Warm roof or cold roof relates to the insulation properties of the roof to a living area: We explore the differences:
During the construction, rigid insulation boards are installed over the timber joists and underneath the flat roof covering of choice (e.g felt, EPDM rubber, fibreglass GRP)
Layers that make up a war roof flat roof system:
- Timber joists. (usually a joiner would install these not a roofing contractor)
- OSB or ply timber boards. (A steel deck is sometimes installed on larger or commercial roof projects.)
- Vapour barrier membrane. (This stops any condensation rising from the living area making contact with the insulation. More info can be found on condensation can be found here.
- Rigid insulation board. (The main component of providing insulation to the living area. A+ rated when compared to the BRE Green Guide 2008)
- Chosen flat roof system. (Homeowner’s or architect’s flat roof covering of choice. e.g felt, EPDM rubber or GRP Fibreglass)
A cold roof construction is the traditional method of laying glass wool insulation (can be found in loft spaces) between the timber joists. A timber deck is then fixed to the joists followed by the chosen flat roof covering system. Because the insulation does not cover the entire flat roof area, there is a small amount of heat loss- this is known as “thermal-bridging.” An air gap between the insulation and under-side of the timber deck is necessary to prevent contact therefore causing subsequent condensation.
In relation to a new build project we would recommend a warm roof system. Due to the thickness of the layers, this would not be possible if you have an obstacle (e.g. patio door leading to a balcony area) As long as there is no patio doors leading onto the roof
In the event of a renovation to an existing living area, a cold roof should suffice. especially if the area won’t be lived in on regular basis. Thermal bridging is an issue, but, with the advances of efficiency regarding modern glass wool insulation this isn’t too much of a concern.