New Build. 150mm cavity. No Cavity Closers Used.

redsheeps · 18-02-2026 06:25PM #1

New build house. Had to do some remedial work on couple of windows. Noticed there are no cavity closers used at all on the reveals. Might get the terms wrong here. Cavity is 150mm pumped bead. The side reveals have a solid piece of PIR between inner and outer leaf just at the reveal. Some of the sill reveals have the same but some have nothing. The airtight tape had to be removed and the beads are just sitting there. Are cavity closers no longer a thing or did the builder skip this…?

Biker1 · 18-02-2026 09:13PM

The PIR is your cavity closer and if it's at least 50mm thick then it is far better than those plastic cavity closers. As it's a new build then 150mm bead in the cavity will not get you the required u-value so you will nee to add an insulated slab to the interior.

redsheeps · 19-02-2026 09:51AM

https://www.boards.ie/discussion/comment/124246769#Comment_124246769

Think it's just 50mm. What makes that better than the cavity closers? Genuinely curious.

Yeah we have 40mm PIR + 12.5mm plasterboard. Condensation analysis all done. In hindsight I would love to go back to the start and do 200mm cavity and not both with the IWI.

mickdw · 19-02-2026 10:02AM

Closer block is not used anymore. You can use specific closer pieces which are just insulation inside plastic. Most use a piece of insulation instead. Keep it within the thickness of the vertical dpc and its A1.

Gumbo · 20-02-2026 12:41AM

https://www.boards.ie/discussion/comment/124247784#Comment_124247784

200mm cavity then requires specific structural

Engineers design and sign off as the 2 leaves can act independently. May mean significant extra cost etc

Exiled Rebel · 20-02-2026 01:03AM

https://www.boards.ie/discussion/comment/124247784#Comment_124247784

200mm cavity would require one of leaves to be block on flat. Total overkill.

I have 150mm with PIR insulation. The house has a negative BER score. It could be heated with a candle if needs be.

As for the cavity closer query the other lads have answered it.

redsheeps · 03-03-2026 09:10AM

https://www.boards.ie/discussion/comment/124250364#Comment_124250364

You've no internal or external wall insulation with that makeup? You must have excellent airtightness and MVHR?

Exiled Rebel · 03-03-2026 02:22PM

https://www.boards.ie/discussion/comment/124280286#Comment_124280286

The airtightness score came in at 1.5ACH and yes indeed we have MVHR installed. With 150mm PIR the external wall has a u-value of 0.136, there's no need for any more.

Calahonda52 · 06-03-2026 01:24PM

https://www.boards.ie/discussion/comment/124281070#Comment_124281070

be intreated in seeing how you arrived at .136

Am struggling to get below 0.19 with 150 at 0.028 and heavy, as opposed to medium density blocks

Exiled Rebel · 06-03-2026 01:51PM

https://www.boards.ie/discussion/comment/124290275#Comment_124290275

see below a snippet from my passive house planning package. while my house isn't technically passive (the ACH is too high to meet the threshold) the house was designed and built with PHPP in mind.

the xtratherm cavitytherm has a lambda value of 0.021 which when combined with its 150mm thickness results in a u-value for the material alone of 0.140. the rest of the wall make-up contributes just .004 giving an overall u-value result of 0.136.

Calahonda52 · 06-03-2026 08:18PM

Many thanks, am going down the same route

How does PHPP cater for wall ties, I can make 1.3 with the U Value calculator I use as an BER assessor if I leave e out wall ties

Thanks again

New Build. 150mm cavity. No Cavity Closers Used.

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