Under-roof spray

Aeneas

A friend has a 1930's two-storey house where there is no felt under the slated roof. One consequence of this is that rainwater occasionally blows in through the gaps in the slates and beneath them. Since there is no felt or membrane under the slates to take the water away it can make the rafters damp. I was wondering if he sprayed the underside with foam would this act in the same way as felt to prevent rainwater penetration and take it down to the gutter? Are there other problems with these under-roof spray systems?

No6

There is no guarantee with this spray foam that this will work, but I have found that it does, provided the slates are in good condition, any loose or broken slates should be replaced. Some people also have difficulties with the foam in that it seals in the timber and may cause rot. I have used it on a number of projects including my own 1920's farm house and it has been fine so far, I would advise treating all the roof timbers with preservative first.

Aeneas

No6 wrote: »

There is no guarantee with this spray foam that this will work, but I have found that it does, provided the slates are in good condition, any loose or broken slates should be replaced. Some people also have difficulties with the foam in that it seals in the timber and may cause rot. I have used it on a number of projects including my own 1920's farm house and it has been fine so far, I would advise treating all the roof timbers with preservative first.

Thanks. I can see the problem with the timbers; and in this case because some of it is already wet there must be some risk of rot if the timbers are sealed. Is it possible to just spray the slates between the timbers?

Aeneas

I have looked up a number of websites in the meantime and most of them point to potential problems with timber rot from these under roof systems. So maybe I will tell my friend to give it a miss. Although he still has the underlying problem to deal with.

No6

Aeneas wrote: »

I have looked up a number of websites in the meantime and most of them point to potential problems with timber rot from these under roof systems. So maybe I will tell my friend to give it a miss. Although he still has the underlying problem to deal with.

It is a very cheap solution to a real problem but there are as I've siad issues with rot etc. If the timber is already rotting in places you could possibly cut out the rotting bits and replace and then spray the roof. As long as your friend realises the in time he may have to replace the entire roof, timbers and all or else he can do it now and strip the roof, replace the rotting timbers and reslate.

PeteHeat

Hi,

Going back as far the mid 80's the sprayed foam was causing disasters and it still does.

The system will not fix the leaks in a roof, what it does is worse in that some of them hold the water on top of the foam to be absorbed by the wood, other types slowly absorb moisture and of course it finds its way into the timbers.

Slate roofs didn't have felt for centuries until the early 1930's and they didn't leak.

I expect your friend will find himself in a similar position to a number of UK County Councils and end up spending a lot more getting the foam removed and the damaged timber replaced than a new roof would have cost at the start.

.

Aeneas

Many thanks for the advice. I think a potential disaster has been avoided.