It is quite common for Main Property Extensions or flats positioned at the top floor level to have an associated flat roof construction. It is also not always possible to measure flat roof insulation in the same way as pitched roof insulation. The available options within the RdSAP software for flat roof insulation are: Flat Roof Insulation Unknown The common mistake within the assessment would be to record the flat roof insulation as ‘Unknown’ as you simply cannot access this space and do not know what insulation is there; however, that is incorrect and could lead to a random or smart audit failure. The correct methodology to record Flat Roof details and the associated insulation would be as follows. Wherever a flat roof cannot be assessed for its insulation, the way to recognise this within the assessment would be to record as: Flat Roof Insulation – You should select ‘Flat Roof Insulation’ for the insulation type If you know there is insulation present, and it can be measured or evidenced through documentary evidence OR if there is no way of identifying whether insulation is present then you would also select this option and record the insulation thickness as ‘As Built’ to let the software determine the appropriate U- Value based upon its selected age band. Recommendations will be made on the EPC thereafter if applicable. Unknown – Caution should be taken with this option. Do not select “unknown” insulation type option for insulation inappropriately as this automatically suppresses any insulation recommendation. “Unknown” should be used only in exceptional circumstances, such as when there is conflicting evidence (inspection and/or documentary) of added insulation whose presence cannot be ascertained conclusively. (Convention 3.03b) This would traditionally be supported in your site notes.