Insulated plasterboard and condensation.
- Thread starter hard-work
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Personally I think there is the potential for interstitial condensation unless there is a vapour control layer on the warm side of the insulation.
Some insulated plasterboard products have an in-built vcl, while others (particularly polystyrene-backed panels) don't.
Some insulated plasterboard products have an in-built vcl, while others (particularly polystyrene-backed panels) don't.
Porous gives a clue.
If there is a gap between the brickwork and the cold side of the insulated plasterboard, moisture could form on the gap-facing surface - particularly with it being a bathroom.
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Yes as Tony said condensation is a risk based on humidity and temperature difference, and permeability isn't a binary yes/no thing, it depends the permeability of the components in the wall buildup relative to their insulation value.
I'm not sure why there are so many threads on this topic suddenly, but I'm very interested as I'm going to add an ensuite shower room on an outside solid wall And want to insulate internally in there.
I'm not sure why there are so many threads on this topic suddenly, but I'm very interested as I'm going to add an ensuite shower room on an outside solid wall And want to insulate internally in there.
How does moisture (ie condensation) form on the surface of a porous material?
Can you extrapolate that in to what actually happens to atmospheric moisture in this type of situation within a wall?
You seem to be applying the bog standard "air condensing on a cold piece of glass in a room" scenario to completely different situation.
In particualr with "risk" analysis, there are the variables of not only what may occur and to what extent, but the consequences of any occurance too.
Note - every single wall of a house has moisture in it.
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You do not know what you are talking about, woody. So stop pretending you do.
Until you accept that you made a mistake, and withdraw your accusation, I will not be going into any further detail, except to suggest you look up 'Sweating Slab Syndrome'.
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Obviously glass is an extreme case for permeability and I was using that example purely to correct the assumption that it was cold air hitting warm surfaces that cause condemnation.
Clearly as surfaces increase in permeability, the risk becomes lower, but the only fully porus thing in your house is fresh air. But even that can have condensation as that's what rain is.
I'm approaching this from a physics point of view, you're using your experience, which I don't have.
Well, the insulated plasterboard is largely impervious to any moisture. Any moisture that will be absorbed in to the board only has the joints for a route and this is limited. Any moisture that might evaporate out at the rear, will be very little as to be insignificant - it will be just normal air and humidity. Any limited moisture will then either be absorbed by the porous brick and moved through the wall, or the higher temperature of the room will always draw moisture back out rather than push it inwards. This is what goes on in any wall or structure.
So bottom line, whether physics or not is that the area of air between the board and the wall has no condensation risk. No moisture, no damp, no nothing. Just normal air, going through a normal cycle of humidty changes, and passing through materials.
Condensation risk is only relevant to timber framed structures, not plasterboard on a brick wall.
So bottom line, whether physics or not is that the area of air between the board and the wall has no condensation risk. No moisture, no damp, no nothing. Just normal air, going through a normal cycle of humidty changes, and passing through materials.
Condensation risk is only relevant to timber framed structures, not plasterboard on a brick wall.
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Have to disagree here, Woods.
Two years ago on a refurbishment, a client applied insulated plasterboard (polystyrene-type, and with no vcl) to a vaulted roof.
There was 25mm Kingspan between the rafters - giving 50mm airgap - and the insulated plasterboard below. There was plenty of draft
in the airgap as it was an old house.
During the first cold snap, brown condensation stains appeared down the ceiling and it had to be taken down and re-done.
On cold, still, Winter's nights there is often little air movement, and the moisture condensed on the cold side of the insulation.
In the OP's case, it is likely there will be little ventilation of the gap, and being a bathroom, the risk is higher.
Two years ago on a refurbishment, a client applied insulated plasterboard (polystyrene-type, and with no vcl) to a vaulted roof.
There was 25mm Kingspan between the rafters - giving 50mm airgap - and the insulated plasterboard below. There was plenty of draft
in the airgap as it was an old house.
During the first cold snap, brown condensation stains appeared down the ceiling and it had to be taken down and re-done.
On cold, still, Winter's nights there is often little air movement, and the moisture condensed on the cold side of the insulation.
In the OP's case, it is likely there will be little ventilation of the gap, and being a bathroom, the risk is higher.
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