WO2007107767A1

WO2007107767A1 - Thermal insulation structures comprising air spaces and low emissivity surfaces

Info

Publication number: WO2007107767A1
Application number: PCT/GB2007/001029
Authority: WO
Inventors: John Payne; Mark Hughes
Original assignee: Hunt Technology Ltd
Current assignee: Hunt Technology Ltd
Priority date: 2006-03-22
Filing date: 2007-03-22
Publication date: 2007-09-27
Anticipated expiration: 2008-09-22
Also published as: GB2436338B; GB2436338A; GB0705558D0; GB0605747D0

Abstract

A thermal insulation structure for a roof space comprises three low-emissivity surfaces bordering unventilated air spaces within a roof structure (1). Two such surfaces are provided by wads of multi-foil insulation material (9) which extend between adjacent rafters (4) and between adjacent back battens (3). A first low-emissivity surface on one side of the insulation material (9) faces the plasterboard (2), and a second low-emissivity surface on the other side of the insulation material (9) faces a series of parallel front battens (6) which provide support for roof tiles. A membrane (5) is attached to the front battens (6) and is provided on the side facing the rafters (4) with a metallised, low-emissivity surface (12). Alternatively, the membrane (5) is un-metallised, and a third low-emissivity surface is provided by foil-backed plasterboard or bubble wrap (2). An additional pair of low-emissivity surfaces may be provided by a double-sided foil suspended between the rafters (4). Booster insulation may additionally be attached between the rafters (4) extending between the foil and the membrane (5) substantially filling the air space. Additional wads of multi-foil insulation material may be stapled between the rafters (4) and between the front battens (6). A polyurethane spacer may be attached between the insulation material (9) and the booster insulation.

Description

THERMAL INSULATION STRUCTURES COMPRISING AIR SPACES AND LOW EMISSIVITY SURFACES

This invention relates to thermal insulation structures for use in buildings and more particularly to thermal insulation structures that contain low-emissivity surfaces in contact with unfilled air layers.

Unventilated air spaces are good barriers to thermal conduction. Small air spaces of less than 20 mm in thickness are less susceptible to convection currents than thicker air spaces. Surrounding the air space by low-emissivity surfaces reduces radiation through the space. The optimum insulation properties for a non- ventilated air space can be calculated using known equations - these are described in BS EN ISO 6946:1996 as follows:

The thermal resistance of an air space R_g is given by:

R_g = l / ( h_a + h_r),

where h_a is the conduction/convection coefficient and h,- is the radiation coefficient.

For heat flow upwards, as would be encountered in a roof system, h_a is the larger of 1.25 or 0.025/d W/m K, where d is the thickness in metres of the air space in the heat flow direction. The value of h_a for different thickness air spaces is calculated as:

The table shows that the component of the thermal resistance due to conduction and convention increases with thickness up to 20 mm. In this region, convection is inhibited and conduction is the major means of heat flow. Beyond this point, the thermal resistance is constant as convection takes over. Clearly the optimum thickness for the insulation capacity of an air space is 20 mm.

h_ris given by: h_r= Eh_ro,

where E is the intersurface emittance and h_ro is the radiative coefficient for a black-body surface. At 1O⁰C, h_r0 = 5.1,

and E = I Z (IZe₁ H- IZe₂-I),

where β_\ and e₂ are the hemispherical emissivities of the surfaces bounding the air space.

This equation can be used to calculate E for surfaces of varying emissivities.

The surface of a normal building material such as wood or plasterboard will typically have an emissivity of 0.8. An air space inside two such materials would have an interspace emittance of 0.67. The thermal resistance R of 5mm and 20mm air spaces in m K/W are shown below:

The table shows clearly two features, as discussed below.

The effect of having two low-emissivity surfaces across a 5mm gap is severely inhibited by the narrow width. By changing from two high-emissivity to two low-emissivity surfaces only an improvement in thermal resistance from 0.12 to 0.18 m²K/W is produced. Even more strikingly, changing from one to two low-emissivity surfaces increases the thermal resistance of the enclosed 5mm air space only negligibly, i.e. from 0.17 to 0.18 m²K/W.

When the air space is increased from 5 to 20 mm, the effect of the surfaces is much greater. In particular, changing from one to two low-emissivity boundaries increases the thermal resistance from 0.45 to 0.55 m KAV, an increase of 22%. Clearly the improvement in thermal resistance of an air layer by low-emissivity surfaces is at its maximum for a 20 mm air layer thickness.

