WO2001028770A1

WO2001028770A1 - Breathable buildings materials

Info

Publication number: WO2001028770A1
Application number: PCT/GB2000/004069
Authority: WO
Inventors: Leslie James Squires; Timothy John Woodbridge
Original assignee: Hunt Technology Limited
Priority date: 1999-10-21
Filing date: 2000-10-20
Publication date: 2001-04-26
Also published as: DE10083517T1; AU1038801A

Abstract

A breathable building membrane (1) includes an under layer (3) formed of a microporous polymeric film and a top layer (5) formed of a filamentous polymeric fabric which is bonded to the under layer, said under and top layers (3 and 5) being disposed in overlying relationship and being stabilised respectively against heat degradation and ultra-violet light degradation (Figure 2). The top layer (5) may be provided with a moisture vapour permeable reflective coating (5c) (Figure 7).

Description

_BREATHABLE BUILDINGS MATERIALS

This invention relates to building materials, in particular to breathable building membranes.

Breathable membranes made from synthetic materials have become increasingly important in the construction industry. They are widely used, for example, as "breather membranes" in the wall cavities of timber frame buildings and are replacing traditional, non-breathable roofing underlay materials such as bitumen-coated felts and the like.

When used as roofing underlays, synthetic breather membranes protect the building from wind-driven hail or snow that might penetrate through the gaps between roofing tiles or slates (hereinafter referred to as "tiles") forming the outer roof layer or covering, thereby retaining the advantages of bituminous roofing underlays by being moisture resistant yet permitting the transmission of water vapour from the roof space between the tiles and the ceiling rafters which reduces roof space condensation.

Roof space condensation is caused by insulating buildings from loss of heat through the roof by means of suitable insulating materials. Nowadays adequate roof space ventilation has become a necessity and has resulted in a plethora of roof space ventilation systems involving ventilation tiles, eaves ventilation and/or ridge ventilation. Accordingly, the manufacturers of roof tiles provide various forms of ventilation systems for use with their roof tiles and specify the kind of roofing underlays to be used. Thus, current tiled roofs can have the benefit of roof space ventilation systems which permit a controlled flow of air through the roof space at the least from eaves to eaves and optionally also from eaves to ridge, substantially to reduce roof space condensation and yet guard against the ingress of wind driven moisture into the roof space though the ridge and through the eaves.

During the construction or repair of a roof, the roofing underlay is frequently the only layer to afford protection to the building before the roof tiles are laid. It is common for roofing underlays to be totally exposed in this way for periods of three months or more.

In timber frame buildings, the internal skins of the cavity walls are made from framed panels which replace the block and mortar internal skins of traditional buildings and the timber panels are faced with wall breather membranes which present the outwardly facing surface of the internal skin. Wall breather membranes (also known as "housewrap") can be applied to the timber panels during manufacture or by the builders on the building construction site. The external skins of the cavity wall are of any traditional material, such as brick, concrete block, masonry block, pebble dashed block or natural stone, all of which may be generically referred to as "building blocks", with the internal skins being attached to the external skins in spaced apart relation by metal wires or straps at intervals to form the wall cavity.

The primary function of wall breather membranes is to act as a condensation barrier in the wall cavity through which warm, moist air from the inside of a building may pass to the outside whilst at the same time protecting the timber frame from any condensation that might form when the warm, moist air meets the cold air of the wall cavity. Condensation in the wall cavity forms preferentially on the breather membrane which lines the internal skin of the cavity, rather than on the timber panels forming the internal skin until the ambient conditions allow the moisture to evaporate.

Another function of wall breather membranes is to provide protection to the timber frame during construction of the building when the internal skin of the cavity wall would otherwise be exposed to the elements until the external skin is erected.

The advantages of the timber frame method of construction are that the main frame of the building is erected very quickly and by a dry process. Internal work can therefore begin as soon as the roof is added. The external wall skins can be left until later. A further advantage claimed by manufactures of timber frame buildings is that it is very easy to increase the amount of insulation compared with masonry buildings, thus making timber frame buildings more energy efficient.

Inventors employed by the Applicant have already invented an improved synthetic breathable building membrane for use as a roofing underlay that is resistant not only to moisture but is more resistant than hitherto to changes in ambient environmental conditions experienced by the underlay when forming part of a roof. This roofing underlay is described In the specification of Applicant's unpublished Patent Application No. 9924954.2, the subject matter of which is incorporated into this specification by reference.

The main object of the present invention is to provide an improved synthetic breathable building membrane that that is not only suitable for use as a roofing underlay but can also be used as a wall breather membrane.

The Applicant has found from recent tests that the roofing underlay described in the specification of Application No. 9924954.2 can also be used as a wall breather membrane and has advantages over the breathable membranes that have hitherto been used in walls.

Accordingly, from one aspect, the present invention resides in a breathable building membrane suitable for use as a wall membrane and as a roofing underlay and formed of a microporous polymeric film and a top layer formed of a filamentous or fibrous polymeric fabric which is bonded to the under layer, said under and top layers being disposed in overlying relationship and being stabilised respectively against heat degradation and ultra-violet light degradation.

Hereinafter, for convenience the terms "filaments" and "filamentous", will be used for the following words, namely "filaments", "filamentous", "fibres" and "fibrous". From another aspect, the present invention resides in a method of manufacturing a breathable building membrane suitable for use as a wall membrane and a roofing underlay, including providing a fabric forming melt of a thermoplastic polymer, adding an ultraviolet stabilising preparation to the melt, forming a plurality of filaments from the fabric forming melt to provide a fabric layer, providing a film forming melt of a thermoplastic polymer, adding a heat stabilising preparation to the film forming melt, forming the film forming melt into a microporous film layer and applying heat and pressure to the fabric layer and film layer to the bond the two layers together in overlying relationship.

Not only is the fabric layer resistant to degradation by ultra violet light when the breathable building membrane is exposed to the elements during building construction or roof repair, but also those parts of the microporous film layer that are vulnerable to increases in temperature are resistant to heat degradation which could otherwise occur by increases in the roof space or building rooms as the case may be. Degradation of polymeric underlays occurs when the long polymer chains which provide the requisite strength break up and become smaller and smaller. Ultimately, this can result in parts of, or indeed the entire, underlay disintegrating into fine powder and thus the function of the underlay is entirely negated.

Preferably, the top fabric layer has a top surface bearing a moisture vapour permeable reflective coating.

Accordingly, from another aspect, the present invention resides in a breathable building membrane, for example for use as a roofing underlay or a wall membrane, including an under layer formed of a microporous polymeric film and a top layer formed of a filamentous polymeric fabric which is bonded to the under layer, said under and top layers being disposed in overlying relationship and being stabilised respectively against heat degradation and ultra-violet light degradation, and said top layer having a top surface bearing a moisture vapour permeable reflective coating.

