GB2319793A

GB2319793A - Insulating buildings

Info

Publication number: GB2319793A
Application number: GB9724979A
Authority: GB
Inventors: John Frisby
Original assignee: LETS GROUP Ltd
Current assignee: LETS GROUP Ltd
Priority date: 1996-11-27
Filing date: 1997-11-27
Publication date: 1998-06-03
Also published as: GB9724979D0

Abstract

A construction for use in the external envelopes of buildings, comprises, in sequence from an outer surface of the envelope to an inner surface thereof, an external weatherproof cladding (30), a cavity (air-space) (32), a vapour permeable and liquid impermeable membrane (34), a thickness of thermally insulating material (36), and an inner lining (internal finish) (38). The components of the construction are supported in their required relative positions by suitable structural members (40, 42, 48) and may be assembled together in the form of prefabricated panels of any required size or shape. The components are manufactured as far as possible from recycled and/or recyclable materials. .

Description

"Construction Cladding System" The present invention relates to a system for use in the construction of buildings. More particularly, the invention relates to a construction cladding system having enhanced thermal insulation properties and which is applicable to walls, flat and pitched roofs and suspended floors.

There is growing international awareness of the need to substantially reduce levels of global warming by simultaneously improving energy efficiency standards and encouraging the wider use of renewable energy resources. In industrialised countries, the primary energy consumption associated with the construction industry has been estimated to be up to 50% of the total national energy consumption. This in turn produces about half the total output of CO2, a major contributory factor to global warming.

In order to improve the energy efficiency of a building, it is necessary to minimise its total energy requirement at all stages of its life-cycle, from the initial selection of materials and components to their recycling in the event of the building being relocated or dismantled. The energy-efficiency of the building while in actual use depends largely upon the provision of an external envelope having high thermal resistance so as to minimise heat-loss.

High thermal resistance requires the optimum use of a dry, cellular, low-density material with a high proportion of small voids to solid material, where the voids do not interconnect. The lower the density of the insulating material the better its thermal performance, but the weaker its structural performance.

However, the insulating material is usually sandwiched between other materials which also provide the loadbearing elements of the external envelope of the building. For example, the inner and outer leaves of a cavity masonry wall contribute to the wall's overall thermal resistance, but their structural performance is far greater than their value as thermal insulation.

All materials which are selected to make up the building's external envelope, including any intermediate air-spaces, have some thermal resistance, but the key to substantially improving the thermal performance of the envelope is the provision of an optimum thickness of unbroken, high thermal resistance material in the correct position within the fabric of the external envelope. The location of the high resistance material does not necessarily affect the overall level of thermal resistance, but it affects the thermal capacity, thermal response and condensation control of the building envelope.

The most widely used unit of measure for thermal transmittance is the "U" value, measured in W/m2K (i.e.

heat loss expressed in Watts per square metre of surface per degree Kelvin equivalent to degree Celsius). The U value represents the thermal transmission through each component of the building envelope and takes into account the building's internal and external surface thermal resistance, together with any intermediate air-spaces within the fabric. If a building's in-use energy efficiency is poor, then its thermal resistance is low and its U value is high.

Therefore, the lower the U value, the lower the energy loss and the more energy efficient the construction of its external envelope.

By way of background example, Fig. 1 of the accompanying drawings illustrates the maximum U values allowable for compliance with the building regulation standards; e.g. the Building Standards (Scotland) Regulations 1990, showing the U values associated with the roof, walls and suspended ground floor of residential, industrial and commercial buildings, A, B, C respectively. The relevant U values are taken through all components of the external envelope and take into account the less thermally efficient loadbearing structural members, which can represent a significant proportion of the overall thermal transmission (15-20% for walls and 10-15% for roofs and suspended floors).

The general object of the present invention is to enable a significant reduction in the energy demands of buildings, to reduce the possibility of interstitial and/or surface condensation in buildings, and to improve their life-cycle performance. This is achieved, in the preferred embodiments of the invention, by the innovative use of an optimum thickness of extremely high thermal resistance material as an integral part of the external building envelope.

Ideally, this should be accomplished without adversely affecting the performance of the building envelope with respect its: (a) thermal capacity, thermal response and condensation control; (b) structural performance; (c) acoustic performance, including impact and airborne sound transmission; (d) fire resistance and resistance to surface spread of flame; (e) buildability.

