Type 'low pitch roof' into your favourite search engine and you'll run headlong into forum after forum of the problems and hassle low pitch roofs can (and have) caused roofers, builders and such like. Building regulations are often the first obstacle someone wanting to put a low pitch roof onto their home or extension will come across, although there are a number of issues with low pitched roofs.
Naturally, a roof should reflect the climate in which the building stands although there aren't many limitations on the actual pitch of a roof in the UK. There are, however, building regulations that stipulate which materials can be used for any given pitch. In addition, regulations will determine the spans and spacing required between rafters for a certain pitch of roof. The first thing to ensure before building an extension, is that the plan for the roof meets the local Building Control regulations as guidelines can between local authorities. Local authorities in places with high annual snow fall require steep pitches, for obvious reasons!
Low pitch roofs require specialist low pitch roof tiles, which aren't all that easy to come by. Anything under 15° will be difficult to tile, and in all honesty, may well be unsuitable for tiling anyway. Wind driven rain is the main problem with low pitch roof tiles. Even if the roof is well protected beneath the tiles with felt and suchlike, the wind can rifle through the tiles, forcing them to vibrate and cause a chattering effect. If there isn't adequate protection underneath the tiles, the consequences can be severe damp and leakages!
As a general rule of thumb any pitch below 30° is too low for plain tiles. Any pitch lower than 17.5° is too low for slate tiles and concrete tiles will suffice down to about 15°.There are some low pitch roof tiles out there, however, with some companies offering tiles suitable for pitches as low as 10°.
The Green Roof Tile Company offers a great solution to problem of low pitch roofs. Their Envirotile is suitable for pitches as low as 12.5° and are also very environmentally friendly. Their lightweight, robust design means carbon emissions are considerably lower for transporting the tiles when compared to traditionally slate. In addition, the Envirotiles are made of recycled material that would otherwise end up rotting in landfill!
Tiles, of course, aren't the only solution to low pitch roof problems. Corrugate metal or ply and felt solutions can be more than adequate, particularly on garages or outhouses.
If you are desperate for a tiled effect, you may be advised to apply a ply and felt solution and then tile over the top. The tiles will of course be purely for decoration but be warned, there are risks with such a method. Some builders will advise avoiding this completely as the roof battens are prone to rotting due to constant damp and the felt is almost unavoidably punctured by the tile nails. Whilst there are of course ways around these problems, inexperienced roofers should probably heed this advice! Talk to a professional and the building regulations to be certain your solution is legal and credible.
To conclude, with careful planning there is no reason why you can't tile a low pitched roof. With careful consideration for regulation and the climate, the risk of damp or damage to a building can be limited to an acceptable level but be sure to consult the professionals if you are in any doubt.