Cavity Closers with inner outer wall variations

AFT4B · 27 Jan 2026

We have a bit of a mix of new window/ door openings and one external doorway where the new wall joins an old wall.

The the new build in some areas has a variation of 10-15mm between the brick and blockwork so the cavity closer would not sit completely flush. I'm not sure what the normal tolerance is but I'm trying to think ahead to plaster boarding/ plastering for a clean square finish on the reveals.

I was thinking of adding some expanding foam behind this to get the cavity close to fit level. Is there a better way?
(Or would this normally be fitted as is and the angle corrected with bonding/ dot and dab on the plasterboard?)

noseall · 27 Jan 2026

AFT4B said:
We have a bit of a mix of new window/ door openings and one external doorway where the new wall joins an old wall.

The the new build in some areas has a variation of 10-15mm between the brick and blockwork so the cavity closer would not sit completely flush. I'm not sure what the normal tolerance is but I'm trying to think ahead to plaster boarding/ plastering for a clean square finish on the reveals.

I was thinking of adding some expanding foam behind this to get the cavity close to fit level. Is there a better way?
(Or would this normally be fitted as is and the angle corrected with bonding/ dot and dab on the plasterboard?)

View attachment 405941

Dab a strip of plasterboard on first, prior to fitting the cav closer.

AFT4B · 27 Jan 2026

noseall said:
Dab a strip of plasterboard on first, prior to fitting the cav closer.

So add now before the closer is fitted rather than after? Or can it be done either way?

Also, what's an acceptable tolerance to not need doing this? As I may end up with the closer protruding more on the inner wall if I do this and it's not required. If you get what I mean?

^woody^ · 27 Jan 2026

Air leakage is the main thing to consider, so make sure however you do it, the cavity is properly sealed.

AFT4B · 27 Jan 2026

^woody^ said:
Air leakage is the main thing to consider, so make sure however you do it, the cavity is properly sealed.

I will be fixing it in place with general grab adhesive and clout nails on the inner walls.

Perhaps I'm needlessly concerned about making it completely level at this stage?

noseall · 27 Jan 2026

AFT4B said:
So add now before the closer is fitted rather than after? Or can it be done either way?

Also, what's an acceptable tolerance to not need doing this? As I may end up with the closer protruding more on the inner wall if I do this and it's not required. If you get what I mean?

Pre-closer.

AFT4B · 3 Feb 2026

A bit confused by the different types of cavity closers available.

I am now wondering if the inner wall is deliberately set slightly back to fit a single flange cavity closer?

noseall · 3 Feb 2026

AFT4B said:
I am now wondering if the inner wall is deliberately set slightly back to fit a single flange cavity closer?

No. You would not deliberately reduce the lintel bearing just to accommodate a certaing type of cav closer.

I make and fit my own with ex-foam because the proprietary ones are pants.

insofit6.JPG

noseall
12 Oct 2025

woodfill2.jpg

noseall
28 Feb 2024

woodfill3.jpg

noseall
28 Feb 2024

Crap Fitting2

noseall
17 Dec 2017

Crap Fitting1

noseall
17 Dec 2017

AFT4B · 4 Feb 2026

Fair enough.

When you say make your own with EX-foam, is it mostly a case of continuing the PIR to the end and filling the gaps? The D&D plasterboard on top?

No concerns with bridging or moisture?

noseall · 4 Feb 2026

AFT4B said:
Fair enough.

When you say make your own with EX-foam, is it mostly a case of continuing the PIR to the end and filling the gaps? The D&D plasterboard on top?

No concerns with bridging or moisture?

As long as you robustly fit the PIR cav' insulation to the rules - i.e. keep the tie wires 100mm - 150mm back in from the jamb and dun DPM up the wall against the back of the outside course.

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Cavity Closers with inner outer wall variations

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