WO2014205502A1

WO2014205502A1 - Building membranes

Info

Publication number: WO2014205502A1
Application number: PCT/AU2014/000674
Authority: WO
Inventors: Michel Bostrom; Craig Andrew LUMSDEN
Original assignee: Silver Batts Pty Ltd
Priority date: 2013-06-27
Filing date: 2014-06-27
Publication date: 2014-12-31
Also published as: AU2014302029A1

Abstract

A building membrane (25) for inclusion in walls, ceilings, floors or the roof of a building, which includes first and second office opposite broad surfaces (29), (30) and perforations (27), (28) that penetrate into the membrane (25) from at least one of the broad surfaces (29) and (30) and which terminate prior to the opposite surface.

Description

BUILDING MEMBRANES

FIELD OF THE INVENTION

[0001] The present invention relates to building membranes for use in building elements comprising wails, floors, ceilings and roofs of domestic and commercial buildings. Such membranes are provided for various purposes, including providing a barrier to prevent ingress of water, ie for waterproofing; a barrier to prevent the loss of conditioned air and a radiant barrier to provide thermal insulation. Building membranes may assist, or impede, as required, the appropriate level of moisture transfer through building elements.

BACKGROUND OF THE INVENTION

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0003] Excessive levels of moisture inside a building can promote condensation on surfaces in the building and lead to mould forming on those surfaces. This can affect the health of residents of affected buildings and can result in damage to building surfaces and even to the structure of the building.

[0004] The issue of moisture within buildings and the effect on the building has become more pronounced in recent years. For example, as recently as twenty or thirty years ago, most houses in Australia were unheated, except for small gas or electric space heaters; and not were either not cooled, or only cooled in one or two rooms. The houses were also well ventilated and importantly, were in general, uninsulated. Houses typically had vents installed in every room to ensure the dispersal of fumes from unflued gas heaters {and earlier from gas lighting) and even when vents were not installed, the absence of caulking around window and door frames ensured a very high rate of ventilation by draught. As a result, water vapour created by internal activities was usually quickly vented to the outside, so that inside damage due to condensation did not occur. [0005] Where mould did form on waits, it usually formed in winter and it tended to disappear over the summer months due to different temperature conditions. Because the wails were generaliy uninsuiated and often ieaky, even if there was significant amount of moisture accumulated in the materials of the wall in cool winter weather, it would quickiy dry out in the warmer weather of spring and summer.

[0006] Now however, houses are commonly heated in the winter and cooled in the summer, and newer or renovated houses are better sealed and insulated than before. These houses are however, often poorly ventilated, so as to effectively prevent excess moisture within the house from escaping. A major contributor to this is that because wa!is of new and renovated houses are now insulated as a standard procedure, the steady state dew point on cold nights is located within the cavity of the walls where the insulation is located. Temperatures within the insulation are relatively more stable than in the cavities of an uninsulated house, so condensed moisture takes ionger to re-evaporate. Thus the moisture can accumulate as water and cause mould and other damage to the structure within the cavity.

[0007] The generation of mould can have an effect on resident health, while major structural problems include degradation of plasterboard, dry rot in timber and, in extreme situations, corrosion of fasteners and other steel components. In addition, these problems can occur weii before water vapour levels in a wall cavity reach the point where condensation is observed. In relation to mould, different moulds thrive under different conditions. The criticai issue is the duration of the specific conditions which favour a particular species of mould. In traditional or older houses, conditions changed from season to season and from day to day. A modern air conditioned building, however, can provide steady-state conditions which can be a perfect incubator for one or a small number of particular species of mould. This is particularly a problem in the wet tropics. Thus, the mould can remain aiive rather than perishing as it would in an older house in which the conditions were subject to more regular change. The key measure needed to reduce the growth of mould is to maintain the relative humidity below 80%.

