Minimum pitch roof?

Theboinkmaster

We're getting extension onto back of kitchen and I don't like flat roofs so want pitched/slanted roof. Roof is going from back of house into the garden.

However issue is height available under window sills on 1st floor. So think the "slant" or pitch might be a low enough angle. We want velux windows in the roof.

Is there a minimum you need for safe flow of water etc?

Penn

Theboinkmaster wrote: »

We're getting extension onto back of kitchen and I don't like flat roofs so want pitched/slanted roof. Roof is going from back of house into the garden.

However issue is height available under window sills on 1st floor. So think the "slant" or pitch might be a low enough angle. We want velux windows in the roof.

Is there a minimum you need for safe flow of water etc?

Generally below 22.5degrees you need specialist slates/tiles/fixings/overlap etc. You can go down as low as 12deg or so with the right design/spec. Veluxs can usually go down to the same (or at least 15deg iirc). All needs to be properly designed, specified and installed though.

Ronney

Think you seam to be describing a lean to roof not a pitched one?

ie: it is all the same height at the house and falls out equally away.

Theboinkmaster

Ronney wrote: »

Think you seam to be describing a lean to roof not a pitched one?

ie: it is all the same height at the house and falls out equally away.

I think so - im adding 20sq or so at back of house, with slanted roof - so from the side of the house it looks like a triangle.

hope that makes sense. Essentisally the back wall of our downstairs house is being pushed back 3-4 metres, with a new roof going on top.

Ronney

Are you planning to use slates?

If so they will dictate your slope.

Given you can build flat roofs there would be no minimum pitch for a lean too roof.

To kick water away from the existing building a fall of 1/40 is plenty (25mm per meter) so only need a fall of 100mm across the 4m less than 1.5 degrees

You could probably push this down to 1/80 (12.5mm /m) if your tight for space

What Height is ...

Sill underside to ground outside?
Sill underside to Finished floor inside?

Intended new Floor to Ceiling height inside?

Penn

Ronney wrote: »

Are you planning to use slates?

If so they will dictate your slope.

Given you can build flat roofs there would be no minimum pitch for a lean too roof.

To kick water away from the existing building a fall of 1/40 is plenty (25mm per meter) so only need a fall of 100mm across the 4m less than 1.5 degrees

You could probably push this down to 1/80 (12.5mm /m) if your tight for space

What Height is ...

Sill underside to ground outside?
Sill underside to Finished floor inside?

Intended new Floor to Ceiling height inside?

Sorry but that's completely wrong. Slates are completely different to a flat roof because there's no path of water ingress with a flat roof membrane. A minimum fall to direct rainwater to the outlet is fine.

With slates though, rainwater can blow water back up through the slates. Hence why once you go below 22.5deg, you have to increase laps of slates (so moisture has further to go before getting through slates). You also need additional fixings because a lower pitch makes it easier for wind to lift them.

Most slate suppliers/manufacturers specify minimum pitches and additional requirements to achieve minimum pitches, and I've never seen any below 10deg (with a specialist slate, not standard). You cannot go below that with a slate roof without creating substantial risk, and all materials used should be as per the manufacturer's instructions/guidance, and I don't know of any slates where the manufacturer allows going below 10deg.

Edit: Re-reading your post, are you suggesting using a flat-roof construction as a lean-to roof rather than slates? Because if so, there's another issue which is that for proper insulation, it would have to be constructed as a warm-deck room, which would mean greater depth of roof construction, possibly negating any benefit of going with that than a minimum-pitch slate lean-to roof.

sydthebeat

Ronney wrote: »

Given you can build flat roofs there would be no minimum pitch for a lean too roof.

???

the min pitch is determined by the finishing material

as already stated....in general slates of tiles will not be guaranteed under a 22.5 degree pitch
there are specilaistslates out there that can be used as low as 15 degrees, but these are more expensive and need extra work and attention to others factors such as felt laps etc