Rigid and mineral cavity fill

[tomfe]

Can both rigid and mineral cavity batts be used in the same cavity, so for example 125mm cavity 75mm kingspan 50mm dritherm?
The mineral batt would keep the pir tight to the internal skin no danger of bridging cavity with snots etc.

 

[^woody^]

No

 

[roboughton]

Rigid needs an air gap, the batts are normally full fill.

 

[stuart45]

There are full fill ridgid boards available for your cavity without needing to mix them.

 

[tomfe]

No

Why?

 

[^woody^]

No

Why?

Rigid needs an air gap, the batts are normally full fill.

 

[tomfe]

Yes and?
You've not explained why it would not work.

You have an air gap in front of the rigid to stop any penetrating damp from tracking across the insulation. You don't need an air gap with a mineral batt because the water can escape from the bat back into the external wall when it drys out.

You can have a 50mm full filled cavity so this must be sufficient to stop penetrating damp.

Therefor woody unless there is something with dew points I don't see how, from what you've explained or lack of, this would be be so unacceptable it warrants just a 'No' answer....

 

[^woody^]

Yes its something to do with dew points and interstitial condensation. And BBA certificates.

Hang on, and wait for someone to explain why it will work.

 

[tony1851]

I'm confused.

 

[roboughton]

There are full fill rigid boards available for your cavity without needing to mix them.

Pretty complex stuff this, I was told that if you used a full fill of board it would cause damp for sure but as you say stuff is available but it looks a bit more complex than just simple boards.

http://cavitytherm.com/accessories/

Go ahead and trial it with the two - let us know the outcome.

 

[^woody^]

Those xtratherm boards still need an air gap, albeit being built into the front of the sheets