The definition of a flat roof is one that is greater than 1:80 (the minimum finished fall allowable under BS 6229) but less than 10 degrees. Common to all roofs is the roof build up, which may be of warm or cold construction. The chosen roof system must satisfy all acoustic, thermal, fire, durability and safety requirements. Please contact your local planning department services for specific requirements.
Cold roof construction
This is the most common construction but is also the least thermally efficient.
The insulation material is placed immediately above the ceiling between the rafters. The 18mm roof grade deck is then fixed on top of the rafters. The DuoPly membrane is installed using the contact adhesive onto the deck.
This means the roof deck and roof space are at or near the external air temperature. Roofs of this type require the void below the roof deck/DuoPly membrane to be well ventilated to prevent condensation.
Cold roofs can also incorporate a top layer of paving, ballast or green roof above the waterproof membrane if a protective/drainage layer is incorporated.
Warm roof construction
This is the most modern method of construction and should be used where possible (although not all situations are able to accommodate this design).
The 18mm roof grade deck is fixed on top of the structural rafters and a vapour control layer is then placed on top of the deck. The insulation material is placed over the vapour control layer. An additional layer of 11mm deck is then placed on top of the insulation (some high density insulation boards do not require the additional deck), which will prevent the insulation from being depressed by foot traffic. The DuoPly membrane is then installed using the contact adhesive onto the 11mm deck.
This form of roof construction ensures that the deck is maintained at a temperature above that which could cause condensation and complies with current building regulations. Warm roofs can also incorporate a top layer of paving, ballast or green roof above the waterproof membrane if a protective/drainage layer is incorporated.