Moving to an extremely low-emissivity surface of 0.05 does not produce a significant improvement. The difficulty of achieving and maintaining such a surface is not justified by the slight increase in the thermal resistance R.

Effective insulation for a roof or wall structure in a building should contain the following characteristics: • Good barrier to heat transfer by all three methods - conduction, convection and radiation;

• Light-weight - to avoid placing additional stress on the components of the building that support the insulation - such as walls, trusses, rafters and joists;

• Thin - to avoid making the building envelope larger than necessary whilst maintaining internal space;

• Low adverse environmental impact;

• Cheap; • Easy to install;

• Not inflammable;

• Retention of properties on ageing or when wet; and

• Airtightness to the roof or wall structure.

It is well known that air layers form effective insulation barriers to the loss of heat by conduction, and indeed air spaces are an important component of many insulated structures such as walls and roofs. However, large air gaps are susceptible to heat transfer by convection as air currents can be established therein, drawing warm air from one side of the air gap to the other. Air trapped in small layers where convection is inhibited forms the basis of many conventional insulation materials such as textile constructions, bubble films, mineral wool and foam boards or panels.

Whilst dry air has a very low thermal conductivity value of 0.025 W/mK, most solid materials have higher conductivities than this. Traditional insulating materials such as mineral wool, polyurethane foam or polystyrene function by trapping air or other gas inside a low-density solid. These systems generally have a thermal conductivity higher than that of dry air since the solid material allows conduction of heat through the structure. Therefore, they are less effective insulators than a dry-air barrier. In addition, these materials will allow heat transfer by radiation. More recent insulating systems seek to reduce radiation heat losses by incorporating into their structure a reflective barrier.

It is also known that the thermal resistance of an air space is increased when the surfaces adjacent to that space have a low-emissivity. The thermal resistance is increased noticeably when both opposing surfaces are of low-emissivity - one surface will reflect any incident radiation, whilst the opposing surface will absorb very little incident radiation.

Energy usage requirements for new and refurbished buildings are becoming ever more demanding, and this is placing additional demands on the performance of the insulation system. Indeed, nowadays, many conventional insulation systems are unable to meet these demands without the use of excessive thicknesses or weights of material.

Air spaces bounded by a low-emissivity surface are known to be effective insulators. Some insulation products use a low-emissivity surface in conjunction with an air space. Examples include foil-backed plasterboard or metallised membranes such as that sold by DuP ont under the trade mark "Tyvek Reflex". Use of these materials generally provides only one low-emissivity surface in the entire insulation structure.

Other insulation products have low-emissivity surfaces on both sides. An example of such a product is bubble wrap with foil on both sides. This type of product is generally used in wall insulation, and gives one low-emissivity air space boundary, since the other low-emissivity side is generally in contact with the wall. This product is not used in conjunction with foil-backed plasterboard or membrane, hence systems with two or more low-emissivity surfaces are not generated.

Glass wool also has surprisingly low emissivity surfaces. This material is used in roof and wall insulation, but traditionally has not been used adjacent to unventilated air spaces.

A final class of insulating material is a multi-foil product having two outer layers with low-emissivity and multiple internal layers bounded by foils. Importantly the surfaces presented by these layers do not border unfilled air spaces but border layers of insulating material such as polyurethane foam or fibre wadding. Such multi-foil insulating systems may comprise up to six foils arranged around layers of low-conductivity material such as foam or wadding. A common feature of such products is that the thickness of the layer between foils is typically around 5 mm. If the layers were any thicker, the material would become unmanageably thick, and hence difficult to manufacture and install. Such multi- foil materials are not capable of giving the 20 - 25 mm air spaces that optimise the thermal resistance of air whilst inhibiting convection.

All these materials have been designed to reduce radiative heat losses, and are recommended for use on either side of an air space to give high thermal resistance to that air space. However, the number of low-emissivity surfaces obtained with such products is limited to two.

The following documents disclose examples of the use of low-emissivity surfaces in insulation systems.

DEl 0236151 describes double glass walls which are evacuated and silvered and which present two low-emissivity surfaces.

In US 2,004,005,450 a multi-layer insulation product has aluminium low-emissivity foils interspersed with bubble wrap with two low-emissivity surfaces in contact with an air layer. There are other surfaces in contact with bubble film, but these are thin (5 mm) layers and contain a solid material which reduces the effectiveness of the low-emissivity surface.

