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TF1
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# Posted: 31 Dec 2024 10:43am
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800 sqft cabin, raised in Quebec. R22 on wall and cathedral ceiling. I have quotes for both r20 and r31 for the floor joists. Cabin is mostly used 3 season and maybe 6 times over winter. Predictably we have condensation on plastic floor items when heating up in the winter. Insulation should clear this up but I’m not sure if I want to match the rest of the building levels or go higher on the floor. Thoughts and opinions welcome. Difference is about $3k, but I could use that difference on flooring ….
Any issues with going with a higher R value ?
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gcrank1
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# Posted: 31 Dec 2024 12:49pm
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Our use profile in south-central WI is similar and 3 diff cabins (fwiw, none has/had as good insulation topside as yours).
#1, 30+ years: 1" blue DOW styro under floor between joists. No condensation on floor stuff
#2, 3years; a shack, no insulation on floor other than 2 layers of board and some cheap linoleum and a thin old carpet (at least it stopped the drafts from below). No condensation on floor stuff
#3, new this past spring, 2" styro under floor, last used 2 days ago (got it up to 82*f inside with LP heater). No condensation on floor stuff
Observations: I sure think I like the 2" best, I KNOW I like it better than the none of the shack! Would 3" or 4" be noticeably better or with the law of diminishing returns would it so incremental as to not?
Also, we run a ceiling fan (set to blow up) to circulate/mix the air, Im thinking that warm air flow back down the walls and sweeping across the floor must help.
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TF1
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# Posted: 31 Dec 2024 02:35pm
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Thanks - that’s what I was leaning towards. Seems a little excessive given the winter use and other limitations. It’s funny how much of a difference there is between ceiling to floor without floor insulation. It’s like going through three different heat zones 
But I only want to do this once ….
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travellerw
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# Posted: 31 Dec 2024 04:25pm
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You can buy a lot of really nice comfy warm slippers for that price difference. You also have to remember that you will have cold spots due to the joists (they bridge the cold without a thermal break).
I wouldn't spend it as I don't think you would see much benefit.
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TF1
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# Posted: 31 Dec 2024 04:36pm
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Thanks. I know there will always be a bridging issue regardless unless I opted to do xps on floor. I’m actually fine with a cold floor, just not the condensation on all the plastic bins on the floor lol. Ironically the condensation on the bucket of antifreeze was rather humorous.
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ICC
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# Posted: 31 Dec 2024 05:02pm
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I have R25 under my floor. 3/4" OSB plus backer board and then ceramic tile. It takes a full day to be warm enough for socks only. I would always insulate a floor .
In your case I would go R20 or maybe a little less if it saved money you wanted to use elsewhere.
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spencerin
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# Posted: 31 Dec 2024 09:21pm
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Have you ever checked the temperature at floor level, like with an IR thermometer? Condensation on floor items when heating up seems to me to be more due to the surrounding air heating much more quickly than the items themselves, and/or humidity management indoors, than floor insulation. Not saying floor insulation wouldn't help, but there's more to it here, which would also lend support to going with the cheaper quote.....
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travellerw
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# Posted: 31 Dec 2024 11:42pm
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Quoting: spencerin and/or humidity management indoors, than floor insulation.
This is a great point. Moisture can't condense on cold items if the moisture isn't in the air. Maybe get a cheap digital humidity gauge and monitor that.
You would be shocked how much moisture can be brought in from snow on boots. However with wood heat, moisture is usually reduced pretty darn fast
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TF1
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# Posted: 1 Jan 2025 09:44am
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Thanks. Moisture was 60% with no windows open. Nothing else was damp (ie sheets etc). I’m going to pick up a temp gun for the stove so I’ll be able to check shortly. The floor has typically read 12-16 % on the meter with walls at 8%. I was planning on laying down some vapour and covering grade late spring.
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TF1
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# Posted: 1 Jan 2025 09:56am
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I should also say it was on items under the bed or in a closet. Anything out in the open was fine. So airflow would be an issue.
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gcrank1
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# Posted: 1 Jan 2025 10:57am
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Wonder what you'd happen if you put a piece of styro under the stuff that you are getting the condensation on?
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paulz
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# Posted: 1 Jan 2025 12:19pm
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Quoting: spencerin Have you ever checked the temperature at floor level, like with an IR thermometer?
Great idea, I’m going to do that comparing my uninsulated floor with the insulated walls at ground level, cold and heated.
