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. The warm roof option is where all the roof timbers of the structure are in the warm, thus the name ‘warm flat roof’.

Quick Facts

Why does a gap have to be provided in between the insulation and the roof deck?

Because it is necessary to allow air to flow, so that the warm, moist air is able to escape rather than coming into contact with the cold deck and then condensing.

What will happen to my roof if I have condensation?

Condensation can lead to rotting decking and/or timbers, damp ceilings and damp insulation, which will means the insulation will no longer be working effectively.

Why do we check to see if soffit vents have been fitted?

External ventilation is essential to  minimise the risk of condensation in a cold roof, therefore it would be ideal to have soffit vents to the underside of the fascia board – however many flat roofs have been built without soffits.

Can an existing cold flat roof be converted to a warm deck insulated roof?

Of course, we can quickly convert any cold deck flat roof to a warm deck flat roof by installing either a single ply membrane or EPDM membrane, whichever suits your needs.  If the existing roof decking is sound, we can fix the insulation straight on top.  For roof decking which may need replacing if it is not in a satisfactory condition, we would install a suitable material like plywood to provide a strong platform for the warm roof.

Any more questions?