[0008] The present invention is principally concerned with the passage of water vapour (not liquid) through the waits of a building, either from the inside out or the outside in, although the invention also has application in floors, ceilings and roofs. Water vapour can travel through the cavity of a building element through air movement, dispersion through still air gaps, or dispersion through building materials.

[0009] Air movement

[0010] In most buildings, the principal mode of water vapour transport through a cavity is by air movement. Warm damp air moving through the interna! lining and circulating within the insulation will be cooied as it approaches the externa! side of the wall. When the air coo!s to the point that it becomes saturated - i.e. at the dew point - the vapour will condense into liquid water. Air movement provides capacity to transport water vapour, into and out of cavity walls and roof spaces; thus it is important to employ air barriers, as well as caulking, to control the flow of air though building cavities, to control condensation.

[0011] Dispersion through still air gaps

[0012] Large amounts of water vapour can readily disperse through small gaps in the wall structure and through porous materials. This vapour dispersion is due not to air movement but to the equalisation of partial vapour pressure in different sections of the cavity. Vapour pressure can be rapidly equalised without significant air movement though relatively small holes.

[0013] Dispersion through building materials

[0014] Moisture can afso move through porous materials under vapour pressure. Water vapour transmission varies with vapour pressure, and therefore with air temperature and relative humidity.

[0015] Buildings that are constructed with masonry, timber and plasterboard materials have a significant hygric capacity. That is, these materials can absorb and release water vapour over normal cycle of changes of wet and dry weather conditions. In the average Australian (186 m2) brick veneer home, approximately 1814 to 2267 kg of wood are in exterior walls. This yields a hygric capacity of approximately 181 to 226 kg of water or 170 to 189 L of water via hygric redistribution.

[0016] Australian brick veneer houses with timber frames have 46% less timber — — equivalent houses in the USA. This is due to the extensive use of plywood or other timber fibreboard sheathing on the exterior of timber framing for bracing in USA.

[0017] Contrary to common belief, in Australia (though not necessarily in other countries which have more severe climates), the principal moisture problem encountered in houses in most regions of Australia during cold and/or rainy winter weather is not water penetration from outside, but rather, it is vapour from inside the house condensing in walls and roof spaces as it attempts to travel to the outside of the building. The opposite direction of vapour travel can occur in summer, with damp external air condensing in the wall and ceiling cavity insulation of air- conditioned buildings, particularly in the wet tropics and sub-tropics. Figures 1 and 2 illustrate the direction of vapour travel through a wall based on the difference in water vapour pressure between the inside of a house and the outside in both winter and summer conditions.

nit ws iaiii: mil ni»s «i ^;m

[0018] In general, vapour moves from the warm side of a wall to towards the cold side. This means that in most of Australia, the direction of vapour drive varies through the seasons from outwards in winter to inwards in summer. It can vary greatiy between houses in the same suburb due to differences in micro-climate, in air conditioning, heating and sealing of the house, and in occupant behaviour. The direction of vapour drive even varies greatly between different walls of the same house, depending on orientation and exposure of the wall.

[0019] In general however, the principal direction of vapour drive in modern houses in temperate regions of Australia is from inside to out, even as far north as South East Queensland, and moisture problems are associated mainly with winter weather. It is therefore important that where the direction of vapour drive is from inside to out, that buildings can "breath" to allow trapped moisture to escape to the exterior in winter weather. Vapour barriers should not be used where there is a significant seasonal reversal of direction of vapour drive as this would lead to condensation behind the vapour barrier during some parts of the year. Thus, in climates where the direction of heat flow and vapour drive varies from winter to summer, a vapour barrier correctly placed for winter conditions will be incorrectly placed, and trap moisture, in summer; and vice-versa. Accordingly, building construction should allow for the flow of moisture in both directions, i.e. from the inside out or from the outside in.

