Possible condensation issue in pitched roof

[MrRob]

Hi all,

First time posting so forgive me if all technicalities are not quite right.

We have recently moved into a house and have just completed renovating our kitchen. The kitchen was originally much smaller and was extended in the late 80's. Previously to this rest of the back of the house was extended and then a few years later the kitchen extended to the same extent.

The house is multilevel and the kitchen is on one side of the hose with vaulted ceiling. We have insulated with clotted between and under the rafters and all was fine until the recent cold weather. We now have damp patches on the joint of the sloping ceiling and the external wall, however this is only in the part of the kitchen that was formed out of the extension.

I was fairly confident that it is not water leaking in (although there are signs of rotten felt at the soffits. The membrane is a traditional non-breathable felt but I was sure to leave a 50mm gap between the membrane and the insulation and also maintained a vapour control layer when installing the insulation.

On closer inspection (and I should have checked at the start but made an assumption) the roof space of the extended part of the kitchen does not meet up with the loft space as there is essentially what would have formed the exterior wall of the first extension before the kitchen was extended. Having looked closer in the loft, the wall is sealed right up to the ridge line essentially making the kitchen roof space its own system.

We have soffit vents but I am thinking that without a vent at the top of the roof or lack of loft space with air bricks there is no passage for air to circulate and therefore warm air is becoming trapped and then condensing.

Yesterday i pushed back 4 or 5 roof tiles at the eaves where the damp issue is and there was clear signs of water running down the outside face of the insulation boards.

I had a roofer round to look tonight to price up installing a tile vent towards the top of the roof space and his opinion was that it is a broken tile allowing water in, but he was happy to install a vent if that is what I wanted. I explained that I did not think it was a leek as we had large amounts of rain 3-4 weeks ago and no sign of water ingress, it was as soon as the temperature dropped that the problem started to show. Also if it were a leak and it did somehow make it through the felt there would only be water drops on the insulation between 2 rafters, not between all the rafters unless it was more than one leak. The part of the kitchen that is in the original house construction shows no issues but this does have free ventilation into the loft.

The other option to installing a roof vent is to core drill some 100mm holes through the wall thus joining the kitchen roof space with the loft - any thoughts on how successful this would be?

I was just after some advice as to whether my logic is correct as I am now doubting myself so I hope someone can impart some knowledge.

Thanks,

Rob

 

[Alastairreid]

You seem to have the gist of things and would try the high level vents first, i wouldnt bother coring into the adjacent attic...continuous venting of the ridge would be better.

 

[freddiemercurystwin]

Your post is a little difficult to follow but if I am following correctly, as alastairreid has intimated ridge vents are really the way to go. You would need a tile vent between each rafter as the voids will be separated by a rafter will they not?

 

[MrRob]

Thanks for the advice so far.

Issue with a continuous ridge vent is that the original cavity wall of the first extension is right up to the ridge. It is as if when they extended the rest of the house that used this wall to support the rafters as this wall would have also been supporting the rafters for the roof of the first extension. To me this makes it impossible to fit ridge vents.

Regarding the vent tile in between each pair of rafters; the ceiling of the kitchen does not follow the roof line all the way to the ridge and there is actually another floor of the house in the upper space. This is our bedroom en suite bathroom and has a flat ceiling and thus there is a common space for air to circulate. I also think this is where a lot of warm moist air is getting in as this has not been insulated or a vcl installed. I was therefore planning to install one vent tile in the centre of this space above the bathroom and hope this will solve the problem.

Again last night was a cold night and the damp issue is worse this morning but it has not rained.

 

[JohnD]

//www.diynot.com/forums/viewtopic.php?t=160032

 

[MrRob]

Thanks JohnD.

I had read that most previously but the link returned "The article does not exist yet"

We have tried to minimise the issue of warm damp air in the house and do also have dehumidifiers running. Relative humidity seems to hover around the 40-45% mark and we do ensure windows are open and extractors on when bathing or showering.

 

[JohnD]

link corrected, thanks

 

[MrRob]

Well, roofer is coming to fit vent tomorrow so fingers crossed that will solve our problem. Have also found a broken tile further up the roof so he will replace that with the one he takes out to fit the vent.