DIY Doctor

Condensation in new brick shed extension puzzle

Postby grayman » Thu Jan 14, 2021 2:46 pm

Hi all.

Had a single brick shed extended to make an office. Its had a New roof, the wall and floor has had a plastic membrain installed. The walls have been battened, boarded and plastered with rockwool insulation in the floor, the walls and the ceiling.
Before the walls were boarded and plastered there was quite a lot of condensation dripping down the walls.

It has a heater in now to drying out the plaster.
Electrical back boxes have quite a lot of condensation and there are small areas of water on the floor near the walls. Seems water is dripping down the inside of the wall onto the floor.
Will this go as the rooms temperature rises and stabilises, or is there a bigger issue?
grayman
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Postby stoneyboy » Fri Jan 15, 2021 9:55 pm

Hi grayman
Hopefully the plastic membrane was fitted after the battens and insulation were in place. If this is so then there is an issue with the joining of the wall and floor membrane and its location relative to floor levels.
Regards S
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Postby grayman » Fri Jan 15, 2021 10:02 pm

Hi.

Membrain, then battons then rock wool, then plaster board.
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Postby stoneyboy » Fri Jan 15, 2021 10:26 pm

Hi grayman
The purpose of the membrane is to stop moisture getting into the insulation and condensing, so it needs to go on the warm side of the insulation with all joints sealed.
Regards S
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Postby grayman » Fri Jan 15, 2021 10:32 pm

Oh dear. Somone has messed up and its now plastered. The outside is going to be cladded. Will this extra air gap help.
Should we insulate the outside as well?
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Postby stoneyboy » Sat Jan 16, 2021 3:47 pm

Hi grayman
This must all be very disappointing for you. You could try insulating and cladding the outside but I doubt you will decrease the temperature gradient of the insulation inside the plastic membrane enough to stop interstitial condensation.
It may be better to cut your losses, remove plasterboard and insulation, cut out the plastic membrane between the battens, then refit insulation, fit the DPM and re-board.
Regards S
stoneyboy
Rank: Project Manager
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Postby grayman » Sat Jan 16, 2021 6:23 pm

Hi. Thanks for the reply.
The heating is on and it seems the areas are drying a little. Im going to externally insulate as im having the cladding fitted anyway. Im wondeing if a dehumidifyer would be an option just in case?
grayman
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