US 4,777,086 discloses an insulating material positioned between reflective films but provides two low-emissivity surfaces in contact with an air layer.

UK 2,398,758 discloses a multi-foil insulation material with interleaved batts and reflective foils. The batts may be perforated giving air holes inside the layers of insulating materials. The material surrounding the perforations nevertheless provides a cold bridge for conduction of heat.

US 4,433,019 discloses tubelets of filamentous material between aluminium films.

Surprisingly there are no insulation systems that seek to optimise the insulation value of air spaces in a roof structure by isolating air spaces of 20 mm thickness using low- emissivity surfaces. The main object of the present invention is to provide a thermal insulation structure for use in buildings which overcomes or at least substantially reduces the aforementioned problems of insulating buildings.

To this end, and from one aspect, the present invention resides in a thermal insulation structure for use in buildings comprising means defining a cavity having at least one surface of low emissivity; separating means suspended within the cavity so as to define at least two air spaces, the separating means comprising two surfaces of low emissivity; thereby to define a structure having at least two air spaces and at least three surfaces of low emissivity.

From another aspect, the present invention resides in a thermal insulation structure for use in buildings comprising: means defining a cavity; separating means suspended within the cavity so as to define at least two air spaces, the separating means comprising at least three surfaces of low emissivity; thereby to define a structure having at least two air spaces and at least three surfaces of low emissivity.

By combining layers of products with low-emissivity surfaces, a solution to the problems of insulating buildings has been developed in which air spaces bordered by at least three low-emissivity surfaces are built into an insulating structure.

The present invention further optimises the insulation value of air spaces in a roof structure by isolating air spaces, i.e. the separating means is preferably spaced from the nearest surface within the cavity by a distance within the range of 5 mm to 100 mm and more preferably within the range of 10 mm to 50 mm and preferably still within the range of 20 mm to 25 mm.

Such insulation structures may be used in a variety of buildings including dwellings and commercial buildings, log cabins, mobile homes and caravans.

The cavity-defining means may comprise one or more of the following: roof rafters, roof joists, battens and timber stud or cavity walls. Advantageously, the low-emissivity surfaces each have an emissivity in the range 0.05 to 0.4, and preferably in the range 0.1 to 0.25.

In a further embodiment, at least one of the low-emissivity surfaces is selected from the following: foil-backed plasterboard, multi-foil insulation, foil-backed or aluminised bubblewrap, foil-backed polyurethane board, aluminised roofing membrane, aluminised film and aluminium film, glass or mineral wool.

The low-emissivity surfaces may alternatively comprise aluminium film coated with one of a thin protective layer and a reflective aluminium tape.

Products with low-emissivity surfaces that can be combined in this way include, but are not limited, to multi-foil insulation material, such as that sold under at least one of the following trade marks: "Thinsulex" by Web Dynamics Limited, "SuperQuilt 14" by Yorkshire Building Supplies and/or "Tri-Iso Super 9" and "Triso Super 10" by Actis SA. Such multi-foil insulation material typically defines a 5 mm insulated space between foils.

Multi-foil insulation material of the type sold under the trade mark Thinsulex™ is disclosed in the specification of the Applicant's International Patent Application No. PCT/GB2005/004085.

Further, the least one of the low-emissivity surfaces may comprise aluminised roofing membrane, as sold under the trade mark "Web27" by Web Dynamics Limited or as "Tyvek Reflex" by duPont Ltd..

In a further embodiment, the cavity additionally contains at least one of the following forms of insulation: mineral wool; glass fibre; natural wool; synthetic wool; synthetic polymers; and bubble film.

Preferably, spacers are used to separate the insulation and hence provide an additional airspace. These spacers constitute any device that serves to keep the insulation separated from at least one of the low-emissivity surfaces. The spacer preferably comprises an insulating material, e.g. polyurethane foam or polystyrene foam.

In a specific embodiment of the invention, the separating means comprises at least one double-sided multi-foil insulating material.

The cavity-defining means may further comprise plasterboard backed with foil to provide a third low-emissive surface, alternatively, foil-backed bubble wrap can be utilised.

The cavity-defining means may further comprise a metallised roofing membrane, such as that described in the present Applicant's Patent No. GB 2355430.

In combination with any of the previously described embodiments of the invention, the separating means may further comprise at least one double-sided foil suspended within the cavity.

