Major condensation in loft space

Major condensation in loft space

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M005

Original Poster:

194 posts

173 months

Wednesday 16th December 2009
quotequote all
The solution to this seemed obvious but seemingly not mad

We live in a 5yr old detached house, have lived here for 3yrs. Every winter when the weather gets cold there is a problem with condensation in the loft, which drips onto everything up there causing mould etc.

It was well insulated, and I have last week added another 170mm to just over 1/2 the space - the 1/2 not covered by boxes etc. I have also found some areas that weren't insulated under some boarding put down by the previous owner, and have added 100mm of insulation board to the loft hatch as well.

None of this has made any difference furious

There is the standard ventilation around the edges, under the eves, which isn't blocked. Certainly the loft space feels cold.

So what am I missing?

Never had this before, even in houses with a lot less insulation, lofts are always dry, dusty places aren't they?

Thanks

motco

12,588 posts

194 months

Wednesday 16th December 2009
quotequote all
The conventional wisdom is roof space ventilation. Have you a central heating make-up cistern up there? If the water in it is hot due to pumping over then that'll do it. Moisture is getting up from living spaces otherwise- you need to make sure no air from the bathroom gets through to the loft.

garycat

3,426 posts

158 months

Wednesday 16th December 2009
quotequote all
M005 said:
The solution to this seemed obvious but seemingly not mad

We live in a 5yr old detached house, have lived here for 3yrs. Every winter when the weather gets cold there is a problem with condensation in the loft, which drips onto everything up there causing mould etc.

It was well insulated, and I have last week added another 170mm to just over 1/2 the space - the 1/2 not covered by boxes etc. I have also found some areas that weren't insulated under some boarding put down by the previous owner, and have added 100mm of insulation board to the loft hatch as well.

None of this has made any difference furious

There is the standard ventilation around the edges, under the eves, which isn't blocked. Certainly the loft space feels cold.

So what am I missing?

Never had this before, even in houses with a lot less insulation, lofts are always dry, dusty places aren't they?

Thanks
Make sure your insulation is not pushed into the eaves, there needs to be a ventilation gap so air can get through vents in the eaves into the loftspace.

Deva Link

26,934 posts

193 months

Wednesday 16th December 2009
quotequote all
Apart from the vent path being clear as mentioned above, you haven't got holes in ceiling, especially in the bathroom, for downlighters, have you? Or even the bathroon fan venting into the roof space?

I also thought of the CH pumping over but on such a new house you presumeably don't have water tanks in the loft.

JuniorD

6,787 posts

171 months

Wednesday 16th December 2009
quotequote all
Sounds like too much insulation. Happened to my old man - zealously insulated the loft and then the place was soaking after a week. Found that leaving the loft hatch ajar solved problem -cold and dry being preferable to warm and wet (well, for lofts at least...)

Edited by JuniorD on Wednesday 16th December 11:59

sleep envy

62,258 posts

197 months

Wednesday 16th December 2009
quotequote all
M005 said:
We live in a 5yr old detached house, have lived here for 3yrs. Every winter when the weather gets cold there is a problem with condensation in the loft, which drips onto everything up there causing mould etc.

It was well insulated, and I have last week added another 170mm to just over 1/2 the space - the 1/2 not covered by boxes etc. I have also found some areas that weren't insulated under some boarding put down by the previous owner, and have added 100mm of insulation board to the loft hatch as well.
wouldn't a 5 year old house have sufficient insulation installed during construction?

it's not that old that the original insulation will have failed or deteriorated and any natural vent may have been blocked by adding more

Deva Link

26,934 posts

193 months

Wednesday 16th December 2009
quotequote all
JuniorD said:
Sounds like too much insulation. Happened to my old man - zealously insulated the loft and then the place was soaking after a week. Found that leaving the loft hatch ajar solved problem -cold and dry being preferable to warm and wet (well, for lofts at least...)
That makes no sense whatsoever. Opening the loft hatch would make it worse.

eps

4,972 posts

217 months

Wednesday 16th December 2009
quotequote all
The problem you have is insufficient ventilation. The next problem is working out why.

You say that the eaves/edges are ventilated and I guess the insulation stops some way short
of that, so that air + moisture may ventilate out. If this is the case, do your eaves have
ventilation vents in them? Most of the time they're visible, from outside..

http://www.harcon.co.uk/eaves/index.aspx

It sounds like something was forgotten or has been covered over... It's finding out what, which
will take time and some investigating.


How big is the house? (metre x metre footprint and roof pitch) Quite often there is extra ventilation in the roof or at the ridge as well, if
the roofspace is large.

What sort of roof covering have you got, tiles, slates or others? What sort of membrane was put under the roof covering?

Goochie

5,497 posts

167 months

Wednesday 16th December 2009
quotequote all
Who built the house?

My money would be on warm air getting into the loft via downlights.

JuniorD

6,787 posts

171 months

Wednesday 16th December 2009
quotequote all
Deva Link said:
JuniorD said:
Sounds like too much insulation. Happened to my old man - zealously insulated the loft and then the place was soaking after a week. Found that leaving the loft hatch ajar solved problem -cold and dry being preferable to warm and wet (well, for lofts at least...)
That makes no sense whatsoever. Opening the loft hatch would make it worse.
I know what you are saying but it worked for him and was the only modification made. Certainly circulation would have increased.

Martin Keene

6,832 posts

173 months

Wednesday 16th December 2009
quotequote all
It will be a ventilation problem. My first house was 9 years old when I bought it and there was no problems with loft condensation for the first 3 years I lived there. Then it started, people where telling me I needed more eve vents, air bricks in the gables (tricky in a terreced house) etc.

