whats the best blocks and cavity insulation to use?

[peasie]

hi building a 2 story side extension and was trying to get a price for materials i have 2 questions

1=whats the best blocks to buy for the internal wall?

2=what 75mm insulation would you all recommend?

cheers steve

 

[b21playa]

1 = thermalite
2 = kingspan

 

[peasie]

cheers
is the kingspan like the rockwool or is it the solid rigid boards?

 

[^woody^]

The question is too vague - best for what - cost, performance, ease of use?

Kingspan/celotex is probably the best insulation for a given thickness, but one of the worst products to use as cavity insulation (from a builders POV) and for the quality of work required and possibilities for problems for poor workmanship

Thermalite/Celcon (or any aerated block) are light to use but prone to cracking and poor fixing into when you're living in there

Choice of blocks and insulation are interdependent - choose one type of block and you may be limited to choose a particular insulation

 

[peasie]

cost really
just drilled some holes in a friends garage to put shelves up and the blocks must have been thermalite so i see what you mean about being soft/weak

 

[jeds]

The external walls should have a minimum U-value of 0.30W/m²K in order to comply with thermal Regulations. You won't get that by partial filling with Kingspan or Celotex in a 75mm cavity and also retaining a 50mm clear cavity. Building inspectors will sometimes relax rules but it depends on the situation - so you should check before committing yourself.

Otherwise you might get somewhere close with one of the highest value thermal blocks and 75mm full-fill cavity batts.