Further combinations of any of the previously described embodiments can also be constructed, provided they generate at least three surfaces in contact with unfilled air spaces and will give improved thermal insulation properties to the structure.

The structure may be arranged for location in a roof space above, below or between rafters; in joist spaces; above a ceiling; inside cavity walls; across timber studs used in timber frame walls or to line solid masonry walls and below flooring of the roof.

The above structures provide extremely high thermal resistances, whilst being very lightweight, thin and easy to install. These structures are able to meet the thermal insulation requirements for buildings as set out in the Building Regulations for England and Wales ("The Building Regulations 2000: Conservation of fuel and power Part Ll" introduced in 2006).

Such insulation structures with low-emissivity surfaces, may be installed in a roof structure in order to form such air spaces and hence effective thermal insulation structures that are light-weight, easy to install, environmentally harmless and do not add extra thickness to the roof structure. In particular, the insulation value of air spaces is maximised by forming non- ventilated unfilled air spaces of around 20 to 30 mm with low-emissivity surfaces on each side.

Thus, the invention extends to a roof structure, a wall structure or a building including any of the insulation structures defined above.

The invention further extends to a method for enhancing the thermal insulation of a cavity within a building, the cavity being provided with at least one surface of low emissivity, the method comprising separating the cavity into at least two air spaces by means comprising two surfaces of low emissivity, thereby to provide a cavity having at least two air spaces and at least three surfaces of low emissivity.

The invention further extends to a method for enhancing the thermal insulation of a cavity within a building, the method comprising separating the cavity into at least two air spaces by means comprising at least three surfaces of low emissivity, thereby to provide a cavity having at least two air spaces and at least three surfaces of low emissivity.

The thermal resistance R of roofing components can be measured using standard techniques such as heat flow meter, guarded hot plate or guarded hot box. The total thermal resistance of a structure containing multiple components can be calculated by adding together the thermal resistances of all the components. Allowance must be made for cold bridges, for examples rafters or battens that provide routes of lower thermal resistance for heat flow through the structure. British Standard 6946:1996 gives a process for calculating the total thermal resistance of a multi-component structure.

The thermal transmittance or U- value of a structure is the inverse of R:

U = 1 / R.

The U- value is determined by first calculating the overall R- value of the structure, then taking the inverse. Software is available for calculating complex R- and U-values, for example the BRE supply a commercial software package entitled "Calculation of U- values following convention in BRE BR 443 'Conventions for U- value calculations', version 1.10".

Building Regulations Part L set strict limits on U-values of different components of the building envelope. For example, at the time of writing it is expected that new build houses must have roof insulation sufficient to give U = 0.2 W/m K. Refurbished roofs, for example in loft conversions, must reach U = 0.3 W/m K.

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

Figure 1 is a perspective view of a standard roof structure;

Figure 2 is a cross-sectional plan view of a thermal insulation structure according to a first embodiment of the present invention;

Figure 3 is a cross-sectional plan view of a thermal insulation structure according to a second embodiment of the present invention;

Figure 4 is a perspective view of the arrangement shown in Figure 3;

Figure 5 is a cross-sectional plan view of a thermal insulation structure according to a third embodiment of the present invention;

Figure 6 is a cross-sectional plan view of a thermal insulation structure according to a fourth embodiment of the present invention;

Figure 7 is a cross-sectional plan view of a thermal insulation structure according to a fifth embodiment of the present invention;

Figure 8 is a cross-sectional plan view of a thermal insulation structure according to a sixth embodiment of the present invention; Figure 9 is a perspective view of the arrangement shown in Figure 8; and

Figure 10 is a cross-sectional plan view of a thermal insulation structure according to a seventh embodiment of the present invention.

Referring to Figure 1 of the accompanying drawings, a conventional roof structure 1 for a building comprises a sheet of plasterboard 2, one side of which serves to provide an inside surface 7, e.g. a ceiling surface, for an interior space in the building, e.g. a loft. A series of parallel back battens 3 run along the length of the plasterboard 2 and are attached to one face of the plasterboard 2. A plurality of parallel rafters 4 are arranged with their lengths perpendicular to the back battens 3. Each rafter 4 is attached to each of the battens 3 at the positions where their surfaces cross and is further attached to a second series of front battens 6 via a membrane 5 which extends over substantially the same area as the plasterboard 2, the membrane 5 draping into the space between the rafters. The front battens 6 lie parallel with the back battens 3, the space between the front and the back battens 3, 6 being substantially equal to the width of each rafter 4. In this structure the front battens 6 act as a mounting facility for the tiles of the roof. The membrane 5 separates the air space within the roof structure 1 into two regions. The first, non- ventilated region extends between each adjacent pair of back battens 3 and between each adjacent pair of rafters 4. The second, ventilated region extends between each pair of adjacent front battens 6.

