been completed; FIG. 8 shows a section of a building similar to that of FIG. 2 during a process of installing a fire barrier in the wall cavity according to the second example of the invention either side of an insulating board; -7 -FIG 9 is cross-sectional a view of the section of building of Figure 8 taken along the direction of the arrow labelled A in FIG. 8; FIG 10 corresponds to FIG. 9 but shown with mesh socks supported on pins within the wall cavity, either side of the insulating board; and FIG 1 I corresponds to FIG. 10 after the mesh socks have been filled with intumescent sealant to create first and second fire barrier portions either side of the insulation board; FIG. 12 corresponds to a view of FIG. 11 taken along the direction of the arrow labelled "B" in FIG. 11; FIG. 13 is a schematic cross-sectional view of one of the fire barrier portions shown in FIG. 11 and FIG. 12; FIG. 14 corresponds to FIG. 12 after the intumescent fire barrier portions have expanded after being heated by a fire; FIG. 15 is cross-sectional view of an exterior wall cavity of a building during a process of installing a fire barrier in the wall cavity according to a third example of the invention; FIG. 16 corresponds to FIG. 15 but with a mesh sock supported on pins within the wall cavity; FIG. 17 corresponds to FIG. 16 after the mesh sock has been inflated with intumescent sealant to form a ventilated fire barrier; FIG. IS is a view of the arrangement shown in FIG. 17 from the direction of the arrow labelled "C"; and FIG. 19 corresponds to FIG. 17 after the heat from a fire has caused the intumescent fire barrier to expand and close the ventilation holes in the fire barrier.

DETAILED DESCRIPTION

[0024] The invention relates to methods of creating fire barriers within wall cavities in buildings using intumescent sealant. The term "fire barrier" as used within the context of this application should be understood to mean both a non-flammable barrier that mitigates -8 -the physical spread of a fire beyond the barrier, as well as a barrier configured to mitigate the movement of gases across the barrier.

[0025] In each case the intumescent sealant used is a high pressure expansion (HPE) water-based acrylic sealant containing graphite. The sealant is supplied as a liquid and cures to form a solid intumescent fire barrier. Such sealant is commercially sold as ROCKWOOL FIREPRO <RTM> and QuelStop HPE Sealant. However, in other embodiments, other suitable intumescent sealants may be used.

100261 Such fire barriers may be needed, for example, where a building has been already been built but then been discovered to have inadequate means of fire prevention in place. Embodiments of the invention are described in the examples below.

EXAMPLE 1

[0027] The first example relates to a method of creating a fire barrier in the external wall cavity of the building 100 described above with reference to FIG. 1 to FIG. 3. The method first involves drilling a plurality of holes 115A, 115B, 115C, 115D through the outer cladding layer, as shown in FIG. 5. In this case the holes 115A-115D are 15 millimetres in diameter, are aligned on a horizontal axis H, and have a centre-to-centre spacing V of 150 millimetres. In other embodiments of the invention the holes may be from 10 to 20 millimetres in diameter.

[0028] A delivery tube 117 is then inserted into the hole 115A and a predetermined volume of intumescent sealant is injected into the cavity 107. The process is repeated by injecting predetermined volumes of intumescent sealant into holes 115B to 115D. The injected volumes of sealant cure to form fire barrier portions I I 9A to I I 9D within the cavity 107, as shown in FIG. 6. The volume of sealant injected into the cavity is dependent on the dimensions of the cavity, the spacing of the holes, and the quality of fire barrier needed. In this example, the volume of sealant has been chosen so that the fire barrier portions 119A to 119D are arranged contiguously, with no gaps between them. Once the barrier portions 119A to 119D have been installed, the holes 115A to 115D are then filled and finished to match the cladding layer, as shown in FIG. 7.

[0029] The fire barrier portions 119A to 119D form a continuous fire barrier 119 that runs along the slab 103 in a length direction L, and spans the width X of the cavity between the slab 103 and the cladding layer 101. Because there are no gaps between the fire barrier portions 11 9A to ii 9D, air cannot flow between the upper part of the cavity 107U and the lower part of the cavity 107L so that the cavity 107 cannot provide a chimney effect in the event of a fire. Furthermore, because the fire barrier 109 is formed from an intumescent material, the size of the fire barrier increases when heated in the event of a fire which improves the sealing effect that the fire barrier 109 has within the cavity and also further reduces the chance of a fire physically breaching the fire barrier 109.

