Loft Condensation,Vapour Barriers,Paints etc

nad1611

Hi All.I know this isn't the first thread about loft condensation but wanted to start a new one in case there were any new products etc.

We had a multi burner stove fitted last winter and noticed several weeks later that we had a really bad case of condensation in the loft. We were among those who had cavity wall and loft insulation done within the last five years.

We used a dehumidifier last winter for an instant resolution to the problem, but want to have a long term solution which is less costly than running the dehumidifier.

To keep costs down we want to do the work ourselves. Our first thought was to take up the insulation bit by bit whilst adding a vapour barrier,polythene or the like under the insulation to reduce moisture getting into the loft space. We've already trimmed down as much as possible any things stored in the loft but we'd also look at whether the insulation is blocking the roof airvents and deal with that accordingly.

I have health problems and my OH is not much better, so we're looking at the easiest and best way to achieve this and wondered if anyone has had any success using a vapour membrane paint on the upper floor ceilings directly under the loft, to reduce the moisture passing through. This would be a much easier solution as we wouldn't need to be bending and kneeling in a fairly confined loft space. Anyway I wondered what types of other vapour barriers are there and what would people suggest.

Thanks in advance.

ariba10

I would look at the possibility of Ventalation .

Did it for us.

nad1611

ariba10 wrote: »

I would look at the possibility of Ventalation .

Did it for us.

Thanks for responding.How bad was your problem? We've heard that if ventilation was the solve all, then you'd never get dew on the grass:). In other words ventilation is fine for removing moisture from warm environments not cold ones.

Hoploz

Oh my goodness, vapour barriers, plastic membrane ...
If there is moisture in the loft, it needs to get out! That's all. Ventilation is the answer.

Has the loft insulation been fitted too close to the rafters, blocking ventilation from happening down through the soffits? There should be gaps at the edges, it should not touch the base of the roof.

Have you had the soffits/fascias covered over or replaced with UPVC without adequate ventilation holes?

These will cause moisture to be trapped in the loft.

Smodlet

Presumably you have a chimney? Daft question, I know but are you sure it is not blocked or, heaven forfend, capped? I know this sounds stupid but not everyone notices these things (OH had to point them out to me )

TheCyclingProgrammer

IMO vapour barrier paint applied to the ceilings below will never form an effective barrier.

Neither will a physical barrier inside the loft unless you know how to fit it properly including all the detailing.

I agree with the above - if a space is well ventilated then there should be no need for a barrier.

Make sure all soffit vents are clear, it's very possible the insulation has been badly installed and is blocking the ventilation.

nad1611

Smodlet wrote: »

Presumably you have a chimney? Daft question, I know but are you sure it is not blocked or, heaven forfend, capped? I know this sounds stupid but not everyone notices these things (OH had to point them out to me )

Yes we do. It's not capped as said had a multifuel burner fitted so definitely not capped either. Thanks.

nad1611

TheCyclingProgrammer wrote: »

IMO vapour barrier paint applied to the ceilings below will never form an effective barrier.

Neither will a physical barrier inside the loft unless you know how to fit it properly including all the detailing.

I agree with the above - if a space is well ventilated then there should be no need for a barrier.

Make sure all soffit vents are clear, it's very possible the insulation has been badly installed and is blocking the ventilation.

I think you may well be correct, hence as mentioned we'll be making sure that the vents are ok. This has only become a problem since the woodburner so obviously a lot more moisture reaching the loft than previously.

Just out of interest if you agree that ventilation is all that's required, then I presume you wouldn't necessarily agree with this summation of the problems of condensation in lofts then?

http://www.telegraph.co.uk/finance/property/advice/11333991/Why-is-there-condensation-in-my-loft.html

Furts

nad1611 wrote: »

I think you may well be correct, hence as mentioned we'll be making sure that the vents are ok. This has only become a problem since the woodburner so obviously a lot more moisture reaching the loft than previously.

Just out of interest if you agree that ventilation is all that's required, then I presume you wouldn't necessarily agree with this summation of the problems of condensation in lofts then?

http://www.telegraph.co.uk/finance/property/advice/11333991/Why-is-there-condensation-in-my-loft.html

A number of coats of a good vinyl silk emulsion paint will form a vapour barrier on a bedroom ceiling. However this cannot be considered a thorough substitute for a membrane above the plasterboard. So give this a try and see what results you achieve.

Why a multi burner stove is considered responsible is a mystery to me - perhaps you are heating to a higher temperature than before it was installed?

Your link refers to dew on grass, and you mentioned it earlier. Here you have to be realistic and accept journalists want to write stories. I take the analogy as almost irrelevant to roof space ventilation.

malc_b

Is the stove and the loft condensation related? Just because they happened at the same time doesn't make it cause and effect. If the loft condensation is caused by the stove then it would happen when you run the stove and there must be some fumes getting into the loft, so you need to get that sorted otherwise you are dicing with carbon monoxide poisoning. BTW I assume this stove has a chimney and isn't one of these no chimney room heaters. If it is then you will get a lot more moisture in the air with those which would add to the moisture load in the loft as hot air rises and I doubt the ceiling is air tight.

I see you say you had loft insulation done. Are you sure that the condensation isn't caused by this extra insulation (which makes the loft colder of course). Typically you need to improve the loft ventilation when you increase the loft insulation. Modern houses have vents at the eaves and at the ridge. Older houses just had them at the eaves and hot (wet) air rises. The usual fix is to wedge open the roofing felt at the overlaps to increase the ventilation. You can buy products to do this, Google felt lap vent to find page like this, or you can be like me a cheapskate and cut triangular wedges from waste polystyrene.

malc_b

nad1611 wrote: »

Just out of interest if you agree that ventilation is all that's required, then I presume you wouldn't necessarily agree with this summation of the problems of condensation in lofts then?

http://www.telegraph.co.uk/finance/property/advice/11333991/Why-is-there-condensation-in-my-loft.html

I would since it is plain wrong! The warmer air is the more water it can hold. The colder the less it can hold. As air cools it eventually reaches 100% humidity, the dew point, and you get condensation. Now the outside air at most could be 100% at the outside temperature. Bring that air into the loft and it will be warmed, just a bit, by the heat leaking from the house. Hence it's humidity will go DOWN.

The opposite effect occurs with air leaking from the house into the loft. That is warm and potentially has a high humidity. When that gets into the loft it cools and its humidity goes up. What you need to do is get that to the outside and replace it with outside air, which is why you vent.

The telegraph says "But if you ventilate an unheated roof space, the replacement air will either be from the warm, moist environment below, or from the cold, damp environment outside the building." which is total rubbish. The outside air maybe cold and damp but warm it in the loft and it becomes less damp. Plus you can't avoid some leakage into the loft from the house. If the loft was sealed to the outside you would get worse condensation.

I would agree that reducing leakage from the house is a good idea, so is having a breathable roof felt. Practically the easiest solution is better ventilation and high up ventilation to get rid of the hot damp air before it cools and condenses.