I am installing underfloor heating between the joists on a new 2nd storey extension prior to the chipboard (anyone have any alternatives?) deck is installed.
I need to put as much rigid insulation in between the joists as possible. The joists will be at 400mm centres so an ideal width of insulation board would be 350mm yet I cannot seem to find anyone that supplies in this width? Has anyone come across a solution to this or is cutting larger boards to size the only option?