problem with condensation in loft insulation

[jonathan.tong]

Our house has about 4" original loft insulation between the joists (some yellow fibre glass stuff) and about 6-8" top-up insulation laid perpendicular to the original. The extra stuff is the Pink Panther white fibre glass (?) inside a perforated pink plastic bag.

The problem is that condensation is building up inside the plastic sheeting and saturating the white insulation, there doesn't appear to be any dampness underneath. The loft appears to be reasonably ventilated, certainly I can see daylight all around the eaves.

Short of debagging the Pink Panther stuff which is probably a nasty job, is there anything else I should consider?

Thanks!

Jonathan

[The Natural Philosopher]

That is really quite unusual..

All I can think of is that somehow there are gaps into the loft from inside the house.

So moist air is entering..

You might do worse than tack a sheet of DPM over all the joits and put the Pink Panther back on top.

[Lobster]

Yes, as the Pink Panther stuff is in a perforated bag that would make sense. My only other thought is was the stuff damp when it went in? I do remember once buying a pack of insulation from one of the DIY sheds, getting it home and finding that it had obviously been left out in the rain at some point.

David

[jonathan.tong]

I'm pretty certain that all the stuff was dry when I put it in. I'll try and work out if the damp/wet bits are above anything obvious.

I'm assuming a DPM is the same speak as a vapour barrier? I'm loath to do this as it would entail lifting ALL the insulation (Pink Panther + original).....

[The Natural Philosopher]

No need to lift the original.

Just put a seal between it and the other..

The original will stay warm enough not to condense..

[adder1969]

If there's condensation already between the old and the new how will putting an impervious sheet inbetween solve the problem?

[The Natural Philosopher]

Ther isn't. There is condensation IN the new.

[Dave Baker]

Is there any moisture on the underside of the roofing felt? I didn't venture into my loft for a couple of years and when I did I found water literally dripping off the roof felt and all the stuff stored up there was going mouldy. Turned out the boiler was pumping over into the loft tank which was therefore full of hot water all the time. The evaporation off this was making the whole loft damp. I fixed the pumping over problem and after a short while it was dry as a bone up there again.

[manatbandq]

Rather than debagging it, just rip each bag open on the top to allow any trapped moisture to escape.

Do check, however, that you haven't got serious leaks from, say, the bathroom into the loft and fix those too.

MBQ

[Andy Dingley]

Insulation always needs a moisture barrier on the _warm_ side. Usually the ceiling materials are adequate for this, sometimes you might need to add polythene. If the moisture is coming from beneath, check for ceiling cracks or leaks. Also check for roofspace damp, such as rain penetration or Dave's boiling boiler.

Humans are warm and wet. The outside is cold. Inside the insulation is a gradual temperature gradient from warm to cold and this _will_ cross the condensation temperature for typical domestic humidity. If you don't keep the insulation free of airborne humidity, then somewhere inside will be the plaen where it condenses. For this reason the moisture barrier goes warm side, not cold side.

[Tony Williams]

I was up in a relative's loft some time ago and noticed beams of light, shining up to the roof.

They'd had an ensuite shower room built into one of the bedrooms and the beams of light were where the lecky had pulled away the insulation and cut away the ceiling to (poorly) mount electrical fittings.

Ensuite shower? Air gaps into the roof? I'm going to have to go back there at some time, to seal the gaps and replace the insulation.

[Lobster]

Yebbut if it's being caused by moist air entering the loft from the house (your suggestion) then any new moist air coming up from below will be stopped by the new vapour barrier and soak the old insulation instead...

David

[The Natural Philosopher]

which will be warm enough not to get wet.

[jonathan.tong]

So this weekend I think I'm going up in the loft and looking for any obvious patterns between the condensation-in-the-pink-panther and the rooms below (and also checking for gaps in ceilings). I suspect I'm going to take the option of opening the tops of the pink panther bags because that seems to be less effort than installing a vapour barrier

*somewhere*. J

[Jonathan Tong]

I finally found the time to go up in the loft (what with having a toddler and a baby). The majority of the Pink Panther has no condensation or mould inside it so I decided to rip open the top of the sections that did and tuck the extra plastic sheeting down the sides - the tops are now completely open to the atmosphere. Unsuprisingly to those in the know, the open sections are over the bathroom and over the airing cupboard (that houses the hot water tank).

There are no obvious holes in the ceiling of the bathroom except for the light fitting so I guess the moist air is being transported through the plasterboard ceiling as a whole?