EXAMPLE 2

[0030] The second example relates to a method of retroactively installing a fire barrier in a wall cavity of a building wherein the wall cavity contains a combustible insulation panel. FIG. 8 shows a section of a building in the region of a slab 303. In this case, the building comprises an outer brick and mortar layer 301 and an insulating polyisocyanurate (PIR) board 321 within the cavity 307, between the brick and mortar layer 301 and the slab 303. The MR board 321 is flammable so a fire can quickly spread within the cavity 307 without a fire barrier in place if the PIR board 321 combusts.

[0031] To install a fire barrier within the cavity 307, a plurality of pins 322 are installed in the cavity as shown in in FIG. 9, which is a top-down view of the cavity 307 in the direction of the arrow labelled A in FIG. 8. Each pin 322 is installed from the outside 330 of the building such that it passes through the mortar of the outer brick and mortar layer 301, through the cavity 307 and PIR board 321 and into the slab 303. The pins 322 are arranged such that they are all spaced apart by 50 millimetres and aligned along a horizontal axis H'.

[0032] An outer mesh sock 323A is then laid across the pins 322 in the outer region of the cavity, between the PIR board 321 and the brick and mortar layer 301, and an inner mesh sock 323B is laid across the pins 322 in the inner region of the cavity, between the PIR board 321 and the slab 303, as shown in FIG. 10. To install the socks 323 within the cavity 307, holes are made at first and second ends 325, 326 of the cavity 307, the socks 323 are -10 -then inserted into the holes at the first end 325 of the cavity and are pulled towards the holes at the second end of the cavity 326. In this embodiment of the invention, the socks 323A, 323B are made from a fire retardant plastic netting. However, other suitable materials may be used in other embodiments of the invention.

[0033] The socks 323 are then filled with intumescent sealant via a delivery tube 317 to form an elongate outer fire barrier portion 3I3A between the PIR board 321 and brick and mortar layer 301, and an elongate inner fire barrier portion 313B between the PIR board 321 and the slab 303, as shown in FIG. 11 and FIG. 12. The mesh socks 323 thereby provide an envelope for receiving the intumescent sealant to hold the liquid sealant in place while it cures so that, for example, the intumescent sealant does not simply fall to the bottom of the cavity 307. The socks 323 also have a preformed shape to control the shape and size of the fire barrier portions. Furthermore, and with regards to FIG. 13 which shows a cross sectional view of one of the fire barrier portions 313, because the socks 323 are formed by a mesh, when the socks 323 are filled, sealant is pushed through the apertures 3231 of the mesh from inside the sock to outside the sock so that the fire barrier portion comprises an inner sealant region 3131 within the sock 323, and an outer sealant region 3132 located around the outside of the sock 323. The outer sealant region 3132 provides the uncured fire barrier portions with an adhesive surface that can bond with the brick and mortar layer 301, the slab 303, the PER board 321, and/or the pins 322.

[0034] When sufficiently heated in the event of a fire, the intumescent fire barrier portions 313 expand as shown in FIG. 14 to crush the PIR board 321, thereby effectively separating the PIR board into an upper portion 32IU and a lower portion 321L, The fire barrier portions 313A, 3I3B thereby form a fire barrier 313 that can prevent a fire spreading through the cavity 307 via the PIR board 321.

EXAMPLE 3

[0035] The third example of an embodiment of the invention relates to a method of retroactively installing a fire barrier in a wall cavity 407 of a building wherein the wall cavity 407 requires ventilation.

[0036] To install a fire barrier within the cavity 407, a plurality of pins 422 are installed in the cavity as shown in in FIG. 16, which is a top-down view of the cavity 407. The pins are installed from the outside 430 of the building such that they pass through the mortar of an outer brick and mortar layer 401, through the cavity 407, and into a slab 403. The pins are arranged such that they are all spaced apart by 50 millimetres and aligned along a horizontal axis 1-F.

100371 A mesh sock 423 is then laid across the pins 422 within the cavity 407, as shown in FIG. 15. To install the sock 423 within the cavity 407, holes are made at first and second ends 425, 426 of the cavity 407 and the sock 423 is then inserted into the hole at the first end 425 of the cavity and is pulled towards the hole at the second end of the cavity 426. In this embodiment of the invention, the sock 423 is made from a fire retardant plastic netting. However, other suitable materials may be used in other embodiments of the invention.

