Depending on whether they used single or double top plates, the board footage
can be the same.  Wood usage and wall thickness are not the only considerations.
The wood used has a relatively low R-value (insulation value, Jeff) per inch, so
the overall efficiency of the wall is helped by reducing the amount of wood that
is exposed to the outside - fewer studs, less exposure.  This is called thermal
bridging.

And now it is recognized that a thin layer of rigid insulation is a good way to
further break the thermal bridge.  Even though an inch of this foam board is
only R-6 and boosts the insulated part of the wall by a third, it more than
doubles the R-value of the framing.

Ed Minch
If it's true that we are here to help others, then what are they here for?


On Apr 17, 2014, at 8:49 AM, Stager, Scott P.  wrote:

> My house (in central Missouri) was built in 1983.  Passive solar was the big
thing back then, and the desire to increase insulation R value on the walls was
rampant.
> 
> Outside walls were framed with 2x6 on 24" centers.  Too lazy right now to
calculate the total wood consumption difference, and don't have the engineering
background to determine the relative stiffness of the two options.  2x6 allowed
thicker batts of fiberglass insulation in the walls.  Probably reduced labor
costs also since fewer framing elements needed to be assembled.
> 
> --Scott