2 x 4 vs 2 x 6

[flyingvan]

Is the 'R' scale a linear function, or an exponential one--in other words, say I built two identical structures except one had a net R value of 1 and the other of 4.  I heat them both to 80 degrees when it's 32 degrees outside.  I shut the heat off.  House R 1 reaches outside temp in, say, 8 hours---would house R 4 take four times longer?  16?

[MountainDon]

Linear. Double the thickness of a layer means half the heat transfer and double the R-value. Similar to electrical resistance.


And it is meant to only measure heat transfer via conductivity IIRC. The numbers touted by those that sell radiant barriers only apply to radiated energy and are not the same as the R-values used for what I call normal insulation... batts, foam... which are thermal conductive insulators.

[Don_P]

Right, R is the resistance to the flow of heat. The radiant bubble wraps are about R1 although their performance can translate to much higher if installed ideally. The interior air film I was talking about is the boundry of still air alongside a wall, I've been told the blind can feel it when approaching a surface, I'm not tuned in that well. It has an R value of about .66 on the interior face of a wall and about .17 on the outside where wind keeps it swept thin. Quadrupling the R value will not quarter the building's response or energy use, there are too many variables to make that statement but that insulation will be 4 times as resistant to the flow of heat through it. One variable, windows are ~R2 when the whole thing is done and said. I've built R40+ walls with large expanses of glass. Where do you reckon the heat decided to leave from. Sort of like putting on a down parka but not zipping it up.