[0020] The movement of vapour within a building is also affected by the ventilation of the building and building designers often have conflicting objectives in relation to ventilation. For example, designers who focus on energy efficiency strive for minimal ventilation rates to reduce heating and cooling loads, while others, with attention to health issues, recommend much higher levels of ventilation. In relation to health, ventilation partially replaces stale contaminated indoor air with fresher outdoor air to improve indoor air quality, indoor contaminants include particles and gases, in which particles include dust, dust mites, pollen, mould, animal allergens and pet hair, white gaseous contaminants are principally volatile organic compounds (VOCs), released from adhesives, paints and building materials. These contaminants degrade indoor air quality, aggravating allergies and precipitating asthma attacks. Unfortunately, many highly energy-efficient homes experience unintended poor indoor air quality and moisture problems.

[0021] The dominant moisture load from the point of view of moisture risk is that exhaled by occupants of a building as indicated in the table below: Table 1. Typical sources of indoor water vapour

[0022] Thus, typical moisture load combined with low ventilation has a significant influence on indoor relative humidity and thereby potential for mould growth.

[0023] Sheeting that is used as a water barrier for waterproofing in roofs and walls of buildings can be perforated to faciittate vapour movement though the roofs and walls. However, the sheeting that is available to date has generally suffered from the problem that the greater the permeability for vapour passage the less effective the sheeting is as a water barrier.

[0024] The applicant has recognised that improved sheeting would be useful that allowed for vapour travel in each direction through the sheeting, but which retains sufficient water barrier or waterproof characteristics. An improved sheeting would be one that satisfies the requirements specified in Australia/New Zealand Standard 4200.1.

SUMMARY OF THE INVENTION

[0025] The present invention provides a building membrane for inc!usion in the walls, ceiling, floor and/or roof of a building. The membrane includes first and second opposite broad surfaces and is perforated from each broad side thereof. The perforations extend or penetrate into the membrane from each broad surface but terminate prior to the opposite broad surface. The perforations that extend through «,^ «^«,^{t i}™ ^ s fface do not meet or intersect with the perforations that extend through the second broad surface. The membrane can be described as having a thickness between the first and second opposite broad surfaces which is of sufficient dimension to enabie the perforations from each side to extend into the membrane but not to extend through the other side of membrane, The perforations extend into the body of the membrane between the first and second opposite broad surfaces, but do not intersect.

[0026] There is potential that some of the perforations will intersect, given the large number of perforations intended to be applied to the membrane, but the intention is that the vast majority of the perforations do not intersect.

[0027] The membrane of the present invention advantageously allows moisture vapour to travel through the membrane but retains waterproof characteristics to resist the ingress of water past the membrane. This occurs because the perforations do not provide a direct passage through the membrane through which water can travel. Water that enters a perforation can travel the full depth of the perforation, but because the perforation terminates within the membrane rather than extending fully through the membrane, the fiow of water also terminates within the membrane.

[0028] In contrast, vapour that enters a perforation that extends from one side of the membrane can travei the full depth of the perforation and at the end of the perforation, the vapour can travel through the membrane until it reaches another perforation that extends to the opposite side of the membrane. In that perforation, the vapour can exhaust through the opposite side of the membrane. The membrane thus permits vapour travel through the membrane but resists water travel.

[0029] The invention relies on appropriate selection of membrane in which the perforations are made. Various suitable forms of membrane are discussed later herein.

[0030] The requirement for vapour to travel through the membrane from one perforation to another allows the perforations to terminate within the membrane without preventing vapour travel. The speed at which vapour can travei through the membrane is slower than the speed at which vapour can travel through a perforation, but as long as there is a vapour pressure difference between opposite sides of the membrane, the pressure will drive the vapour in the desired direction. Thus, while mission will not be as fast through a membrane of the present invention as it would through a membrane in which perforations of comparable calibre extend completely through from one side to the other, the vapour will nevertheless still move through the membrane and the membrane will provide superior water resistance compared to membranes in which the perforations extend completely through from one side to the other.

