Loft insulation

[wonderwire]

I am planning to insulate my loft ceiling (floor, not rafters). This is just for storage and not habitation.

I want to use Celotex insulating board, rather than Rockwool.

If I insulate between the joists and then a layer on top of them (to achieve the required U-value), can I then place chipboard directly on top of the Celotex, or does it need supporting?

Do I also need to leave a ventilation space between the plasterboard and celotex in the joists to avoid interstitial condensation (as with insulating rafters?).

Thanks

 

[^woody^]

You can do what you propose, and it won't need venting.

 

[wonderwire]

Thanks. Will celotex hold weight if laid directly across the joists, or do I need to support it with chipboard underneath (and then more chipboard on top)?

 

[John D v2.0]

Should be fine, just make sure it really is supposed by the joists and not resting on the ceiling itself