Insulating concrete roof.

[Jacob]

I have an outbuilding with a 6 inch concrete flat roof that suffers from condensation on the inside. Not helped by the fact i brew my beer in there :-(

I wish to insulate the underside and was thinking of fixing battens at approx 400mm centres to the surface, with polystyrene insulation wedged between the battens and overboarded with ply or t&g/pvc cladding.

If I go down this route, should I incorporate a vapour barrier between the insulation/battens and the overboarding?

Do you think this will be sufficient to cut down the condensation, or does anyone have a better plan for me to follow?

The ceiling height is 7 feet, so I am somewhat restricted to the thickness of any insulation I can use, but what would be your minimum recommendation regarding the thickness I *should* use?

Any help would be greatly appreciated.

[Rob Morley]

Better to use something like Kingspan (pitched roof) panels if the ceiling is low, and easier to glue it than fix into concrete (plus it eliminates thermal bridging). You'll still need to sort out the ventilation if you're brewing in there though.

[Tom]

Have you thought about putting the insulation on the outside and felting over, you will get a more even temp in there due to the thermal inertia of the concrete and you wont suffer from interstitial condensation above your internal insulation. Look up Warm Deck and Cold Deck flat roof systems. Tom