Damp patch on ceiling of newly built extension

Hi There,

I had an extension built late last year and shortly afterwards I noticed a damp patch, approx. the diameter of a coffee cup in one area of the ceiling. The patch would come and go and would sometimes be smaller. There is a brown ring mark there as a result.

I got the builder back to investigate and he lifted some tiles from the roof and noticed that there were a few small tears in the breathable felt that had been battened to the roof timbers. He said this was likely to have been the cause of the problem, re felted the area and then told us to see how it goes.

Well that was 3 weeks ago now and the damp patch is still appearing occasionally, although not all of the time. Also, I've noticed that the patch doesn't appear immediately when it has been raining, but quite often a day or so later.

I mentioned this to the builder and he said that when he removed the tiles to re-felt, there was a fair amount of residual water sitting on top of the foil backed cellotex insulation, and that what is probably happening is that when the wind blows up underneath the tiles it is blowing this water over and down a join in the insulation and it is then appearing on the ceiling. He said that due to the cellotex, the area is unable to dry out very easily in a natural way until the summer comes, and that we may continue to see the damp patch appear on and off for a while yet.

Does this sound plausible? I am unable to properly paint the ceiling until I know the problem is definitely resolved.

Any thoughts on this would be most appreciated.

Thanks.

What is the pitch and what type of tiles are they? Got a photo or two, not just the damp bit but the roof too

Hi There,

Here are a couple of pics of the roof. The pitch is 22 degrees and the tiles are I assume concrete interlocking type. They have a smooth finish to allow the water to run off more easily.


Regards,
Robert,

By the way, although the roof has Velux windows, it is not thought that the water is getting in around them. The damp patch that appears on the ceiling is quite a way away and there is no sign of damp near the windows themselves.

Here are a couple of pics of the damp patch. The second one isn't very clear, but wanted to get a picture of the damp patch in relation to the window. You can probably see a small damp spot in the centre of the brown stain. This was bigger this morning but has dried out a bit since. We haven't had any rain today and there's hardly any wind either.


Regards,
Robert.

Condensation drip.

I would take a guess that pitch is more like 18 degree's. I think if you stop the rain water running off the main roof and down your extension roof then it might dry up.

Hi noseall,

We have wondered about condensation but it's strange that it doesn't do it on the kitchen side, where there is obviously a larger source of moist air.

There were definitely some tears in the felt, which have apparently subsequently been fixed, so that's why it is assumed it is a leak, either still there or from residual water.

Thanks for your comment catlad, I may suggest that the builder adds some drain pipework to take the rainwater away from the extension roof.

It does seem strange that the patch is only in that one small area though. Does anyone have any possible explanations for this?

Thanks,
Robert.

Also, if the pitch is 18 degrees then do you think it should still be ok in principle, i.e. the pitch itself shouldn't cause any issues?

Even if the felt was torn the roof should not leak!

Agree with noseall, the condensation drip is right next to the downlighters.

Those tiles are 22.5 degree minimum so if you roof is lower than that then it would be unwise to flood the roof with the water from the main roof, condensation is a possibility but it will be easier to move the down pipe first and take it from there.

Hi all,

Many thanks for all your replies so far.

I had considered condensation but I don't understand why it only ever appears in that one small area. Also, it may not be that clear in the photo's but the damp patch is around 2 feet away from the down lighters. Also, it doesn't make sense why there's no problems on kitchen side of the wall, even though there's lots of moist air generated from cooking etc.

Another thing on the subject of the downpipe. Is there supposed to be another section of piping attached to the bottom of the pipe, where it meets the roof? It just looks a bit odd and my gut feeling is that something is missing as it doesn't look right.

If the felt is torn I assume water could still get through to ceiling if wind is blowing water up under the tiles? That's what my builder thinks may have happened, but even he isn't sure!

Regards,
Robert.