The invention also resides, from another aspect, in a method of manufacturing a breathable building membrane, comprising providing a fabric layer formed from a plurality of bonded filaments, that has a top surface and which is stabilised against ultraviolet heat degradation, applying a moisture vapour permeable reflective coating to the top surface of the fabric layer, providing a film forming melt of a thermoplastic polymer, adding a heat stabilising preparation to the film forming melt, forming the film forming melt into a microporous film layer and applying heat and pressure to the fabric layer and the film layer to the bond the two layers together in overlying relationship with the reflective coating facing outwards.

The combined effect of the ultraviolet and heat stabilisation of the under layer and top layer and moisture vapour permeable reflective coating, reduces the infra-red loading of the entire building membrane, thereby further increasing the resistance of the building membrane to degradation. Moreover, when the building membrane serves as a roofing underlay, during the construction or repair of a roof when the underlay can be totally exposed for periods of three months or more and affords the only protection to the building, the moisture vapour permeable reflective coating enhances this protection.

In order to provide protection and strength, the top fabric layer is advantageously of relatively heavy weight as compared to the under film layer as it provides the first defence against ultraviolet light degradation and is therefore, also highly ultraviolet light stabilised.

For protection of the under film layer against inadvertent damage by builders and for added strength which is preferred, the under film layer may be sandwiched between two of fabric layers of which one forms the top layer which is ultraviolet stabilised and has a top surface that is preferably provided with any of the moisture vapour permeable reflective coatings defined above and the other forms a bottom layer which does not necessarily have to be ultraviolet stabilised nor be provided with a moisture vapour permeable reflective coating on its exposed surface.

Thus, by means of this aspect of the invention there is provided a laminated breathable building membrane for use as a roofing underlay for tiled roof structures, or as a wall membrane, said underlay being made from a spunbonded nonwoven ultra violet light stabilised top fabric layer with a top surface preferably provided with any of the moisture vapour permeable reflective coatings defined above and a microporous heat stabilised film layer which is preferably sandwiched between the top layer and another synthetic fabric layer.

Expressed in another way the invention resides in a breathable laminated building membrane such as a roofing underlay for use with tiled roof structures or a wall membrane, said laminated building membrane being made from a spunbonded nonwoven ultra violet light stabilised top fabric layer with a top surface preferably provided with any of the moisture vapour permeable reflective coatings defined above and a microporous heat stabilised film layer which is sandwiched between the top layer and another synthetic fabric layer.

Applicant has found that by making the reflective coating of a thin metallic layer, such as aluminium, that the infra-red reflectance of the building membrane can be significantly improved. However, aluminised or other metallised monolithic film products are not suitable for presenting a reflective surface since they would inhibit the moisture vapour permeability of the composite building membrane.

Accordingly, a moisture vapour permeable reflective coating, in accordance with one embodiment of the invention, is achieved by plasma deposition of a suitable metallic material, such as metallic aluminium, that does not interact with the substrate, onto the top surface of the top layer. For example, Applicant has found that metallic copper is not suitable because it interacts with polypropylene so as to promote chain degradation. The resulting fabric is both air and moisture vapour permeable whilst being reflective to both visible light and infra-red radiation. Whilst it is possible to control the deposition such that the metallic material is deposited onto one or both surfaces of the top layer, deposition of the metallic coating onto just one surface of the top layer has been found to be sufficient for spunbonded fabric component to achieve the desired reflective effect for breathable building membranes.

Typically, the deposited metallic layer has a thickness of about 40nm.

Preferably the filaments of the fabric layer are nonwoven and are bonded together by a bonding method that includes entanglement of the filaments using high pressure water jets, adhesive bonding, ultrasonic bonding or thermal bonding. Thermal bonding involving the use of a combination of heat and pressure to bond the filaments is preferred but ultasonic bonding or adhesive bonding may alternatively be used. Thermal or ultrasonic bonding by spunbonding or spunlaying is preferred.

When the fabric of the top layer is made from spunbonded filaments, the deposited metallic coating such as aluminium does not form a discrete layer on the top surface of the top layer but coats the surfaces of the individual filaments which collectively form the surface layers of the spunbonded fabric top layer.

The metallised coating may be applied to the spunbonded fabric surface of a completed building membrane, i.e. a membrane of which the under layer, top layer and any additional layers have already been bonded together or which has already been laminated, as referred to above. However, such bonded building membranes, especially when used as wall breather membranes, are commonly wider than the maximum processing width of current aluminisation coating equipment capable of processing open structures such as a spunbonded fabric. Wall breather membrane widths of greater than 2.5m are common, for example 2.6m and 2.7m, compared to a typical relevant aluminium coating process width of 1 6m

Applicant has found that it is possible to coat a spunbonded fabric with an aluminium coating and then subsequently to process the aluminised spunbonded fabric, using thermal or ultrasonic bonding, for example, to form the completed building membrane, without destroying the aluminium coating The adhesion of the aluminium coating to the surface of the filaments may not be 100% and some of the aluminium of the coating is relatively easily removed by friction from the fabric surface Adhesion of the aluminium to the top fabric layer may be enhanced by reduced pigment loading of the spunbonded fabric and/or by surface treatment, such as corona discharge treatment of the fabric surface, prior to aluminisation

However, even without these aids to adhesion, Applicant has found that an aluminised spunbonded fabric may be processed to form an aluminised reflective, breathable building membrane for use as a roof underlay, as housewrap or even as an underfloor breather support membrane for fibrous board/slab insulation between joisted timber floors

Manufacturing the building membrane in this way, incorporating an aluminised spunbonded fabric as a raw material component in the bonding or lamination process, enables aluminised building membranes to be manufactured without regard to the limiting width of the aluminisation process since aluminised spunbonded fabric rolls can be processed side-by-side to give the requisite laminate width It should be noted, however, that this method of manufacture, using thermal or ultra-sonic bonding, means that the spunbonded fabric requires a one-sided coating of aluminium only since an aluminium coating on the top and bottom surfaces of the top fabric would interfere with the ability of the fabric filaments to form a thermal or ultrasonic bond with the under layer It is thus necessary for the spunbonded fabric to have an uncoated bottom surface adjacent to the under micro-microporous film layer and for the aluminised surface to form the top surface of the top fabπc layer that, in use, presents the outer or top surface of the building membrane laminate In spunbonded nonwoven production of the top fabric layer, a melt of a thermoplastic polymer is produced and continuous filaments of thermoplastic polymer are extruded through thousands of spinnerets to form a loose web which is then bonded using heat and pressure or alternatively ultrasound to form the finished fabric. Thermoplastic polymers, such as polypropylene, polyamide or polyester, only are suitable for manufacturing spunbonded fabrics and polypropylene is preferred.

This is because polypropylene has a melting point in the region of 165°C and is the preferred thermoplastic polymer for manufacturing the top fabric layer because it is relatively low cost, easy to process at moderate temperatures, and has good physical properties and chemical resistance characteristics and is inherently hydrophobic.

