As from 1st October 2010 it is now compulsory to incorporate wall insulation when adding a new layer to an existing solid wall or replacing an existing layer.
This applies to internally removing plaster from the walls or rendering/cladding an external wall that is currently not covered or has a covering that needs replacing.
The Regulations that govern these actions come under Part L1B of the Building Regulations for England and Wales and they lay down a range of target thermal values to achieve when carrying out any renovation or building work to a solid wall, a floor or a roof.
The responsibilty for complying with these rules lies with the architect, builder/installer and also the home-owner and any avoidance can lead to financial and retrospective penalties on all of the above parties. This is not a Planning Permission issue in that you simply notify the Council you will be having work done and that it will comply with the rules.
The process for complying with the Building Regs starts with a Building Notice application to your local Council’s Building Control and these are very helpful in answering any questions.
After paying a small fee the Building Inspector will arrange with your builder to come out and visit site at various stages of the work to ensure it is done correctly. At a successful completion of work an Approval Certificate is issued which must be kept with your house documents.
To find your local Building Control click Part L1B