An issue overseen by many when putting together tender documents is the pitch of a roof, and what materials are suitable for the difference in the gradient of the roof.
This article looks at the different reasons for roof pitches, which pitches suit which materials and why this subject needs to be considered when planning a roofing project.
Understanding the pitch of the roof is crucial. This is non-negotiable. You can’t use a material which is unsuitable for the pitch, because not only will it leak, but in many cases, it won’t hold suitable traction and in extreme weather, may get blown off.
The purpose of creating a pitched roof, is to shed the precipitation away from the building on which it falls. In high mountainous areas, such as the European Alps, you may have noticed that traditionally roofs have very steep pitches.
This is so that they can shed the precipitation, in this case usually snow, quickly before it can build up and overload the roof structure. The same is true in the UK where we have a lot of rain and the dominant roof design is traditionally pitched at around 30° to 40° degrees.
In hot climates where it hardly ever rains, they are content with flat roofs; it doesn’t matter if they hold water slightly, because the hot weather will soon dry everything out.
In recent times everything has changed and this common sense approach has been overtaken by economic necessity, which has been supported by advances in Engineering.
The Swiss have started developing hotels and chalets with much lower pitched roofs and even flat roofs and the same is true here in the UK.
Traditional materials used in the UK generally aren’t affective on low pitches, for the reasons we’ve just discussed. Owing to the fact that roofs with a low pitch were not a traditional design here.
Slates, for example, should not be used on a roof pitch below 22.5° degrees and plain tiles shouldn’t be used on a pitch below 35° degrees.
So what do we do if we find you have a low roof pitch, for instance 12.5° degrees?
For a pitch as low as this we would have to use a concrete or clay interlocking tile. These large format tiles interlock with each other and have anti-capillary features along their bottom edge, ensuring driving rain isn’t forced behind the system.
There are a wide range of products suitable for low pitch roofs both manufactured in the UK and imported; varying from very deep bold profiles to flat surfaced tiles, some of which can be mistaken for slates.
Another option for a low pitch roofs is to use a pressed metal roof tile. These are made by pressing steel sheets to form a panel containing a series of tile profiles and the surface is coated with a mineral finish to give the appearance of a normal roof tile or slate.
These systems can be used on roof slopes as low as 5° degrees. They are also vandal proof and so lend themselves to places where this might be a problem, such as single storey buildings in public areas like sports pavilions or public conveniences in parks.
Bear in mind that these guidelines are based on ‘normal’ situations and do not take account of extreme local climatic conditions, buildings on high ground, near airports or wind farms and other factors, such as long rafter lengths etc.
Therefore, we would always recommend that you seek professional advice from a competent roofing contractor. For any issues relating to the pitch of a roof, and advice regarding any commercial roofing dilemma you might have, do not hesitate to get in touch with one of the team here.