For ease of manufacture and for ensuring uniformity of stabilisation throughout the entire top fabric layer, the ultra violet light stabiliser conveniently is added to the thermoplastic melt prior to the production of the web-forming thermoplastic filaments. Ultraviolet stabilisers may be of any suitable kind but applicants have found organic hindered amines are most advantageous, and that poly [[6[(1 ,1 ,3,3,tetramethylbutyl)amino]-s-triazine 2,4diyl][2,2,6,6,-tetramethyl-4-piperidyl) imino] hexamethyiene

[2,2,6,6,tetramethyl-4-piperidyl) imino]] is particularly effective.

Again, the heat stabilisers may be of any suitable kind but applicants have found that phenolics are most advantageous, in particular benzenepropionic acid:-3,5-bis(1 ,1-dimethylethyl)-4-hydroxy,2,2bis[[3-[3,5bis(1 ,1dimethylethyl)- 4-hydroxyphenyl]-1 -oxopropoxy]methyl]-1 ,3,-propanediylester.

Thermal bonding of the thermoplastic filaments of the loose web for the top fabric layer may be achieved by the application of heat and pressure or by ultra sonic bonding applied intermittently so that discrete areas only of top fabric layer are bonded which enables the filaments to move relatively freely in the areas between the bonded points and enhances the transmission of moisture vapour received through the micropores of the under film layer. Discrete or point bonding may be achieved by the use of a calendar system comprising two heated rolls, one smooth and one carrying a raised embossing pattern on its surface. The loose web of filaments are bonded together as they pass through the nip between the two calendar rollers to bond the loose web of filaments thermally together to produce a spunbonded nonwoven ultra violet light stabilised top fabric layer which is resistant to ultraviolet light degradation.

The under layer of microporous film may be made of any suitable polymeric material by any known film forming technique but thermoplastic polymers, such as polypropylene, polyamide or polyester are preferred for compatibility with, and ease of bonding to, the preferred thermoplastic polymers of the top fabric layer.

For example, in a preferred method according to the invention involving thermoplastic polymers, finely divided calcium carbonate of a predetermined particle size is finely dispersed in a melt of the thermoplastic polymer resin in an extrusion die together with specified proprietary chemical compounds that control certain properties of the melt such as crystalinity so that the ultimate under film layer has the desired characteristics such as flexibility for example which is important with roofing underlays that need to be draped between the roof rafters. The composite thermoplastic melt is extruded from the die to form a film. This film is stretched by a predetermined amount and manner consistent with obtaining the desired size of 0.2 micron approx. micropores which are in the form of tortuous microcracks or micropathways produced via the finely dispersed calcium carbonate particles. However, other sizes of micropores may be suitable provided that they have the requisite water vapour transmission characteristics.

Alternatively, the micropores in the microporous film may be provided by forming the film of microfibres. Polypropylene is the preferred thermoplastic polymer for under layer of microporous film and for the top fabric layer and for the bottom fabric layer when provided for the reasons stated above and because there is no risk of non-compatibility with any of the layers of the building membrane when they are all made of the same thermoplastic polymer.

Discrete or point bonding also has an effect on the properties of the bonded film and fabric layers, in particular permeability to water vapour but also on the appearance, drape, softness and strength of the underlay.

As with the top fabric layer, for ease of manufacture and for ensuring uniformity of heat stabilisation throughout the entire under film layer, the heat stabiliser conveniently is added to the thermoplastic melt prior to forming of the film.

If desired or appropriate, the under film layer may also be stabilised against ultraviolet degradation, preferably by adding an ultraviolet light stabilising preparation to the thermoplastic melt, although the degree of ultraviolet light stabilisation may not need to be so significant or so great as that for the top fabric layer which is highly ultraviolet light stabilised.

Bonding of the under film layer to the top fabric layer can be by any suitable means, provided that it is intermittent bonding to facilitate moisture vapour transmission through the micropores of the under film layer and through the fabric of the top fabric layer. Thus, intermittent bonding may be achieved by means of an adhesive, ultrasound or the application of heat and pressure. When the under film layer is made of a thermoplastic polymer, the under film layer is conveniently bonded to the top fabric layer by the application of heat and pressure.

To maximise moisture vapour transmission through the underlay, the under film layer is advantageously bonded to the top fabric layer by feeding it along with the top fabric layer of which the filaments have already been intermittently bonded together as aforesaid through the nip of the spunbond calendar system comprising two heated rollers, one smooth and one carrying a raised embossing pattern on its surface.

Alternatively, the under film layer may be fed along with the loose web of filaments through the nip of a spunbond calendar system comprising two heated roils, one smooth and one carrying a raised embossing pattern on its surface which simultaneously applies intermittent heat and pressure to the loose web of filaments or fibres to form the top fabric layer and to bond the under film layer thereto so that discrete areas only of the two layers are bonded thermally together. As mentioned previously, intermittent bonding enables the filaments of the top fabric layer to move relatively freely in the areas between the bonded points and to move relatively to the under film layer

When the loose web of filaments of the top fabric layer has been bonded prior to feeding the bonded fabric layer with the under film layer into the nip between the rollers of the calender unit to produce a thermally bonded building membrane, the degree of register of the discrete bonded areas of the fabric layer varies. For example, the discrete bonded areas of the fabric layer may be 8% to 24%, and are preferably 19% in register with the discrete bonded areas of the film layer.

From yet another aspect, the invention resides in a method of erecting a building construction using any of the breathable building membranes defined hereinabove.

When the building construction is a tiled roof in which any of the said breathable membranes are fixed to roof rafters in substantially horizontal overlapping relationship beneath the roof tiles, this method of the invention provides a roofing underlay that resists ultraviolet light and resists heat degradation because of the heat stabilised under layer. When the moisture vapour permeable reflective coating is applied to the top fabric layer, the infrared loading of the entire building membrane is reduced. So the combination of metallised permeable coating and ultaviolet light and heat stabilisation that is moisture resistant and breathable to assist in guarding against roof space condensation, further increases the resistance of the building membrane to degradation, thereby increasing its life and durability,

The invention also comprehends a tiled roof structure having roof rafters and any of the breathable membranes defined hereinabove fixed to roof rafters in substantially horizontal overlapping relationship beneath the roof tiles.

Alternatively, the building construction may be a wall and thus the invention comprehends a cavity wall in which any of the breathable membranes defined are fixed to the outwardly facing surface of an internal wall of the cavity.

