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Thoughts on insulation for a no-HVAC house.

Started by JonahAP, December 22, 2019, 03:33:41 AM

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JonahAP

 

 

So, I'm in the preliminary planning stages of a TF house. Right now, I've got the basic idea laid out (pending input from the wife), so I'm trying to figure out to insulate the thing. Most, if not all, of the how-tos that I've read are predicated on a TF frame having either SIPs or a conventional frame shell over the outside, along with the usual vapor barriers all the way around. And, granted, that works, but it requires having HVAC to control moisture, and I'll be off-grid, running on solar, so running a house fan 24/7 just won't happen.

Plus, for the amount of work I'm putting into this, I want the aesthetic beauty of dark timbers and white plaster, because it's about as choice as houses get. Lime plaster is bug resistant, weather resistant, looks good, is easy to maintain, etc, and will last centuries if kept up. However, I'm in climate 5B, and I can't ignore the 10*F winter nights here, so insulation is a requirement, and the traditional methods aren't necessary as good in that regard as the new ways.

What I want to do is build the TF in the usual way, do the traditional lathe-and-plaster on the outside, then spray the back side of the lathe, after the plaster hardens, with a thin (1" or so) layer of open-cell insulation foam. That *should* pretty permanently fix air gaps, because the foam will have some flex to it thus preventing the aging of the house from opening gaps. I'll fill the bulk of the rest of the space (9" out of a beginning 12") with fiberglass batt insulation or similar, then panel the inside with whatever wood we choose. 

For the roof, I basically want to do this in reverse. I'll deck over the purloins with 1" boards, spray the foam down on that, and then fill the roof box with insulation, then skin that with plywood and attach ye olde water barrier. I'll put rows of 1/2" strips down over the water barrier, and attach the metal roof to that, thus giving it a bit of airflow to prevent moisture from accumulating anywhere.

The bottom floor will be done the same as the roof, basically. Floor, spray foam, and batts.

This *should* leave me with a waterproof (but vapor permeable) house, so I won't need to worry about household humidity rotting the house. Obviously, I'll have vent fans for the kitchen and bathrooms, but I shouldn't need to do much more than that for the house. Summers are hot and dry, and we don't have AC in the house we have now, so we know that works for us. In the winter, we'll have a woodstove or fireplace (decision pending finances) to heat the house.

I've attached a pic of the basic idea.

Is there anything I'm missing? Moisture control seems to be one of the biggest problems in building a house, so I wanted to get a second/third/dozenth opinion before I get too set on a plan.

Ljohnsaw

 :P
Hmm, to tell you the truth, I never even thought about moisture control on my project.  Still not framed but plans approved, foundation in, floor joists in.  I plan on a full timber frame, 1" cedar boards on the outside walls, 2" pine roof planks, Tyvex, 5" Styrofoam wrapped on the walls, 6" on the roof.  Then 1x4 vertical strapping with Hardi plank wall board.  Roof will have 1x4 vertical then horizontals for a metal roof.  Wood stove heat, no A/C - off grid.  I will have an exhaust fan in the bath and kitchen.

Looking forward to comments on this thread.
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

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