Flat roof causing condensation inside...

[paulw0t]

I've a problem with a flat roofed house and was wondering if anyone had any thoughts on the planned solution.

The problem is that the roof is cold and the heat from the house hits the ceilings (which are solid concrete) in the upstairs rooms causing condensation and is starting to turn the ceilings black.

To combat this I've have had a few sugestions the one I'm thinking of going with is to create a fake ceiling below the current one by putting up battons and insulation up and then plasterboarding over this

I've seen it done before but was wondering if anyone has any experiance with this or has any thoughts on things to look out for ?

Thanks

Paul.

 

[joe-90]

That should sort it Paul. Not a big job.

 

[^woody^]

Yes that will do but take care with the detailing

Battens on the concrete with insulation between and the plasterboards over will lead to pattern staining of the new plaster ceiling where the battens are - this is due to the thermal bridge caused by the timber

Batten the ceiling and insualte between them, but then use a futher insulation layer across the whole lot before plasterboarding.

If the insuation does not have a foil face, then fit a vapour check layer behind the plasterboard or use foil backed plasterboard

 

[smashngrab]

I dont reccon this will work,you will still have a cold concrete slab above the insulation.Your going to have to stop all heat getting through the plasterboard,if not the drips will soak the insulation then it gets on the ceiling again.
Now if the flat roof above was insulated and re-roofed that would work.We used to lay down that polystyrene then fibreboard on top this,then whatever flat roof you were going for.

 

[^woody^]

The insulation against the slab removes the cold surface, and the vapour barrier prevents moisture from the air getting behind the new ceiling.

It works every time

 

[paulw0t]

Yes that will do but take care with the detailing

Battens on the concrete with insulation between and the plasterboards over will lead to pattern staining of the new plaster ceiling where the battens are - this is due to the thermal bridge caused by the timber

Batten the ceiling and insualte between them, but then use a futher insulation layer across the whole lot before plasterboarding.

If the insuation does not have a foil face, then fit a vapour check layer behind the plasterboard or use foil backed plasterboard

Hi Just wanter to clarify... Battoning to the ceiling then insulation between the battons... Then do I put more battons on the existing battons cross ways and plasterboard to this ?

Also how important is the foil faced insulation / plasterboard ? As I've started working without it.

Thanks

Paul.

 

[^woody^]

No, you batten, then insulate between them, then you either fit insulation board or plasterboard direct to the battens so that there is no air gap

Foil backed plasterboard are an insurance against moisture getting through the boards and condensing or causing rot.

 

[alittlerespect]

Hi

If not too late why don't you consider a 'warm deck' flat roof (insulation on the external), this would eliminate the condensation problems encountered with cold deck (insulation on the inside of the building) while at the same time allowing the concrete roof/ceiling to act in the same way as a trombe wall.

Regards

 

[ajrobb]

Alternatively, Celotex (at least 20mm) against the concrete held in place with battens every 400mm on the warm side. Tape joins between insulating slabs to complete VPL. Plasterboard on battens. Tape and fill plasterboard joins then sand or tape and skim.