Cavity Walls (Hansard, 19 January 1998)

§ Angela Eagle

On behalf of the Department of the Environment, Transport and the Regions the Building Research Establishment has undertaken research into water penetration in cavity walls filled with insulation.

As part of my Department's ongoing programme of research into rain penetration in cavity walls, I have, in consultation with my hon. Friends the Minister for London and Construction and the Minister for Local Government and Housing, asked for precautionary checks to be carried out on the condition of galvanised steel wire wall ties in a representative sample of homes with cavity walls filled with insulation. This follows the preliminary results of research which indicate that there is a possibility that the life expectancy of green coloured galvanised steel wire wall ties might be shortened when used in conjunction with Urea Formaldehyde foam cavity fill. The tests were undertaken on dwarf walls without the protective features found in real houses. I wish, therefore, to establish whether the effects indicated in the BRE research occur in real houses.

I want to stress that there is no conclusive evidence of a safety risk involving galvanised steel wire wall ties in cavity wall insulation. But it would be wrong if, as a result of the preliminary findings, we did not investigate quickly and thoroughly whether or not the possible problems with green coloured galvanised steel wire wall ties in some cavity fills were occurring in people's homes. This is a prudent, precautionary measure and I have asked that further research be carried out as soon as possible.

The expert, independent, advice I have received from the BRE is that, while it believes that its initial findings indicate the need for a wider study, it is strongly of the view that it would be premature to place any firm interpretation on its findings until it can be established whether they are representative of conditions in the UK housing stock.

While the number of homes containing galvanised wire wall ties with a green film, in cavity wall insulation, is a small portion of the housing stock, it is prudent to carry out these precautionary checks which will be extended to examine other forms of galvanised wire wall ties in cavity fill.

BRE' s test results show: Accelerated corrosion has occurred to galvanised steel wire wall ties which have been coated with a green identification film when embedded in moist urea formaldehyde foam cavity insulation. Whilst there was visual evidence of corrosion of "grey" (without the green film) galvanised steel wire wall ties embedded in moist cavity fill insulation, the measurement of loss of zinc was too small to be significant. 375W No significant corrosion was found in either form of galvanised steel wire wall tie embedded in moist blown mineral wood or mineral wool batt cavity insulation. There was some visual evidence of corrosion on both types of galvanised steel wire ties at the gap which occurs between the masonry and all three types of wet insulation. Stainless steel wire wall ties showed no signs of corrosion irrespective of the cavity fill material and exposure.

The results were obtained from experimental walls after 12 and 18 months subject to regimes of accelerated exposure. Copies of BRE's Research report have been placed in the House Library.