what are the main issue with having a roof pitch considerably lower than the tile spec? the pitch I'm loking at is 9 deg and the spec is 17.5 deg, also what are the relevent regs, cheers
I've used Marley Moderns (17.5 min) on an extension with a pitch of 16 degrees. Generally it's OK, but on two occasions of really severe weather I have had water come inside in two small patches (which I guess is wind blown).
This is in Hants which isn't a particularly exposed area of the country.
It will depend on where you are, what membrane you're using, are you having skylights (and therefore need to cut the membrane), etc - but I'd say you're probably pushing your luck at 9 degrees.
Hi. Covering a low pitch such as you have described with tile or slate is high risk, both wind and capillary attraction, the physic of which can not be changed are working against you.
However there are metal roofing solutions to your problem. Zinc, Copper or Lead sheet can be used with the confidence of knowing you will not get problems. The only issue being will the look of the roof fit in with the general architecture / characteristics of the building? Good Luck
For exposed conditions there is nothing to beat a fibre glass roof!
Fibre glass has been used in boat building for over fifty years and many of the originals are still afloat.
If you ever visit Wales you will see many flat fibre glass roofs in places where they have the most extreme weather - wind blown sheets of water flying through the air, no problem!
Anything below 10 degrees is technically a flat roof, no interlocking roof tiles will perform at this pitch (some tile effect sheeting will though). The problem is related to the tiles ability to shed the water landing on it. The lower the pitch the greater the risk of water overoming the features designed into the tiles to keep it out (interlocks, headlaps etc.)
You best bet is to look at flat roofing systems to solve this problem.
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