14x24 Little House in the desert

[chili]

My plans arrived (yay!) and I'm trying to work a few things out before I get started on my 14x24 Little House.

My property (20 acres) is in the chihuahuan desert and my goal is to maximize insulation to keep cool (bulk of the year) and warm in the winter. My initial thought is to frame with 2x6s and use the pink fiberglas R-21 sandwiched between layers of foil bubble wrap insulation with two inches of perlite concrete on both the exterior and interior for a total of roughly R-46. On top will be pink fiberglas R-38 and foil bubble wrap with a light colored metal roof.

The rear of the house will face south with no windows. I will put solar fans there in place of the transom windows for air circulation. I found an interesting rocket stove design that I may use in place of a wood stove since there isn't a supply of timber in the area. Lots of bushes, though.

There will be two windows in the bedroom and kitchen and one entry door.

[John Raabe]

You may be overdoing the walls. For a small house like that going to 2x6 w/ high density batts makes sense and perhaps doing an inch of foamboard as well. But you want to match these insulation levels in the roof and floor before going further with the wall.

The only system that I have heard of where reflective foil insulation actually worked was in a vented attic where it could re-radiate the roof heat. Even there as dust built up on the foil its insulation effectiveness went down to almost zero. Much more effective (and cheaper) is putting on a white roof. Rereading your post I see you are already considering this.

You can probably use evaporative cooling with your fans. Assume there is no power for a small AC.

Info on reflective bubble wrap as insulation: http://www.healthyheating.com/Page%2055/Page_55_o_bldg_sys.htm

[chili]

Thanks for the link, John. Very interesting on the inefficacy of foil-backed bubble wrap insulation. The floor and roof will definitely have as much insulation as I can apply.

The property is off-grid and I will have an approx 1kw solar/wind system. One problem I've found so far with dc ac units is the upper limit of the ambient for them to operate well and they are very pricey. My little corner of the desert is often above the 110-115 degree limit. Fans, misters and siestas will be the order of the day.

[John Raabe]

Here is a pretty good research article that was in JLC - might have an actionable idea or two.

http://www.coolmetalroofing.org/elements/uploads/news/TMI_CaseStudy_13.pdf

[chili]

Great article. Thanks, John. I knew the light colored metal roof is definite for my project.  I'm planning a shed/flat roof. Would a single or double layer of R-38 along with a radiant barrier beneath the metal roof be the best way to go?

[chili]

Never mind. I just realized building a 2' space beneath the roof is silly. One layer of R-38 and the radiant barrier should suffice coupled with the light metal roof.

[John Raabe]

I would provide a vented area above the radiant barrier.