Cavity Insulation advice

[jassdhali]

Guys,

Adding porch to side of house and as no building regs are required needed some advice. The walls will be built from blocks and have a 100mm cavity. Question is what is the best type of insulation, although building regs don't apply, would still like to keep it withing recommended U values.
Looking at some older posts they recommend dritherm slabs but I wanted to know if I could use PIR Insulation like Celotex?
Thanks For any advice

 

[freddiemercurystwin]

You can use PIR but with that type of insulation you need to maintain an air gap 50mm to be safe. Really not a lot in it between the two although arguably if the bricky can't be trusted to keep the wall ties/cavity meticulously clear dritherm could be the route to take.

As its only a porch you may aswell stick 50mm in and have a 50mm cavity.

 

[jassdhali]

FMT the porch is going to be an uninhabitable room off the main kitchen seperated by an external door, so on that basis would 100mm be better?
Thanks

 

[freddiemercurystwin]

I believe 50mm of Celotex will get you a lower U Value but I've not checked tbh, the difference will only be marginal though its a moot point anyway, its only a porch and you're retaining the external door!

 

[jassdhali]

Retaining the door which most of the time will be open in an opening of 7 foot

 

[theoldun]

Retaining the door which most of the time will be open in an opening of 7 foot

If that is the case then do not even consider insulation, just throw a half brick/block skin wall up.
Howver if you do wish to insulate and obtain u value of 0.28W/m2Ktnen use
Rendered 100mm Plasmor Aglite block, strength 7.3N with a k value of 0.32w/mk.
100mm cavity fully filled with Dritherm 34.
100mm block inner skin all as external skin
Regards oldun