Loft Insulation

[blackthorn]

Hi

I intent to board out the centre section of the loft. The joists are 3” deep. Would it be OK to use 75mm
Polystyrene boards to insulate below the chip board flooring,

 

[DarrenThomas]

We'll they'll fit, but i don't know how well they hold in heat compared to other insulation products. Even with something like Celotex i think you would need 150mm thickness to meet the new recommendations for insulation levels. usually you'd need 250-270mm if it was typical rockwool type insulations.

 

[mointainwalker]

Ignoring the regulatory requirement for 250 mm + of insulation which is way beyond reasonableness at current energy costs, expanded polystyrene has the same insualtion value as fibre-wool but costs twice as much.

Between joists the wol is better as it can be made to fill the available space.

Lay a plastic-sheet on the ceiling before the wool as a vapour-barrier to avoid possible condensation problems.