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TF1
Member
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# Posted: 19 Aug 2024 11:27am
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My cabin has been built now for a year now and has been sealed up with vapour barrier for a few months now. Walls are reading 7-9% but the subfloor ranges from 9-16%. Cabin is 2-3 feet above ground with full airflow.
It’s been very humid and rainy all summer. Will a vapour barrier on the surface plus vinyl plank be okay or do should I be looking at installing something in the joist cavity to help reduce? For reference I left a rubber entrance mat at the front door and it started to mould on the underside.
Thanks
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gcrank1
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# Posted: 19 Aug 2024 01:18pm
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All closed in, as in not ventilating?
Can you get a fan going, ime air has to be moving and have a way to vent.
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TF1
Member
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# Posted: 19 Aug 2024 01:25pm
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Thanks I have a full roof vent cap for air above the insulation and I leave the windows slightly open (apart from the gable end windows that are open full time. Full off grid so I only run a dehumidifier and fan when I’m up. I’m not sure what other options are while I’m not there.
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Brettny
Member
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# Posted: 19 Aug 2024 01:32pm
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Did you ever arrive to a cold cabin and outside was warmer and then you opened the place up?
There are other ways to run a dehumidifier offgrid but it can be pricy. DC direct from solar mini split.
Also some times leaving the place closed up allows for less temp change and less condensation to form. How much floor insulation do you have?
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TF1
Member
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# Posted: 19 Aug 2024 05:28pm
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There is currently no floor insulation. I’ve been trying to decide if I want to put in spray foam or rigid.
I don’t think the numbers are that bad (only the subfloor that has higher than ideal), I just didn’t want to add a vapour barrier the flooring only to add foam or rigid later. Both would trap moisture if vapour laid on top of sub floor.
I don’t have any visual signs, I just happened to check. The humidity (Quebec) has been horrendous this summer so I was also hoping to see what it would be in more normal conditions.
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TF1
Member
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# Posted: 19 Aug 2024 05:29pm
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Sorry - yes it’s typically cooler inside than out before everything gets open. I was under the assumption that little window cracks would be better than fully sealed.
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Brettny
Member
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# Posted: 19 Aug 2024 10:24pm
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Outside warm air hitting cold interior objects makes condensation. Either way with no insulation your fighting a loosing battle. You need floor insulation to slow heat/cool loss.
I would definitely do ridgid foam right against the bottom of the subfloor.
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Nobadays
Member
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# Posted: 19 Aug 2024 11:31pm
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Quoting: TF1 I’ve been trying to decide if I want to put in spray foam or rigid.
If spray foam is reasonable in your area, it is probably the best way to go as it will seal most if not all air intrusions as well.
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ICC
Member
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# Posted: 20 Aug 2024 12:13am
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I would pay someone to install spray foam rather than do foam sheets myself.
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SCSJeff
Member
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# Posted: 20 Aug 2024 02:23am
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Same setup.. Cabin on piers. No insulation underneath.
I had the same problem once or twice too when conditions were "just right"... Moisture under the floor mat at the door.
My floors aren't finished yet and I didn't worry about it.
However, I do want to be cautious about what flooring I put down in conjunction with what insulation underneath. I don't want an impermeable surface on top (ie: vinyl plank, etc.) with also an impermeable surface underneath. Spray foam, vapor barrier, etc...
According to Building Science, one side or the other should be able to "breath"
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TF1
Member
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# Posted: 20 Aug 2024 07:02am
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What flooring are you considering now ?
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Brettny
Member
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# Posted: 20 Aug 2024 10:13am
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I'm doing vinyl plank flooring with poly iso foam under the subfloor. With no air gap you leave little room for moisture.
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jsahara24
Member
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# Posted: 20 Aug 2024 03:45pm
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I had our place spray foamed, best decision I've made....
First of all it sucks crawling around underneath the cabin, let alone having to install rigid foam board while crawling around.
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TF1
Member
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# Posted: 20 Aug 2024 07:14pm
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Thanks. I’ll start to price out both iso and spray.
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Nobadays
Member
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# Posted: 21 Aug 2024 01:50pm
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Quoting: jsahara24 I had our place spray foamed, best decision I've made....
Same here! We did under the floor one year and then the perimeter skirting the next.
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TF1
Member
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# Posted: 22 Aug 2024 02:08pm
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What R value did you have sprayed? Early quotes are 20/31.
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