Draft behind plasterboard in new extension

[Splamone]

This pic shows the kitchen ceiling. You can see the gap left at the top left of the image. No wonder there is a draft! Have a feeling I will have to drill and foam the top of that wall and hope that works!

 

[Ian H]

There’s no insulation under the rafters.

 

[Splamone]

There’s no insulation under the rafters.

There is! They put 100mm between and about 25mm across them before plasterboarding. Just can see it in the pics as the board hadn’t be cut round the window in that pic. Definitely there though! However, celotex is not the ideal insulation to prevent drafts as it’ll never be cut to perfection.

 

[Ian H]

Oh right sorry, couldn’t see it but I can see the boards aren’t cut now you mention it.

I think your builder has let you down. He should have foamed then taped the joints between the 100mm and the rafters and then foamed and taped all the gaps in the 25mm (which I also thought should have been at least 50mm).

Are the walls plastered now or still just boarded?

 

[Splamone]

Hi, may have been 50mm! Can’t remember now. I don’t think anything was taped either but they seemed to be rough for most things. I think I was getting on their nerves by asking them to do everything properly. Ubfortunately I wasn’t aware of the need to make it air tight for dot and dab otherwise I would have been on it. Unfortunately it’s all boarded and plastered now. I’ve sanded down the plaster in the lounge (don’t get me started there!) but not painted yet so can attempt repairs. I wondered if I could slide up the roof tiles and get to it from above but that might not be possible as the tiles have been mortared at the end now.

It’s been a hard conversation with the builders as they tell me that it’s impossible that there is a draft since they put the celitex there. Either that or they blame me for wanting cables in certain places. Complete rubbish of course! I’ve pretty much had it with that guy as he treats any comments as a personal attack on his ability.

I think I’m going to have to fix this myself as I’m not confident they will do it properly. It’s a shame my kitchen is already in (and very drafty!) and the floor is being laid in a couple of days to finish it off. I haven’t painted the top coat yet so can drill and fill holes to squirt foam in. Not sure how easy that will be but I assume it’s my only option without ripping the kitchen out!

Any advice on how to do this properly first go and not damage anything? I assume I need to be careful not to squirt too much in but just enough. I guess there’ll be room for expansion down the wall.

The lounge is a pretty big job to do and I’m not 100% sure that filling the top of the wall will be enough. Might have to do the diagonals too and maybe around the bifolds? I know that the walls are filled in the cavity but the slightest gap could cause a draft. Dry disappointed by it all and not what I expected I’d have to deal with.

 

[Ian H]

If you do drill the holes and foam it i’d recommend you get a foam gun, they are much much more controllable that the cans with a nozzle on.

Sounds like you’ve had a tough time with it

 

[Splamone]

If you do drill the holes and foam it i’d recommend you get a foam gun, they are much much more controllable that the cans with a nozzle on.

Sounds like you’ve had a tough time with it

Already bought some no nonsense foam that I was going to use on the skirting and other holes but can get a proper gun and can if that’ll help do a good job! Anything in particular you suggest or is any gun and foam fine to use? Could get something from amazon or screwfix/toolstation. Thanks!

 

[garyo]

celotex is not the ideal insulation to prevent drafts as it’ll never be cut to perfection.

It seems to be the case with insulation materials that specification (thickness) is one thing, and then attention to detail in the fittng is another. With PIR that can really bite, as you've found. At least you don't have it in your walls too!

but can get a proper gun and can if that’ll help do a good job!

The problem is you're doing it blind so you never really know how much you're pumping in or how far it's going. I can't see what you access looks like, but if it was me I'd really think about lifting a couple of rows of tiles and going in through the roof.... all possibly much easier in the end even if it feels more daunting to you compared to filling and sanding 83 drill holes.

 

[Munzy]

Already bought some no nonsense foam that I was going to use on the skirting and other holes but can get a proper gun and can if that’ll help do a good job! Anything in particular you suggest or is any gun and foam fine to use? Could get something from amazon or screwfix/toolstation. Thanks!

https://www.screwfix.com/p/soudal-window-door-installation-foam-kit-gun-grade/1740h

This will give you plenty of foam, the applicator gun and the all important cleaner!

 

[pilsbury]

If you were going to go the hole method with expanding foam you’ve got a lot of holes to sand and fill so I’d go the full hog and avoid the “doing it blind” by drilling twice as many holes and foaming every other one making sure foam popped out the alternate ones. That way you know you’ve made the full fill. Then buy shares in polyfilla.

 

[Splamone]

I’ve filled so many holes in the last 5 years with very dodgy walls that I’m not bothered by the hole filling really. I had a quick check if I could access the void from above and noticed that there is a 1-2inch gap under the first row of tiles before the Facia board starts. Another issue to deal with I’m sure! The first row of tiles are nailed but the second row aren’t and can be easily moved. I suppose it’s an option to go in from above (pulling the celitex board up to get underneath) and I’ll check with the builder before doing that. However, the hole foaming is something I can do easily myself and not rely on my builder messing it up! I’m sure that will work just fine but it’s a bit of a mess. I’m hopefull that this fix the issue!

 

[Splamone]

Had the floor latexes today ready for the flooring and could see the draft from the walls drying the latex out! Not even breezy today at all! You can see the light areas on the pic.

 

[M Forbes]

I've just had an orangery added to the house and I'm having a similar problem - there's a draft coming from under the skirtings and through the recessed spotlights. Its not a big draft, you can only feel it with your hand right up against them. Both the roof and wall cavity were insulated but externally they have added vents just under the flat part of the roof behind the guttering. I'm guessing the roof space needs to breathe?

 

[Splamone]

My problem was with the plaster boards not being sealed at the top and bottom. I drilled a load of holes an inch or so from the ceiling and filled with foam. This helped but I then found that there were gaps at the edge of the screed blowing air from below the house! This is mainly an issue in the corners where the screed hasn’t sealed right against the wall. Will be filling these holes with foam too and that should make a big difference!

 

[M Forbes]

My plasterboard was attached to the brickwork via studs (I think) and I was more concerned with the cold air getting in there and the roof in the first place. I was looking for the source of the drafts when I spotted the gaps behind the guttering. However, when I took the guttering down to fill these with foam I realised that the gaps were in fact vents. I know people who have had the fascias overboarded with uPvc and had condensation problems because they didn't allow for sufficient ventilation. I decided to just leave it. The drafts aren't too bad and we probably lose as much heat through the glass anyway.