Flat roof insulation is really important for increasing the energy efficiency of a space that would normally lose a significant amount of heat. Normally, these spaces include extensions, garage conversions or utility rooms. The heat loss can affect the energy efficiency of your entire home though, as the drop in temperature can cause draughts throughout your property. The main form of flat roof insulation is a rigid PIR board.
Flat roofs, often found over dormer windows, extensions and bathrooms, can really decrease the energy efficiency of your home. As well as allowing the cold to seep in, they can be prone to leaking.
To reduce these problems, it is best to insulate the roof when replacing the roof covering. There should be a weatherproof layer on top, then rigid insulation with an R-value greater than 3.7m ²K/W, then a weatherproof membrane before the timber or concrete deck below.