Polystyrene insulation

[happyman1010]

hi all
have tried a search, i am building a conservatory, as it does not need planning, or building reg inspection, but would like to build to building reg or better,
my question is concerning insulation,
as it being built in block walls both sides, my builder says it better to use thermalite block for booth skins ? as well as using thermalite trench block also?
plus instead of using slab insulation in the cavity, could use Polystyrene sheet which is a better u value?
i know building reg changed from Polystyrene to celotex a few years ago,
for the slab so will have to use 100mm celotex for this
any one got views on theses questions?
thanks
rob

 

[jeds]

AAC blocks to both skins is technically OK but I steer clear myself because they are prone to cracking and if they do the render sometimes cracks with it.

I'd use Dritherm in the cavity. 80mm or 100mm Kingspan in the floor. It doesn't really matter what you use in the trench.