insulation in extension wall... solid or rockwool?

[unclebob1]

From an insulation performance point of view, is it better to go with putting something like foil backed kingspan or mineral wool (rockwool?) in a cavity?

pros vs cons? (assume cost isn't an issue at the moment - i'd rather spend a bit more now and save over the life of me living in the house!)

Best practices for installing ? ties in the middle? seal between joints - vs squashing in mineral wool?

 

[jeds]

I always specify full fill mineral. It's easier to install with a lot less likelihood of being installed incorrectly. Standard mineral batts are approximately twice the thermal conductivity of PIR foam so you need 100mm to be equivalent to about 50mm foam. If you need slightly better to get your u-value up go for one with a better thermal conductivity. Dritherm 34 or 32.