In order that the invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic diagram of a production line for manufacturing a breathable building membrane including a spunbonded fabric layer and a microporous film layer in accordance with the invention;

Figure 2 is a partial side view to an enlarged scale of a breathable building membrane made on the production line of Figure 1 and in accordance with one embodiment of the invention;

Figure 3 is a detail view through the nip between two rollers of a calendar unit of Figure 1 showing the production of another embodiment of breathable building membrane in accordance with the invention; Figure 4 is a partial side view to an enlarged scale of a breathable building membrane made on the production line of Figure 1 and in accordance with Figure 3, of another embodiment of the invention;

Figure 5 is diagrammatic part-longitudinal section through a pitched tiled roof structure in the region of the roof eaves and incorporating the breathable membrane of Figure 2, Figure 4, Figure 7 or Figure 8 as a roofing underlay;

Figure 6 is a schematic diagram of a production line for manufacturing a breathable building membrane including an aluminised spunbonded fabric layer and a microporous film layer in accordance with the invention;

Figure 7 is a partial side view to an enlarged scale of a breathable building membrane made on the production line of Figure 6 and in accordance with another embodiment of the invention;

Figure 8 is a partial side view to an enlarged scale of a breathable building membrane made on the production line of Figure 6 and in accordance with Figure 3, of another embodiment of the invention; and

Figure 9 is a perspective detail view, with parts cut away, of a cavity wall incorporating the breathable membrane of Figure 2, Figure 4, Figure 7 or Figure 8 as a wall membrane.

A moisture resistant breathable building membrane which is generally indicated at 1 in Figure 2 includes a film layer 3 formed of a microporous thermoplastic polymeric film and a fabric layer 5 formed of a filamentous thermoplastic polymeric fabric. Both layers 3 and 5 are of extruded polypropylene and are intermittently thermally bonded to each other in overlying relationship in respective discrete areas 6. When the breathable membrane 1 is installed in a roof structure as a roofing underlay or in a cavity wall as a wall membrane, in use, the film layer 3 lies under the fabric layer 5 which is thus the top layer and has a top surface 5b that faces outwards. The film layer 3 has a multiplicity of tortuous microporous pathways, referred to herein as micropores 7 having an average overall size of 0.2 microns. The micropores 7 permit the transmission of water vapour through the film layer 3 and out through the fabric layer 5 in the direction of the arrow 8 yet prevent the passage of, wind driven hail and snow in the case of a roofing underlay and moisture in the case of a wall membrane, in the opposite direction. As can be seen from Figure 2, the fabric layer 5 is made from a multiplicity of filaments 9. Because of the discrete bonding areas 6, the filaments 9 can move freely with respect to each other in the regions between the discrete areas 6 which facilitates the passage of water vapour from the micropores through the fabric layer 5.

The film layer 3 is stabilised against heat degradation by means of a phenolic heat stabilising preparation of which benzenepropionic acid, 3,5-bis(1 ,1- dimethylethyl)-4-hydroxy-,2,2-bis[[3-[3,5-bis(1 ,1-dimethylethyl)hydroxyphenyl]-

1-oxopropoxy]methyl]-1 ,3,-propanediylester has been found to be effective.

And, the fabric layer 5 is highly stabilised against ultra-violet light degradation by means of an organic hindered amine ultraviolet light stabilising preparation of which poly[[6-[(1 ,1 ,3,3,-tetramethyl butyl)amino]-s-triazine-2,4-diyl][2,2,6,6,- tetramethyl-4-piperidyl)imino] hexamethylene [2,2,6,6,-tetramethyl-4-piperidyl) imino]] is particularly effective.

The fabric layer 5 is of relatively heavy weight as compared to the film layer 3 to provide the requisite protection and strength. Because the fabric layer 5 provides the first defence against ultraviolet light degradation, it is also highly ultraviolet light stabilised. However, the film layer 3 can also be ultraviolet light stabilised but this does not need to be significant because the fabric layer is more fully exposed to ultraviolet light. Whilst consideration has been given to heat stabilising the fabric layer 5, applicants have found that it is essential for the heat stabilisation to be within the film layer 3. The breathable membrane 1 is manufactured in the production line shown in Figure 1 to which reference will now be made. A thermoplastic polymer feed constituted by a polypropylene resin is fed into a fabric extruder which is heated to produce a fabric forming melt to which the organic amine hindered ultraviolet light stabilising preparation is added. Continuous filaments of thermoplastic polymer are extruded through a spinneret comprising thousands of spinnerets to form a loose web of unbonded filaments.

Film for the film layer 3 is manufactured in a film extruder into which is fed a thermoplastic polymer feed constituted by a polypropylene resin. Finely divided calcium carbonate of a predetermined particle size is finely dispersed in the melt of the thermoplastic polymer resin together with specified proprietary chemical compounds that control certain properties of the melt. The composite thermoplastic melt is extruded from the extruder die to form a film. This film is stretched by a predetermined amount and manner consistent with obtaining the preferred size of 0.2 micron approx. micropores 7 which are in the form of the tortuous micropathways which are produced via the finely dispersed calcium carbonate particles.

The microporous film and loose web of unbonded filaments is then passed into the nip between two feed rollers to bring the microporous film and the loose web of filaments into overlying relationship and present the overlying layers to a calendar unit comprising two heated rollers 10 and 12. One of the calendar rollers 10 is smooth and the other calendar roller 12 has a raised embossing pattern 14 (Figure 3) on its surface. Thus, as the overlying loose web of unbonded filaments and microporous film are passed through the nip 16 between the two calendar rollers 10 and 12, they are thermally bonded together by the combination of the application of heat and pressure. Simultaneously, with the bonding together of the loose web of filaments and film, the filaments of the loose web are thermally bonded together during which process the filaments are entangled. Thus, there is formed the underlay 1 collected into a roll for ease of storage and transportation to site and comprising an under film layer 3 and a top spunbonded nonwoven fabric layer 5 which are intermittently bonded to each other in overlaying relationship at the discrete areas 6 as shown in Figure 2. The embossed pattern 14 on the roller 12 is responsible for the discrete bonding areas 6 which enable the filaments to move relatively freely in the regions between the bonded points 6 and enhance the transmission of moisture vapour received through the micropores of the film layer 3.

When the loose web of filaments 9 of the fabric layer 5 have been bonded prior to feeding the bonded fabric layer 5 with the film layer 3 into the nip between the rollers 10 and 12 in the bonded membrane, the degree of register of the discrete bonded areas of the fabric layer varies.

The breathable membrane 1a of Figure 4 differs from that of Figure 2 in that it includes an additional fabric layer 5a of lower weight than the fabric layer 5. The fabric layer 5a corresponds to that of Figure 2 and is manufactured in the same way except that the thermal bonding action of smooth roller 16 is over the entire area of the film layer 3. The additional fabric layer 5a of lower weight provides protection to the undersurface of the microporous layer to maintain its integrity against damage by builders when incorporating the breathable wall membrane in a cavity wall during erection by builders or as a roofing underlay in a tiled roof during laying of the tiles by roof tilers. Because of the position in use of the additional fabric layer 5a, i.e. it is the bottom fabric layer 5a of the membrane 1a, it is not essential to stabilise this layer against degradation by ultraviolet light. However, some degree of ultraviolet light stabilisation may optionally be provided. It should be appreciated that the fabric layer 5a also provides additional support for the microporous layer 3.

