Condensation in Loft

[Clickem]

We moved into a bungalow about 15 months ago and have completely renovated everything, including new gas heating, bathroom, kitchen, windows and doors. The house tends to be damp, so that we can find mould on things in wardrobes or on the backs of kitchen cupboards. We try to combat this with heating and good ventilation. The damp seems to come from the general area that we live in. Low lying, on clay soil with springs in the garden. The RH in the house rarely falls below 70%

My concern is in the roof void, where in cold weather we get damp on the roofing joists. It has been bad enough to have water dripping onto the insulation. The roof was renewed some years ago and the old felt was not removed and I have been told by a roofer that the new felt, just laid on the old is not “breathable”

The walls have had the cavities filled and there is about 4” of insulation in the loft. I had intended to increase the insulation, but have held off as it would make the loft colder and therefore the RH higher

The soffit boards were replaced some years ago, and badly done in that air vents were fitted in the plastic, but not drilled through the existing wood facia boards, that were left in place. Since last winter we have installed air bricks in each gable end and 4 ventilation tiles in the roof. In the cold weather I run a dehumidifier in the loft.

What is the best way forward? More air bricks, fit ridge tiles with ventilation slots (not recommended by roofer as we live in a windy place), replace facia boarding with new that includes more ventilation. At the moment I think that the dehumidifier reduces the moisture level, but seems to be in conflict with improving the ventilation, so that I end up trying to dehumidify the whole world

 

[andyroo1]

I would try rafter vents if you have not already
http://www.allproroofing.ca/roofing/roof_ventilation/RAFTER-VENT.jpg

They will increase the air flow and reduce the problem. But whatever you do, make sure you dont leave it as it will only get worse & rot your timbers which will cause a real issue (+ expensive one!) also is there space around the edges or has the insulation been tucked tight to the wall?
If so you need to leave an inch or so at least gap to allow airflow- this should also help.

 

[freddiemercurystwin]

//www.diynot.com/wiki/building:condensation_in_houses

How does the content of the link fit in with what you have tried/researched so far?

 

[Clickem]

Thank you for those replies

We have taken steps to reduce condensation in the house. Bought a tumble drier that is vented and fitted, and use, extractor fans in the kitchen and bathroom

Sounds like we need to increase the ventilation through the facia boards, use rafter vents and sort out the insulation

Many thanks

 

[Markerpen]

Whilst all that has been said regarding ventilation is obviously correct, I do wonder what is the source of that amount of moisture. OK, a lot of water surrounding the property, but surely that would have little to do with the internal humidity.
If there are tanks in the loft, is there a fault with the heating/hot water that is pumping hot water over from the open vent pipe back into the tank? - a common problem.
Is it possible there could be another , as yet undiscovered water leakage, under the ground floor maybe?
Another common soruce is downlights fitted in bathrooms and kitchens.
It just seems rather too bad to solve by ventilation alone.

 

[Clickem]

1. If there are tanks in the loft

No, we have a new heating system with a condensing boiler and the loft is dry

2. Is it possible there could be another , as yet undiscovered water leakage, under the ground floor maybe?

Whenever I have looked under the floorboards, always as dry as snuff and at least 4 near neighbours have similar problems

3. Another common soruce is downlights fitted in bathrooms and kitchens.

No downlights at all

We are in a low spot on our road, and as mentioned the effect is similar for a couple of our neighbours either side. We have a pond opposite the house and it was boggy land before the houses were biult over 50 years ago. we don't flood but seem to have a high humidity around us

4. It just seems rather too bad to solve by ventilation alone.

One neighbour has installed positive pressure ventilation, which pumps air into the house, so air is pushed out of gaps, rather than air being pulled in. These systems usually push air from the loft into the house to give a positive pressure. I cannot see the benefit of pushing already humid air from the loft into the house, unless you are going to heat it first

 

[Markerpen]

Thanks for the feedback.
Thats a few possibilities of mine all gone. As you say, it does seem too bad for ventilation alone, and that was the way I was thinking.
After all, moisture has got to be getting to the loft from somewhere, yes, some can pass through the structure, but that much!
could there be any holes/gaps etc in the ceilings, especially in the kitchen or bathroom?
At least without tanks, you afford to increase ventilation and insulation without fear of freeze ups.

