Condensation in my roof help please

Postby James Aldred » Sun Jan 04, 2009 3:41 pm


Im hoping someone can give me some practical advise to a problem I have just discovered and is really worrying me.

Ive just returned from our Christmas break and went up into the loft to find the black felt was damp in places this was dripping onto the loft board floor and the eaves. Its not penetrated any ceilings, just some of the boxes in the loft are a little damp, just I may have caught the problem in time.

The loft is fully insulated and there was no problem a couple of weeks ago when I last went up. The house is 35 years old.

So the only things that were different in December was that we used our gas fire more up to Christmas, turned the heating down over Christmas (whilst away) then turned it back up on our return.

I've heard of a couple of products called easyvent and lapvent that can help with this problem, has anyone any experience of using them? How much would they cost for a 4 bed detached house?

Also are there any immediate things I can do to reduce the condensation.

Thank you greatly for any advice you can give.

James Aldred
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Joined: Fri Mar 21, 2008 7:47 pm


Simply Build It

Postby thedoctor » Sun Jan 04, 2009 4:03 pm

Go to our project in the DIY Projects section, called condensation. Read it through and click into the banner at the top. The company there, PRS will give you free, no obligation advice, either by phone or email and can point you in the right direction to solve the problem.
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Postby the specialist » Tue Jan 06, 2009 7:29 pm

Hi James,

If you have never noticed this problem before I suggest waiting and monitoring it for a while. Let me explain why.

It may be that under normal weather conditions your roofspace ventilates properly.

However cross ventilation requires air movement outside which is quite common in our country. When we have extreme cold spells with very little air movement (no breeze or wind) the air in the loft becomes stagnant and the moisture within condenses onto the coldest surface - the felt - and then drips off as if it is raining.

When the air starts to move again everything returns to normal which is why I suggest waiting.

If it is a more prolonged problem you will notice other signs such as mould starting to develop on the felt and, if severe, on the roof timbers. If this is the case then you will need to improve ventilation.

Hope this is helpful.

the specialist
Posts: 87
Joined: Wed Dec 31, 2008 10:16 am

Postby James Aldred » Thu Jan 08, 2009 7:29 pm


Thanks for the feedback very helpful and in line with what I have been told by a friend who had exactly the same problem.

Ive also been recommended to try a product called lap vent or easy vent, does anyone have any experience of them, how much they cost to supply and to fit?

I was also told that if the problem is down to poor laying down of the original tiles that the whole roof could need replacing, this struck me as excessive as Ive not seen anyone of any of the diy forums needing to do that.

Any guidance that can be given would be appreciated, as this problem is worrying me a little.

Thank you all so much for your input.

James Aldred
Posts: 5
Joined: Fri Mar 21, 2008 7:47 pm

Postby the specialist » Fri Jan 09, 2009 2:33 pm

Hi again,

Just to put your mind at ease re-roofing wont be required to solve a ventilation issue. If its not raining in and you haven't noticed any loose/broken slates leave well alone.

the specialist
Posts: 87
Joined: Wed Dec 31, 2008 10:16 am

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