The additional fabric layer 5a is typically fed into the calendar unit rollers 10 and 12 at the position A^ indicated in Figure 1. If desired or necessary, a still further additional fabric layer may be fed into the calendar unit at the position

Al indicated in Figure 1 in which case this additional fabric layer would be highly ultraviolet light stabilised. In the embodiments of Figures 2 and 4, the discrete bonding areas 6 can be seen as a pattern (not visible in the drawings) on the bottom layer which is the film layer 3 in Figure 2 and the additional fabric layer 5a in Figure 4.

The breathable membranes 1b and 1c of Figures 7 and 8 differ from those of Figures 2 and 4 respectively in that the top surface 5b of the fabric layer 5 in each case bears a moisture vapour permeable reflective coating 5c, shown for clarity of illustration in dashed lines. The reflective coating 5c is of a metallic material, in this case aluminium, to provide an aluminised top spunbonded fabric layer 5, 5c. The aluminised breathable membranes 1b and 1c are manufactured by the process which is shown in Figure 6, the aluminium coating having been applied by plasma deposition to the spunbonded fabric layer 5 before being fed to the nip between the rollers 10 and 12.

By way of example only, Applicant has produced an aluminised breathable building membrane 1c (Figure 8) in the following way.

A grey, 50g/m² spunbonded polypropylene fabric layer was coated on one surface only by plasma deposition with an aluminium coating of approximately 40nm thick with the aluminium not forming a discrete layer on the top surface of the top layer but coating the surfaces of the individual filaments which collectively form the surface layers of the spunbonded fabric top layer 5. The reflectivity of the two (top coated and bottom un-coated) surfaces of the fabric was then measured in the infra-red region over the wavelength range 800nm to 1100nm using a reflectance spectrometer. The aluminised surface of the spunbonded polypropylene fabric showed increases in infra-red reflectance of 114% to 1507o over the reflectance of the uncoated surface of the fabric, depending on the wavelength at which the reflectance was measured.

The grey, aluminised spunbonded fabric 5, 5c was then incorporated into a laminate structure by thermally bonding (laminating) it, aluminised coating 5c outermost, to a 25g/m² microporous layer 3 and an unpigmented 35g/m² spunbonded fabric 5a. All component layers were polypropylene based. The process of thermal lamination using a combination of heat and pressure applied through the intermittent bond pattern shown in Figure 8, caused some of the aluminium coating to transfer to the surface of the embossed calender roll 12 (Figure 3). The loss of aluminium in this way caused a slight but visible loss in reflectance when subjectively assessed. However, when the infra-red reflectance was measured using the same method as was used to measure the reflectance of the unlaminated spunbonded fabric 5, the aluminised surface of the laminate showed increases of 76% to 101% over the non- aluminised surface of the spunbonded fabric. Thus, a significant increase in infra-red reflectivity was achieved despite the losses incurred in the thermal lamination process.

Examination of the finished, aluminised, laminated breathable membrane has revealed further considerations when incorporating aluminised, spunbonded fabric by thermal or ultrasonic lamination, as opposed to aluminium coating the finished laminate as previously mentioned herein.

The spunbonded fabric 5 is intermittently bonded during its manufacture, as illustrated in Figures 2, 4, 7 and 8, that is the filaments 9 are bonded together using heat and pressure in the discrete areas 6 that typically comprise 8% to 24% of the total fabric area. In the areas 6 of the discrete bond, the individual character of the filaments is lost as they are softened, melted and pressed into a small area resembling a film. These discrete bonded areas 6 give the spunbonded fabric 5 its strength and integrity whilst the free filaments between the point bonded areas confer textile character. When such a material is coated with aluminium, the aluminium is disposed over the surface of the individual filaments comprising the top surface layer of the spunbonded fabric and also over the surface of the discrete bond areas. The aluminised discrete bonded areas 6 are visible as shiny, reflective areas arranged in a regular pattern over the surface of the fabric, the pattern being the bonding pattern of the embossed calendering roll 12 (Figure 3). It follows that the reflectivity of the aluminised spunbonded fabric 5, 5c can be improved by choosing fabrics with a higher bond area. Thus a 19% bond area fabric will be more reflective after coating with aluminium than a corresponding fabric having a bond area of 8%, and a laminate made with the higher bond area aluminised fabric will also have higher reflectivity than if made with a corresponding fabric with a lower bond area.

When a spunbonded (non-aluminised fabric) such as the fabric 5 is processed, the bonded areas 6 of the spunbonded fabric will sometimes be in-register with the lamination areas of the laminating calender roll 12 and sometimes they will be out of register. As the aluminised spunbonded fabric 5, 5c is fed between the calender rolls 10, 12, (Figure 3), the aluminised, discrete bonded areas 6a on the surface of the spunbonded fabric will occasionally be in register with the lamination areas (embossed areas) of the laminating calender roll 12. When this registration occurs, then the aluminium coating on the discrete bond area is reduced through friction and transfer to the lamination roll. Only those discrete bonded areas on the surface of the spunbonded fabric that are not in register with the discrete bonded areas caused by the calender roll 12 retain their original level of aluminium coating. By ensuring that the laminating (embossed) pattern is chosen so as to optimise the non-registration of the lamination points with the bonding points, the reflectivity may be further enhanced.

Referring to Figure 5 (and Figures 2, 4, 5, 7 and 8), this shows the eaves region of a tiled roof structure 20 having roof rafters of which one only is visible at 22. In this case, the breathable membrane 1 , 1a, 1 b, or 1c is a roofing underlay 1 ,1a, 1b or 1c. The roofing underlay 1 ,1a, 1 b or 1c supplied in rolls is unrolled, cut and shaped as necessary and starting at the eaves 21 where the underlay is lapped well into the roof guttering 23 and working upwards to the ridge (not visible), is jointed by lapping with the requisite horizontal lap that depends upon the rafter pitch and is fixed as by clout nails to, and between, the roof rafters such as 22 in overlying relationship thereto in a series of substantially horizontally extending overlapping layers 24 extending up the roof. Wooden tiling battens 26 are nailed to the roof rafters such as 22 in overlying relationship with overlapping underlay layers 24 at a spacing that is consistent with the lengths of the particular tiles 28 being used. The tiles 28, that are plain tiles, are then laid from the eaves 21 upwards on the roof battens 26 by means of hanging nibs 29 and/or nails in overlapping leading edge to trailing edge and side by side relationship to form a tiled roof 30.

The underlay 1 , 1a, 1 b or 1c and the ceiling rafters, of which one is indicated at 32 and between which is disposed insulation 34, define the roof space 36. Not only does the underlay 1 , 1a, 1b, 1c act as a moisture resistant barrier to hail and snow passing into the roof space 36 but also acts to permit the transmission of water vapour therethrough from the roof space 36 thereby assisting the usual roof space ventilation systems (not shown) in reducing the build up of undesirable condensation within the roof space 36.

