Block & Beam Ceiling - Interstitial Condensation...

[machineage]

Hi all!

Have a question on behalf of a friend.

He has just built a single story extension - block and beam ceiling (sound absorption - it's gonna be a studio) under a pitched roof.

BC have been in and suggested he places insulation under the ceiling inside the room - as well as above the ceiling in the loft space.

Is this advisable? I read elsewhere that it would be better to place the insulation above the ceiling to reduce any chance of interstitial condensation within the beams?

//www.diynot.com/forums/viewtopic.php?t=5198

Would placing say 100mm under and 400mm above be OK?

Thanks!

 

[Deluks]

Maybe the room side inso was proposed for acoustic treatment?

So concrete ceiling with a standard pitched roof above? Will still need to vent the roofspace either normally or mechanically. Ditto the studio itself.

 

[^woody^]

Would placing say 100mm under and 400mm above be OK?

No.

Sandwiching a cold material like concrete in between two insulators is a recipe for interstitial condensation

Insulate above or below only

If this studio is for sound then above would be better to use the mass of the concrete ceiling for sound absorption

If this studio is for nude photography, then perhaps insulating below the ceiling would keep things a bit warmer

 

[machineage]

Hi Woody

Thanks for your reply

As I understand the outcome of his proposed detailing - the heat loss into the block / beam ceiling 'slab' would be reduced by the insulation below - but still raise the temperature of the slab above the dew point - and the insulation above further reduce the heat loss from the slab so maintaining the slabs temperature? The room is likely to be maintained at a constant habitable temperature as it incorporates underfloor heating. He could also incorporate a vapour check above the insulation to the underside of the slab to stop any room borne water vapour permeating into the slab.

What would be the benefit / deficit of having all of the insulation above / below?

The insulation recommended by BC is rockwool.

Could you elaborate why this would cause a problem in a more detailed manner so we can make sense of the situation and the likely problems caused by interstitial condensation in a structure of this type?

Many thanks again

 

[machineage]

*bump*

Anyone?

Thanks

 

[JohnD]

vapour barrier should be on the warm side of the insulation, not the cold side.

 

[Deluks]

So then, music studio or other?

Will the room be plasterboarded out internally? Is the concrete ceiling also the roof? Or is there a seperate roof above this with space in between?

 

[JohnD]

...- block and beam ceiling (sound absorption - it's gonna be a studio) under a pitched roof....

 

[Deluks]

hmhmhmnnnnn, Then I would go with 300mm on top and treating the room acoustically inside with rockwool slabs in corners and where walls meet ceiling, but not a continuous insulation layer on the underside of the ceiling.