How to fill 150mm cavity

[Iceverge]

On 04/04/2026 at 08:35, allthatpebbledash said:

What was the cost difference between using PIR and the wool batts? Are there any alternatives to this specific brand?

 

I want to ideally beat the new wall construction u-value of 0.18w.

 

I did some calculations online using that German website I seen linked on here. Keeping a cavity at 150mm, the PIR on paper appears better. But that’s the topic being discussed here, theoretically it does. If construction doesn’t meet proper standards, how much of the supposed r value is lost?
 

PIR achieves 0.15W

Mineral wool batts gives 0.18W

 

I can build a wider wall of course and throw in more mineral wool? Then for the lintels use split lintels and avoid the catnic thingies?

 

 

 

 

 

That "mineral insulation panel" has a k value of 0.045W/mK.  try it again with a "mineral wool 035" or "hk 33" for the EPS beads. 

 

 

 

 

[Oz07]

On 02/04/2026 at 19:57, DannyT said:

I’m a bricklayer.

Just had planning approved for south Scotland. Was told rigid boards (PIR) is the standard with 50mm air gap. I sent a email over to building control about having Dritherm 32 fulfill along with the BAA certification.

They replied saying I can go ahead with it as long as installed to manufacturers standards.

There was no way I would do PIR. Even on my own build taking all the time in the world it would be a nightmare to install. Looks great on a drawing but it just don’t happen in real life and when the bricklayers not getting paid much to take the time you end up with a right mess as shown in photos above.

It repels moisture too so won’t get through the cavity, even in exposed locations like mine.

 

You can still full fill up there then? I thought it went on exposure zones? The stuff is deffo water repellent. An offcut can sit in a puddle for a week and is no heavier for it. 

[Oz07]

On 05/04/2026 at 07:57, JohnMo said:

Or don't bother with cavity - block wall and external insulation? You can see exactly what is going on.

Not as good for finance or future sales purposes I think?

[JohnMo]

2 hours ago, Oz07 said:

Not as good for finance or future sales purposes I think?

People say the same for timber construction, which is standard building method in Scotland. No one has issue with finances or sales.

 

External insulation has been given out free for ages by the government, so not seeing the issue there either.

 

Personally I wouldn't do block or cavity build, it would be ICF or twin stud timber frame, as I could do both myself.

[Oz07]

23 minutes ago, JohnMo said:

People say the same for timber construction, which is standard building method in Scotland. No one has issue with finances or sales.

 

External insulation has been given out free for ages by the government, so not seeing the issue there either.

 

Personally I wouldn't do block or cavity build, it would be ICF or twin stud timber frame, as I could do both myself.

I think timber frame and block cavity are easy with finance. You'd have to check with CML or uk finance whatever they're called now make sure the majority of lenders are happy

[Oz07]

29 minutes ago, JohnMo said:

People say the same for timber construction, which is standard building method in Scotland. No one has issue with finances or sales.

 

External insulation has been given out free for ages by the government, so not seeing the issue there either.

 

Personally I wouldn't do block or cavity build, it would be ICF or twin stud timber frame, as I could do both myself.