Airtightness Query

creedp · 18-11-2010 1:21pm #1

I know there have been many threads on this issue before but I'm really confused at present. My builder is installing a false ceiling under hollowcore. The hollowcore was wrapped in a sheet of DPM but he doesn't think its necessary to tape this to the wall. Neither has he scratch coated the wall (Quinnlite block) under the bison down below the false ceiling. Is this an absolute requirement?

At present he is proposing to put up false ceiling creating a 150mm void using timber battons. In this void runs MHRV ducts and electric cable. He is proposing ot fill the void with rockroll. He will then tape the batton along the perimeter wall to the blockwork and install a 25mm insulated plaster board which will be skimmed. I think the plasterer will also use a drylining tape to take the plaster board joins. Will this detail give me an acceptable airtightness result. Or should I insist on taping the DPM to the blockwork and scratch coating the entire block wall?

All views will be greately appreciated I assure you!

Wavehopper · 18-11-2010 2:44pm

Hi Creedp,
I've just finished this part of air-tightness on my own build and this is how it was done:

I have open ends hollow-core wrapped in air-tightness membrane that has been covered with expanding metal on inner leaf of external walls.

Membrane has then been covered with sand/cement layer from top of slabs down about 9" that thins out as it goes down (this is allow scratch coat to be done up to ceiling level and not have a thick sand/cement coat already to cover).

The suspended ceiling has been erected after this and plasterboards fixed. All walls will get sand/cement scratch coat and then skim over the coming week.

There is no plan to fill in service void (where HRV, electrical wiring, waste-pipes are running) with insulation.

I'm not saying that this is the best and only way to do this but hope it helps

creedp · 18-11-2010 7:00pm

Thanks Wavehopper

Your detail is what I wanted but unfortunately the battons for the ceiling have gone up without scratch coating the wall. The builder did tape the hollowcore to the block wall however. He was also suggesting he would tape the batton adjacent to the perimeter wall to the block below but I don't see the advantage to this as the ceiling void will be open to the room below due to downlighters

I was interested in seeing that you do not plan to insulate the ceiling void. Is this because you think there will be no significan heat loss in the void or maybe it the thermal mass of the hollowcore is beneficial? I suppose also the ceiling will be adorned with downlighters so these will leak air and heat into the void irrespective if you insulate it or not. Anyone have any views on this issue?

Peanut81 · 03-12-2010 9:12pm

Hey Guys,

Would you have any details / drawings on wher joists run into a cavity wall and how to make the area airtight??? Thanks.

Saddleview · 18-03-2019 11:20am

[QUOTE=Would you have any details / drawings on wher joists run into a cavity wall and how to make the area airtight??? Thanks.[/QUOTE]

Long shot here with the amount of time that has gone by but did you ever get an answer to this question?

BryanF · 18-03-2019 11:33am

dont dig up old threads, if you have a question start a thread

Airtightness Query

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