Fitting Insulation to solid brick walls

LUHG1878

Hi,

I'm planning to insulate our front bedroom, which has two external solid brick walls. I'm going to strip off the lath & plaster and skirting etc over the course of the next few weeks. (not looking forward to that! )

After that, I have two options;

1) fit insulated plasterboard, instructions online suggest this should be done using adhesive and then mechanical fixings.

2) stud line the wall with 2x3 timber, fit PIR insulation boards, and then fit plasterboard on top. (or insulated plasterboard)

I'm leaning towards option 2, mainly because I think this will be easier for me to fit, albeit it might take longer, and it will be easier to hide cables, fit radiator supports etc, but have some questions;

1) Once I expose the brickwork, and brush it off any debris, do I need to treat the brickwork before fitting the insulation?

2) Should I leave an air gap between the brick and the insulation board, to allow ventilation to the brickwork?

3) I'm not concerned about sacrificing on the room size, it's only two walls, and the room is large at 4.5m x 4.8m, so is it a case of fitting the thickest insulation boards I can afford, would 50mm do, or would the gain between a 50mm and a 70mm be noticeable? I only plan to do this once, so would rather pay a bit more now on the insulation if it's going to make a difference.

4) i'm also going to fit a lowered ceiling. I only plan to lower it by around 200mm, current ceiling is >3m, but it's lath & plaster, with plaster cornice, and I don't want to go to the hassle of removing all that as well. Anyway, my question is, should I fit insulation board between the new ceiling joists? (the loft above is already insulated, so I guess i'm concerned about having an unvented space between. Not sure if I should be preventing hot room air passing to the space, of going with no insulation to allow the space to breath through the plasterboard?

Any advice would be greatly appreciated.

FreeBear

LUHG1878 wrote: »

2) stud line the wall with 2x3 timber, fit PIR insulation boards, and then fit plasterboard on top. (or insulated plasterboard)

Third option - Warm batten. With this, you fix (for example) 50mm thick PIR boards across the full width/height of the walls. Then place 2x1 battens on top of the boards and mechanically fix these to the brickwork. The space between the battens is then filled with 25mm PIR board and then plasterboard fixed to the battens.

Advantages - No cold bridging where the battens are. No need to put a DPM between the timber & wall. Savings on timber.

chappers

FreeBear wrote: »

Third option - Warm batten. With this, you fix (for example) 50mm thick PIR boards across the full width/height of the walls. Then place 2x1 battens on top of the boards and mechanically fix these to the brickwork. The space between the battens is then filled with 25mm PIR board and then plasterboard fixed to the battens.

Advantages - No cold bridging where the battens are. No need to put a DPM between the timber & wall. Savings on timber.

That's what I would do, either with or without the extra 25mm.
With regards to your question re, the amount of insulation. the more the merrier. If the room is currently feeling noticeably colder towards those walls, you will definitely feel the difference by adding 50mm, I very much doubt you will physically be able to notice the difference between 50 and 70mm

Grenage

I left a gap between the battens and the wall, filled with 100mm celotex, covered with 25mm PIR, and used foil-backed plasterboard.

jackyann

I very much recommend this stuff: https://www.fermacell.co.uk/
It is both heavy and expensive, but fantastic insulation, and you don't need to plaster. I priced it out and thought it worthwhile.

Regarding the ceiling, someone may be along who knows more than I do about current building regs, but we were not allowed to lower a ceiling because of the fire hazard. This was so long ago that I can't remember any details, but would suggest checking - apologies if you have already.

LUHG1878

Thanks for comments folks, much appreciated!

@Freebear - I had read about this option, but kinda dismissed it as I thought if I was going to fix the insulation to the wall, then why not just use the insulated plasterboard, then I wouldn't need any timber?

@Chappers - if you don't think there will be a noticeable gain between say a 50mm and 70mm board then i'll probably just go with the 50mm as I think the difference in cost is around £15 per board, and i'll need at least 12.

@Garange - I take it you noticed a big difference once the insulation was fitted? 125mm is a lot of insulation, were you recommended to use that much for a reason? What was the reason behind leaving the gap?

I'm just conscience about airflow and letting the brick breath, as i've read lots of stories about insulation causing problems in older houses, and don't want to go through this and end up making matters worse.

LUHG1878

Hi Jackyann, i'll look into the Fermacell, never heard of it before, thanks.

I also hadn't even considered building regs. Even when lowered the ceiling would be higher than most modern homes, so hopefully it won't be an issue, I guess I better check this too!

Many thanks.

jackyann

As I recall, and we are talking 40 years ago, the issue was of fire spreading in that space. I do know there had been some issues with large public buildings. I think it may have been ' playing safe 'at the time, and may be different now.
I always found Building Inspectors very helpful, useful to talk things over with. But I have not done any work on the house for some years now.

Grenage

LUHG1878 wrote: »

@Garange - I take it you noticed a big difference once the insulation was fitted? 125mm is a lot of insulation, were you recommended to use that much for a reason? What was the reason behind leaving the gap?

Oh God yes, the difference was amazing, and that was only dealing with a large cupboard in the kitchen. Modern regs for insulation are quite high, and I could spare the space.

I left the gap simply to avoid potential moisture from tracking across to the stud and insulation - not that'd ever had water ingress.

FreeBear

LUHG1878 wrote: »

i'll look into the Fermacell, never heard of it before

I also hadn't even considered building regs.

On the subject of building regs - As you are upgrading/adding a thermal element to more than 25% of a wall, you should be aiming for compliance with Part L (I think that is the right section...).

When I did some rough fag packet calculations for the solid brick walls of my house, I cam up with around 65-75mm of PIR insulation being needed. PIR foam boards have a lamda value of around 0.022W/mK where as Fermocel is quoted at 0.32W/mK - You are going to need a very thick layer of the latter to get close to building regs requirements..

jackyann

That is interesting, as I had thought Fermacell exceeded requirements - it certainly did when we used it 5 years ago. However, it does seem that OP needs a chat with the local Building Inspector - I hope they are as nice and helpful as the ones I have dealt with.
If you get a chance to update us, I would be interested