Understanding the Flat Roof Design


A flat roof design that features a waterproofing system is always supported by a roof deck. The deck is typically a timber boarding of some kind, which is supported on joists. The ceiling, if any, is normally fixed to the joints’ undersides.

Requirements for Insulation

Whilst garages may be uninsulated, most roofs above a house will require insulation to meet building regulations. In homes, the insulation is sometimes added right above the ceiling. In some instances, it is placed over the deck before waterproofing is applied.

Some specialised insulations may also be applied above the waterproofing. However, this type of construction is usually confined to industrial or commercial structures, and therefore is rarely used on domestic builds.

Warm Flat Roofs

In Britain, Sidcup roofers who specialise in flat roofs construct warm roofs and cold roofs. Warm roofs are normally recommended. A warm roof features insulation over the roof deck, and thus maintains warmth on the deck.

This is normally a preferred construction for a home as it prevents the need for roof ventilation. That is because the membrane is affixed to the insulation. Therefore, a conventional warm roof features surface protection on the top followed by waterproofing, insulation, a vapour control layer, the deck, a furring strip, a structural joist, and the ceiling.

Cold Roof Designs

In a cold roof design, the flat roof has the waterproofing laid onto the deck, and the insulation placed above the ceiling. This type of arrangement permits the deck to become cold. Therefore, in cold weather, the roof is prone to condensation, which leads to distortion and decay of building materials. To lower this risk, through-ventilation must be placed in spaces over the insulation. However, this can be difficult to do if the roof abuts a house’s wall.

Successful flat roofs should provide protection from snow and rain as well as sun and frost. They should also safeguard a home from condensation, wind, and fire. An inspection for this type of roof is recommended twice annually, or in the months of March and November. Arrange an inspection after a rain to check for water drainage.


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