We are having a wood shed 12’x14’ built to house a small (7’x7’) above ground heated therapy pool so we can use it year round. The shed/building is being built on a gravel pad with no wooden floor due to weight of the water and to avoid damage if a leak should happen.

We have a window on each end of the 12’ dimension that can be opened, two windows along one of the 14’ walls, and several windows along the same 14’ wall, up high. They can be opened as well. The pool will be heated to about 85-90 degrees. We want to heat the inside of the building with a sealed electric oil heater.

We are concerned about humidity and want to know the best way to insulate the building and not trap moisture in the walls to cause mold.what would be some products we could choose from.

Is there anything that should be applied to the walls before insulating and what do we need on the room side of the insulation. We are not looking for a fancy finish. We just need functionality with a reasonable budget consideration.

Any suggestions would be appreciated.


Rethink the number of windows. Any window is going to be a condensation nightmare fall, winter and spring with an 85-90 °F pool in the building. If it's a window that came with a "garden shed" it will probably be atrocious in thermal performance, as garden sheds are not typically heated and good windows are expensive, but even a good "high performance" window is a spot of terrible insulation in a well insulated wall, and that means that it will be cold, and with an open warm pool in the building it will drip most of the year.

Given small pool and high temperature differential, I'd rob some interior space to make a very thick wall (another set of studs, offset from the studs of the wall) with lots of insulation, and a roof structure that allows having a lot of insulation and a vented, cold roof on top of that.

This basically means building a room inside the cabin so you have adequate space for a lot of insulation material, since working with the (presumably 3-1/2" thick) spaces provided between studs will be woefully inadequate. Using a well-detailed (all holes get fixed, try not to make too many) vapor barrier on the inside keeps the insulation dry. Cellulose tends to tbe the best cost ratio when you provide the space, rockwool is another good option.

The other approach to this would be to use sheet foam products, filling the wall cavities with insulation, and installing vents in the roof cavities before sheeting them over (leaving them empty for ventilation) with rigid foam on the interior, sealing the joints for vapor-tightness and then finishing with a fire-protective layer such as drywall (foil faced foam MAY qualify in some areas. Exposed foam is a deathtrap in a fire due to the fumes it releases.)

  • A lot of closed cell spray foam insulation is "fireproof"
    – Seth B
    Feb 8 '21 at 16:31
  • ...and a lot of it isn't...
    – Ecnerwal
    Feb 8 '21 at 22:49

Use closed-cell spray foam

Closed-cell is water resistant and has VERY high R value

I have no connections with Eskimo Insulation

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  • 1
    Eskimo insulation. That guy looks familiar. OH wait, he is in Texas. Texas, really?. If you split Alaska in half, Texas would be the third largest state. Closed cell foam is an insulation and a vapor barrier in one.
    – Alaska Man
    Feb 8 '21 at 0:40
  • OK, I'll say it. That "comparison" chart is useless. It doesn't compare anything! Also, while the insulation itself may be water resistant, what does the OP need to do to protect the rest of the structure from the 24/7/365 humidity bath it will be exposed to?
    – FreeMan
    Feb 9 '21 at 14:03

It doesn't matter what wall material you use or how much insulation there is inside the walls. What you want to focus your attention on is exhausting the moisture before it settles on the walls.

There are moisture sensing fans (hydro static?) that turn on when a set moisture level is reached.

Gable vents or exhaust fans will prevent moisture from accumulating. Placed higher on the wall is best to remove rising steam and moisture.

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