- If it gets wet, even once, you're screwed.
- Very difficult to air-seal any butt joint, such as to a post or window buck. We're kind of stymied here.
- Dimensional instability - sagging and settling opening gaps.
- Labor-intensive construction method.*
Redbeard's quite concerned about the air sealing of this cottage. I have one half-assessed data point to back him up. Thursday-Friday the inside temperature held pretty steady at 70 F with the 17000 Btu backup heater running flat out. The outside temp was (I think) pretty steady around 20 F. In steady state:
Q = U*A*(Tin-Tout)
17000 Btu/h = U*A*(70F-20F)
UA = 17000/50 Btu/hF
A=Awall+Aroof=2*(18*12+43*12) + 18*43=1464+774=2238 ft^2
U = 17000/(50*2238) = 0.152 Btu/hft2
R = 1/U = 6.6 hft2/Btu
R 6.6 seems pretty bad for a cottage with nominally R 100 walls and ceiling. I think it is an indication of the awesome power of air infiltration to undermine efforts at super-insulation. This is admittedly a crude calculation on a shallow database. If you assume for example that half the heater power was going into the ground, you could justify R 13 for the above-grade structure. La-de-da.
That R 6.6 is however, about three times better than the long term average R-value which Kimpossible and I came up with for Powerpole's more conventional type of house, based on several years of propane bills. His nominally R 13-19 sort of house was effectively about an R 2.2.
*Postscript: Your correspondent has struggled to understand why some people in the sustainability movement are so positive on labor-intensity. To me it seemed like an obvious step backward. My current understanding is that labor-intensive approaches make sense if your economy is bad and there is a lot of unemployment, such as in a lot of the third world and potentially in the first world, post-gridcrash.