GB2031985A

GB2031985A - Thermal insulation of buildings

Info

Publication number: GB2031985A
Application number: GB7839123A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-10-03
Filing date: 1978-10-03
Publication date: 1980-04-30

Abstract

For enhancing the thermal insulation of walls while allowing moisture to be drawn without substantial resistance from the cavity to the outside atmosphere by vapour pressure, a relatively loose packing material 13, e.g. glass or mineral wool, is located at the upper end of the cavity wall 10 to allow moisture to be drawn therethrough to the outside atmosphere while maintaining a relatively stagnant pocket of air in the cavity to enhance thermal insulation of the wall by preventing convection heat losses. The loft space may be insulated from the outside atmosphere by a barrier 14 extending between the underside of the sloping roof of the building and the uppermost ceiling at a position inwardly of the cavity wall. <IMAGE>

Description

SPECIFICATION Thermal insulation of buildings This invention relates to the thermal insulation of buildings.

Buildings, particularly houses having sloping roofs, having a cavity wall construction, normally have the upper ends of the cavity open to allow air containing moisture in the cavity to be drawn out of the cavity. This movement of air however results in convection heat losses in the cavity walls. In order to increase the thermal insulation of the cavity walls it is known to inject an insulating foam which substantially fills the cavities. However not only is this a relatively expensive method of insulating, the foam filling the cavity also hinders the passage of moisture from the cavity.

It is also known in houses having sloping roofs to cover with boards the spaces between the eaves of the roof and the walls of the building in order to prevent cold air from the surrounding atmosphere from passing into the loft space between the roof and the uppermost ceiling of the buildings. In this way the temperature in such loft space is maintained at a relatively higher temperature to reduce heat losses from the building through its uppermost ceiling.

However a disadvantage of this construction is that air containing moisture which is drawn out of the uppermost end of the cavity walls is prevented from passing to the outside atmosphere and therefore passes into the loft space.

In one aspect of the invention there is provided a method for thermally insulating buildings having cavity walls comprising locating along the upper end of the cavity or cavities a light packing of moisture permeable packing material which maintains a layer of stagnant air in the cavity while allowing moisture to pass through the layer.

Moisture in the internal rooms of the building is drawn into the wall cavities by vapour pressure produced by a temperature difference existing between the inner and external atmospheres. The layer of packing material at the upper end of the cavity, which is for example a loosely packed fibrous material such as fibreglass, allows moisture to pass therethrough while containing within the cavity a layer of relatively stagnant air which enhances the thermal insulation of the cavity wall by preventing convection heat losses. There is therefore provided an effective and inexpensive method of enhancing the thermal insulation of the cavity wall for the building without any substantial interference with the normal moisture outflow from the cavity.

In another aspect of the invention manes are provided to form a barrier between the internal surface of the buildings roof and the uppermost ceiling of the building art a position located inwardly of the outer cavity walls of the building, the upper end of the cavities of such walls being open to the outside atmosphere to allow moisture drawn out of such cavities to pass to the surrounding atmosphere.

The advantage of adopting this feature is that the loft space defined between the sloping roof and the uppermost ceiling is isolated from the outside atmosphere whilst moisture emanating from the cavity wall can pass directly to such atmosphere.

The aforesaid barrier prevents the moisture from passing into the loft which usually occurs with the aforementioned construction in which the eaves are built in but the aforesaid barrier also provides a measure of thermal insulation between the loft space and the surrounding atmosphere which at some times during the year will be considerably colder. The barrier means may be provided relatively inexpensively by aluminium strips of generally channel shaped section having flanges along opposite edges for securing to the roof beams and the ceiling joists respectively. Further insulation material, for example fibreglass packing, is preferably located in the spaces between the ceiling joists, the roof beams and the respective flanges of the aluminium strips.

The invention also provides a building when insulated by a method according to the invention.

The invention further provides thermal insulation means for insulating such a building.

A specific embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure lisa cross-section of a portion of a house which is thermally insulated by a method according to the invention, and Figure 2 is a detail in perspective of the construction of Figure 1.

