Cavity wall

[DevilDamo]

yes the wall will be rendered on the outside, not sure how this is relevant though, as no insualation will go into that.

Because it IS relevant! I wouldn't be asking otherwise

 

[freddiemercurystwin]

Take a look at page 6 of this LABC guidance PDF : http://www.derrycity.gov.uk/buildingcontrol/downloads/Herts U Values.pdf

...and you'll see why there are so many questions. Even your interior surface finish is a factor.

You blocks have a K value of 0.25 (see page 9) so according to the table on page 6, your wall is over specified - you could get away with an 85mm cavity.

Gary

How do you work that out Gary? The OP is using Isover but the table refers to Crown! Only sure way is to contact Isover for a U value check.

 

[^woody^]

seriously, will someone just answer the question

You are missing the point.

Your builder should be building to the approved plans, not deviating to how he sees fit.

And more importantly, not quoting you for the specification on the plans and then using whatever materials he can find cheaper to increase his profit margin

Conforming to the appropriate u-value for the wall is irrelevant to you, if the builder has used some cheap lightweight blocks totally inappropriate in other respects

The wall's insulation value is just part of the criteria, not all of it

 

[garyo]

How do you work that out Gary? The OP is using Isover but the table refers to Crown! Only sure way is to contact Isover for a U value check.

Yep you're right...

Gary

 

[theoldun]

British Gyps Isowool. Lamba 0.036. Achievable U value at 100mm full fill 0.27.
Knauf Crown Dritherm. Exactly the same.
Hope this helps.
oldum