What is a cold flat roof?
A cold flat roof is where the insulation is placed between the joists under the flat roof, so that the roof and the roof timbers are cold. Therefore, the cold roof ventilation needs to be provided to create airflow to the front and rear of the roof to prevent condensation.
This is a slightly more expensive flat roof system to build in comparison to a warm flat roof system. Also, it’s not as good thermally as the warm roof option due to more exposure.
The advantage of the cold flat roof system is that no additional height is added to the structure – however with today’s building regulations, it is necessary to insulate internally underneath the ceiling inside the house. As you can imagine this causes problems such as moving electrical fittings and can cause a big disturbance to the household during the works. A warm roof is a far better option as no ventilation is required and the insulation will be above your flat roof.