Warm Flat Roof Soffit Detail

Steve from london flat roofingexplains how warm flat roof construction works in this excellent short video.

Warm flat roof soffit detail.

For a simple duo pitch roof bs 5250 specifies sufficient ventilation as being. The sandwich warm deck roof is the most common type of flat roof. This ensures that the deck holds a warm temperature during the winter. No ventilation is required for these types of roofs.

A warm deck roof is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation. The insulation is placed below the waterproof covering and is either mechanically fixed or bitumen bonded on to the top of the deck. Warm roof or cold roof which would you choose if you have a choice. Like a cold roof warm roof ventilation is required at high and low level to remove moisture laden air from the batten cavity and comply with approved document c and the british standards bs 5250.

Warm roof ventilation specification. Roofs tend to be either pitched or flat and typically in residential construction timber is the most common material used. However in many situations the insulation may need to be primarily or entirely below the flat roof membrane and between the roof joists if so what are the best options. As well as the small selection of roof detail drawings shown here many of the building notes have a related construction detail drawing with specific dimensions eg rafter sizes spans insulations types for purchase with the building specifications.

On a flat roof this could be air in at one ventilated facia soffit and air out via an opposite ventilated facia soffit. The resultant action of which does not allow condensation to occur to any significant effect. Unvented flat roofs a technical discussion flat roofs have often been built with the insulation all on top of the vapor closed drainage plane as this avoids dew point condensation issues inboard of the roofing. Due to the insulation being over the top of the roof the timber structure beneath is warm which is why the term warm roof is formed.

The abutment detail of a flat roof is vital in order to prevent moisture penetration. A warm flat roof is formed by placing a layer of insulation over the top of the roof structure. Additional construction details drawings.