When selling a house, one of the 'services'  estate agents offer is to provide a EPC(Energy performance certificate) for the seller. If you are selling your house then you must provide a certificate but it's actually quite cheap in the scheme of things (maybe £50-150) and you don't need an estate agent who may add a mark up to it. The performance is based on algorithm which sums up negative and positive attributes of the house to derive an overall energy rating - it's not based on actual performance. The Domestic Energy Assessor  completing the EPC rating makes assumptions and doesn't check for presence of insulation. They will write things like (flat roof assumed no insulation). In older houses, retrofit insulation does a lot to push up the rating: However, what happens when you have damp insulation? Technically It's a negative rating as heating the inside of the house causes large thermal loss via heat transfer through the damp wall into the sog...