A cold flat roof insulation requires more work, taking off old boards and replacing them and the roof surface. The thermal efficiency isn’t as good as with warm roof insulation.
A warm deck roof is much easier to install, offers great thermal performance but adds height to the flat roof. As a result of the height difference, warm roofs cannot be used on balconies and flat roofs extensions with doors leading onto the roof. In these cases, a cold roof is a preferable alternative to warm roof insulation