Leaking kitchen extension roof - 12 degree pitch

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Hello all,

We had a 3m single story kitchen extension done earlier in the year, with two Velux windows. It was fine for the first couple of months but now we regularly get damp patches on the ceiling when it rains (doesn't have to be particularly heavy).

Spoken to our builder and he is adamant that he has done plenty of 12 degree pitches with Velux windows and has never had problems. Do we believe him?

I've looked at the tiles they've used and they are for a minimum 17.5 degree pitch and I think Velux recommend a minimum 15 degree pitch?

What do you think would be the best remedial action for this. Is there any way new roof tiles would sort it? Or does the roof need to come off and be redone? Or would it be easier/cheaper/better to change the windows and roof to a fortcrete (or similar?) window/roof system?

Any help or advice you could give would be hugely appreciated as we really don't know what to do.

Thanks in advance,

Dave.
 
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How long ago was this built? Whether the builder is adamant its worked on previous extensions or not, its not working on yours and he is fully aware that neither the tiles nor the velux windows should have been used in this instance and surely is upon him to rectify the problem?

Where you made aware that the roof pitch may become an issue in the future? Did any drawings specify roof detail?

Where are you getting damp patches? Do you know whether a transverse drainage gutter and under felt co!lar were fitted when installing the velux windows?
 
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Its amazing how many low pitch leaking skylights I have been too
and never once have I seen a storm collar used.
 
Thanks CJRatch for getting back to me.

The roof went on very early January. You're right, it is the builder’s responsibility to sort and he says he will but hasn't given us any details as to how (I’m concerned he will botch it rather than fixing the issue properly).

We weren’t made aware, but only found out the pitch might be the issue after looking online after they’ve been out to try to fix it three times (by relaying the tiles). Unfortunately, no details about roof pitch on drawings.

The damp patches are on the ceiling between the bottom edge of the window and the back wall, and run down to the back wall.

Don’t know how the Velux was fitted, but can find out. Do you think it could be rectified just by refitting the Velux?


Leak 2.jpg
Leak 1.jpg
 
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Things to consider are fitting the correct tile for the pitch. Your choices at 12 degrees will be very limited. The velux windows only go down to 15 degrees but if fitted with the gutter and collar (the reason builders dont fit these is because its an added extra ontop and is often overlooked because velux windows can be fitted without. It costs around £50 depending on window size and goes a long way to weather proofing a roof) along with the correct tiles they should hold up.

Are the battens cross battened or fitted normally? If fitted normally you need a slight sag in the roof membrane between each joist to allow for any rain which passes your tiles to drain away. Did the builder do this? If cross battened this won't be a problem.

Did the builder fit an eaves support tray?

Id want the correct tiles for the pitch at a bare minimum. If rain cannot pass your tiles whatever goes on beneath shouldn't matter although fitting the gutter and collar should also be done if the tiles are going to be removed anyway.
 
Spoken to our builder and he is adamant that he has done plenty of 12 degree pitches with Velux windows and has never had problems. Do we believe him

He may well have done, and whether you believe him or not does not matter, as yours is leaking and it needs rectifying, and he needs to sort it out and redecorate too - including any blown plasterboard.
 

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