Referring to Figure 2, a thermal insulation structure according to a first embodiment of the invention comprises three surfaces of low emissivity bordering an unventilated air space within a roof structure. The first two surfaces of low emissivity are provided by a wads of multi-foil insulation material 9, such as that marketed under the trade mark "Thinsulex". The ends of each wad are stapled to an adjacent pair of rafters 4 such that each wad of the material 9 extends the full distance between the rafters 4 and extends over the region between an adjacent pair of back battens 3. The multi-foil insulation material 9 may be installed as a continuous sheet of material, rather than separate wads, and may be fixed in position at the ends of the rafters 4. In this way the material 9 separates the first, non- ventilated region of the air space, described above with reference to Figure 1, into two groups of sub-regions, the first group extending between adjacent pairs of back battens 3 and the second group extending between adjacent pairs of rafters 4. A first surface of low emissivity (one side of the mutli-foil insulation material 9) faces the plasterboard 2 and a second surface of low emissivity (the other side of the multi-foil insulation material 9) faces a membrane 5. Furthermore, the side of the membrane 5 facing the rafters 4 has a metallised surface 12, thereby providing a third surface of low emissivity. The other side of the membrane 5 is not metallised and is attached to a series of parallel front battens 6 which in turn provide support for tiles 8.

Referring to Figure 3, a second embodiment of a thermal insulation structure incorporates the features of the first embodiment, except that the membrane 5 is not metallised, and a third surface of low emissivity is instead provided by foil-backed plasterboard or bubble wrap 14 which replaces the plasterboard of the first embodiment.

A perspective view of the second embodiment is shown in Figure 4, in which the multi- foil insulation material 9 can be seen extending into the air space formed between the rafters 4. Only a single wad of insulation material is shown for the sake of enhanced clarity but it may extend in a continuous sheet, lying across the end of each rafter and being attached thereto.

Referring now to Figure 5, a third embodiment of a thermal insulation structure incorporates the features of the first embodiment of a thermal insulation structure, except that an additional pair of surfaces of low-emissivity are provided by a double-sided foil 16 suspended between each adjacent pair of rafters 4 at a position substantially mid- way between the front and back battens 6, 3. The double-sided foil 16 thus separates the air space formed between the rafters 4 into two. The multi-foil insulation material 9 and the double-sided foil 16 together provide four surfaces of low-emissivity next to an air space. As in the first embodiment, the membrane 5 has a metallised surface 12. In addition the plasterboard 2 is backed with foil 14 which faces the air space formed between each pair of back battens 3. This structure therefore provides six surfaces of low emissivity bordering an unventilated air space.

Referring to Figure 6, a fourth embodiment of a thermal insulation structure includes a layer of multi-foil insulation material 9 as in the embodiments described above, together with a double-sided foil 16 as in the third embodiment. Li addition, booster insulation 18, e.g. glass wool, is attached between the rafters 4 and extends between the foil 16 and the membrane 5 filling most of the air space. The air space is exaggerated in Figure 6 for the sake of clarity. The plasterboard 2 is additionally backed with foil 14 which faces the air space formed between each pair of back battens 3 to provide a fifth surface of low emissivity.

Referring to Figure 7, a thermal insulation structure according to a fifth embodiment of the invention comprises a layer of multi-foil insulation material 9 as in the above- described embodiments. Third and fourth surfaces of low emissivity are provided by the surfaces of a double-sided booster insulation 18 suspended between the rafters 4 at a position substantially midway between the front and back battens 6, 3. The double-sided booster insulation 18 separates the air space formed between each adjacent pair of rafters 4 into two. The multi-foil insulation 9 and the double-sided booster 18 insulation together provide four surfaces of low emissivity bordering air spaces. In addition, the membrane 5 has a metallised surface 12, the plasterboard 2 is backed with foil 14 which faces the air space formed between each pair of back battens 3. This structure therefore provides six surfaces of low emissivity bordering unventilated air spaces.