Before the tiles are laid, the underlay 1 , 1a, 1b or 1c is exposed to ultraviolet light and after the roof tiles 28 are laid ultraviolet light passes through the usual cracks between the roof tiles 28. However, the fabric layer 5 is resistant to ultraviolet light degradation because it is highly ultraviolet light stabilised. Moreover, the heat stabilisation of the microporous layer 3 guards against heat degradation which could be caused by undesirable changes in the ambient temperature of the roof space 36. Moreover, the breathable membranes 1 b and 1c reduce the infra-red loading of the entire building membrane thereby further increasing the resistance of the building membrane to degradation.

Turning now to Figure 9, a timber frame building includes a partly shown cavity wall 40 having internal and external skins 41 and 42 defining a cavity 43. The internal skin 41 comprises structural frame members 44 and an outer layer of timber board 45 between which is disposed insulation 46 and an inner layer of plaster board 47 and forms a framed panel. A breathable building membrane 1 , 1 a, 1b or 1c as described with reference to Figures 2, 3, 7 and 8 respectively is fixed to, and lines, the outwardly facing surface of the inner skin 41 , presented by the timber board 45. Whilst the rest of the building is being constructed, the exposed breathable membrane 1 , 1a, 1b and 1c protects the framed panel forming the internal skin from the elements until the external skin 42 is built of bricks and the internal skin 41 is attached to the external skin 42 as by steel ties 48. During the period of time in which the breathable building membrane 1 , 1a, 1b or 1c is exposed, the ultraviolet light stabilised fabric layer 5, resists degradation from ultraviolet light.

Condensation in the wall cavity 43 due to the passage of warm, moist air from the inside of the building through the internal skin 41 and the building membrane, forms preferentially on the breathable building membrane 1 , 1a, 1 b and 1c, rather than on the framed panels forming the internal skin 41 , so that the building membrane acts as a condensation barrier in the wall cavity 43.

In the case of the building membranes 1b and 1c, the reflective coating 5c enhances the condensation barrier effect when there is build up of condensation moisture on the reflective coating 5c, because there is an increase in the resistance of the membranes 1b or 1c to the transfer of moisture through the membrane 1b or 1c to the wall inner skin 41.

Moreover, by virtue of the heat stabilised microporous under film layer 3, heat degradation due to rises in temperature from the passage of warm air through the membrane is prevented.

Whilst, particular embodiments have been described, it should be appreciated that various modifications may be made without departing from the scope of the invention as defined in the appended claims. For example, instead of the microporous under film layer 3 being made with tortuous micoporous pathways in the manner described, it may be formed from a layer of micro- fibres with the pores being formed by gaps between the fibres. Whilst aluminium has been specified as the metallised material of choice for the water vapour permeable metallised coating of the top fabric layer, other suitable metallic materials may be used. Instead of thermal bonding of the layers of the laminates, ultrasonic or adhesive bonding may be used. Although the described breathable building membranes herein have been described as roofing underlays and wall membranes, these building membranes could be used for any other purpose in the building industry, that has need for their particular characteristics. For example the embodiments of Figures 7 and 8 may be used as underfloor breather support membranes for fibrous board/slab insulation between joisted timber floors.

Claims

1. A breathable building membrane includes an under layer formed of a microporous polymeric film and a top layer formed of a filamentous polymeric fabric which is bonded to the under layer, said under and top layers being disposed in overlying relationship and being stabilised respectively against heat degradation and ultraviolet light degradation.

2. A breathable building membrane, wherein said top layer has a top surface bearing a moisture vapour permeable reflective coating.

3. A breathable building membrane includes an under layer formed of a microporous polymeric film and a top layer formed of a filamentous polymeric fabric which is bonded to the under layer, said under and top layers being disposed in overlying relationship and being stabilised respectively against heat degradation and ultraviolet light degradation, and said top layer having a top surface bearing a moisture vapour permeable reflective coating.

4. A breathable building membrane as claimed in claim 2 or 3, wherein the reflective coating comprises a thin metallic layer.

5. A breathable building membrane as claimed in claim 4, wherein the reflective coating is of aluminium.

6. A breathable building membrane as claimed in claim 4 or 5, wherein the thin metallic layer is applied by plasma deposition onto the top surface of the top fabric layer.

7. A breathable building membrane as claimed in claim 6, wherein the deposited metallic layer has a thickness of about 40nm.

8. A breathable building membrane as claimed in claim 6 or 7, wherein the fabric of the top layer is made from spunbonded filaments and wherein the deposited metallic coating coats the surfaces of the individual filaments which collectively form the top surface layers of the spunbonded fabric top layer, such that the deposited metallic coating does not form a discrete layer on the top surface of the top layer.

9. A breathable building membrane as claimed in any one of claims 1 to 8, wherein the film layer comprises tortuous microporous pathways.

10. A breathable building membrane as claimed in claim 9, wherein the tortuous micoporous pathways have an average size of about 0.2 microns.

11. A breathable building membrane as claimed in any one of claims 1 to 10, wherein the filaments of the fabric layer are nonwoven and are bonded together by a bonding method that includes entanglement of the filaments using high pressure water jets, adhesive bonding, ultrasonic bonding or thermal bonding.

12. A breathable building membrane as claimed in claim 11 , wherein discrete areas only of the fabric layer are bonded, thereby enabling the filaments to move relatively freely in those regions between the discrete areas.

13. A breathable building membrane as claimed in claim 12, wherein discrete areas only of the film layer are bonded to the fabric layer, thereby facilitating transmission of water vapour through the bonded film layer and then through the fabric layer.

14. A breathable building membrane as claimed in claim 13, wherein the sfilaments of the top fabric layer are bonded together prior to bonding to the under film layer, the discrete bonded areas of the fabric layer being 8% to 24%, and preferably about 19%, in register with the discrete bonded areas of the film layer.

15. A breathable building membrane as claimed in any one of claims 10 to 14, wherein the overlying film and fabric layers are bonded together by thermal bonding involving application to the overlying layers of a combination of heat and pressure.

16. A breathable building membrane as claimed in any one of claims 10 to 15, wherein the filaments of the fabric layer are bonded together by thermal bonding involving the application of a combination of heat and pressure.

17. A breathable building membrane as claimed in claim 16, as appendant to claim 15, wherein the filaments of the fabric layer have been thermally bonded together simultaneously with the thermal bonding of the film and fabric layers.

18. A breathable building membrane as claimed in claim 11 or any claim appendant thereto, wherein the filaments of the fabric layer are made from a thermoplastic polymer.

19. A breathable building membrane as claimed in claim 11 or any claim appendant thereto wherein the film layer is made from a thermoplastic polymer.

20. A breathable building membrane as claimed in claim 18 or claim 19, wherein the thermoplastic polymer is selected from polypropylene, polyamide or polyester.

21. A breathable building membrane as claimed in any one of claims 18 to 20, wherein the filaments of the fabric layer have been extruded from a melt of thermoplastic polymer.

22. A breathable building membrane as claimed in claim 21 , wherein the filaments of the fabric layer have been extruded through a multiplicity of spinnerets to form a loose web which is bonded by application of heat and pressure to form the fabric layer.