[0031] The pace of vapour transmission through a membrane of a given composition and thickness can be controlled by suitable selection of the size and depth of the perforations, the density of the perforations from either side and the distance between perforations from one side and corresponding perforations from the other side. For example, the following represents different arrangements of the perforations that can be made in the membrane:

• perforations through one side can extend to a greater depth into the membrane than the perforations through the other side.

• perforations through one side can extend to the same depth as the perforations through the other side.

• perforations through each side can be less than half the thickness of the membrane so that there is no overlap between the perforations of the respective sides, or in other words, the perforations of the respective sides stop short of each other and can be aligned so that if the perforations were longer they would intersect. In this case, the perforations of the respective sides can be of the same length or they can be different.

• perforations through one side extend past the perforations of the other side so that there is an overlap between the perforations of the respective sides through the thickness of the membrane. This can be by each of the perforations of the respective sides having a depth which is greater than half the thickness of the membrane, or the perforations that extend through one side having a greater depth than the perforations that extend through the other side.

• the axis of the perforations through one side can be aligned with the axis of the perforations through the other side, so that the perforations would intersect each other from opposite sides of the membrane if they had sufficient depth.

• the axis of the perforations through one side can be offset from alignment

I the axis of the perforations through the other side, so that the perforations can extend past each other from opposite sides of the membrane to overlap.

• the density of the perforations can be the same on each side of the membrane or they can be different. Thus one side of the membrane can have a greater number of perforations than the other side. The density of perforations can also vary on each of the sides of the membrane, so that there is an uneven density on one or each side of the membrane.

• the perforations can be formed by a sharp pointed projection or needle or by a less sharp or more blunt shape, the latter resulting in greater damage to the internal structure of the membrane, such as the cell structure of a foam membrane and therefore resulting in greater permeance within the membrane.

[0032] In some forms of the invention, the permeance of the membrane is approximated by a quadratic function asymptotically approaching an upper limit as the number of perforations, the width of the perforations, and the depth of the perforations increase, and as the distance between the perforations from opposite sides of the membrane decreases, whereby the absolute upper limit of permeance is the permeance at which the membrane can be relied on to maintain a waterproof barrier.

[0033] The selection of the form of perforation from the above options will depend on two, or at least two design criteria, being:

1 ) The desire to minimise compromising the mechanical strength of the membrane, which can be achieved by maximising vapour transfer between perforations in preference to increasing the number of perforations; and

2) The desire to achieve increasing permeance through the thickness of the membrane to avoid the accumulation of moisture within the membrane, i.e. to ensure that the dew point occurs outside the membrane so that water does not condense within the membrane.

[0034] The perforations can most easily be made as straight perforations that penetrate the membrane, which in a preferred arrangement is a membrane foam, generally perpendicular to the surface through which the perforations extend. However, the perforations can penetrate at an angle (not perpendicular) to the ugh which they extend in order to achieve a given rate of vapour transmission, in some forms of the invention with smaller number of perforations damaging the membrane surface and thereby reducing mechanical strength. The perforations of one side could penetrate at a different angle to the perforations of the opposite side. For example, the perforations that extend through one side could extend generally perpendicular to the surface through which the perforations extend, while the perforations of the other side could extend at an angle to perpendicular. The perforations of one side could also vary in re!ation to the angle of passage through the membrane. For example, the angle of the perforations could change through different portions of the membrane.

[0035] In a basic form, the membrane can be polyethylene foam, such as an expanded polyethylene foam. Other materials can include expanded and extruded foams composed of polystyrene, polyurethane, polyisocyanurate, although many other materials could be employed.

[0036] The membrane can thus be formed just from foam, or it can include other components. For example, reflective foil can be applied to one or both of the opposite surfaces of the foam layer of the membrane foam. The reflective foil can be an aluminium foil or a metallised plastic film or other reflective material.

