Outlines available guidance on how to ensure buildings comply with the latest revision of Part L of the Building Regulations, which specifies minimum requirements for the insulation of building services. The essential Tier 2 documents for building services engineers are: "Domestic heating compliance guide"; "Non-domestic heating, cooling and ventilation compliance guide", and "TIMSA guidance for achieving compliance with Part L of the Building Regulations". The first two guides by NBS deal with heating, cooling and ventilation as a whole for the relevant buildings, including some information on insulation. The TIMSA guidance contains the standards on minimum heat loss or gain in the domestic and non-domestic guides. Article expands on the standards, including thickness of insulation for a range of thermal conductivities, and explains compliance for domestic and commercial buildings.