Internal walls exposed to attic. Is it ok to seal the gap?

jackofalltrades

As you can see from the above pictures the internal walls that attach to the blockwork are exposed to the attic.

So the cold air from the attic can get behind the walls of at least the 1st floor rooms.

Am I right in thinking that this is bad for heating/a possible fire hazard and that I should seal it up?

If so whats the best way to do it? I was thinking airtight expanding foam or tape.

Thanks in advance for any help.

MicktheMan

Use compressed earthwool (fibre insulation) packed tightly between the blockwork and timber joist.

10-10-20

https://www.boards.ie/discussion/comment/123168517#Comment_123168517

What do you think of the fireproof expanding foam? I think it might be an easier solution to apply, but it won't be as moisture permeable as earthwool, if that's a concern.

https://brooksonline.ie/arc-b1-fire-rated-gun-grade-expanding-foam-up4703

MicktheMan

https://www.boards.ie/discussion/comment/123169163#Comment_123169163

I don't have any experience with that particular product so can't really comment. But in general, I view expanding foams as gap fillers, not sealers and I note in the blurb there is a certain amount of surface prep required before application so is this practical in a confined and dusty space such as an attic. Also, I believe there is a risk of a chemical reaction with electrical cables and these are often present in these spaces too.

Yellow_Fern

Compressed rockwool or expanding foam will make a large improvement but let me clear, assuming there is no nidden a/t membrane, what you see is a major defect in terms of home energy efficiency and rockwool or foam at rim will only reduce the harm, not eliminate it. To totally eliminate you prob need to take down the plasterboard.

standardg60

https://www.boards.ie/discussion/comment/123173542#Comment_123173542

What is the standard construction in this regard? Is the inner leaf not classed as being a warm wall free to absorb heat and hold it? I don't see the gap being a major source of heat loss versus that through the leaf itself.

Deagol

Do not use expanding foam in that space. Good chance that it will expand down and pop the plasterboard out. I've heard a few stories of people not realising how much force that stuff can exert behind plasterboard.

If it was me, I'd follow the advise of using the insulation pushed down. Pretty sure it's not a firehazard, the plasterboard is fire resistant, any fire that would spread down would be behind the plasterboard.

jackofalltrades

Thanks for all the comments guys, really appreciate it.

I've a can of airtight expansion foam that's electrical wire safe so I'll test to see if I can make that stick to the wall without falling down. I'd use rockwool but I'd say it could be tricky to pack it in properly in some places, I also have airtight tape that should be wide enough for the gap too.

10-10-20

https://www.boards.ie/discussion/comment/123175833#Comment_123175833

If a small amount of it falls down then it won't be an issue. It's only a problem if the unexpanded foam gets into an area where it can't further expand into a void, it then pushes outwards with great force. Trust me, I know from experience. About 15 years ago I 'expanded' the reveal off a doorway - came out around 4cms with horrible plasterboard cracking sounds and such. It was very solid and well insulated after that… 😝

Yellow_Fern

https://www.boards.ie/discussion/comment/123175179#Comment_123175179

I think the house is leaking heat into the attic. The inner block leaf would seal to the ceiling or you might have some kind of membrane doing the same role. The plasterboard will have many perforations and will not be a great seal. Aslo, the block has a lot of mass which is useful and not being exploited fully as it appears.