[0037] The membrane can include other layers including an anti-glare coating, a fabric weave for reinforcement, such as a polymer weave or a scrim made of fibregiass, nylon, polyester, Kevlar®, or some other woven or non-woven fibre, for adding or increasing tear resistance and tensile strength, an adhesive to adhere the polymer weave to the foam, an extrudate, such as a polyethylene extrudate, operating as an adhesive and providing the membrane a greater resistance to compression at a given point, such as along the line of a stud or other framing member.

[0038] A membrane according to the invention may be flexible and can be installed according to norma! installation techniques already used to install known membranes. A membrane according to the invention can be glued and stapled in the normal manner of conventional installation.

[0039] Alternatively, a membrane according to the invention can be a rigid materia! and can be installed according to norma! installation techniques already

II known rigid sheathing or sarking materials. [0040] A membrane according to the invention can be incorporated in a muitipie layer wail panel with a finished outer and inner layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which:

[0042] Figures 1 and 2 illustrate the present invention as applied to a solid wall with a 25mm cavity (Figure 1 ) and a solid wail without a cavity (Figure 2).

[0043] Figure 3 is an exploded view of a building membrane according to one embodiment of the present invention.

[0044] Figure 4 is a cross sectional and exploded vie of a portion of a membrane according to the invention.

[0045] Figure 5 is a cross sectional and exploded view of a portion of another membrane according to the invention.

[0046] Figure 6 graphically illustrates water vapour transmission relative to perforation density for a membrane according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0047] With reference to Figure 1 , a cross sectional view of the floor and wall of a building is shown. The wall is a solid wall with a 25mm cavity. The view includes a concrete slab 10 and a layered wall construction 11. The wall construction includes an internal wali lining 12 which might be a plasterboard, a stud wall 13, a dampcourse/termite barrier 14, a batten 15, a fibre cement sheet 16, a building wrap 17 and a reinforced render 18.

[0048] The same reference numerals in Figure 1 are used in Figure 2 to represent the same features. The wall is a solid wali without a cavity. Thus, the arrangement in Figure 2 includes a slab 10 and wall construction 11 formed of an internal wall lining 12, a termite barrier 14, a cement sheet 16 and a reinforced render 18. [0049] The difference between the Figures 1 and 2 arrangements and the components illustrated in those arrangements will be readily apparent to a person skilled in the art and no further discussion of those arrangements needs to be made.

[0050] In each of the Figures 1 and 2 arrangements, a building membrane 20 in accordance with the invention is provided. In Figure 1 , the membrane 20 is positioned between the stud wall 13 and the batten 15. in Figure 2, the membrane is positioned on the inside of the cement sheet 16,

[0051] While Figures 1 and 2 show the membrane of the present invention as it is applied to wall constructions, It needs to be appreciated that the invention can also be utilised in different forms of wall constructions, as well as ceilings, roof spaces and floors.

[0052] Figure 3 is an exploded view of a building membrane according to one embodiment of the present invention. The membrane 25 shown in Figure 3 comprises a central expanded polyethylene foam (XPE) core 26 within which several perforations 27 and 28 can be seen. The perforations 28 extend from a first of first and second opposite broad surfaces 29 and 30 of the core 26 and it can be seen that the perforations 28 extend for only a short depth through the thickness T of the core 26 compared to the depth of penetration of the perforations 27. More commentary will be made on that aspect of the invention later herein.

[0053] While a foam membrane according to the invention could comprise just the foam core 26 and the perforations 27 and 28, in most forms of the invention, further layers are illustrated in Figure 3 for application to one or both sides of the foam core 26 and those layers can comprise one or more of the following components:

• an anti-glare coating 31 ,

• an aluminium foi! 32 (97% reflective),

• a polymer adhesive 33,

• a polymer weave 35 and

• a polyethylene extrudate 36. [0054] On the opposite side to the components mentioned above, simitar components can be applied, except that in Figure 3, no antiglare coating is applied to the opposite side. Accordingly, for application to the surface 30 is;

♦ a polyethylene extrudate 37,

* a polymer weave 38,

• a polymer adhesive 39 and

• an aluminium reflective foil 40.

