Cavity wall insulation

[nalle59]

Can someone help,what thickness insulation do I need for cavity wall (concrete block outside and celcon inside) the cavity is 80mm wide.
Can I use Earthwool Dritherm cavity slab 32 Ultimate 75mm and what fixings do I need? or is Rockwool as good? thanks.

Also how many concrete blocks do I need for a triangular cable wall 9.5 metres wide at bottom to 3.2 metres top, I calculated 10 blocks to 1 square metre = tl. 304 blocks ?

 

[jeds]

75mm won't be enough. 90mm minimum but I'd go for 100mm. A 9.5x3.2 gable gable would be 152 blocks plus a few for cuts.

 

[nalle59]

How do you put 100mm insulation in a 80mm cavity?It won't fit !

 

[flameport]

Rather obviously, you build the cavity so it is 100mm wide, rather than 80mm.

Failure to install the correct insulation will mean the structure doesn't comply with building regulations. This could end up with the wall being removed and rebuilt properly.

 

[nalle59]

Rather obviously, you build the cavity so it is 100mm wide, rather than 80mm.

Failure to install the correct insulation will mean the structure doesn't comply with building regulations. This could end up with the wall being removed and rebuilt properly.

The reason for the 80mm cavity is that we are building UP from an old 80mm cavity wall ! so cannot widen it !
So what is the correct width of rockwool inslulation to fit in this cavity?

 

[freddiemercurystwin]

Full fill insulation of 80mm won't meet the regs. You need 45mm Celotex nowadays with fairly standard blocks if your BCO will let you get away with a 35mm air gap.

 

[nalle59]

75mm won't be enough. 90mm minimum but I'd go for 100mm. A 9.5x3.2 gable gable would be 152 blocks plus a few for cuts.

I have just used online calculator someone kindly suggested for the blocks and it comes to more than double than YOU suggest !more than 304 !

 

[^woody^]

Full fill insulation of 80mm won't meet the regs.

It will if he uses Solar celcon blocks

 

[nalle59]

Full fill insulation of 80mm won't meet the regs. You need 45mm Celotex nowadays with fairly standard blocks if your BCO will let you get away with a 35mm air gap.

Our building control surveyor has lookded at the plans which say rockwool to cavities and inside the wall 12mm drylined,we will put boards with insulation attached to it perhaps 25mm.He has not said it would not be ok.

 

[freddiemercurystwin]

Yea well having Themaline on the inside is obviously gonna help! FFS why not say that at the beginning of the thread! Muppet!

 

[nalle59]

Yea well having Themaline on the inside is obviously gonna help! FFS why not say that at the beginning of the thread! Muppet!

SORRY, YES I AM A MUPPET.

 

[jeds]

It would have helped if you'd said you were restricted to 80mm cavity. Easiest way in that case is to increase the specification of the inner blocks. A Celcon solar with 80mm insulation batt will give you a u-value of 0.28.

Gable wall 9.5 base x 3.2 high is 9.5x3.2/2 = 15.2m² which at approx 10 blocks per metre is about 152 blocks.