MULTI-LAYER INSULANTS

There are a number of “high-tech” multi-layer insulants on the market. The first few originated on the continent where they have been used for several years. They consist of multiple layers of a metalised material interleaved with wadding and foams, and are typically 25mm thick.

These materials tend to act as barriers rather than insulants as we have come to think of them, and as a result manufacturers claim that their true thermal performance cannot be accurately assessed using the British Standard “Hot Box” test. Manufacturers have therefore sought to develop new test methods which involve comparisons between their own product and another insulating product (usually mineral wool).

Such tests set out to demonstrate that the actual energy consumption of buildings using multi-foil insulation will be equivalent to (or better than) an identical building using mineral wool insulation, and having done so, claim the same “R” value for the multi-foil product as would be accepted for the test thickness of mineral wool. This comparative testing has resulted in claims from multi-foil manufacturers that the insulating properties for their products is approximately three times better than can be verified using existing test standards.

Unfortunately there are no currently accepted National or European standards for performing tests in this way, and it is therefore not possible to be sure that the results of such tests give a fair comparison of performance between competing multi-foil products, or indeed between multi-foils and existing insulation products which have been tested to established standards. On this basis, LABC (Local Authority Building Control) have issued a guidance note to all local authorities regarding the use of these foils. This guidance note recommends that where the works on-site are required to comply with part L of the Building Regulations (April 2006 edition), multi-foil insulation should only be used on the basis of test values obtained in accordance with paragraph 3.10.2 of BR443. This effectively means that such insulants will only be acceptable if additional insulation is also provided.

LABC strongly supports the proposal by the Confederation of Multi-foil Manufacturers to obtain European Technical Approval, and hope that this can be achieved as quickly as practicable to resolve the current confusion surrounding the suitability of these products.

In the meantime, it is considered appropriate to allow the use of these foils in conjunction with other insulating materials. Typical constructions to achieve a U-value of 0.2 would include the use of a multi-layer foil insulant, together with either 130mm mineral fibre or 75mm PUR foam product. U-value calculations in support of these constructions are required by Building Control, and it is essential that the manufacturer’s details are strictly adhered to.