Flat Roof Insulation - County Flat Roofing

Warm Roof

As part of the Kyoto Agreement, the UK Government agreed to reduce emissions of ‘greenhouse gases’ in an attempt to reduce the speed of climate change.

The UK has committed to reducing emissions by 4.3%, third only to Japan 8.5% and Germany 7.4%. In the UK a large proportion of emissions are carbon dioxide and, a large proportion of these are down to the thermal inefficiency of buildings. Government legislation to reduce heat loss from buildings is already here.

The requirements of Building Regulations Approved Document Part L (Part J in Scotland) require that each part of the building has to adhere to a new higher thermal efficiency. This measure of heat leakage is commonly known as the U-value. Many will be familiar with the current Part L in England and Wales that requires windows to meet a U-value of 2.0/m² °C. In Scotland, Part J, a U-value of 1.8/m² °C has to be met. For flat roofs the U-value must meet 0.25/m² °C.

Traditional vs Warm Roof Construction

All new-build flat roofs require a warm roof construction to comply with Part L. The traditional cold roof construction is not recommended in Scotland and is unlikely to fully comply with Part L "Robust Details".

Composite Sarnadeck warm roof is made from a rigid insulation board/plywood composite with integral foil backing that is placed above the roof joists and onto which the Sarnafil is laid. There is a clear space between the ceiling and the roof deck. The air remains warm and the foil vapour control layer protects against condensation. The system insulates whilst removing the requirement for ventilating the roof space. This is particularly important for a flat roof over a kitchen, bathroom or utility area.

Compare this with the traditional method used in flat roofing where the insulation material is placed between the rafters above the ceiling. Without proper ventilation the warm air condenses and can lead to rotting timbers and, eventually, collapse of the roof deck.

Glazed conservatory roofs must also adhere to a given U-value. A debate has recently started about overheating. While Part L covers heat leakage it also covers overheating, an inherent problem with glazed roofs. In warmer weather conservatories can become very hot. There are many ways to combat this; tinted glazing, ventilation, blinds but not air-conditioning if it can be avoided because this uses more energy than heating the space. But, without these additions, what remains is a room that is cold in the winter and hot in the summer.