Mezzanine areas should in effect be treated as two story extensions. The method adopted should be to enter the part of the property above and below the mezzanine deck as a two story extension whilst the remaining part is treated as a single level with the full floor to ceiling/ roof height. If the mezzanine is situated such that it has no heat loss perimeter then assign a nominal 1m perimeter to each floor of the mezzanine part and deduct 1m from the heat loss perimeter of the other part. The Lifespan SAP Team