Cold Roof and Flat Roof Ventilation

Fri, 28/05/2021

Questions about cold roof and flat roof ventilation are common - including to what degree insulation and ventilation are linked, where the joists come into the equation, whether "cold roofs" are more prone to ventilation problems than "warm roofs", what the difference is between warm and cold roofs and so on. 

Certainly, different types of roofs have different requirements when it comes to ventilation - with factors including the pitch of the roof, its size, shape, substrate materials, proximity to a warmer wall, and the degree of insulation present. Cold roofs are less efficient, with poorer ventilation and greater proneness to condensation but that doesn't mean they are bad roofs. They are just suited to outdoor buildings such as detached garages and outbuildings. Elsewhere, Building Regs can insist upon warm roof installation, and indeed for some outdoor buildings such as heated studio workshiops or "granny flats", warm roofing would of course be the choice.

The way both ventilation and insulation work on cold roofs and warm roofs is different, which is explained with diagrams on this page.

With flat roofs there are a number of other considerations, with the pitch of the roof affecting how warm air moves beneath the roof and where it tends to find its way out (so where the condensation spots might be). Flat roofs have the further consideration of surface water that does not run off, detritus build-up (e.g., leaves) and the continual exposure of the entire surface to UV and other elements. As a result, light tapering of tee flat roof is usually desirable but this in turn affects the insulation layer, which ties back into ventilation. 

We have unfortuantely been called in to fix many roofs where the initial contractors have had a poor understanding of these interplays. Not only have their mistakes caused inconvenience, they can also be extremely costly if not caught soon enough, with moisture build-up contributing to rot, damp and even structural degradation. 

We know our stuff and are happy to share our knowledge or to put it into practice on your roof. For more information take a look around the webssite (including our dedicated sections - follow nav links above) or call today on 07855 535581.