[0055] White the layers illustrated in Figure 3 are shown in a particular order, they could be rearranged as required so that they are not in the specific order shown.

[0056] Figure 4 is a cross sectional and exploded view of a portion of a membrane 40 according to the invention. The membrane 40 is very simitar in construction to the membrane 25 of Figure 3, however the perforations 41 and 42 of the membrane 40 differ from those of the membrane 25.

[0057] The perforations 41 of the membrane 40 extend through five layers before entering the foam core 43. The five layers are shown spaced from one another in Figure 4 for ctarity only and are the same as the layers 31 to 36 of the membrane 25 of Figure 3. The perforations 42 extend through four layers before entering the foam core 43. The four layers are likewise shown spaced from one another and are the same as the layers 37 to 40 of the membrane 25 of Figure 3. Accordingly, no further discussion wilt take place in relation to the form of the layers applied to opposite sides of the foam core 43 and the same reference numerals of Figure 3 are used in Figure 4 to denote the same layers, plus 100.

[0058] The Figure 4 membrane 40 has an 8mm thick XPE foam core 43, expanded 30 times and reinforced with the polymer weaves 35 and 38 which is a polymer fabric weaved from tapes (or threads) 1.2 mm wide and adhered to the respective surfaces 29 and 30 of the core 43 by the polyethylene extrudate 36 and 37. The core 43 is perforated by a chisel shaped pin, 1 mm in diameter. Approximately 6,000 perforations/square metre are made. Experiments suggest that with this type of core and perforation, increasing the number of perforations beyond this density provides onty modest further improvements in permeation. The rwsrfrvatinnc: 41 and 42 extend to different distances through the core 43. The perforations 41 extend approximately 2mm into the core 43. The perforations 42 extend approximately 4mm into the core 43. The longitudinal axis of the perforations 41 and 42 are off-set approximately 2 mm from each other, Ieaving approximately 1 mm of material between perforations.

[0059] In all forms of the invention, a successively higher permeance through the membrane can be achieved by reducing the number, diameter and/or the depth of perforations on the side of the membrane with higher vapour pressure (generally the warm side). Where a denser, less permeable membrane core is used, the number of perforations can be increased to improve permeance, if a different reinforcement were used, the perforations might made be smaller or larger depending on the properties of the reinforcement material.

[0060] Accordingly, in all forms of the invention, there can be variations from the illustrated forms of the invention and Figure 5 shows a further variation. In Figure 5, perforations 45 and 46 penetrate into an 8mm thick XPE foam core 47. In Figure 5, X = approximately 7mm and Y - approximately 1 mm. The perforations 45 and 46 extend through the same layers as shown in Figures 3 and 4 and therefore the same reference numerals used in Figure 3 are employed to denote the same layers, plus 200. No further discussion will take place in relation to the form of the layers applied to opposite sides of the foam core 47.

[0061] The perforations 45 extend past the perforations 46 so that there is an overlap between the perforations 45 and 46 through the thickness of the membrane. The perforations 45 and 46 have a depth which is greater than half the thickness of the core 47. The axes of the perforations 45 are offset from alignment with the axes of the perforations 47, so that the perforations 45 and 46 can extend past each other from opposite sides of the core 47 to overlap as illustrated.

[0062] The perforations 45 and 46 extend approximately the same distance through the core 47, which is about 7mm info the core. The longitudinal axes of the perforations 45 and 46 are off-set approximately 1.6mm from each other, ieaving approximately 0.8mm of material between perforations.

[0063] Figure 6 is a graph that illustrates water vapour transmission in grams per square meter relative to perforations per square meter through a membrane one embodiment of the invention. While increasing the number of perforations increases the permeance, there is a trade-off here between permeance and tensile strength of the membrane. As the number of perforations increases, the increase in water vapour transmission slows, but the loss of tensile strength continues proportionately to increase. If tensile strength is important, a reinforcing weave is used and the number of perforations limited. If the membrane is to be installed where it is supported, e.g. by timber sheathing, the number of perforations can be increased and a much higher water vapour transmission achieved.

