is the pitch of slate roof a building control matter?

[RobertL]

Please can someone tell me whether the pitch of a slate roof is a building control matter?

We are at the early stages pf planning an extension on a victoriian house. The roof (slate) currently has a pitch of 16 degeees. Ideally we like to use 13.5 degrees like the back bedroom has. Both of these are very shallow.

I want to either extend the roof (by about +50%) or replace it with a larger one of the same pitch.

I will contract building control to ask them but I thought I'd ask the opinion here first as people often have useful extra hints on such matters which can be good to know before contacting BC.

thanks,

Robert

[The Natural Philosopher]

I am not dead sure, but I think it is, from the POV that the roof has to not leak..

[neverwas]

That's what our roofer and also BCO told me in passing . And there was a thread about this quite recently -

[Calvin Sambrook]

Yes and the regs are online, google odpm building regs. They're not too bad to read and at least you can talk with some confidence to the BCO.

[Rob G]

I find these angles surprising - even with heavy Scots slate the recommended minimum angle to prevent rain being driven under the slates is around 37 degrees to the horizontal. I'm also surprised at a Victorian era building having such a shallow pitch as that doesn't really fit with Victorian design.

There's something that doesn't make sense here as the other factor with shallow pitch is the wind getting under the slates and lifting them. The neighbour's new extension with a pitch of 30 to 40 degrees and Spanish slates is suffering from the slates lifting in a high wind. Rob

[Jules]

Maybe we need to multiply by 2.54 to convert imperial to metric ;)

I thought the same - I had a quick google though and saw some companies quoting 16 degree minimums (couldn't see any at 13.5 though), so it looks like it's possible even though it doesn't 'feel' right.

cheers

Jules

[neverwas]

You need to allow for the Victorian terraces with a low* pitched roof to the "back extension". I live in one and there are very many thousands more still standing.

*By low here I do not mean

[The Natural Philosopher]

Wityhout further attention like a flat roof technology underneath, my architect said

Thatch: 55 degrees Tiles 40 degrees but builders are thick, and 45 degrees is easy to calculate. Slate about 37 degrees, but can be done lower with special care. Machine tiles that interlock, about 18 degrees..depending on the BCO.

It was the latter that caused teh valley leak that finally made me decide I was sick of the old house..

[Simon]

I'm using forticrete centurion interlocking concrete tiles, which can be layed down to 10 degrees on a very simple roof (monopitch, no valleys etc), 12.5 degrees otherwise. They have various extra mouldings (OK a ridge and a dent - that's hi tech with tiles !) to block and divert wind-driven rain, and must all be clipped down. Simon.

[Andy Dingley]

Was it Lutyens who hated 45=B0 pitch and described it as "the evil angle" ?

[RobertL]

[Hugo Nebula]

On Wed, 17 Jun 2009 02:59:56 +0100, a certain chimpanzee, The Natural Philosopher randomly hit a keyboard and produced:

Your architect's a tool, then. The pitch of concrete interlocking tiles is laid down by the manufacturer. It's not something that is varied, unless, as you say, you have some additional protection under.

[The Natural Philosopher]

So you think that if the manufacturers say '17.5 degrees' the roof will be 100% watertight at 18 degrees and leak like a sieve at 17?

Nothing is exact and precise, and the BCO knows it, and the architect knows the BCO knows it.

[david william tainsh]

Robert The pitch of your proposed roof is very much a building control matter, if your are proposing to use slate the minimum recommended pitch is 22.5. Any lower pitch them building standards will require details from supplier confirming the suitability of the roof pitch

Mr T building standards surveyor

url:

[Donwill]

You could of course use onduline undersheeting as I did in a previous house which allows you to use a lower pitch, I had to convince the BC before starting, but they were quite happy once I'd shown them the literature. See :

[The Natural Philosopher]

The failure of a low pitched valley was the final nail in the coffin of my old house.

Leaked like a sieve.

Don't try and be smart with tiled and slated rooves. Or rely on membranes underneath

Get the pitch right.