I found this hard to believe as it had been fine for 12 years. When I sat down and though it through, I realised it started after swmbo moved in and a lot of stuff got put in the loft. Being terreced the vents where on the front and rear eves and we had the contents of the loft on a boarded section across the middle.

A damn good clear out, and rearranging what was left against the party Walls in the loft removed the condensation. We had blocked the airflow in the loft with all the st in there.

I now look at it like this, if it needs storing away somewhere like a loft, I don't need it and it gets binned. As a result the loft in the new house is empty bar an aerial.

Sam_68

9,939 posts

193 months

Wednesday 16th December 2009
quotequote all
As others have said, the conventional, historic solution to this problem has been to increase the ventilation of the loft space.

Unfortunately, for technical reasons that I won't bore you with, we've reached the limit of viability as far as this solution is concerned and we're reaching the point where no matter how much ventilation and/or breathable roofing felt you use, it won't totally cure the problem.

If you've just added another 170mm of fibreglass quilt, you've just made your own problem worse, I'm afraid.

The solution for house builders, ultimately, will be to go over to 'warm roof' construction techniques (where the insulation is at rafter level instead of ceiling level and the actual loft space is 'warm'), using different types of insulation.

If you have already maximised the cross ventilation of your loft (as others have said, make sure that the eaves ventilation isn't blocked and if the roof form is such that you have limited cross ventilation from the eaves (ie. lots of gables) consider fitting air bricks in the gables or additional ridge vents, thought they will only help a little), consider removing some of the insulation. Breathable roofing felt would also help a little, but of course you'd need to re-roof the whole house to install it.

Out of interest, who built you house? PM me if you don't want to quote their name on open forum.


Sam_68

9,939 posts

193 months

Wednesday 16th December 2009
quotequote all
Goochie said:
My money would be on warm air getting into the loft via downlights.
This can certainly exacerbate the problem, as can a badly sealed loft hatch, but it's seldom the sole cause.

BRGV8S

251 posts

154 months

Wednesday 16th December 2009
quotequote all
Had a similar problem in a new build scheme, checked vents, bathroom extract, lighting units, soil pipe, all with no success. On a visit i took a walk down the garden to look at the building (gable) and you could clearly see the 'plume' of condensation on the stone above the balanced flue outlet to the ridge.

Right in the middle of the gable above ceiling level were two 225*150 air bricks to ventilate the roof void, it became clear that this was the cause of mosture entering the cold roof void and causing the problems.

Might be worth checking

Busamav

2,954 posts

156 months

Wednesday 16th December 2009
quotequote all
I suspect it is due to a lack of ridge ventilation , particularly if you have a steepish roof pitch .

Wings

5,354 posts

163 months

Wednesday 16th December 2009
quotequote all
Can one not buy ventilated/air vent roof tiles?

Sam_68

9,939 posts

193 months

Wednesday 16th December 2009
quotequote all
Busamav said:
I suspect it is due to a lack of ridge ventilation , particularly if you have a steepish roof pitch .
What leads you to this conclusion?

andy43

6,263 posts

202 months

Wednesday 16th December 2009
quotequote all
Sam_68 said:
As others have said, the conventional, historic solution to this problem has been to increase the ventilation of the loft space.

Unfortunately, for technical reasons that I won't bore you with, we've reached the limit of viability as far as this solution is concerned and we're reaching the point where no matter how much ventilation and/or breathable roofing felt you use, it won't totally cure the problem.
I'd not be bored! I spent ages on our dormer conversion (cold flat roof contruction) with rolls and rolls of foil tape taping together a full additional layer of 25mm kingspan underdrawn to external walls and ceiling, to get an airtight seal (obviously only airtight until the plasetrboard screws went in...). Pleeeease tell me I wasn't wasting my time and my timber framed dormer walls aren't now dripping wet.

motco

12,588 posts

194 months

Wednesday 16th December 2009
quotequote all
...and I've bonded and fastened 50mm of Celotex board to the concrete ceilings of my son's flat (top floor with 1938 concrete slab/asphalt coated roof) with aluminium foil tape on the joins and silicone sealant around the edges, and a Clipso stretch suspended ceiling a couple of inches below as a finish. Please tell me that will be okay... xmas

M005

Original Poster:

194 posts

173 months

Wednesday 16th December 2009
quotequote all
Thanks all, some great tips.

In response to the questions;
  • The bathrooms do have vents, but to the outside, with the pipe being insulated as it passes through the loft space. We don't have the fans turned on.
  • There are no downlighters upstairs.
  • House is a large 4 bed, from memory when we bought it the upstairs was quoted ~ 795sqft.
  • Persimmon BLOOR built the house.
  • The ventilation by the eaves is covered with a plastic mesh.
  • No CH items up there, just the cold water tank & header tank, all pipes are well insulated.
  • Roof space is very large, apex is ~ 15ft high and distance between the triangular roof supports is ~ 10ft, with a futher ~10ft each side of that to the eaves. Total length of the space (length of apex) is ~ 40ft+ at a guess.
A few comments from above have got me thinking about airflow. Whilst the majority of the stuff is within the middle section (i.e. the middle 10ft) there is increasingly more stuff down one side in the outer 10ft to the eaves, which will be greatly affecting airflow.

I'm just about to head up there and have a good sort out / rearrange all the stuff and see of that makes a difference.

Thanks for all the inputs, I'll keep the thread updates with progress.

Edited by M005 on Thursday 17th December 09:09