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spencerin
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# Posted: 1 Jan 2025 08:18pm
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60% humidity, although not "high" high, in my opinion is enough to allow condensation. Items in closets are also likely to be colder than surrounding air, also the case with items under beds, where air circulation isn't likely to occur.....
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Brettny
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# Posted: 2 Jan 2025 11:15am
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When heating up a cold cabin your going to get condensation on things. In the warning process you have cold items with hot air. This causes condensation to form on the cold items. Beds being typicaly thenmost insulation take longer to heat up thus stay colder longer.
Last winter we had no floor insulation at all and was getting alot of condensation on a far corner from the wood stove even after days of the cabin being warm. This winter with 4in foam in the floor I get none after the items have warmed up. Our warm up time is about 20*f per hour. We also have the door open alot un packing.
Other things that cause condensation is non vented propane heaters.
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DRP
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# Posted: 2 Jan 2025 08:23pm - Edited by: DRP
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More grist for the mill.
Quoting: Brettny In the warning process you have cold items with hot air.
Warm air does not cause condensation, moist air hitting cold things, below dew point, does. Warm air can hold more moisture. You breathing, your unvented heater, that boiling pot, those are the sources of moisture and the warming air can hold more moisture, enough so that when it hits the cold corners, they are below the dew point and condensation forms on the cold surfaces.
Heating up cold outside air dries the indoor environment. Cold air cannot hold much moisture, without any other moisture input, heat that cold dry air up and the relative humidity crashes.
Plastic doesn't absorb moisture and so moisture condenses on its surface. Other materials like wood or cloth act more as hygric buffers, absorbing minor amounts of moisture and then releasing it when drying conditions resume. Condensation happened but it raised the moisture content of those materials rather than pooling on an impervious cold surface.
Keep an eye on those hygroscopic materials. For instance when wood gets above ~25% moisture content it can support mold and decay fungi when the temps warm back up (the black attic).
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Brettny
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# Posted: 3 Jan 2025 05:53am
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Quoting: DRP moist air hitting cold things, below dew point, does
And you need temperature change for this to happen...like a warming up cabin.
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ICC
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# Posted: 3 Jan 2025 10:44am
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Quoting: Brettny Quoting: DRP moist air hitting cold things, below dew point, does And you need temperature change for this to happen...like a warming up cabin.
If all you do is turn up the heat using a dry source such as electric, vented gas, wood stove with external fresh air supply, the humidity in the cabin will drop. If there is already condensation in a cold corner given time the elevated temperature could cause the conde sation to be reduced. With no other changes other than dry heat no further condensation will occur.
As DRP stated if you introduce more moisture into the warming interior by boiling water, using a non vented heater or having a crowd of people exercise or have hot showers, the equation changes.
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paulz
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# Posted: 3 Jan 2025 11:09am
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I get no condensation in cabin. Non vented wood stove going almost constantly lately. Low of 40f when got here this week. I often dry wet cloths on a rope across the room. Maybe it’s my ‘custom’ non air tight construction.
Old pickup is another story. Often condensed windows, will clear with defroster or driving with windows down.
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gcrank1
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# Posted: 3 Jan 2025 02:13pm
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Our place, dead cold between the occasional trips now, doesn't have a condensation problem even with the non-vented 30k btu lp wall heater. Maybe it is because of having two 1"x 30" window gaps (across room from each other) for combustion air and to vent humidity?
Btw, we did the same with our old wood stove primarily for the combustion air but it sucked any humidity up the stack (pretty much one 1 3/4"x 32" window). And we dried wet clothes whenever we had em as well as keeping a pot of water on for humidity and hot water as needed.
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paulz
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# Posted: 3 Jan 2025 03:55pm - Edited by: paulz
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Quoting: paulz Quoting: spencerin Have you ever checked the temperature at floor level, like with an IR thermometer? Great idea, I’m going to do that comparing my uninsulated floor with the insulated walls at ground level, cold and heated.
We'll finally got some readings. Hardest part was finding the temp gauge, took me two days of going through the cabin junk cabinet. Unfortunately by then I had the wood stove well going. By now, the floor is measuring in the low 60s. The insulated walls are a bit higher, up to mid 60s and the wall right behind the wood stove 71. Double pane windows about the same as floor. Inside temp 73, outside 51.
Going to be another week before we leave and return to do the arrival temp. The good news is I now have the gauge and the junk cabinet is rearranged and relabeled.
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