It is also particularly desirable that the system should employ essentially recycled or recyclable materials and components derived from renewable resources, to further reduce energy consumption during their manufacture.

Current methods of building construction rely on complex arrangements of layers of materials in order to achieve the relatively modest thermal performance indicated by the U values in Fig. 1 that meet current construction standards, and even these standards are often not met as a result of over-riding demands to minimise construction costs. Fig. 2 of the drawings shows sectional views of three conventional envelope constructions, by way of illustration of the relevant prior art. In each case, "OS" represents the outer surface of the envelope and "IS" the inner surface.

Fig. 2A shows a conventional brick/block and ventilated cavity wall structure, having inner and outer brick/block leaves 10, 12, cavity (airspace) 11 with partial (as in the case illustrated) or full cavity insulation 14 and an internal finish of plaster 16.

This construction typically exhibits a U value of 0.45 W/m2K, excluding thermal bridging from wall ties, lintels and/or mortar joints.

Fig. 2B shows a first type of conventional brick/block and timber frame wall construction, comprising an outer brick/block leaf 20, a drained and ventilated cavity 21, structural timber frame 22 including close-spaced structural studs 23 and incorporating insulation 24, and internal finish 26, and also including a breather membrane (bm) on the outer surface of the timber frame 22 and a vapour control layer (vcl) between the inner surface of the timber frame 22 and the outer surface of the internal finish 26. This construction typically exhibits a U value in the range 0.38 - 0.45W/m2R, excluding thermal bridging from the structural studs 23 etc.

Fig. 2C shows a second type of conventional brick/block and timber frame wall construction, similar to Fig. 2B and in which like components are designated by like numerals. This construction differs from 2B by its increased depth of structural studs 23 and insulating material 24, and the provision of an (optional) service void 28 behind the internal finish 26. The U value in this case is typically in the range 0.23 - O.35W/m2K, excluding thermal bridging from the studs. The studs 23 in this example are of an I-section type having a central portion 29 of reduced thickness, thereby reducing their thermal transmission.

In accordance with a first aspect of the present invention there is provided an improved construction for use in the external envelopes of buildings, comprising, in sequence from an outer surface of the envelope to an inner surface thereof, an external weatherproof cladding, a cavity (air-space), a vapour permeable and liquid impermeable membrane, a thickness of thermally insulating material, and an inner lining (internal finish).

The external weatherproof cladding may be of any type, but, for the purposes of improving the overall energy efficiency of the construction, is preferably of a type comprising re-cycled and/or re-cyclable materials, such as timber-based weather boarding.

The cavity is preferably at least 35 mm in width, and is preferably also drained and ventilated.

The vapour permeable and liquid impermeable (i.e.

breathable) membrane may be of any type which permits the natural passage of vapour from the inside of the building while acting as a barrier to liquids from outside. Suitable materials include certain types of non-woven polyethylene material, such as TYVEK (from Du Pont).

The insulating material is preferably a high performance, vapour permeable type, preferably having a thickness of at least 200 mm, and is substantially continuous (unbroken) by structural members or services (plumbing, electricity etc.).

The inner lining is preferably substantially continuous (unbroken). Preferably also, the inner lining has a vapour resistance at least five times the vapour resistance at the outer surface of the breathable membrane. Again, for the purposes of improving the overall energy efficiency of the construction, it is preferably of a type comprising re-cycled and/or recyclable materials with adequate racking strength and fire resistance.

The construction preferably also includes support means for supporting said external weatherproof cladding, vapour permeable and liquid impermeable membrane, thickness of thermally insulating material, and inner lining in their required positions relative to one another.

Preferably, said support means includes battens located in the cavity between the outer weatherproof cladding and the vapour permeable and fluid impermeable membrane.

Preferably also, said support means further includes a first plurality of elongate structural members located behind the vapour permeable membrane and connected through the inner lining and the insulation to a second plurality of elongate structural members located on the inner surface of the inner lining.

Preferably also, the aligned pairs of said first and second elongate structural members are connected by connecting means comprising rigid members of small cross-section and low thermal transmittance.

Preferably, said connecting means comprises a lattice structure. An innermost finishing layer may also be secured to the second plurality of structural members.

The construction in accordance with the invention may be implemented by installing the various components at the time of building. However, the components may be completely or partially prefabricated in panels of any suitable size or shape.