[0064] As indicated in Figure 6, the perforation density can be below 2000 perforations per square meter and beyond 24000 perforations per square meter. The invention covers these density ranges and all ranges in between.

[0065] For perforated XPE products the pins that are used to make the perforations can be either hot or cold pins. 'Hot' means that the pins are heated by an element inside the perforation roller and 'cold' meaning they are not heated and are at the same temp as surrounding air temp. The perforations could be laser cut in an alternative arrangement.

[0066] Throughout the description and claims of this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

[0067] The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the present disclosure.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A building membrane for inclusion in wails, ceiling, floor or roof of a building, the membrane including first and second opposite broad surfaces and perforations penetrating into the membrane from at least one of the broad surfaces thereof and terminating prior to the opposite surface.

2. A building membrane according to claim 1 , the membrane including a core having first and second opposite broad sides and a layer attached to one broad side of the core.

3. A building membrane according to 2, the layer being a reflective layer.

4. A building membrane according to claim 2 or 3, the membrane including a layer attached to each broad side of the core.

5. A building membrane according to claim 4, the layers attached to each broad side of the core being reflective layers.

6. A building membrane according to any one of claims 2 to 5, the core being a flexible foam.

7. A building membrane according to claim 6, the foam being selected from one or more of expanded and/or extruded polystyrene, polyurethane or polyisocyanurate.

8. A building membrane according to any one of claims 2 to 5, the core being a rigid material.

9. A building membrane according to any one of claims 1 to 8, the perforations extending through one broad surface of the membrane extending to a greater depth than the perforations extending through the other broad surface.

10. A building membrane according to any one of claims 1 to 8, the perforations extending through one broad surface of the membrane extending to the same depth as the perforations extending through the other broad surface.

11. A building membrane according to any one of claims 1 to 8, the length of the perforations extending through each broad surface are iess than half the thickness of the membrane.

12. A building membrane according to claim 11 , the perforations of the respective sides being of the same length.

13. A building membrane according to any one of claims 1 to 8, the perforations extending through one broad surface extend past the perforations extending through the opposite broad surface, so that there is an overlap between the perforations of the respective broad surfaces.

14. A building membrane according to claim 13, the perforations of the respective broad surfaces having a depth which is greater than half the thickness of the membrane foam.

15. A building membrane according to claim 13, the perforations that extend through one broad surface have a greater depth than the perforations that extend through the other broad surface.

16. A building membrane according to any one of claims 1 to 8, the axis of the perforations extending through one broad surface being aligned with the axis of the perforations extending through the opposite broad surface.

17. A building membrane according to any one of claims 1 to 8, the axis of the perforations extending through one broad surface are offset from alignment with the axis of the perforations extending through the other broad surface.

18. A building membrane according to any one of claims 1 to 17, the density of the perforations being the same through each broad surface of the membrane

19. A building membrane according to any one of claims 1 to 17, density of the perforations being different through each broad surface of the membrane.

20. A building membrane according to any one of claims 1 to 17, density of perforations varying on one or both broad surfaces of the membrane.

21. A building membrane according to any one of claims 1 to 20, the perforations being formed by a sharp pointed needle.

22. A bui!ding membrane according to any one of claims 1 to 21 , the perforations being straight perforations that penetrate the membrane generaliy perpendicuiar to the broad surface through which the perforations extend.

23. A building membrane according to any one of claims 1 to 22, further layers being attached to one or each of the broad sides of the core, the further layers including one or more of:

• an anti-glare coating,

* an aluminium foil,

* a poiymer adhesive,

♦ a poiymer weave, and

• a polyethylene extrudate.

24. A building including a building membrane according to any one of claims 1 to