GB2306984A

GB2306984A - Preventing condensation in framed walls

Info

Publication number: GB2306984A
Application number: GB9623386A
Authority: GB
Inventors: William Hunter Watson
Original assignee: CAS ARCHITECTS Ltd
Current assignee: CAS ARCHITECTS Ltd
Priority date: 1995-11-09
Filing date: 1996-11-11
Publication date: 1997-05-14
Anticipated expiration: 2016-11-11
Also published as: GB9623386D0; GB2306984B

Abstract

In a wall of a building, having a frame (5) of timber studs, sheathing material (1) secured to one face of the studs, walling material (4) secured to an opposed face of the studs, and insulating material (7) between the sheathing material and the wailing material, the sheathing material has a plurality of through holes (2) at intervals over its area to allow ventilation therethrough. The ventilation allowed by the presence of the through holes in the sheathing material means that moisture can be ventilated from the framing timber and thus the ventilation can prevent the build up of interstitial moisture, which could otherwise lead to rotting of the framing timbers.

Description

A Wall of a Building The present invention relates to a wall of a building, particularly a wall of timber frame construction.

Common timber frame practice in the UK incorporates component panels assembled in the factory of timber studs with a sheathing material. This sheathing material is normally of plywood or "Sterling" board and is factory fixed to give the panels rigidity while being handled. Once erected on-site to form an internal wall, the timber studs and a layer of insulation are enclosed between the sheathing material and, typically plasterboard. The sheathing material then gives racking strength to the building.

Unfortunately, plywood and "Sterling" board have a high vapour resistance and this gives rise to periodic interstitial condensation within the completed internal wall. This interstitial condensation gives rise to a risk of rot to the timber studs and the sheathing material and reduces the effectiveness of the thermal insulation within the completed wall.

The present alternative to ply-sheathed panels is the practice adopted in Scandinavia, and occasionally adopted in the UK, which is a timber frame assembled on site and clad in a sheathing material with a low vapour resistance, such as bitumen impregnated fibreboard (woodwool slabs have also been used). The disadvantages of this approach are: (i) that such materials, of suitably low vapour resistance, have less (fibreboard) or no (woodwool) racking strength, and may therefore, depending on the type of material adopted and the loading on the building, require additional reinforcement; (ii) fibreboard requires a substantially greater amount of fixing to the timber frame to maximise its racking strength; and (iii) erection on site is often an expensive option due to the effects of the weather and site conditions.

The Building Research Establishment have tested an option which includes using plywood as a sheathing material while reducing its vapour resistance by introducing ventilation slots to the top and bottom of the panels. When a clear gap was provided between the insulation layer and the sheathing material, allowing the free flow of air to the ventilation slots, it was found that there were no problems with interstitial condensation. This, however, involved the introduction of an additional layer of construction in the form of battens which were required to provide this clear passageway of air. When, however, the insulation was placed hard up against the sheathing material it was found that interstitial condensation problems recurred and that the ventilation slots were ineffective.

According to the present invention there is provided a wall of a building, having a support frame, sheathing material secured to a first face of the frame, walling material secured to an opposed face of the frame, and insulating material between the sheathing material and the walling material, wherein the sheathing material has through holes at intervals over its area to allow ventilation therethrough.

This invention also provides sheathing material for use in the construction of the wall of a building wherein the sheathing material has a plurality of ventilation holes at intervals over the area of the sheathing material.

This invention also provides a building panel for use in constructing a wall of a building, the panel having a support frame, and sheathing material secured to the frame, the sheathing material having holes at intervals over its area to allow ventilation therethrough. The panel is preferably prefabricated, and the frame is preferably of timber.

Preferably the diameter of the ventilation holes is between 5 and 35mm.

More preferably the diameter of the ventilation holes is between from 15 and 25mm.

The ventilation holes may be made by any suitable method, such as drilling at centres spaced at between 100 and 450mm apart. Most preferably the ventilation holes are at centres spaced between 250 and 350mm apart.

The ventilation holes may be circular, or any regular or irregular shape.

The smaller the ventilation hole, the smaller the distance between spaced centres should be to effect adequate ventilation of the wall.

The ventilation holes may be spaced horizontally, vertically and/or in any regular or irregular pattern over the area of the sheathing material.

Suitably the sheathing material may comprise plywood, "Sterling" board or other wood or wood composite material.

The suggested materials have high vapour resistance, high strength and are inexpensive compared to materials which are used in on-site assembly.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Fig 1 is a front view of a sheet of sheathing material with ventilation holes in accordance with the present invention; and Fig 2 is an end sectional view of a cavity wall incorporating the sheathing material of Fig 1, in accordance with the invention.

The sheathing material of Fig 1 is in the form of a sheet of plywood 1 of a grade commonly used in the construction of timber-framed buildings. The sheet 1 has ventilation holes 2 of 19mm diameter bored through it, in this case at regular intervals. The holes are spaced vertically and horizontally at 300mm centres over the entire area of the sheet 1.

In Fig 2 the cavity wall has an external wall 3 of brick and an internal wall 4 spaced from it, of timber frame construction. The internal wall has timber studs 5 to the external face of which is secured the sheet 1 of plywood sheathing material to form a prefabricated panel which is transported in that form to the building site.

A sheet 6 of plasterboard is secured to the opposite, internal face of the studs 5 through a vapour check 8, and a layer 7 of glasswool quilt insulating material fills the space between the plywood sheet 1 and the plasterboard sheet.

As the glasswool quilt insulation material 7 has a low resistance to the passage of vapour, the spacing of the ventilation holes 2 in the plywood sheet 1 is sufficient to prevent interstitial condensation within the internal wall 4 in most conditions.

It is possible that under severe conditions, such as during periods of very low temperatures and while there are exceptional levels of moisture generation within the building, that small levels of interstitial condensation may occur, but the provision of the ventilation holes 2 will dramatically reduce the severity and frequency of such occurrences as compared to conventional constructions and will hasten the reduction of moisture to safe levels through the normal cycle of drying out.

Claims

1 A wall of a building, having a support frame, sheathing material secured to a first face of the frame, walling material secured to an opposed face of the frame, and insulating material between the sheathing material and the walling material, wherein the sheathing material has through holes at intervals over its area to allow ventilation therethrough.

2 A wall according to Claim 1, wherein the holes are spaced apart by between 100 and 400mm.

3 A wall according to Claim 2, wherein the holes are spaced apart by between 250 and 350mm.

4 A wall according to any one of Claims 1 to 3, wherein the holes have a diameter of between 5 and 35mm.

5 A wall according to Claim 4, wherein the holes have a diameter of between 15 and 25mm.

6 A wall according to any of the preceding Claims, wherein the sheathing material has high vapour resistance and provides racking strength to the wall.

7 Sheathing material for use in constructing a wall of a timber framed building, the sheathing material having a plurality of holes at spaced intervals over its area.

8 A building panel for use in constructing a wall of a building, the panel having a support frame, and sheathing material secured to the frame, the sheathing material having through holes at intervals over its area to allow ventilation therethrough.

9 A building panel according to Claim 8, which is prefabricated.

10 A building panel according to Claim 8 or Claim 9, wherein the frame is of timber.

11 A wall of a building substantially as hereinbefore described with reference to and as shown in Fig 2 of the accompanying drawings.

12 Sheathing material as hereinbefore described with reference to and as shown in the accompanying drawings.

13 A building panel substantially as hereinbefore described with reference to and as shown in Fig 2 of the accompanying drawings.