Velux on roof with pitch at 13 degrees not 15

swindon189 · 18 May 2008

Hi,

We want to install a Velux but I know that you should only install at minimum of 15 degrees. Our roof is 13 degrees. What are the risks I'm taking with a lower pitch? If flashing is installed well, will it matter?

Any guidance appreciated, particularly if someone has taken the risk of putting one in!

Thanks

SurreyRoofingEstimator · 19 May 2008

The risk you run is that it will very likely leak even if the fashing is `installed well'.

If you really need an openable window you'll need a Velux flat roof window.

If you just need the light it would be worth looking into sun-pipes.

^woody^ · 19 May 2008

I wonder how accurate the 15 degrees stated by Velux is?

Bearing in mind the fact that when using rough sawn timber, it can be very easy to be out by a couple of degrees or so when forming the rafter pitch.

So, I would presume that Velux would allow for this, and quote a figure that is a little above the absolute minimum.

Likewise, is the OP's roof really 13 degrees or actually 14 or close to 15? Or even 11

noseall · 19 May 2008

^woody^ said:
Bearing in mind the fact that when using rough sawn timber, it can be very easy to be out by a couple of degrees or so when forming the rafter pitch.

ah, come on now woodster, this may apply to a single element but generally the roof will turn out at the correct pitch provided there are more than 3 rafters that is.

swindon189 · 19 May 2008

Thanks for responses.

The window is just to put on an extension into the kitchen and I don't need it to open. I don't need a sunpipe as have taken suspended ceiling out. Where's the best place to buy a skylight I could get installed? The flat roof system looks a bit ugly so would be keen on just a window I couldn't open.

May check pitch but pretty sure is 13 degrees

^woody^ · 20 May 2008

noseall said:
....generally the roof will turn out at the correct pitch provided there are more than 3 rafters that is.

Yes probably.

But its very easy to be 1 or 2 degrees out over a short span, and with rough sawn timber it doesn't help.

You can wedge a corner of the rooflight up to get the casement to open smoothly and it can then be 1 or 2 degrees different to the roof

So, in Velux's calculations is it 15, 14.99, 14.5 or 14 degrees when the water starts getting in? They must have made some allowance

9494jones · 9 Jul 2011

Hi there. It may be a little late but have a look at the wedge style flashing with Roto Roof windows. This is ideal for this kind of situation as it tilts the window so it is greater than 15 degrees.

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Velux on roof with pitch at 13 degrees not 15

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