Therefore, a second aspect of the invention provides a panel for use in the construction of external envelopes of buildings, comprising, in transverse cross section, at least a vapour permeable and liquid impermeable membrane and a thickness of thermally insulating material.

The panel may also include an inner lining on the opposite side of the insulating material from the membrane. The panel may also include outer weatherproof cladding spaced from the vapour permeable and liquid impermeable membrane, and support means and an innermost finishing layer as referred to above.

Alternatively, the panel may comprise at least the combination of the insulating material and the inner lining.

The preferred characteristics of the components of the panel are as noted above. The panel may be fabricated from discrete components. Alternatively, it is possible that the panel could be manufactured as an integrated unit incorporating some or all of the required components (i.e. the external weatherproof cladding, the cavity, membrane, support means, insulating material, and inner lining).

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 illustrates typical thermal performance standards currently required by building authorities for various types of building; Fig. 2 illustrates conventional types of composite and timber frame construction for the external envelopes of buildings; Fig. 3 is a sectional view of one example of a cladding construction for use in the external envelopes of buildings, in accordance with the invention; and Fig. 4 illustrates the thermal performance achievable by a building using the present invention.

Referring now to Fig. 3 of the drawings, an improved construction for use in the external envelopes of buildings, in accordance with the invention, consists of the following sequence of components or "zones": an external weatherproof cladding 30, a drained and ventilated cavity (air-space) 32, a vapour permeable and liquid impermeable membrane 34, a substantially unbroken thickness of thermally insulating material 36, and a substantially unbroken inner lining (internal finish) 38. The construction further includes support means for supporting these various components in their required relative positions, as shall be described further below.

The membrane 34 is required to permit the natural passage of water vapour from the interior of the building while acting as a barrier to liquids from the exterior. This enables the envelope of the building to "breathe", while being resistant to the ingress of liquids, thereby substantially increasing the performance of the insulation and reducing the likelihood of interstitial condensation. Suitable materials for the membrane 34 include certain types of non-woven polyethylene material, such as TYVEK (from Du Pont).

It is known in the art that the transfer of vapour from the interior to the exterior of a building envelope may be promoted by controlling the relative vapour resistances at the inside of the envelope and the outside of the thermally insulating layer (more specifically the outer surface of a breathable membrane such as bm in Figs. 2B and 2C); suitably, the inner vapour resistance should be at least five times the outer vapour resistance. This phenomenon is exploited in the present invention. The use of a vapour permeable and liquid impermeable membrane in accordance with the invention improves upon known systems by being highly resistant to the ingress of liquids from the outside.

The remaining components of the construction may comprise any combination of known types. However, in keeping with the general object of the invention to improve the overall energy efficiency of the construction, these are preferably of a type comprising re-cycled and/or re-cyclable materials, such as timberbased products (particularly for the outer cladding 30 and support means).

The cavity 32 is preferably at least 35 mm in width and is preferably also drained and ventilated to minimise condensation in the air-space. The insulating material 36 should be a high performance type, having a thickness of at least 200 mm. The insulating material 36 and the inner lining 38 should be substantially continuous (unbroken) by structural members or services, as far as is practicable.

When implemented in an optimal or near-optimal configuration, the present invention may exhibit a U value as low as 0.13W/m2K at no additional cost over conventional systems, this being a significant improvement over such conventional systems. In the best case, the invention may provide U value as low as O.OW/m2K. The construction may be used for walls, roofs and suspended ground floors, as illustrated by Fig. 4.

Obviously, the required components may be applied individually during the construction of a building.

However, it is preferred that the invention be implemented by the use of pre-fabricated panels incorporating some or all of the sequence of components which make up the complete cladding system. Such panels may comprise the membrane 34 plus the insulating material 36 and suitable structural members providing support means, with the inner lining 38 being applied separately, or the insulating material 36 plus the support means and inner lining 38, with the membrane 34 being applied separately, or all of these components.

The pre-fabricated panels may further include the weatherproof cladding 30 and cavity 32.

Panels of this type could be fabricated from discrete parts providing some or all of the components as noted above. However, it is possible that the panel could be manufactured as an integrated unit incorporating the required components; for example, by using a single material which can be selectively manufactured with "zones" of suitable thicknesses, insulation properties, structural and fire resistance performance, and permeabilities.