 

[KenGMac]

hI,

Ok this ain't going to solve your problem, BUT.

In my day job in the last week I have seen this problem 5 times !

Scenario runs generally like this, loft is re-insulated with a massive volume of fiberglass up to in one case about 300 mm thick.

Someone goes into the loft [to get the christmas tree / lights Etc and finds the boxes are wet on top?

On the ones I have seen the new Insulation installers who installed in mid Summer [generally] had rammed the Insulation into the eaves, no cross venting at all result predictable.

Now this type of problem is really taking off, what with FREE insulation of lofts and walls.

interesting point the degree of condensation occurring appears to be totally random, sone loft spaces are soaking, one i saw only had one area that was dripping water on a gable end with the wind coming directly at it

my only advice is massively increase the cross venting by any means possible, retro fit bore in circular proprirtory vents, ridge tile vents anything that will increase air flow.

Point to ponder why do the cowboys fitting this insulation not advise on ventilation and stop ramming it into the eaves?

 

[Markerpen]

KenGMac makes a valid point, also that it does appear random. My own house has no roof space ventilation at all - dry as a bone!
My concern with all this insulation, is of the pipework and tanks in older properties. There is only so much that can be done to reduce the risk of freezing.

 

[catlad]

If I read this correct you have a modern membrane laid on an old non breathable felt, then cut the old felt out from the inside with some tuff scissors and obviously ridge and eaves vents.

 

[Clickem]

Sorry for delay in responding - having probs with Broadband access

Firstly there are no gaps in the ceilings of kitchen or bathroom. One has been tiled with honeycomb plastic sheeting and the other has just been newly plastered. We do not create excessive moisture - couple of OAP's not students showering 3 times a day

I had a look in the loft this week and the underside of the roof felt is damp, and the joints are damp where they touch the felt and the RH was 100%. Dehumidifier is taking out about 5litres a week

My neighbour was telling me that he has added insulation to his loft and has made the problem much worse - fits in with comments above

My response is going to be to replacing the plastic facia and soffits - needs doing anyway, with lots of ventilation slots. Fitting rafter vents to ensure that ventilation can get into loft and probably fit some ridge tile vents.

Not sure that I would dare take a knife/scissors to the under layer of roof felt

I would like to increase our level of loft insulation. This week the house was 18 deg, outside was 3.3 and the loft was 4.9, so the level of insulation at the moment seems to keep the loft fairly cold

Thanks for all the comments, seems the way forward is to VENTILATE and eventually be able to stop using a dehumidifier

 

[1969mike]

Hi guys,

Just joined DIYnot and noticed this thread, so bear with me.

The source of the condensation is hot moisture condensing on the impervious roof felt, so the first thing to do is to upgrade the insulation to 300mm thick, cross laid (100 between joists and 200 laid in the opposite direction) to prevent the heat from escaping from downstairs. Don't forget the loft hatch. If you don't upgrade the insulation, then you will always have moisture in the roof void.

Now, all insulated roofs with the insulation within the void (cold roof) need to be ventilated. If the pitch of the roof is lower than 35 degrees, then only low level cross-flow ventilation (thats the key, vents need to be opposite each other) needs to be installed. If greather than 35 degrees then both high and low level ventilation is required. The ventilation needs to be unobstructed and as stated above, the key is to keep the eaves clear where it is prone to being rammed with quilt insulation. It pays to use high density insulation at perimeters and quilt for the main loft area, and 50mm clear air gap is the minimum. Alternatively, use inline tile vents, 10,000sqmm air flow, not cheap but more attractive than cowls, spaced at 2m centres on front and back slopes. This will keep your loft cold and moisture free. If the roof is hipped, then place them on the side as well.

Soffit vents are OK, but they need to be fitted to each rafter void and you will need to ensure the junction at the rafters and ceiling joists is clear.

Hope that helps.

 

[noseall]

Condensation issues can be wholly attributed to the lifestyle of the occupants.

In other words, condensation levels can differ greatly in identical houses/locations depending upon how they are lived in.

I know because Woodbine said so.

 

[JohnD]

We do not create excessive moisture

so nobody drapes wet washing around the house or over radiators.

That's good, because it's the main cause of condensation, damp and mould in UK homes.

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