23. A breathable building membrane as claimed in claimed in any one of claims 1 to 22, wherein the fabric layer is stabilised against ultraviolet light degradation by means of at least one ultraviolet stabiliser constituted by an organic hindered amine.

24. A breathable building membrane as claimed in claim 23, wherein the at least one organic hindered amine ultraviolet light stabiliser is poly[[6-[(1 ,1 ,3,3,- tetramethylbutyl)amino]-s-triazine-2,4-diyl][2,2,6,6,-tetramethyl-4-piperidyl) imino] hexamethylene [2,2,6,6,-tetramethyl-4-piperidyl) imino]].

25. A breathable building membrane as claimed in claim 23 or claim 24 as appendant to claim 21 or any claim dependent thereon, wherein the at least one ultraviolet light stabiliser has been added to the thermoplastic fabric melt prior to the production of the web-forming thermoplastic filaments.

26. A breathable building membrane as claimed in any one of claims 1 to 25, wherein the film layer has been extruded from a melt of thermoplastic polymer.

27. A breathable building membrane as claimed in claimed in claim 26 as appendant to claim 9 or any claim dependent thereon, wherein finely divided calcium carbonate of a predetermined particle size has been finely dispersed in the thermoplastic polymer film melt and the extruded film has been stretched, thereby to produce said tortuous pathways via the finely dispersed calcium carbonate particles.

28. A breathable building membrane as claimed in claimed in any one of claims 1 to 27, wherein the film layer is stabilised against heat degradation by at least one heat stabiliser constituted by a phenolic heat stabiliser.

29. A breathable building membrane as claimed in claim 28, wherein the at least one phenolic heat stabiliser is benzenepropionic acid, 3,5-bis(1 ,1- dimethylethyl)-4-hydroxy-,2,2-bis[[3-[3,5-bis(1 ,1-dimethylethyl)-4- hydroxyphenyl]-1 -oxopropoxy]methyl]-1 ,3,-propanediylester.

30. A breathable building membrane as claimed in claim 28 or claim 29, as appendant to claim 26 or any claim dependent thereon, wherein the at least one heat stabiliser has been added to the thermoplastic film melt prior to the extrusion of the film layer.

31. A breathable building membrane as claimed in claim 11 or any claim dependent thereon, wherein the top fabric layer is a spunbonded layer of filaments.

32. A breathable building membrane as claimed in any one of claims 1 to 31 , wherein the top fabric layer has a relatively heavy weight compared to the under film layer.

33. A modification of the breathable building membrane as claimed in any of claims 1 to 32, wherein the film layer is sandwiched between, and is bonded to two such fabric layers, with the three layers being disposed in overlying relationship.

34. A laminated breathable building membrane for use with tiled roofs as an underlay, said underlay being made from a spunbonded nonwoven ultra violet light stabilised top fabric layer and a microporous heat stabilised film layer which is sandwiched between the top layer and another synthetic fabric layer.

35. A laminated breathable building membrane for use as a wall membrane, said wall membrane being made from a spunbonded nonwoven ultra violet light stabilised top fabric layer and a microporous heat stabilised film layer which is sandwiched between the top layer and another synthetic fabric layer.

36. A laminated breathable building membrane as claimed in claim 34 or 35, including a moisture vapour permeable reflective coating, as claimed in any one of claims 4 to 8 applied to the top surface of the top layer.

37. A breathable building membrane substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

38. A breathable building membrane substantially as hereinbefore described with reference Figure 4 of the accompanying drawings.

39. A breathable building membrane substantially as hereinbefore described with reference to Figure 7 of the accompanying drawings.

40. A breathable building membrane substantially as hereinbefore described with reference to Figure 8 of the accompanying drawings.

43. A tiled roof structure having roof rafters, tiling battens fixed to the roof rafters and tiles supported by the battens in leading edge to trailing edge and side by side relationship and a breathable building membrane as claimed in any one of claims 1 to 34, claim 36 as appendent to claim 34 and claims 37 to 40 forming a roofing underlay fixed to the roof rafters beneath the tiling battens in substantially horizontal overlapping relationship.

44. A tiled roof structure substantially as hereinbefore described with reference to Figures 2 and 5 of the accompanying drawings.

45. A tiled roof structure substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.

46. A tiled roof structure substantially as hereinbefore descπbed with reference to Figures 5 and 7 of the accompanying drawings.

47. A tiled roof structure substantially as hereinbefore described with reference to Figures 5 and 8 of the accompanying drawings.

48. A method of constructing a tiled roof structure having roof rafters, said method including fixing a breathable building membrane as claimed in any one of claims 1 to 33, claim 35, claim 36 as appendant to claim 35 and claims 37 to 40 as a roofing underlay to the roof rafters in overlying relationship thereto in a series of substantially horizontally extending overlapping layers, fixing tiling battens to the roof rafters in overlying relationship with said underlay and laying roof tiles on the battens in leading edge to trailing edge and side by side relationship to form a tiled roof.

49. A method of constructing a tiled roof structure substantially as hereinbefore described with reference to Figures 2 and 5 of the accompanying drawings.

50. A method of constructing a tiled roof structure substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.

51. A method of constructing a tiled roof structure substantially as hereinbefore described with reference to Figures 5 and 7 of the accompanying drawings.

52. A method of constructing a tiled roof structure substantially as hereinbefore described with reference to Figures 5 and 8 of the accompanying drawings.

53. A cavity wall having an internal skin including a timber frame and an external skin of building blocks, in which a breathable building membrane as claimed in any one of claims any one of claims 1 to 33, claim 35, claim 36 as appendant to claim 35 and claims 37 to 40 is fixed to the outwardly facing surface of the internal skin with the top layer facing outwards.

54. A cavity wall substantially as hereinbefore described with reference to Figures 2 and 9 of the accompanying drawings.

55. A cavity wall substantially as hereinbefore described with reference to Figures 4 and 9 of the accompanying drawings.

56. A cavity wall substantially as hereinbefore described with reference to Figures 7 and 9 of the accompanying drawings.

57. A cavity wall substantially as hereinbefore described with reference to Figures 8 and 9 of the accompanying drawings.

58. A method of constructing a cavity wall having an internal skin including a timber frame and an external skin of building blocks, in which a breathable building membrane as claimed in any one of claims 1 to 33, claim 35, claim 36 as appendant to claim 35 and claims 37 to 40 is fixed to the outwardly facing surface of the internal skin with the top layer facing outwards.

59. A method of constructing a cavity wall substantially as hereinbefore described with reference to Figures 2 and 9 of the accompanying drawings.

60. A method of constructing a cavity wall substantially as hereinbefore described with reference to Figures 4 and 9 of the accompanying drawings.

61. A method of constructing a cavity wall substantially as hereinbefore described with reference to Figures 7 and 9 of the accompanying drawings.

