Re: Pitched roof angle

[Peter Crosland]

Ask your local building control office who will give their advice free.

[Lawrence]

Lawrence

usenet at lklyne dt co dt uk

[invalid unparseable]

It depends on the roofing material. My kitchen extension has a pitch of 17.5 degrees, and it had to have special roof tiles that worked at that pitch (which had a minimum useable pitch of 17.5). The tiles had to be laid with a certain overlap, and the architect was so paranoid about the angle that he specced trussed rafters, much to the builder's annoyance.

Suggest you find a suppplier of slate tiles and ask them about pitch.

[Tony Bryer]

If slate type interlocking tiles are acceptable you can get down to 15 degrees with Redland Cambrian

or

then follow the trail

[Christian McArdle]

I've heard it can be done down to 18 degrees without it getting too complicated, but much further takes some doing.

Christian.

[The Natural Philosopher]

It is totally dependent on the tiles or slates used. I had one - still got teh tiles if you want - horrid things - at about 20 degrees - wasn't bad till the valleys strated leaking. So I knocked the house down and built a new one.

Normal tiles 42 degrees is roughly it, but builders like 45 cos it

makes the maths doable by a gibbon with a CSE in Graffiti.

Thatch is 50 minimum.

[Rick Hughes]

The pitch depends on the tiles or slate you are going to use ..if you look at the web site of whoever's tiles you want to use, the tech sheet will state the minimum pitch.

There is typical no max pitch as you can carry out vertical tiling. Rick

[Bluestars]

Not quite what the OP asked but... My low pitched corrugated asbestos garage roof drips condensation from the underside in cold damp conditions. What pitch does the roof need to be to cause the condensation to run down rather than drip off?

Roger

[robgraham]

I built an extension where the roof had to have a very shallow pitch - about

10 degrees. It was slated, but under the slates was felt laid in the normal way. On top of the felt were vertical laths with horizontal laths nailed across to take the slates. This way no nails went through the felt and the thing has been perfect so far (10 years).

Rob Graham

[The Natural Philosopher]

Now there is a curious question.

With MANY variables, like teh surface tension ofteh water, and teh stickiniess of the roof interiors, its roughness and so on.

In short, it depends on too many variables to give any answer other than a really rough one.

[The Natural Philosopher]

However the felt is not supposed to stop water, but airflow. Its NOT a good idea to have sagging felt with puddles forming in it around your timber battens. Mind you, as a bodge, its a good one.

You can use slates on a low pitched roof but you need to overlap more. I suppose the true answer is something to do with the maximum height water can be driven up a slope for a given airflow. Machine tiles fit very accurtely, so aiflow through the gaps is very restricted, hence they water dosn't drive up very far.

Slates are a lot worse, and don't have interlocking ridges, but my guess is that 30 degrees is probably (near) the limit unless you go for BIG overlaps.

Peg tiles - especially hand made - are the worst as they are irregular with large gaps.

[David]

That's surely going to depend hugely on the nature of the surface which the condensation is running down... I would imagine a completely smooth surface like glass would allow drops to run at a much shallower angle than say, rough sawn timber, where there will be a tendency for drops to propagate at a high point like a splinter, and fall off. I expect it might make a difference whether the surface is absorbent or not?

David

[dg]

IIRC, Redland (now LaFarge) do a tile down to 12 degrees. I think it is the "Regent" interlocking concrete tile.

Manufacturers specify the minimum angle, but with proper precautions in terms of lap, fixing and underfelt, then you can go down a few degrees more.

dg

[Tony Bryer]

That's what the counter battens are for. We used to allow low pitched roofs built like this, but only with ply over the rafters to support the felt

[geoff]

Surely it would be possible to bend the rules a bit and thatch the roof internally (using baling twine to hold it in place of course)