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Loft condensation

Postby armitageshanks » Thu Dec 11, 2008 10:32 am


I have recently insulted my loft with rockwool insulation.
Following this I then boarded out the centre of the loft with loft boards.
I now appear to have a condensation problem with the roof felt building up with moisture and dripping onto the contents of the loft.

I haven't insulated up to the eaves.
The loft is fairly full.
The pipes are lagged.
The cold water tank that is in the loft is covered ratehr loosely by a bit of board.
There are no roof vents.

Prior to insulating and boarding the loft, there were no issues with condensation.
Can anyone advise on how to get rid of it?

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Simply Build It

Postby camel_face69 » Fri Dec 12, 2008 3:05 pm

Hi there Shanksy,

I had exactly the same problem a couple of years ago along with mould growth on the woodwork up there.

A few ridge vents along the top of the roof soon sorted the problem. This will drag fresh air through the eaves then it will escape through the ridge vents instead of hitting the felt and condensating.

I havent had any repeat of the problem since :D

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Postby stoneyboy » Fri Dec 12, 2008 3:48 pm

A temporary solution would be to put a de-humidifier in the loft, preferably one with a permenant drain. A permanent solution is to ventilated the loft area with eaves vents and tile vents or a combination of both depending on your roof configuration. It would be wise to fully lag your cold water tank(s) but make sure there is no loft insualtion under the tanks.
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Postby armitageshanks » Mon Dec 15, 2008 8:56 am


Thanks for that, it would appear that the best solution would be to fit roof vents in the roof.
If I were to do this myself, presumably the vents simply replace the existing tiles. Do I remove the felt underneath to allow maximum ventilation?
Also is there a recommended amount of vents per foot?
I'm not sure whether I'm happy yet to walk around on the roof so I might get a builder in...

Presumably the reason the the condensation didn't used to be there is because there was hardly any insulation and therefore the temperature wasn't vastly different from the house/outside.

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Postby TheDoctor5 » Fri Jan 30, 2009 9:53 am

If you type the key words of your question into our search box to the left of the site you may find the answer is already posted or is in the DIY projects section of the website. Every post goes through a monitoring process and using the search box may speed up your answer.
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Postby pumpkin26 » Mon Nov 29, 2010 11:18 am

Hi armitageshanks

Try putting lapvents in your loft. I had the same problem in my loft last year so I installed 4 lapvents and after about 3 days the condensation was completely cured. They are really easy to install aswell and from what I can gather they are the only fully approved product on the market.

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