insulation in extension flat roof

[hardtail]

hi guys ive just took down the plasterboard on the ceiling of the extension due to building work and seems theres been a leak at some point and the rockwall 150mm seems to have held the water like a sponge anyway when the building works done i was thinking of using 75mm polystyrene sheets and foiled bubble stapled to the joists would you think this will be better than rockwall for thermal insulation as celetex is a bit out of my budget

 

[noseall]

It is highly likely that the damp is a build-up of condensation.

You are better off rebuilding the flattie as a 'warm deck' using celotex across the tops of the joists particularly if b.c. are involved.

Otherwise you run the risk of more condensation build-up.

 

[mointainwalker]

Deleted -didn't read title

 

[noseall]

This could be because of badly-installed bathroom extractors venting into the loft-space, downlighters penetrating the ceiling or the lack of a vapour-barrier across the loft floor.

Don't forget that loft-hatch also needs to be sealed ( check retailers for products)

Loft needs to remain ventilated above the insulation, so check that insulation hasn't been taken out into the eaves and blocking vents there.

Read the title Mointain....

 

[mointainwalker]

Ooops - got partly mixed up with another thread !