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Damp in timber framed extension
Currently in the insulation stage of a timber frame extension at my own property.
It appears there is some damp there is plenty of dpc in the brickwork and between the brick and timber plate. Is it just this time of year where there is no heating in the extension yet or could it be something more serious
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13 Replies
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Normal, the whole structure will start to dry when you’re fully dried in and heating on
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Is the room well ventilated? Somtimes you will get trouble building with damp meterials/freshly poured concrete etc when you close things up. Moisture can’t get out so condenses on osb as it’s cold.
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Have been water tight for over 6 weeks now but there is no heating and the floor is still block and beam I’m going to put a vapour barrier over the top of the insulation before plasterboard. Do I need to stop let it dry out? Or can I carry on and when he heating is on and the floor has been sealed it will improve ?
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Hit it with a hot air stripper. Better to try and dry it out a bit . Than leave the dampness in there
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No vapour control layer so warm air goes around edges of the insulation and hits the cool relatively impermable OSB and condenses.
Need to check the outside face of the frame is well ventilated, warm side of insulation needs completely continuous sealed VCL, also potentially reduce internal moisture load with internal ventilation.
Don’t encourage more air movement from warm side of insulation to cold side by leaving a gap behind the insulation as some have implied. It’s all about the VCL and external ventilation
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Cold bridging maybe. Had similar but with plasterboard dot and dab on external brick walls with round mould spores (not penetrating or rising damp) appearing. Happened after skimming…moisture in air settles on cold spots due to bridging. Easily wiped away/mould sprayed and not returned since.
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What is the external skin ? Brickwork or cladding ? What air space is between the external skin & face of the timber frame ? Look carefully at that detail especially at DPC level
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Timber frame 200mm studs with osb fire board then breathable membrane 25mm batton and hardie plank cladding the hardie plank only went on yesterday though
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I deal with this a lot. It’s called interstitial condensation, when you fit insulation this creates a cold side and a warm side of the insulation, this is warm moisture laden air getting to the now cold surface behind the insulation and condensating on the cold surface (similar to taking a glass bottle out of a fridge on a warm day) causing damp and resulting in mildew, this destroys flat roofs and timber buildings. This is precisely why a vapour barrier is required and has to be fully sealed and unpunctured for sockets lights and switches etc.
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Ventilation blocked at the soffit vents maybe? Common problem if you have pushed insulation to far out of the building maybe
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No vents it’s a cold roof so needs venting should have cross latt the joists side and boarded onto that and put vents in your facia and if it’s joining into brickwork, you should’ve built a vent into that
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Is there through ventilation in each void?
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the void outside is 25mm batton with hardie plank this is vented too and bottom the void behind the insulation is not vented. And I think l where I am doing it in stages and the vcl has not been applied yet the warm air is getting through to the osb which is cold n theres my problem
building control have not come out to inspect this stage yet there next stage will be insulation they have signed off all so the stages of the build so far
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