Roof systems manufacturer Marley explains how to create the perfect low pitch roof on an extension.
Thanks to the permanent relaxation in planning laws, this year many builders and roofers will find they are working on more single-storey extensions. While homeowners often prefer the look of pitched roofs for this type of project, they do need to be carefully designed with both aesthetics and weatherproofing in mind.
As well as trying to match existing roof tiles, contractors will usually have to create a lower pitch roof for single storey extensions, due to the position of first floor windows, which can be restrictive and has implications for water run-off.
Here we give our top tips for creating the perfect low pitch extension roof:
- While the planning laws have been relaxed, you still need to match the new roof to the roofing material on the original property and in some designated areas, such as conservation areas, the homeowner will still need to get planning permission.
- If the tiles you want to use don’t go down to the minimum pitch you need, consult the manufacturer for alternative options. We have a selection of low pitch tiles that can be used to match a traditional clay, slate or concrete aesthetic (see our pitch checker). This includes the brand-new Mendip 12.5, a concrete interlocking tile which has been designed for extension projects. Its special weatherproofing channels mean that it can be used down to a very low 12.5 degree pitch.
- Never be tempted to use a tile below the manufacturer’s recommended minimum pitch, even by half a degree, as it could invalidate your warranty! If you have to install at a lower pitch, then seek manufacturer advice as a weatherproof sub roof system may be required.
- If you need to match in with existing clay tiles, there are some very good low pitch options on the market. For example, our Melodie clay interlocking tiles have a single pantile profile but can be used on pitches as low as 12.5 degrees, making them particularly suited to extension projects. We also offer two other interlocking clay tiles which can be used down to 17.5 degrees, the Lincoln pantile and Maxima double roman.
- In low-pitch projects, because driving rain has to be considered, natural slate can be limited by geography. This means that pitches of 20 degrees can be achieved with natural slate, but it requires increased head laps and therefore more slates, with the consequences of additional weight. However, there are some very good slate effect tiles that can replicate the slate look at a lower pitch for extension work. For example, our Edgemere range of thin-leading edge concrete slates give a slate look but are more cost effective and can be used down to pitches of 17.5 degrees without geographical restrictions. They come in a variety of colours and textures, including Riven, to help contractors match the slate aesthetic they need.
- Extensions still need to comply with Building Regulations and British Standards. Therefore, pitched roofs on extensions should be fixed according to BS 5534. You can get a free fixing specification for your project from our website, marley.co.uk/specritetool
- Consider using ventilation terminals if mechanical extract or soil vents are to terminate through the roof tiling on low pitch roof slopes. This will ensure minimum pitches of the chosen vents are achieved. Normal in-line contour vents can usually only be used down to a pitch of 20 degrees, so vents with cowls may be the best alternative as they will share the same minimum pitch as the tile. For low level roof space ventilation, continuous over facia eaves vent systems can be used.
- A low-pitch roof on an extension may have to deal with an increased amount of water coming from a larger roof above, so it needs to be designed carefully with consideration given to where the water run-off will be.