100381 The sock is then filled with intumescent sealant via a delivery tube 417 to form an elongate fire barrier 413 that runs along the length of the cavity 407, supported by the pins 422, and spans the gap between the outer brick and mortar layer 401 and the 403 slab. The sock 423 used in this embodiment of the invention is formed with a plurality of ventilation apertures so that when the sock 423 is filled with intumescent sealant the sock 423 forms a fire barrier 413 comprising a plurality of ventilation apertures 427 through which air can freely pass between the lower region of the cavity 407L and the upper region of the cavity 407U, as can be seen in FIG. 17 and FIG. 18.

[0039] In the event of a fire, the intumescent sealant expands to close the apertures 427, as shown in FIG. 19, so that the cavity 407 does not provide a chimney effect in the event of a fire. As such, the resulting fire barrier 413 provides a function that is analogous to the fire barrier 213 described above with reference to FIG. 4.

100401 Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0041] In a further embodiment of the invention that is similar to the second example, first and second ventilated fire barriers may be installed on either side of an insulating board or -12 -another member contained within the wall cavity. Other embodiments of the invention may involve installing a mixture of ventilated and non-ventilated fire barrier portions. In another embodiment of the invention similar to the second embodiment of the invention, an elongate sock can be filled to create a fire barrier that blocks the entire cross-section of a wall cavity that does not contain an insulating board. Instead of using pins to support the sock, other suitable supporting members may be used. In some embodiments of the invention the sock(s) may be supported by the adhesive used to bond the cladding layer to the slab. Instead of elongate socks, multiple smaller socks may be used. For example, a fire barrier similar to that provided by the method of the first example could be provided by filling a plurality of smaller socks with intumescent sealant to provide a plurality of fire barrier portions that are arranged along the length of the slab.

100421 Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-13 -CLAIMS1. A method of making a fire barrier in a wall cavity of a building, the method comprising the step of injecting a liquid intumescent sealant into the cavity via a first inlet formed in a wall that bounds the cavity to form a first fire barrier portion, the first fire barrier portion serving as a fire barrier between an upper region of the wall cavity and a lower region of the wall cavity.
2. A method according to claim I comprising the further step of injecting an intumescent sealant into the cavity via the a second inlet formed in a wall that bounds the cavity to form a second fire barrier portion.
3. A method according to claim 2, wherein the second inlet is spaced apart from the first inlet along a length of the wall cavity and the second fire barrier portion is formed adjacent the first fire barrier portion.
4. A method according to claim 3, wherein the second fire barrier portion is formed contiguously with the first barrier portion, the first fire barrier portion and second fire barrier portion forming a continuous fire barrier that extends between the two inlets and serves as a fire barrier between the upper region of the wall cavity and the lower region of the wall cavity.
5. A method according to claim 2, wherein the first barrier portion and the second barrier portion are spaced apart across a width of the wall cavity and are located either side of a cavity member.
6. A method according to any preceding claim comprising the steps of making hole(s) in the wall(s) that bound the wall cavity, the hole(s) providing the inlet(s) via which intumescent sealant may be injected into the cavity.
-14 - 7. A method according to any preceding claim, wherein a wall that bounds the cavity on a first side is a cladding layer.
8. A method according to claim 7, wherein the first inlet is formed in the cladding layer.
9. A method according to claim 7 or claim 8, wherein the cavity is defined on a second, opposite side by the edge of a slab forming a floor of a building.
10. A method according to any preceding claim, wherein intumescent sealant is injected via the first inlet into a preformed envelope to inflate the preformed envelope, the inflated preformed envelope forming the first fire barrier portion.
11. A method according to claim 10, wherein the preformed envelope is defined by an outer wall and there are a plurality of apertures formed in the outer wall.
12. A method according to claim 10 or claim 11, wherein the first fire barrier portion is supported by one or more supporting members within the wall cavity.
13. A method according to any of claims 10 to 12, wherein the preformed envelope is elongate and forms an elongate first fire barrier portion that runs along a length of the cavity when inflated with intumescent sealant.
14. A method according to any of claim 10 to 13, wherein the inflated envelope defines one or more ventilation ducts therethrough such that the first fire barrier portion is formed with ventilation ducts configured to allow the flow of gases between the upper region of the wall cavity and the lower region of the wall cavity via the ventilation ducts.
15. A method according to any of claims 10 to 14 when dependent on claim 2, wherein intumescent sealant is injected via the second inlet into a second preformed envelope to -15 -inflate the second preformed envelope, the inflated second preformed envelope forming the second fire barrier portion.
16. A method according to any preceding claim, wherein the uncured intumescent sealant is a high expansion water based acrylic sealant containing graphite.