laying insulation on attic floor - vapour barrier or not?

[maggie73]

I need to insulate the floor of the loft as what is there appears to be of the "blown" type and not even of the required depth. I think I will go with the Eco wool advertised at B&Q but need to know whether I should lay a vapour barrier between the joists before putting down the insulation. The house was built around 1860 and the roof is slate, with felt, then sarking board- dont know if it is a breathable felt, the house was renovated in the 60's so perhaps not.
I was concerned at some areas of light white mould and one night the nails were dripping a little with condensation, but everything is dry up there and never noticed condensation since. We have had an extractor fan put in the bathroom ceiling, which goes out through the roof, especially because the loft hatch is in the bathroom.
Our roofer put in the vent for the extractor but said that there was plenty of airflow in the loft (i think maybe air comes through the eaves) and was reluctant to put in more vents, as he didnt want the loft space to get too cold and pipes to freeze. He seemed very happy with the condition of the roof and not concerned with the light mould.
So, should I lay vapour barrier or not? Obviously it would stop some moisture getting into the roof and condensing on the (colder) roof but can it cause problems elsewhere?

 

[Penners]

We had a similar post to this recently, which caused some controversy.

Personally, I wouldn't bother with a vapour barrier underneath the loft insulation - particularly if you're going to have a good thickness of insulation. Condensation occurs when warm, moist air meets cold air, and the insulation should keep your warm household air and the chillier loft air apart.

This being the case, there's no need for you to remove the blown insulation that's already between the ceiling joists. Just lay your new insulation on top.

 

[chuckey]

I would not bother with the membrane, because it will just trap any moisture and that will (in time) effect your ceiling fixings. If you have mould you should put in more ventilation into your loft and ungrade your tank and pipe insulation. I had this problem, felt sarking, no ventilation, puting in soffit vents cured it. Pipes and tank have ~ 4" glassfibre and felt insulation on them. I would not trust a roofer for information on condensation.
Frank

 

[maggie73]

Thanks for your replies. I think maybe I will even out the blown insulation and overlay with eco wool, ensuring the eaves aren't blocked. Then I will monitor the loft to see if I am getting any condensation: if so I will get vents put in and increase the lagging on pipes etc. I do actually have faith in my roofer - Im sure he's seen alot of roof spaces in his 20 years experience and must know something about condensation!

 

[Raylea]

Not much help roof wise, but sorry to sound like doom watch, I don't trust any professional of late, the only person I trust to do a good job is my good old dad and a little old roofer we had do a job, worked on the side for himself was more then honest said he could do job without scaffs and up he shimmied and he didn't charge the earth (and cleared up his mess).

Hope I am not raining on anyones parade, nothing personal just my opinion and I am glad you've found someone you trust.

Raylea

 

[Lime]

I wouldn't use a membrane.
Ensure the pipes and tank/s are well insulated.
If you are getting condensation now then with more insulation it will get more frequent and more severe.
I'd be concerned about the loft hatch allowing condensation into the loft.
Don't forget to seal and insulate the hatch too.

 

[maggie73]

We havent seen any condensation in over a year and all our stored items in the attic are dry (partner up there alot over the last month cos one of the valves needs replacing on the tank ball cock or something.) I think most of the moisture that makes its way into the roof space is undoubtedly coming via the hatch - what is the best way to seal it effectively?
The reason I like our roofer is that we were really keen to get air vents and he talked us out of the job, saying we just didnt need them, certainly at this point. he did other work and his rates were great, and work very professional and tidy.
There are about 15 houses in our terrace, none with vents, but some Im sure with much better insulation than ours, though thats obviously not to say they are all condensation free!
Talk about can of worms - you think you are doing something good by insulating but then get completely para about the knock on effects, like the roof joists rotting before your very eyes!!

 

[Lime]

We havent seen any condensation in over a year and all our stored items in the attic are dry (partner up there alot over the last month cos one of the valves needs replacing on the tank ball cock or something.) I think most of the moisture that makes its way into the roof space is undoubtedly coming via the hatch - what is the best way to seal it effectively?
The reason I like our roofer is that we were really keen to get air vents and he talked us out of the job, saying we just didnt need them, certainly at this point. he did other work and his rates were great, and work very professional and tidy.
There are about 15 houses in our terrace, none with vents, but some Im sure with much better insulation than ours, though thats obviously not to say they are all condensation free!
Talk about can of worms - you think you are doing something good by insulating but then get completely para about the knock on effects, like the roof joists rotting before your very eyes!!