Referring to the drawings, there is shown a house having an outer cavity wall 10, an uppermost ceiling 11 and a sloping roof 12. The construction of the wall, ceiling and roof is of conventional design, namely a cavity wall of spaced brick wall sections, an uppermost ceiling supported from generally parallel wooden joists and a sloping roof having layers of tiles laid on wooden strip members which extend between a series of parallel roof beams which extend at an angle to the ceiling joists and at their lowermost ends overhang the upper ends of the cav itywalls.

Moisture insidethe house is drawn through the inner layer of the cavity wall into the cavity by vapour pressure which is produced by a temperature gradient across this wall section. For example the temperature inside the building may be 18"C and the temperature of the surrounding atmosphere at certain times of the year may be 0 C or less. The resulting moisture collecting in the cavity wall will be drawn through the upper end of the cavity and will pass through the space between the eaves and the upper end of the cavity wall 10. In accordance with one aspect of the invention a layer of packing material in the form of loosely packed fibreglass blanket or wool is located within the cavity wall along the upper end of the cavity.This layer of packing is formed to have interstices sufficient to allow passage therethrough of moisture drawn from the cavity by a vapour pressure created by the temperature difference between the surrounding atmosphere and that within the cavity. The packing however is sufficiently dense to withstand convection movement and contain within the cavity a relatively stagnant pocket of air which assists in enhancing the thermal insulation of the outer wall by preventing convection heat los ses. A suitable material for this layer is a fibrous packing of glass or mineral wool of light (low) density.

It is desirable to leave unobstructed the space between the eaves of the roof 12 and the upper end of the cavity wall 10 to allow an unrestricted passage of moisture from the cavity wall to the outside atmosphere. Therefore in order to provide a measure of thermal insulation for the loft space defined between the roof 12 and the uppermost ceiling 11 from the outside atmosphere, it is proposed according to an other aspect of the invention to locate a channel section aluminium strip 14 to provide a barrier between the roof 12 and the ceiling 11 around the periphery of the loft space but at a position spaced inwardly of the cavity wall 10. This barrier therefore does not prevent the passage of moisture from the cavity wall to the surrounding atmosphere as is the case with built-in eaves and therefore the moisture is transmitted outside the house rather than into the loft space.The edge flanges of the strip 11 bridge and are stapled to the roof beams and the ceiling joists 15, respectively. Fibreglass or other heat insulating packing material 17 is located in the spaces defined between the flanges of the aluminium strip and the roof beams, and the ceiling joists, respectively in order to complete the barrier.

Conventional heat insulating material, for example in the form of a fibreglass blanket, may be laid between the ceiling joists 15 as is commonly done at the presenttime. Further insulation of the loft space may be achieved relatively inexpensively by locating further heat insulating strips between the roof beams, these strips being held in place by strips of aluminium foil 16 laid across or vertically down the undersides of the roof beams after the packing material has been disposed therebetween, the foil being stapled to the beams.

It will therefore be appreciated that a method of enhancing thermal insulation of buildings having cavity walls and sloping roofs as described above is relatively inexpensive to put into practice while overcoming disadvantages of some of the commonly adopted expedients used at present and as described earlier in the specification.

Claims

1. A method of thermally insulating a building having cavity walls comprising locating along an upper end of the wall cavities a layer of moisture permeable packing material which serves to contain a pocket of relatively stagnant air in the cavity while allowing moisture to be drawn through the layer due to a vapour pressure produced by a temperature gradient across the layer.

2. A method as claimed in Claim 1, wherein means are provided for forming a barrier between the internal surface sloping roof sections of the building and the uppermost ceiling of the building at locations spaced inwardly of the outer cavity walls of the building, the upper ends of the sealed cavities of the outer walls being left open to the outside atmosphere to allow moisture drawn through the packing to pass outside the building.

3. A method of thermally insulating a building having cavity walls, comprising locating barrier means between the internal surface of a sloping roof section of the building and the uppermost ceiling of the building at locations spaced inwardly of the outer cavity walls of the building, the upper end of the outer walls being left open to the outside atmosphere to allow moisture drawn from the wall cavities to pass outside the building.