I have heard about Part L. What are the new insulation requirements for loft conversions?
Approved Document L of the Building Regulations which became effective on 1st of April 2002 requires that the materials used in any construction meet certain thermal performance requirements. In the case of roof windows this means that the āuā value (thermal performance) must be less than 2W/m K. All Colt Roto Roof Windows meet this standard.