Warm Flat Roof Ventilation Requirements

There are two ways to insulate a roof.

Warm flat roof ventilation requirements.

The insulation is applied above the roof deck with waterproofing on top which eliminates the need for ventilation and keeps the roof warm. 25mm at eaves on each slope and 5mm at ridge. If ridge or eaves ventilation is not possible ventilation tiles can be used at high or low level to achieve the required airflow. The roof itself is therefore kept warm.

Air paths should not be obstructed. Warm deck this is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation. In a warm deck roof the insulation is positioned above the structural deck and no ventilation is required. With the introduction of vapour permeable plastics underlays the need to create ventilated voids above inclined insulation and the requirement to ventilate cold roof lofts may be reduced.

Why is it important to ventilate a flat roof. By majority the rule of thumb is that in a domestic house not flats approximately a third of the total thermal performance of insulation can be placed below the deck with two thirds above the deck sometimes this is called a hybrid warm roof. No ventilation is required for these types of roofs. A little bit but ventilation is still key to prevent some serious problems that might develop in your building otherwise.

When thermal insulation is placed below the deck the ventilation must also be on the underside. A minimum 50mm free air path should be maintained between the top of the insulation and the underside of the roof decking. In this case ventilation is required and the roof can still become wet with condensation which may cause materials to decay. After all aren t those vents letting your warm conditioned air escape outside.

Ventilation is not needed in a warm roof. There are two types of flat roof systems warm and cold roofs which affect the positioning of the ventilation. Warm roof ventilation specification for a simple duo pitch roof bs 5250 specifies sufficient ventilation as being. Additionally if the span is greater than 10m the overall ventilation area should be increased to at least 0 6 of the total roof area.

The enclosed void of a warm pitched roof may not require to be ventilated but this is usually subject to the requirement to install a fully sealed air and vapour control layer avcl in conjunction with an air open roof covering. Especially during the winter you might wonder why your roof needs vents. Warm roofs are recommended for homes.