As is also shown in Fig. 3, the components of the system are preferably connected and mutually supported by support means such as inner and outer elongate structural members 40 which are preferably connected together by, for example, a lattice of rigid members of small cross sectional area and low thermal resistance. The inner members 40 are located on the inner surface of the inner lining 38 and the outer members are located behind the membrane 34. This arrangement provides the required support for the components of the cladding, while presenting a heat transfer path having very low thermal transmittance, thus reducing thermal bridging by substantially maintaining the continuity of the insulating material.

With this arrangement, an additional innermost finishing layer 44 may be secured to the inner structural members 40. This also provides a service void 46.

The outermost weatherproof cladding 30 may also be connected to outer structural members 40, through the membrane 34, by means of additional battens or the like 48, located in the cavity 32.

Improvements and modifications may be incorporated without departing from the scope of the invention.

Claims

1. A construction for use in the external envelopes of buildings, comprising, in sequence from an outer surface of the envelope to an inner surface thereof, an external weatherproof cladding, a cavity (air-space), a vapour permeable and liquid impermeable membrane, a thickness of thermally insulating material, and an inner lining (internal finish).

2. A construction as claimed in Claim 1, wherein the external weatherproof cladding comprises re-cycled and/or re-cyclable materials.

3. A construction as claimed in Claim 2, wherein said weatherproof cladding comprises timber-based weather boarding.

4. A construction as claimed in any preceding Claim, wherein said cavity is preferably at least 35 mm in width.

5. A construction as claimed in any preceding Claim, wherein said cavity is drained and ventilated.

6. A construction as claimed in any preceding Claim, wherein said vapour permeable and liquid impermeable (i.e. breathable) membrane is of a type which permits the natural passage of vapour from the inside of the building while acting as a barrier to liquids from outside.

7. A construction as claimed in Claim 6, wherein said membrane comprises non-woven polyethylene material, such as TYVEK (from Du Pont).

8. A construction as claimed in any preceding Claim, wherein said insulating material comprises a high performance, vapour permeable type.

9. A construction as claimed in Claim 8, wherein said insulating material has a thickness of at least 200 mm, and is substantially continuous (unbroken) by structural members or services (plumbing, electricity etc.).

10. A construction as claimed in any preceding Claim, wherein said inner lining is substantially continuous (unbroken).

11. A construction as claimed in any preceding Claim, wherein said inner lining has a vapour resistance at least five times the vapour resistance at the outer surface of the breathable membrane.

12. A construction as claimed in any preceding Claim, wherein said inner lining comprises re-cycled and/or re-cyclable materials with adequate racking strength and fire resistance.

13. A construction as claimed in any preceding Claim, further including support means for supporting said external weatherproof cladding, vapour permeable and liquid impermeable membrane, thickness of thermally insulating material, and inner lining in their required positions relative to one another.

14. A construction as claimed in Claim 13, wherein said support means includes battens located in the cavity between the outer weatherproof cladding and the vapour permeable and fluid impermeable membrane.

15. A construction as claimed in Claim 13 or Claim 14, wherein said support means further includes a first plurality of elongate structural members located behind the vapour permeable membrane and connected through the inner lining and the insulation to a second plurality of elongate structural members located on the inner surface of the inner lining.

16. A construction as claimed in Claim 15, wherein aligned pairs of said first and second elongate structural members are connected by connecting means comprising rigid members of small cross-section and low thermal transmittance.

17. A construction as claimed in Claim 16, wherein said connecting means comprises a lattice structure.

18. A construction as claimed in any one of Claims 15 to 17, further including an innermost finishing layer secured to the second plurality of structural members.

19. A construction as claimed in any preceding Claim, wherein the components of the construction are completely or partially prefabricated in panels of any suitable size or shape.

20. A panel for use in the construction of external envelopes of buildings, comprising, in transverse cross section, at least a vapour permeable and liquid impermeable membrane and a thickness of thermally insulating material.

21. A panel as claimed in Claim 20, further including an inner lining on the opposite side of the insulating material from the membrane.

22. A panel as claimed in Claim 20 or Claim 21, further including an outer weatherproof cladding spaced from the vapour permeable and liquid impermeable membrane.

23. A panel as claimed in any one of Claims 20 to 22, further including support means for supporting the components of the panel in their required relative positions.

24. A panel as claimed in any one of Claims 20 to 23, further including an innermost finishing layer.

25. A panel for use in constructing the external envelopes of buildings, comprising at least the combination of a layer of insulating material and an inner lining.