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Small Cabin Forum / Cabin Construction / Mold prevention
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# Posted: 31 Oct 2018 19:19

My place is an 1800 log cabin, chinked with new windows and doors. It's pretty air tight. But as a result, it stays pretty cool in there, especially in the summer. You open the door and warm air gets in and you get moisture. Now I haven't seen moisture but I know it's there as there is a slight musty smell. The attic is not insulated but I'm afraid if I do, it'll seal it up tighter causing more of a temperature differential. 2 questions...should I insulate and what do you do to keep moisture out?

# Posted: 1 Nov 2018 13:26

We wrestled with mold this summer becuase I insulated ceiling and walls with a concrete slab. The slab was not insulated and no vapor barrier. I knew i would have a moisture problem after i put the foam board insulation between rafters because i hadnt put roof vents in. I began to put a steel roof over the old shingle roof this week and had to cut in a ridge vent. There was some dampness in the peak on the plywood when i opened it up. I wasnt too concerned because the cabin was closed up tightlike that for a few months and the plywood is solid. After the ridge vent I'll install soffit vents so the roof can breath. I have about a 3/4" gap between the foam sheeting and the roof plywood for air flow.

I didnt put vapor barrier on the inside walls because the outside plywood has probably 6-7 coats of paint and i didnt want to trap moisture in the walls. My thought is insulate but let the cabin breath. Its only 240 SF so a little air passing through the walls is nothing. I have a digital humidity meter hanging on the wall and if the moisture problem returns next summer, I may install a small bath fan on a humidistat.

# Posted: 1 Nov 2018 18:56

Yeah, I should have put in a ridge vent. I do have soffit vents. I have a crawl space with sandstone foundation, dirt floor with vapor barrier. The floor is simply plywood with a 3/4 cedar floor.

# Posted: 5 Nov 2018 13:42 - Edited by: KinAlberta

Hope this ties in with the discussion. Don’t mean to hijack the thread.

Last fall I noticed a lot of moisture in our cabin. First time I’ve ever noticed that. I guessed that I’d trapped it in there on the last visit or it was due to the considerable fall rains and then an early freezeup.

Anyway, it got me thinking that since we had an attic space, may I should be cracking open the attic hatch prior to long unoccupied periods. (Or creating a venting system -maybe a couple vents (sealable vents) to pull a bit of air through when the building is empty). Maybe even pulling in attic air and counting on the whirlybirds to create air exchange.

We have soffit vents and whirlybirds so they are creating circulation in the attic. Opening up the hatch might have prevented the moisture buildup - but would also likely pull some moisture in when the outdoor humidity rises.

Are you getting condensation build up inside your Log Cabin? | Cabins Unlimited p-inside-your-log-cabin/

# Posted: 6 Nov 2018 08:33

I recently started a Mold thread on here, too re. moisture issues at my cabin this year...there was some good advice from folks , so that may be helpful to find the thread and review it.
I had to seal my cabin up like a drum (insulation and vapour barrier - code requirements) and for the first time ever had mold in the cabin this summer because of the humidity. I cracked all my windows for a few weeks and then - like KinAlberta suggested- I made a small screen door to replace my attic door when I'm not there to promote air circulation. There was no mold upon my return...but that could also have something to do with the Fall season and temps / humidity equalizing, getting cooler, etc. A few guys did post to say they noticed mold in their cabins first time this year because it was such a wet summer in many parts of Canada and USA. Cheers!

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