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Author: Subject: How to stop condensation in the attic!

posted on 28/11/10 at 12:03 PM Reply With Quote
How to stop condensation in the attic!

Got a bit of a problem that seems to be getting worse and i've no idea how to stop it.

Basically i've got a lot of condensation in half of my attic, and its worse on one side of the half than the other! Its so bad i have wet lines on the floor boards from drips. Yesterday i mopped up about a quarter to 1/8 of a pint on the central floor boards, there is more on the insulation either side. Luckily today its all frozen on the roof!

Over the summer i've had my boiler replaced (including removing water tanks in the attic). This has freed up space so i've removed the existing insulation in the middle, and replaced it with insulated floor boards (removed about 20cm of orange and foil covered insulation and put in 15cm thick polystyrene boards bonded to a loft board in its place). Also had all the windows done. When they did the windows they removed the guttering, boxed in the end of the rafters (like normal houses have) and put the guttering back. Along the length of the board that has the guttering their is a 1 inch plastic vent at the top by the tile.

As i started to notice condensation a few days ago i made sure on the side that has the worst condensation i pulled back the original (between rafters) insulation so there definately is a gap between the eves.

The half of the house without hte problem has the same insulation in the sides, but the middle just half 75mm of insulation and loft boards.

What i don't understand is why its all in at one end of the house and mostly on one side.

The house roof goes north to south, the side that gets the most condensation is on the east side.

So what is causing it and how the heck do i stop it?

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David Jenkins

posted on 28/11/10 at 12:07 PM Reply With Quote
What sort of ventilation do you have in the attic, and how much?

You must have air-bricks, vents in the eaves, or *something*, otherwise you will get condensation.

You didn't block any vents when you installed the insulation, did you?

The older I get, the better I was...

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posted on 28/11/10 at 12:08 PM Reply With Quote
condensation is normally down to a lack of ventillation, if insulated as a cold roof with insulation at ceiling level what sort of loft ventillation do you have is the some at the dry end but not at other?
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posted on 28/11/10 at 12:11 PM Reply With Quote
Guessing when they put the vents in the soffit they did not put some vents high up?

You need more airflow
Either in a gable if you have it or from Ridge ventilators (Have a look at new houses)

Beaten to the reply

[Edited on 28/11/10 by bmseven]

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posted on 28/11/10 at 12:16 PM Reply With Quote
in theory, along the entire length of the guttering i've got a 15mm vent into the roof space. Plus if i look down the felt i can see daylight. I'm worried somehow the gutter vent can't get into the roof space. When they imitally fitted the plastic to the apex side of the house you could see lots of cracks of daylight until they siliconed it up. There are no vent bricks and the walls are cavity insulated.
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Mr Whippy

posted on 28/11/10 at 12:18 PM Reply With Quote
Sounds like you just need to add some more vents to get the air flowing, most houses are quite daftly in the lofts etc to keep them dry and foil barriers are also quite bad at preventing the moisture escaping and can actually make things worse. Do make sure you don't have a roof leak though and itís probably the side that isn't facing the sun and is there for much cooler than the rest of the roof. Try just holding a piece of tissue in the roof space and it doesn't move on a windy day then you have not got enough ventilation, in my loft I can feel the wind on my face and itís never damp.

is there any way for the air to flow out the ridge? like in the pic... on mine there is a 2 inch gap all the way along the roof and the ridge tiles let heaps of air through.

The point is you need air flow not just vents or the air will just stagnate

[Edited on 28/11/10 by Mr Whippy]

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posted on 28/11/10 at 12:47 PM Reply With Quote
You dont have a load of those downlights do you, perforating your ceiling and allowing warm moist air to flow into your loft space?
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posted on 28/11/10 at 12:47 PM Reply With Quote
all the above is good points, the other aspect is to reduce how much warm moist air can enter the loft. A can of expanding foam might be a good start. Afterall, if no moisture enters the loft then no condensation can form.

Beware! Bourettes is binfectious.

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posted on 28/11/10 at 01:16 PM Reply With Quote
We had the same thing after we had a new roof years ago the roofing felt was as tight as a drum all the way round, I cut a couple of squares out of the felt on either side of the house and the problem cleared immediately.

[Edited on 28/11/10 by splitrivet]

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posted on 28/11/10 at 01:26 PM Reply With Quote
just be a little carefull with expanding foam. If you go sealing off gaps and the loft is not completely dry then all you are doing is trapping the moisture in the loft. This will lead to mould. Also expanding foam is open cell, its hydroscopic so will absorb moisture. Also despite what it says on the tin it is not fire resistant. You can buy "Fire" resistant foam, but it will burn and release poisonous gases. If you dont beleive me just check the manufacture's web site and look for their test data. The test done to show "fire resistance" will be the foam at the bottom of a 400mm deep hole in concrete about 6mm in dia, then back filled with compacted paper. This will then be subjected to fire. Oh look the product didn't burn so it must be fire resistant. Just my point of view................(based of FIRAS test data)
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