Christian McArdle wrote:

But rockwool is half the price for equivalent insulation.


Yes, but if it means that you can board over and still get enough
insulation, the price is worth paying. I bet Celotex/Kingspan is cheaper
than installing deeper joists so you can board.

Christian.


I would not be to sure of that, at least if DIY and labour costed at zero.

Celotex is improbably expensive.