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I live in north TX near Fort Worth. Not a humid place but a very hot place, averaging 104 degrees in the summer outside in afternoon.

I was planning to buy a Tuff Shed 16 X 20 shed with asphalt roof and a standard home door and a single small window. I contacted Tuff Shed and discussed my interest in making this a climate controlled building with air conditioning/heating unit and insulation.

They said that insulating it would be something I would have to set up on my own.

But, I don't know how that is possible as they pre-fabricate walls with OSB siding. Essentially 2 x 4 framing and OSB. I have a TS now and they are very solid and well built. Been in place for 11 years without issue.

I would think the shed would require a climate barrier layer wholesale on the shed prior to siding. In other words a plywood layer with vapor barrier and then siding. Does that make sense?

This implies that Tuff Shed may not be the best route to go but rather a custom built shed if climate control is desired.

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You probably don't need to worry about a vapor barrier in your climate. Most building scientists recommend against them since they impede drying of the structure in at least one season of the year. (They are still required for northern climate zones) While it would be best to have a continuous layer of insulation under the siding, homes have been built without such for many years. Between 40-50% of your energy escapes through air leaks, not insulation and while air sealing the sheathing is easiest it is still possible to do a good job from the inside.

The best solution would be to spray foam the wall cavities, ideally with a closed cell foam. This gives you a nice airtight seal, and the foam has a high R value per inch. This is, however, probably cost prohibitive for a small project. (If you could combine it with upgrading your home insulation it might be worth considering)

If you are handy I would recommend "poor man's spray foam". Basically you fill the walls with sheet foam panels that are cut slightly smaller than the width between studs. The gaps are then filled with canned foam to make a nice airtight seal. This gives much of the same benefits as spray foam but it is slightly cheaper and more DIY friendly.

Once you have the walls insulated you can put up a drywall or interior paneling, again working to make the system as airtight as possible.

If the building is nice and air tight you should be able to climate control with a mini-split heatpump and you will have a very comfortable space.

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I did get some feedback from Tuff Shed and I posed the question of "can they accommodate my request for vapor barrier" and they forwarded that onto a person who can answer it properly in a timely way. They do not supply any insulation or insulation installation. The only option I see so far that they offer is radiant barrier.

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Since these are the same kinds of design challenges as a "Tiny House", you might want to cast your net a little wider, and look at actual Tiny Houses. There's quite a community online.

People have put good design and testing into building structures that are "more than a shed". You don't need all their tricks, but they can save you a bunch of time reinventing.

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Tuff Shed is too smart to get involved with vapor barriers and insulation.

Normally the vapor barrier would be installed on the inside of the wall, but if you air condition the space, then the vapor barrier should be installed on the exterior side (which could be the moisture barrier under the siding).

Remember, moisture (in the form of vapor) moves from the warm side to the cool side. When it hits the Dew Point, it turns to moisture. Keeping the vapor out is done by correctly placing the vapor barrier on the correct side of the wall.

  • Recent experiments have shown that most moisture that enters wall cavities does so via flowing air. Actual vapor diffusion is fairly low. In most cases if you control bulk water ingress and have a tight, continuous air barrier a vapor layer actually causes more problems than it solves. – mfarver Jul 12 '18 at 0:36

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