Cavity insulation 100mm which type

[Ab12]

I have just had the builders round to do the DPC layer of semi-engineering bricks and they have left a space for insulation which they say should be 100mm when moving into the rest of the wall (not at DPC layer)

What are people using in between these cavity walls? Should I get a typical cavity slab of 100mm which looks like the fiberglass roll style or is 100 mm celotex board the way to go?

The cavity wall will be made up of yellow stock on the outside and thermalite blocks for the inside

 

[jeds]

Which regs. Pre or post Jun22?

 

[Ab12]

I assume post June 22 as I'm building now?

 

[freddiemercurystwin]

When you applied is the critical date?

 

[Ab12]

Only applied 4 months back

 

[jeds]

Sorry, should have asked before; is this an extension or a new dwelling? Edit; it must be an extension, or you'd be following a thermal design.

Assuming the cavity is fixed at 100mm, you could use 100mm cavity batts (Dritherm 34 or similar) but you'd then need about 40mm PIR internal lining as well. Alternatively, you will need full fill PIR - Unilin CT/PIR or similar.

Either way it would be wise to have the u-value calculated and agreed with building inspector before you commit.

 

[Ab12]

It's an extension to the existing house on permitted development. Existing house is 1930s

 

[Ab12]

Sorry, should have asked before; is this an extension or a new dwelling? Edit; it must be an extension, or you'd be following a thermal design.

Assuming the cavity is fixed at 100mm, you could use 100mm cavity batts (Dritherm 34 or similar) but you'd then need about 40mm PIR internal lining as well. Alternatively, you will need full fill PIR - Unilin CT/PIR or similar.

Either way it would be wise to have the u-value calculated and agreed with building inspector before you commit.

Thanks!

Would these be okay then - full fill 100mm as you mentioned above.

Cavity is fixed at 100mm

100mm Unilin Thin-R CT/PIR CavityTherm Full Fill Insulation (pack of 4)

100mm Unilin CavityTherm wall insulation board is a high performance composite board of enhanced PIR core with a lambda value of 0.021W/mK. The boards have gas tight facings with one face bonded to a profiled HIPS skin during manufacture to provide a drainage plane. Unilin CavityTherm's unique

www.insulationshop.co

 

[jeds]

That will do it. With a standard thermal block internal leaf that should achieve a u-value of 0.17. (The minimum is 0.18)

 

[Ab12]

That will do it. With a standard thermal block internal leaf that should achieve a u-value of 0.17. (The minimum is 0.18)

Would you mind letting me know how you calculated that! Just incase I get a different type of full fill 100mm cavity ?

 

[jeds]

I have some of the specifications I use regularly pre-calculated for use in my CAD system. Best thing you can do is go onto the Unilin website and look up a u-value or request a calculation if you want something not on the standard tables. Or any other manufacturer website, come to that.

 

[Mr Chibs]

I'm helping a mate do his extension, the council officer is giving one years' grace to allow cavity to be 100m (full fill batts) instead of 150mm.
50mm of celotex has to be added to the inner blockwork of external walls.

 

[Ab12]

That will do it. With a standard thermal block internal leaf that should achieve a u-value of 0.17. (The minimum is 0.18)

I don't need any internal wall celotex with this approach though

What about 100mm celotex, I has a thermal conductivity value of 0.022 and the unilin 0.021. can't be that much different?

 

[Mr Chibs]

PIR is claimed to be nearly twice as efficient as rockwool, so you should have a more thermal efficiency, over cost.

 

[noseall]

Thanks!

Would these be okay then - full fill 100mm as you mentioned above.

Cavity is fixed at 100mm

100mm Unilin Thin-R CT/PIR CavityTherm Full Fill Insulation (pack of 4)

100mm Unilin CavityTherm wall insulation board is a high performance composite board of enhanced PIR core with a lambda value of 0.021W/mK. The boards have gas tight facings with one face bonded to a profiled HIPS skin during manufacture to provide a drainage plane. Unilin CavityTherm's unique

www.insulationshop.co

Yes we've just used them on our current build. Horrible to cut, horrible to install, very expensive and add much extra time to the whole cavity insulating process.
Otherwise - crack on.