Referring to Figure 8, a sixth embodiment of a thermal insulation structure comprises a layer of multi-foil insulation material 9. In addition, further identical wads or a single continuous wad of multi-foil insulation material 10 is stapled to each one of the rafters 4 such that it extends the full distance between the rafters 4 and lies between an adjacent pair of front battens 6. Additional vertical battens 24 may be positioned between the multi-foil insulation material 10 and the membrane 5 to provide an airspace between the two surfaces. This structure provides four surfaces of low emissivity bordering unfilled air spaces, two of which oppose one another. A fifth surface of low emissivity is provided by coating the plasterboard 2 with a layer of foil 14.

A perspective view of the sixth embodiment is shown in Figure 9. The opposing insulation material 9, 10 is shown, and may extend as previously described along the roof space fixed at the edges of the rafters 4. Referring to Figure 10, a seventh embodiment of a thermal structure comprises first and second layers of multi-foil insulation material 9, 10, as in the sixth embodiment described above providing four surfaces of low emissivity. As with the fifth embodiment, double- sided booster insulation 18 is suspended between the rafters 4, and provides an additional two surfaces of low emissivity each bordering a respective air space. This structure provides six surfaces of low emissivity bordering unfilled air spaces. A seventh surface of low emissivity is provided by coating the plasterboard 2 with a layer of foil 14. A polyurethane spacer 20 is shown to be attached between the insulation material 9 and the booster insulation 18. An alternative spacer 22 is also shown in the drawing, although it is envisaged that there would normally be only a single type of spacer used in a given roof space.

The invention will now be further described with reference to the following non-limiting Examples:-

A roof system includes:

12.5 mm foil backed plasterboard (e = 0.1) 50 mm air space Thinsulex™ multi-foil insulation material (e = 0.4) 100 mm rafter space Roofing membrane (high e)

This system was constructed, and the thermal transmittance, or U- value, measured by the National Physical Laboratory in a guarded hot box test to be U = 0.48 W/m²K at a roof pitch of 45°.

This sample contains one 50 mm air space with low- and medium-emissivity surfaces, one multi-foil insulation product, one 100 mm air space with a medium- and a high- emissivity surface. If this system is built into a roof structure with exterior tiles, then the U value of the overall roof structure is 0.48 WAn²K. The air spaces make a significant contribution to the overall thermal resistance. Calculated Values

The R-values in m²K/W of some variations on this roofing structure have been calculated using the BRE U- value calculation software:

Example 1

The emissivity of the outer layers of the Thinsulex™ surfaces is reduced to 0.2.

The U- value of this roof is 0.46 W/m²K, which has been improved by an amount of 0.02 simply by reducing the emissivity of the Thinsulex™ layer. The calculated R- value is not simply a sum of the individual R-values due to the cold bridging effects of the wooden rafters and battens.

Example 2

A foil-backed or aluminised breather membrane is introduced in the sample

The U-value for this roof is 0.45 WZm²K. Once again, an improvement in thermal transmittance has been gained by adding a low-emissivity layer.

Example 3

When the Thinsulex™ surfaces are reduced to 0.2 and a foil-backed or aluminised breather membrane is introduced in the sample, the U-value is 0.34 W/m²K

Example 4

The U-value is 0.39 WYm²K when a foil is introduced into the centre of the rafter space. Example 5

When Thinsulex™ multi-foil insulation systems are installed above and below the rafter space the U-value is 0.28 W/m²K

Example 6

Thinsulex™ multi-foil insulation systems are applied above and below the rafter space and a two-sided foil inside the rafter space. U = 0.25 W/m K

Example 7

Thinsulex™ multi-foil insulation systems are installed above and below the rafter space and 60 mm Rockwool™ mineral wool is positioned inside the rafter space. Specifically, the Rockwool™ mineral wool is not in contact with the Thinsulex™ multi-foil insulation but is spaced to retain the air layer.

This roof structure has a U-value of 0.20 WVm²K and satisfies the Building Regulations Part LlA 2006 for new-build dwellings.

Example 8

Thinsulex™ multi-foil insulation systems are installed above and below the rafter space and 100 mm polyurethane foam is positioned inside the rafter space. The rafters are 150 mm depth rafters in order to maintain the air layer intact.

This roof structure has a U-value of 0.14 WZm²K and satisfies the Building Regulations Part LlA 2006 for new-build dwellings.

Example 9

As previously described in Example 6 with the addition of two metallised foils across the rafter space. The U-value for this structure is 0.22 W/m²K. Example 10

As previously described in Example 6 but with the addition of three metallised foils across the rafter space. The U-value for this structure is 0.20 ^"WVm²K.

