The Building Regulations 2000 Approved document Part L 2010 aims to achieve an overall 25% saving in carbon output from new UK buildings when compared with the 2006 version. It also seeks to ensure energy efficiency is upgraded during substantial refurbishment of existing buildings. Yet SPRA understands that a major opportunity to improve energy efficiency in roofing will be missed because of interpretation of the new Part L2B for exiting non-dwellings. SPRA Director Jim Hooker sums up the problem in his enquiry to the Department of Communities and Local Government:

“I have a particular concern regarding the interpretation of ADL2B in respect of membrane or ‘flat’ roofing.

Clause 5.8(b): ‘replacing the water proof membrane on a flat roof.’

The word ‘replacing’ implies the removal of the existing and installation of new waterproof covering. That is clear enough, but does not take account of the overlaying of an existing failed or perished waterproofing with another. Typical examples of this include the following:

·         Mastic asphalt (which is expensive to remove) is retained and covered with bitumen or single ply membrane, or coated with a site-applied polymeric liquid waterproofing.

·         Single ply membrane is overlaid with a new layer and restrained by mechanical fastening or ballasting. It may also be coated with a site-applied polymeric liquid waterproofing.

·         Built-up bitumen membrane is retained, repaired and covered with additional bitumen or single ply membrane, or coated with a site-applied polymeric liquid waterproofing.

·         Liquid-applied membrane is cleaned and over-coated with a similar product.

The durability of such systems is increasing, thus extending to as much as twenty years the period before an opportunity will next arise to upgrade thermal performance. The cost difference between  ‘option 1’ (an overlay) and  ‘option 2’ (a thermal upgrade) is widening so the building owner, who for this type of work may be the direct employer of the roofing contractor, may be further discouraged from taking up the opportunity for carbon saving.

‘Replacing’ could also mean removing the waterproofing membrane, whilst retaining the other components beneath it, usually thermal insulation and vapour control layer. I assume that this circumstance would come within the scope of L2B:2010 as would the complete stripping down to the supporting deck but again this is not clear. However, this practice is increasingly rare, because of the alternatives available and because it exposes the roof to the elements; impractical if there is continuous occupation of the building.”