Insulating solid wall

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Hi

I want to insulate a solid brick wall and it’s been suggested I use insulation backed plasterboard and glue it on.

This is fine, if you all agree, but the wall isn’t straight, it’s about 2 inches out floor to ceiling. The new plasterboard would therefore be the same, so it would be great to resolve this as well.

I’ve been told using batons screwed to the wall isn’t a good idea as it creates a vapour bridge?

So what options are there? Build a new thin stud wall in front of the brick wall, without contact between the two, other than perhaps glue?

All suggestions are welcome.
 
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Depending on the work, building regulations might apply and require the thermal insulation of the element to be upgraded to a reasonable standard.

If you speak to the insulation manufacturer they might do you a U-Value and condensation risk calculation for free for you to use as a basis.

Once you have that you can decide on the best construction method; an example from the Kingspan Kooltherm 118 PDFs; mechanically fixed insulated plasterboard onto 25 x 47 mm treated softwood timber battens (with DPC strip behind the battens) that you could then pack out.

To note, not all insulated plasterboard is made equal - they all have varying levels of (or no dedicated) vapour resistance despite saying they are vapour resistant or include a vapor resistance layer - the suppliers tend to not have this information to hand. So check!
 
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You can use battens no problem. Ignore what you've been told. This will potentially allow for better insulation values.

Or use insulated plasterboard and use thinner dabs at the top than the bottom to allow the boards to be fitted vertical.
 
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Thank you Swwils and Woody.

Which would you do?

In my mind another reason to use batons is being able to screw through into the brick, rather than glueing the insulated boards to the existing plaster, which surely relies on this still being solid (which it does feel like it is).

With condensation, are we worried about it being trapped in the wall (and presumably mould growing etc) or affecting the plasterboard (in which case moisture resistant board could be used I guess)?

I’m a competent DIYer but don’t want to get this wrong if condensation is an issue.

For info, the house is rendered on the outside if that makes a difference.

Thanks
 

JP_

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I stick 50mm kingspan boards to the wall with Everbuild dry fix pink foam, then stick plasterboard on this with same foam. Done 5 rooms like this over 3 years, and nothing has fallen off yet!
I've posted here about it, but cannot find my old posts now. Reasons for this approach:
  • easier to work with than insulated plasterboard
  • better vapour barrier
  • more insulation for the price (or cheaper)
Here's a photo - I also did the floor. No more mould, no need to have heating on at night (even when below freezing outside).

IMG_20180827_152356895.jpg


and another bedroom, with a window

IMG_20190125_103857820.jpg
 
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In theory, if Part-L1B applies (25% more wall is being renovated), the minimum U-Value that the improved wall should achieve is 0.30 W/m2K. This can be achieved by Solid Wall + 70mm PIR + Plasterboard. This is the thinnest possible for internal solid wall insulation to hit the regulation (if for whatever reason you are being challenged).
 
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I stick 50mm kingspan boards to the wall with Everbuild dry fix pink foam, then stick plasterboard on this with same foam. Done 5 rooms like this over 3 years, and nothing has fallen off yet!
I've posted here about it, but cannot find my old posts now. Reasons for this approach:
  • easier to work with than insulated plasterboard
  • better vapour barrier
  • more insulation for the price (or cheaper)
Here's a photo - I also did the floor. No more mould, no need to have heating on at night (even when below freezing outside).

View attachment 221878

and another bedroom, with a window

View attachment 221879

Thanks, looks good. I assume the plasterboard sticks to the foil on the insulation ok? Or do you peel it off first?
 
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There needs to be mechanical fixing, ie screws. And the problem with screwing through to the wall is the risk of pattern staining on the surface due to the screwheads and cold bridge.

I have a post somewhere with how to batten. I'll look later.
 
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There needs to be mechanical fixing, ie screws. And the problem with screwing through to the wall is the risk of pattern staining on the surface due to the screwheads and cold bridge.

I have a post somewhere with how to batten. I'll look later.

Thank you, that would be great if you can send the link.
 

JP_

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Thanks, looks good. I assume the plasterboard sticks to the foil on the insulation ok? Or do you peel it off first?

Yes, just stick on, don't peel off the foil, that's the vapour barrier.
 
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