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Ridge board and spars damp above offshot after re-roof

I live in a 1910 Victorian Terrace with solid stone walls on the front of the house and brick cavity walls on the rear. The off shot of the house is divided at the ridge with next door as this is the party wall as such. The loft was previously installed with insulation in between the ceiling joists and at 90 degrees over the top.

approximately 6 months ago I had the slate roof re-laid over the whole house including breathable felt membrane. However I recently only notice after going in the loft the ridge beam of the off shot and spars is damp although the main roof is fine with no sign of damp timber.
First off I thought the ridge tiles must be leaking but appeared odd the spar is damp the whole way along as I didn't think water would travel this far along.
After speaking with the roofer he did not over lap the felt at the ridge of the off shot because this would mean taking a couple of course of next doors slates off and re-laying.
He reused the old ridge tiles because he said they are better than the new ones. Can the ridges become porous they will be over 100 years old.

There is no ventilation in the off shot part of the roof but a ventilation pipe was put in the main part of the roof for a future on-suite extractor, however this is not connected up so ventilated from the loft to outside.

The roofer is convince it is condensation and recommends a ridge tile vent and a slate vent in the off shot part of the roof.

Previously there was no felt membrane and effectively this is the only difference to how the roof was previously with also the addition of the ventilation pipe in the main part of the roof.

Has anyone any similar problems occur when re-roofing a old house ?

3 Answers from MyBuilder Roofers

Best Answer

I suggest to change the ridges
To a dry ventilated ridge system witch you can see me. Personally install
This lets your roof breath and keep water tight at the same time.


Answered 19th Jan 2017

Ive seen this in both new and old houses. From what you have explained condensation sounds the most likely cause especially if previously there was no felt. Two ways we have gotten over the problem are as your roofer has suggested, ventilated ridges and slates or what we have had specified before is to not take the new membrane right over the top which I personally didn't like but you can see the logic in.
hope this help ease your mind and you get it sorted soon.


Answered 13th Jan 2017

i got same in my house,the water was streaming down the walls .i opened up the loft hatch to let air circulate and it has stopped but like your roofer said u probally need a better air vent


Answered 13th Jan 2017

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