Pumping walls . What's minimum gap depth between leafs

allycavs · 07-01-2026 11:00PM #1

Hi

2 companies stated different things.

Company 1 said there's only 50mm in the gap between leafs.this would need to be pumped but is not enough to make difference so external wrap will be needed too

Company 2 drilled wall at 2 different points and estimated there's 100mm gap between leafs. Looking at a vent I measured 75mm between leafs. Assuming it's only 75mm is this enough to get a good benefit in heat retention without external wrap .this was company 2 recommendation

As extra note the windows are lall width of each room too so quite big windows

Anyn advice be great as this is for my elderly parents

sydthebeat · 07-01-2026 11:16PM

First of, if there's nothing in the cavity then anything will be significantly better.

It should be very easy to measure the width of the cavity.

Open a window and measure the distance between the face of the inner wall and face of the external wall. Take 20mm off for internal plasterwork, take 30mm off for external render and reveal. Then take 200mm off for the width of the two block leaves.

Whatever remains is the cavity width.

The next step is to look at it from a money point of view. Pumping cavities is relatively cheap. External wrap is relatively expensive.

Pumping 50mm will bring the house walls to approx 2000 levels. Pumping 100mm will bring it to roughly 2010 levels.

If you're looking for grant assistance then you will need to reach a min u value of 0.35, which should be achievable with 50mm pumping.

allycavs · 08-01-2026 11:57AM

Thanks for advice ya the first company effectively took window method and didnt. Think there was anything more than 50mm. Second compwny drilled in 2 places into 200mm (well dust in but was 200mm) but vent showed 75mm . 2000-2010 standaeds would be great given it's blank cavity now. Thank you

MicktheMan · 08-01-2026 06:55PM

Are you sure OP the wall is a cavity wall (double leaf) and not a cavity block wall (single leaf)?

allycavs · 08-01-2026 10:30PM

Well both companies said there's a gap between the 2 leafs .but they both think it's different sizes

DC999 · 16-01-2026 05:04PM

How does it work on a semi-d when pumping a cavity wall (double leaf)? Does it not just settle into the cavity of your neighbours at a 45 degree angle? What I'm asking is how the cavity wall is closed (or not) between both semi-d houses.

sydthebeat · 16-01-2026 05:16PM

https://www.boards.ie/discussion/comment/124153155#Comment_124153155

well, fire regulations say that there should be a barrier in the cavity at the party wall line.

if there isnt then you have a serious issue.

anyway, the beads are pumped in with a glue, not dry. so that means that if there is no barrier it doesnt spread wild. id imagine the would be able to control the pumping so that the spill over is insignificant

Calahonda52 · 31-01-2026 05:28PM

https://www.boards.ie/discussion/comment/124127653#Comment_124127653

Nice piece of math: wall width minus 250 = cavity!

Pumping walls . What's minimum gap depth between leafs

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