These examples all give an increase in R- value for the roof — but very little additional weight or thickness to the roof. Some of these examples bring the overall U-value of the roof structure below the critical values of 0.30 and 0.20 WAn²K required to satisfy the recent building regulations.

Various modifications may be made without departing from the invention. For example, the metallised coating on the membrane and/or the foil coating on the plasterboard may not be present, provided that the structure has at least three surfaces of low emissivity. Furthermore, the Thinsulex™ multi-insulation material of the preferred embodiment may be replaced by any other suitable multi-insulation material.

Claims

CLAIMS:

1. A thermal insulation structure for use in buildings comprising: means defining a cavity having at least one surface of low emissivity; separating means suspended within the cavity so as to define at least two air spaces, the separating means comprising two surfaces of low emissivity; thereby to define a structure having at least two air spaces and at least three surfaces of low emissivity.

2. A thermal insulation structure for use in buildings comprising: means defining a cavity; separating means suspended within the cavity so as to define at least two air spaces, the separating means comprising at least three surfaces of low emissivity; thereby to define a structure having at least two air spaces and at least three surfaces of low emissivity.

3. A structure according to claim 1 or claim 2, wherein the separating means is spaced from the nearest surface within the cavity by a distance within the range of 5mm to 100mm.

4. A structure according to claim 3, wherein the distance is within the range of 10mm to 50mm.

5. A structure according to claim 4, wherein the distance is within the range of 20mm to 25mm.

6. A structure according to any preceding claim, wherein the cavity-defining means comprises one or more of the following: roof rafters, battens and cavity walls.

7. A structure according to any preceding claim, wherein each the low-emissivity surfaces has an emissivity value in the range 0.05 to 0.4.

8. A structure according to claim 6, wherein the emissivity value is in the range 0.1 to 0.25.

9. A structure according to any one of claims 1 to 7, wherein at least one of the low- emissivity surfaces is selected from the following: foil-backed plasterboard, multi- foil insulation, foil-backed or aluminised bubblewrap, foil-backed polyurethane board, aluminised roofing membrane, aluminised film and aluminium film.

10. A structure according to claim 9, wherein the at least one of the low-emissivity surfaces comprises multi-foil insulation as sold under at least one of the following trade marks: "Thinsulux" by Web Dynamics Limited, "SuperQuilt 14" by Yorkshire Building Supplies and/or "Tri-Iso Super 9" by Actis SA.

11. A structure according to claim 9, wherein the at least one of the low-emissivity surfaces comprises aluminised roofing membrane as sold under the trade mark

"Web27" by Web Dynamics Limited.

12. A structure according to any one of claims 1 to 8, wherein the at least one of the low-emissivity surfaces comprises aluminium film coated with one of a thin protective layer and a reflective aluminium tape.

13. A structure according to any preceding claim, wherein the cavity additionally contains at least one of the following forms of insulation: mineral wool; glass fibre; natural wool; synthetic wool; synthetic polymers; and bubble film.

14. A structure according to claim 13, wherein at least one of the low-emissivity surfaces is separated from the at least one of the forms of insulation by a spacer.

15. A structure according to claim 14, wherein the spacer comprises an insulating material.

16. A structure according to any preceding claim, wherein the separating means comprises at least one double-sided multi-foil insulating material.

17. A structure according to any preceding claim wherein the cavity-defining means comprises plasterboard backed with foil.

18. A structure according to any preceding claim wherein the cavity-defining means comprises a metallised membrane.

19. A structure according to any preceding claim, wherein the separating means comprises a double-sided foil suspended within the cavity.

20. A structure according to any preceding claim and arranged for location selected from the following: in a roof space above, below or between rafters; in joist spaces; above a ceiling; inside cavity walls; and below flooring of the roof.

21. A roof structure, a wall structure or a building comprising a thermal insulation structure as claimed in any preceding claim.

22. A method for enhancing the thermal insulation of a cavity within a building, the cavity being provided with at least one surface of low emissivity, the method comprising separating the cavity into at least two air spaces by means comprising two surfaces of low emissivity, thereby to provide a cavity having at least two air spaces and at least three surfaces of low emissivity.

23. A method for enhancing the thermal insulation of a cavity within a building, the method comprising separating the cavity into at least two air spaces by means comprising at least three surfaces of low emissivity, thereby to provide a cavity having at least two air spaces and at least three surfaces of low emissivity.