Yes many "improvements" to older housing have negative aspects attached to them, insulation being one of them roofing felt and draught-proofing two others.
Electric cable should not be run inside the insulation either as it can get hot.

How you seal the loft hatch depends on how good the lid fits the hole.
If it is a relatively good fit all round then most sponge or brush adhesive door draught-excluder will be fine.
if the gaps are very large then perhaps they need repairing or filling before sealing is done.
The top of the loft hatch lid/door/light can be insulated with a cut-to-fit piece of Kingspan or similar. It can be made thicker by sticking two or more pieces together using a contact adhesive.
Keep an eye on the damp.
A cold still day where the roof tiles on the outside are damp with dew is a good time to look.

ps. Don't insulate under the water tanks, ensure they are sealed (so that water vapour cannot escape) and give them the same thickness of insulation on and around them as the rest of the loft.
Also don't forget to insulate the overflow pipe/s.

 

[maggie73]

Been up in the loft today to check for condensation - was pretty cold last night, and still and cold this morning, and condensation on bedroom windows. there are undoubtedly some nails which have a bead of water on them, and where I can see felt, I can see small beads. However, there are lots of cardboard and plywood surfaces up there as well as blown insulation, and nothing is damp to touch at all, and the loft does feel airy.
There is definately a fine white mould on the sarking boards: I am now getting really worried that although all the sarking/timbers feel dry that they are slowly rotting where I cant see them! We have made real efforts to reduce moisture in the house, and I will seal the loft hatch, which actually doesnt fit that well, before laying more insulation. Think am going to splash the cash and gets sheeps wool insulation as it is a relatively small space, about 35m2 and should be about £400 to get to top of joists.
If indeed the sarking is rotting behind, and the roof needs to be stripped/refelted and retiled, would i be able to claim on insurance at all? or maybe just getting more vents in would help at this stage and prevent further damage.

 

[skier-hughes]

You won't be able to claim on the insurance for normal wear and tear, only if a gale blows some tiles off and the water gets in, but then you'd be expected to put it right before all your wood rotted away.

 

[Flyfisher]

Agreed. And if a gale did blow off all your tiles exposing a whole load of rotted timbers that needed repairing/replacement, I wouldn't expect the insurance would cover the repairs to the rotten woodwork, only for the damage caused directly by the wind. In general, insurance won't cover any 'betterment' and will only cover replacement/rebuild to the condition immediately before the insured damage occurred.

 

[Lime]

I would expect problems of condensation if the loft hatch was a poor fit and it opened into the bathroom.
Don't get too worried just get the hatch sorted and sealed.

 

[charlie-ia]

we recently insulated our loft and have noticed condensation on the cold water tank. we didnt insulate under the tank. it doesnt look like there was much condensation before we insulated. but it looks like a problem now.
what can we do about it?
the tank rests on wooden batons across the joists, with a plasterboard ceiling below.

 

[Lime]

charlie-ia the tank needs to be sealed and insulated too otherwise you will get caught out in freezing weather.
If it is an old flat-sided galvanised tank then what some people do is box it in using Kingspan.

 

[Nemesis]

But not under it!

 

[maggie73]

this might be another daft question, but given that my loft hatch is in the bathroom, should i leave the door open when showering/bathing, if possible? I do put on the extractor, but sometimes open the bedroom windows to let the moisture out. we dont have problems with condensation anywhere else in the house really, apart from gathering on single glazed sash windows.
also got some foam seal for the hatch, which my partner has declared to be c***. the hatch is made of about 8mm plywood and actually is fairly snug if put down properly, but I suppose moisture laden air could easily work its way round the edges. my partner put the foam round the edges and now it wont fit. should i just put a well fitted vapour barrier and insulation on the back of the hatch and forget about it?

 

[Penners]

should i leave the door open when showering/bathing, if possible? I do put on the extractor, but sometimes open the bedroom windows to let the moisture out

Remember that if you have an extractor in your bathroom, trying to draw the air out, it will only work effectively if there's somewhere else that the air can get in. This is often provided by leaving a bit of a gap under the bathroom door.