Draft behind plasterboard in new extension

[Splamone]

I have plenty of air flow below the tiles on the roof, which is important to prevent condensation. If you have a draft blowing through your spotlights then I guess you don’t have any insulation around them. I think you are supposed to create a box or hood for the lights and insulate around that if you can. If it’s not insulated properly then you’ll get a lot of cold air coming through the lights. This will also suck some warm air out of your room. As for the draft through the skirting. Any idea if it’s coming from above or below? If above then you could drill holes and squirt in some expanding foam near the top of the walls. That can really work. If it’s coming from the floor then foam around where the floor meets the wall would help (behind the skirting).

 

[M Forbes]

Thanks for the advice. It’s not too bad at the minute but let’s wait and see when the snow comes!

 

[CoxHQ]

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!

Hi Splamone, I have the same issue with cold air coming in behind the plasterboard. How far apart did you drill your holes for the expanding foam? And did you have any issues doing it? I was concerned about forcing the boards off of the wall but as you said in a previous post there should be room down the wall for expansion. So I’m thinking I can go to town with the foam (I’ve bought a gun), the more the merrier?

 

[Leofric]

Have Building Control been inspecting the work , what do they have to say ? There are rules for new building work regarding air tightness and sealing joints .

 

[Splamone]

I had no issues with foam pushing out the boards. I drilled all the holes first, about 3-4 inches apart, and just squirted in some foam. It’s guesswork how much but, with other holes predrilled, the foam would come out of one of those if it had to. I found that the corners of the floor were an issue too and air was coming up where the floor wasn’t sealed due to overlapping dpm. Spraying foam in the corners behind the skirting helped more than the ceiling! I don’t feel a breeze coming out of the holes now but I’m sure there is still some air leaking behind. Still, much better than it was and only cost me a couple of bottles of foam. I didn’t need a gun in the end as it didn’t have to be that precise.

As for building control, they checked that insulation and building materials etc were correct but didn’t do any checks on air tightness. They can’t witness everything that’s going on anyway as they are not there during the build so I’m sure loads of bits were missed that haven’t been done properly. Edge insulation for the screed being one! Shame they didn’t fit any of that, especially as I have under floor heating! Hoping that the screed not going right up to the wall and preventing drafts will actually be a good thing and prevent issues down the line with expansion! Not particularly happy with the quality and knowledge of the builders!

 

[CoxHQ]

Thanks for the advice. I’ll do the same for the walls but hopefully the floor will be fine. I asked them to seal around the edges when they put it in, I just didn’t think to ask about the ceiling and walls.

Building control signed everything off for me too. It’s a shame as it’s an easy step for the builders to have done at the time.

 

[Leofric]

Yes, building control only inspect the work on site at certain stages. You need a good builder/site manager to inspect the work throughout the job.

 

[JacobZo]

Hi Everyone, I'm having a similar issue in a retro fitted lightweight solid roof on my conservatory.

The existing structure has a dwarf wall adjacent to the neighbor which has been built up to full height (block and brick with cavity insulation) then dot and dab boarded and skimmed. I seem to be getting a few issues however:
i) a draft coming down behind the boards (no skirting on yet). The roof was insulated properly and has insulated plasterboards on it too, but i never saw what detail they did to seal at the connection with the wall, i feel like this was just left as a void.
ii) moisture forming on the currently tied floor (visible droplets and grout between tiles is wet) but only along part of the edge of the room. This never happened before and I've done the upside down glass test to check its not damp coming from floor (anyway, the DPC in the foundation hasn't been touched so this should all be fine).

The problem with the damp is it caused the plasterboard to get slightly damp at the base and form mold. It went through a couple of weeks of drying out fine then getting wet again. I found if I laid an insulation board on the floor the floor didn't get wet (the board also blocked up mst of the gap at the base of the plasterboard), which makes me think it might be condensation forming, with the cold tile floor acting as the dew point between the cold draft and the warm house (the conservatory doors are now left open tot he house).

The plan is to eventually lay 20mm insulation boards directly onto the ties, then electric under floor heating mats and then laminate on top. The doors between conservatory and house will be removed so will be warm all year round.

Any help would be greatly appreciated!? Do you reckon trying the drill hole and expanding foam at the top of the wall might help?