62. A method of constructing a cavity wall substantially as hereinbefore described with reference to Figures 8 and 9 of the accompanying drawings.

63. A method of manufacturing a roofing underlay, including providing a fabric forming melt of a thermoplastic polymer, adding an ultraviolet stabilising preparation to the melt, forming a plurality of filaments from the fabric forming melt to provide a fabric layer, providing a film forming melt of a thermoplastic polymer, adding a heat stabilising preparation to the film forming melt, forming the film forming melt into a microporous film layer and applying heat and pressure to the fabric layer and film layer to the bond the two layers together in overlying relationship.

64. A method as claimed in claim 63, including applying a moisture vapour permeable reflective coating to the top surface of the fabric layer.

65. A method of manufacturing a breathable building membrane, comprising providing a fabric layer formed from a plurality of bonded filaments, that has a top surface and which is stabilised against ultraviolet heart degradation, applying a moisture vapour permeable reflective coating to the top surface of the fabric layer, providing a film forming melt of a thermoplastic polymer, adding a heat stabilising preparation to the film forming melt, forming the film forming melt into a microporous film layer and applying heat and pressure to the fabric layer and the film layer to the bond the two layers together in overlying relationship with the reflective coating facing outwards.

66. A method as claimed in claim 64 or 65, wherein the reflective coating comprises a thin metallic layer.

67. A method as claimed in claim 66, wherein the reflective coating is of aluminium.

68. A method as claimed in claim 66 or 67, wherein the thin metallic layer is applied by plasma deposition onto the top surface of the top fabric layer.

69. A method as claimed in claim 68, wherein the deposited metallic layer has a thickness of about 40nm.

70. A method as claimed in claim 68 or 69, wherein the fabric of the top layer is made from spunbonded filaments and wherein the deposited metallic coating coats the surfaces of the individual filaments which collectively form the top surface layers of the spunbonded fabric top layer, such that the deposited metallic coating does not form a discrete layer on the top surface of the top layer.

71. A method as claimed in claim 69 or claim 70 as appendant to claim 69, wherein the reflective coating is of aluminium and applied to the top surface only of the top fabric layer, with the bottom surface of the fabric layer being uncoated and wherein the reflectivity of the coated and uncoated top and bottom surfaces was measured in the infra-red region over the wavelength range 800nm to 1100nm using a reflectance spectrometer and showed increases in infra-red reflectance of 114% to 150% of the coated surface over the reflectance of the uncoated surface, depending on the wavelength at which the reflectance was measured.

72. A method as claimed in any one of claims 63 to 71 , wherein an ultraviolet stabilising preparation is added to the film forming thermoplastic melt to stabilise the film layer against ultraviolet degradation.

73. A method as claimed in claim 72, wherein the degree of ultraviolet stabilisation of the film layer which lies under the fabric layer in use is significantly less than that for the top fabric layer which is highly ultraviolet light stabilised.

74. A method as claimed in claimed in any one of claims 65 to 73, wherein the at least one ultraviolet stabiliser is constituted by an organic hindered amine.

75. A method as claimed in claim 74, wherein the organic hindered amine ultraviolet light stabiliser is poly[[6-[(1 , 1 ,3,3, -tetramethylbutyl)amino]-striazine- 2,4-diyl][2,2,6,6,-tetramethyl-4-piperidyl)imino]hexamethylene[2,2,6,6, tetramethyl -4-piperidyl) imino]].

76. A method as claimed in any one of claims 65 to 75, wherein the film layer is stabilised against heat degradation by at least one heat stabiliser constituted by a phenolic.

77. A method as claimed in claim 76, wherein the phenolic heat stabiliser is benzenepropionic acid, 3,5-bis(1 ,1-dimethylethyl)-4-hydroxy-,2,2-bis[[3-[3,5- bis(1 ,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropoxy]methyl]-1 ,3,- propanediylester .

78. A method as claimed in any one of claims 65 to 77, wherein the thermoplastic polymer is selected from polypropylene, polyamide or polyester.

79. A method as claimed in any one of claims 65 to 78, wherein the filaments of the fabric layer are extruded from the thermoplastic fabric forming polymer melt.

80. A method as claimed in any one of claims 65 to 79 , wherein the filaments of the fabric layer are extruded through a multiplicity of spinnerets to form a loose web which is bonded by application of heat and pressure to form the fabric layer.

81. A method as claimed in any one of claims 65 to 80, wherein the film for the microporous film layer is extruded from the thermoplastic film forming polymer melt.

82. A method as claimed in any of claims 65 to 81 , wherein finely divided calcium carbonate of a predetermined particle size is finely dispersed in the film forming thermoplastic polymer melt and wherein the composite thermoplastic melt is extruded to form a film for the film layer.

83. A method as claimed in claim 82, wherein the film for the film layer is stretched to form tortuous micropaths produced via the finely dispersed calcium carbonate particles, thereby to form the microporous film layer.

84. A method as claimed in claim 83, wherein the tortuous micoporous pathways have an average size of about 0.2 microns.

85. A method as claimed in any one of claims 65 to 84, wherein the film layer and the fabric layer are intermittently bonded together by the application of heat and pressure so that discrete areas only of the two layers are bonded thermally together.

86. A method as claimed in claim 85, wherein the discrete bonded areas of the film and fabric layers enable the filaments to move relatively freely in those regions between the discrete areas and to facilitate transmission of water vapour through the bonded film layer and then through the bonded fabric layer.

87. A method as claimed in claim 85 or 86, wherein the discrete bonded areas of the fabric layer are 8% to 24% in register with discrete bonded areas of the film layer.

88. A method as claimed in claim 87, wherein about 19% of the discrete bonded areas of the fabric layer are in register with discrete bonded areas of the film layer.

89. A method as claimed in any one of claims 86 to 88, wherein the heat and pressure is applied to the overlying layers by feeding the film and fabric layers in overlying relationship between the nip of two heated rollers of which one is smooth and one has a raised embossing pattern on its surface.

90. A modification of the method as claimed in claim 89, as appendant to claim 80 and any claim dependent thereon, wherein a loose web of filaments for forming the fabric layer is fed between the rollers in overlying relationship with the film layer so that the heat and pressure simultaneously and intermittently bonds the filaments of the loose web together and the fabric layer to the film layer.

91. A modification of the method as claimed in any one of claims 65 to 90, wherein the film layer is bonded to, and sandwiched between, two of the said fabric layers in overlying relationship therewith, with one of said fabric layers forming a top layer which is ultraviolet light stabilised and the other of said fabric layers forming a bottom layer which is not necessarily ultraviolet stabilised.

92. A method of manufacturing a breathable building membrane substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

93. A method of manufacturing a breathable building membrane, substantially as hereinbefore described with reference to Figures 1 , 3 and 4 of the accompanying drawings.

94. A method of manufacturing a breathable building membrane, substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.

95. A method of manufacturing a breathable building membrane, substantially as hereinbefore described with reference to Figures 6 and 8 of the accompanying drawings.