Cold Draught in Loft Extension

[Eremos]

We've recently had a full loft extension with dormer conversion. As it was finished in spring we haven't had a chance to see what it is like in cold weather!

At the moment there seems to be a cold draught in both the corners of the dormer conversion. I've lifted the carpets, sealed any gaps between the floorboard and skirting board, put the carpet back down and put some draught proof strips down.

The draught is still there! Any ideas if there could be another problem? Could there be a problem outside? As no water is leaking, I can't understand if it is a problem inside or outside.

The loft meets all building regs, etc and was passed without a problem.

Thanks in advance,

Arif

 

[Penners]

Your problem is that any roof space should be well ventilated, in order to avoid condensation, which can rot the timbers. So I suspect that your roof is well ventilated, but that whoever did your loft conversion failed to isolate the loft room from the ventilation!

All you can do is keep on hunting for cracks, gaps and so on. You'll find it easier to detect these if you wet your hand - the draught will cool that area of your hand noticeably, and help you identify the exact source.

 

[Eremos]

Thanks for this. Sounds logical!

When you say that my loft is well ventilated do you mean that the gaps are providing the insulation?

Also is there any other way to seal the gaps between the skirting board and floor? There is one corner where there is definitely a draught (your "wet hand" test proves it!) but I can't seem to find where the gap is.

 

[Penners]

When you say that my loft is well ventilated do you mean that the gaps are providing the insulation?

Not sure I understand you there.

 

[Eremos]

Sorry! I meant to say are the gaps providing the ventilation?

How should the ventilation have been designed? My understanding was that lagging between the plasterboard with vapour check was enough ventilation. Is there anything that can be done to rectify the problem?

 

[GK]

To add to what Penners is saying, the roof space, ie not the bit you live in but the void formed by the loft conversion, should be well ventilated but that should already be taken care of - often by gaps in the soffit with plastic mesh over. It shouldn't be ventilated to the habitable part so if there are any gaps you can safely block them up.

The vapour check is a line of defence to stop moisture entering the cold roof void where it may condense.

There ought not to be any gaps into the roof void but you may have suffered some timber shrinkage and less than perfect workmanship.

You say the draughts are in the corners of the dormer conversion. You mean, you have a flat roofed window broken out of the roof? (not literally broken!)

Sounds a bit like you may have draughts caused by cold bridging - uninsulated bits of the conversion causing cold spots on the wall surface. Do you know if the insulation was dressed fully around the dormer part? If there are some bits missed off this could cause draughts -but even if not the thickness of insulation around a dormer window and the cheeks might be less than the rest of the construction where there's loads of space.

I'd get in there and see what the insulation is like.

 

[Eremos]

Hi GK,

Thanks for the detailed explanation. Having looked at the soffits when the builders were here, this has been taken care of well. So I will look into blocking up any other gaps.

Whats the best way to deal with any gaps in the roof void? I may have found out the reason why I am suddenly getting the problem. About a week ago I found some water leaking in through one side of the dormer. I called the builders back and they found that a small portion of the old roof files which we unfelted, etc moved slightly letting the in the water. They promptly replaced all the tiles with new interlocking ones. It was then (when I had the carpet and underlay rolled up on one side of the dormer) that I first noticed a draft. Since then I have noticed that it is in in the other side of the dormer as well.

The draughts are mainly in the corners of the dormer a few inches off the floor. If I chech the dormer higher up there is no draught- it seems completely at floor level. Not sure what a flat roofed window is! I have two "normal" windows in the new dormer. I assume that this is the same?

When the loft was being completed the insulation was dressed all the way around as far as I can remember. Just to clarify I assume you are asking was the entire back of the house (i.e. the new dormer wall where the windows are) completely insulated?

Is there any way of dealing with cold bridging without having to break into the walls, etc? My understanding of the insulation thickness was that it met the building regs.

Any advice would be much appreciated!

regards

Arif

 

[GK]

Not sure what you mean by gaps in the roof void - you mean leaks?

Flat roofed window -I meant flat roofed dormer but maybe yours is pitched where it comes out of the main roof.

Yes, the entire construction should be insulated, including the dormer cheeks and the vertical bit of wall below the dormer window. I hope we understand the same thing by dormer - I mean the part of the loft conversion that forms the area where the roof window is.

You don't think it's just a movement of cooler air around the glazing?

If it was my house I would have requested a removeable panel so that I could crawl into the roof void. If you can't get in, you can't really identify and fix the problem.

Another possibility is that the insulation was fitted correctly but has become saturated and useless with water ingress.

 

[Eremos]

Yes I meant the leaks.

My loft conversion has a flat roofed dormer that comes out of the main roof. I think that we mean the same thing when we say dormer. Just to complicate things I have a Velux on the front part of the conversion.

It could possibly be movement of cooler air around the glazing, but is it strange that the cooler air is located at floor level, a 2.5 feet below the flat roofed window? If not, then this could be one answer.

Also the dormer is on the north facing side of the house which has draughts on the ground and first floors. So perhaps this could be another answer?

INot sure how I could have had a removeable panel. The only place that this could be done is on the opposite side of the house that does not have the dormer. As we built all the way down into the eaves there is very little space left.

I'm not sure that the water could be problem. Not that much water managed to get in during the roof tile problem. Is there any way of replacing parts of the insulation from the outside (i.e pulling up the roof tiles?)

 

[GK]

OK, I understand the void isn't very big now so a way in would be of little use.

With regard to the physics of air movement- that's beyond me - I'll have to leave it to your judgment as to what might be causing the draughts. If you think my theory is worth checking out, then you could take off some tiles, cut back the felt and battens and get in and replace it all afterwards. You would need more felt than you started with to overlap where you cut.

It's really a job for a roofer or determined (and knowledgeable) diy-er. Seems a last resort but if the problem is in there and it's spoiling the comfort of your extension, well, it should be fixed. Try and absolutely rule out just cooler air in the dormer area first though. As I said, even correctly insulated, the dormer area won't be quite as efficient as the rest- there often just isn't the space at the cheeks to get the same thickness. If you've got a triangle of wall which is effectively outside wall, not against the roof void, it's bound to be cooler.

 

[Penners]

Eremos - are you sure that these draughts at floor level aren't simply coming in under the skirting board? I imagine your attic room walls are plasterboard, and if a gap was left at the bottom of the plasterboard - and not fully covered by the skirting - this could cause draughts.

If you suspect that this is the case, and provided the gaps are only a few mm, you can block them with ordinary decorator's caulk (mastic). If they're wider, then you may have to stuff them with something springy like carpet underlay.

Just one other idea. If the draughts aren't coming under the skirting, could they be coming in under a poorly sealed in window sill? Remember that cold air falls and warm air rises, so draughts from there could just drop to the floor.

Your wet hand should help you trace the source.

 

[Eremos]

Hi GK, Penners,

Thanks for all your advice. I've pulled up one side of the carpet today and found some rather large gaps between the skirting board and floor! It looks as if this was the draught that was circulating at floor level. I've put some expanding foam to seal it. At the moment it seems as if it has done the trick. As soon as I know that it works wil do the second room to see if that solves the problem.

I've learnt so much about the loft in the last day or so from you guys!

Thanks again,

Arif

 

[Nemesis]

Oh not expanding foam - nasty stuff, which is pretty hard to get rid of!

 

[Eremos]

Tell me about it- its all over my hands! But the good news is that the draught seems to have disappeared. I will check again in the morning to be sure.

 

[Penners]

its all over my hands!

If you're going to use it again, invest in some latex or vinyl gloves. It'll take a week of scrubbing to get it off your hands.