Humidity too high in cabin

[Chew]

Hey guys. Looking for some advice.

We will be living in a 20x16 cabin for several months while we build our retirement home. It's very humid inside. I'm running a pretty big dehumidifier when we are there on the weekends. Seems to help us get some sleep...but it's still too humid. Wife is uncomfortable and wants me to fix it. Everything just fills damp...but not visibly so.

Description of cabin:

Basic hardiplank type "storage shed". Framed out with a 7x7 restroom, and the rest is open space. Put this insulation in all walls:





I'm thinking the problem may be the ceiling. I only put up some foam type insulation. I think it was 1/2" thick. Stapled to the inside of the roof.



Cabin isn't really air tight due to the shoddy construction. We can see some daylight around these eaves, but haven't had any problems with insects or leaking.



Cooling is from a mini-split AC....definitely rated for more square footage than we have...but just can't cool us off due to the humidity...

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So...looking for advice to reduce the humidity. Will rolled insulation in the ceilings help? I just haven't had time to do that and find a suitable ceiling material to cover it. I really don't want to pull all the foam insulation sheets from between the rafters (stapled up there), but not sure the rolled insulation will fit. Suggestions? Anything else that may help?

Thanks!

[lanceodom]

I would think you need to have a vapor barrier on the floor. something to keep the ground moisture from coming up.

[Dale Moser]

Humidity too high in cabin

An AC guy will probably be able to tell you right away. At first glance I’d put batt insulation in the ceiling, you can leave the foam and staple the batts in to the rafters, they have paper at the edges for that. Use great stuff foam on any and all gaps, and holes, and put something over the floor. Add a window unit ac to the other end if needed.


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[Quackerbox]

I pretty much have the same thing at our camp with a 15,000 BTU window unit. Even in September we dont have that issue and it will freeze you out once the sun goes down. Its 12x20

I do have vapor barrier on all but maybe 5x10 of the floor along with the walls, I have R19 in the walls and 21 in the ceiling which was stapled in and put some tin and beadboard over that. Mine is set on blocks if that matters. Composite roof but will probably put tin over that this deer season

all that said, I try some batting in the ceiling. If that dont work, vapor barrier on the floor and lay another layer of plywood over it. Or you could try to add some foam sheets under it if there is room for that. Ive been meaning to do that to mine and havent. The floor gets cold when we see 40 and lower temps

[SabineHunter]

Chew, I believe that until you keep air from circulating from outside, the cabin will always be humid. A dehumidifier will suck that air in too. First thing that must be done is plug those holes.

[Fordnandez]

If the unit is too big for the space it is probably short cycling and not running long enough to get the humidity out of the air.

[Traildust]

Bigger A/C Bobby. Foam those cracks

[Quackerbox]

If the unit is too big for the space it is probably short cycling and not running long enough to get the humidity out of the air.

this is also possible. You can actually oversize and AC

[Snowflake Killa]

Dehumidifier fixed my problem

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[dclifton]

i suspect roof insulation is your problem. Bat it like Dale said. Ac being to big is a valid thought also. What if you lower temp way down. kind of weird its not getting better in the evenings.

That 1/2 foam board has little R value. It takes 1-2in to really get somewhere.

[S-3 Ranch]

this is also possible. You can actually oversize and AC

My vote, a over or under on Hvac, I am clueless on mini split, window unit might help

[Chew]

I can't really do anything with the floors....have laminate down on padding. A skinny feller might be able to put something underneath the building. Thanks for all the input. I'll start with spray foaming gaps and insulating the ceiling.

[Benno]

If the unit is too big for the space it is probably short cycling and not running long enough to get the humidity out of the air.

X2. Sounds like your AC isn’t running long enough to remove the humidity. I have basically the same set up. 16x20 Camp is raised 3’, no floor insulation, R13 in walls and rafters. I have 2 5000btu units. 2nd one is for summer time during the day, have never had any humidity problems. And I promise my camp house is not air tight. Hell its not even wasp tight.

[Chew]

Well the mini split cost too much to downsize so that ain't happening. Seems to run quite a bit without shutting off so I'm not sure what's going on with that. I'll work on some of these issues and see if it helps

[Dusty Britches]

Bobby I have found fans help a lot with humidity. I hate having to turn on the AC but the humidity usually drives me to it. So I run the ceiling fans constantly. Also, in my 12x14 shop, I run a turbo tower fan. The circulating air helps a bunch.