Extruded polysterene as attic insulation- between joists??.
I was wondering which of these plans is best: to cut and place rigid extruded polystyrene boards between attic joists, or to form a "floor" of polystyrene boards on top of the joists - in this case, I assume I would have warm air between the wood ceiling boards and the polystyrene boards. So some of the heat from the house would accumulate there between the joists. Would that mean "losing" heat from the house? On the other hand, placing the insulation between the joists, do you think the joists themselves would act as reasonably good insulators? (I think they are 10 cm wide x 15 cm high). Thank you.