How To Cross Vent A Flat Roof

To ensure sufficient ventilation enough space must be provided to allow for the movement of air preventing the risk of condensation forming within the roof.

How to cross vent a flat roof.

2011 code of practice for control of condensation in buildings stipulates that there should be a ventilation gap between the insulation and the bottom of the flat roof deck of at least 50mm. To create cross ventilation place a window mounted box fan facing inward in one window and a second fan facing outward in another window. The 25mm batten space creates a clear airpath to the roof void below so reducing the possibility of condensation and mould growth. 1 box roof vent.

As my builder buggered off without putting in the soffit vents i had bc out last week and lo and behold it s changed and we need cross ventilation on the flat roof of my extension and we re not able to just put in the soffit vents on the front overhang but rather being asked to do it from side to side. Installing the vent on a flat roof is no different than installing one on an angled roof. Where there is a parapet or an external wall abutment to the flat roof the fv250 ventilator can be used above a 150mm timber upstand battened off the wall by 25mm as shown below. Alternatively install a reversible fan which will let you change the direction of the fan based on the wind in your area.

From reading about flat roof ventilation i ve learned to be cautious about its likelihood for success since the deck heats up a lot in the summer and that hot air won t have a natural chimney to escape from. The difference is the vent itself. In a concrete deck for example this gap could be created by fixing 50x50mm timber battens at 600mm centres and attaching the insulation to underside of these battens. Diagram below explains the build up.

This is a basic aluminum roof vent that is square or rectangular in shape. The article notes that the ventilation cannot overcome the significant humidity drive into the flat roof structure caused by small air leaks. Even if you have a small shed you should allow for a proper vent to keep the air fresher in the space. The box of the vent covers the piping with a large cover to shield the vent from.

Building regulations state that a ventilation gap of at least 50mm must be in place between the insulation and the underside of the flat roof deck. They are used in a lot of commercial applications but also in larger homes. Consequently the article concludes that the concept of venting a flat roof is no longer safe and instead don 039 t vent the flat roof and install a smart vapor retarder inboard. As the hot air rises in your room the second fan will suck it out.