where do you get data on 2x4 boards loosing 1/2 the thermal heat of 16" on center walls? Wood is an insulator. If you have good insulation between the studs, you wont have 1/2 heat loss?
Yes doing an extra layer on your external wall is best, has anyone heard of double pane windows, or triple?
A 2x stud is under 2" thick, about 1.5" (which helps your insulation). 16" on center, you have 14.5" fiberglass batt insulation, 1.5" wood.
If thermal conductivity of wood is 10 times that of the fiberglass insulation, half you heat would escape through each.
Insulation is usually quoted in R value, and thermal conductivity in units representing the inverse.
R value is BTU/hour lost through 1 square foot area of material 1" thick if 1 degree F temperature difference between inside and out.
(for engineering Conductivity is usually quoted as W/mK, Watts conducted per degree K (or C) through a cube 1m thick, 1m x 1m area.
thicker (Z) of course reduces conduction, and more area (larger X or Y) increases conduction.)
en.wikipedia.org
Table on that page shows:
High Density Fiberglass Batts R3.6 to R5
Softwood (most) R1.41
Hardwood R0.71
So using these numbers, fiberglass insulation is 7x higher R value that hardwood, 3.5x higher than softwood.
Also I read that wood conducts heat better with the grain than across it.
My "half the heat loss" figure appears close given these values.
If area of studs is 1/10th area of insulation, R value of wood in parallel with insulation is:
1/(1/(10/11*5) + 1/(1/11*1.41)) = 3.52 for softwood, a bit better than half of R5
1/(1/(10/11*5) + 1/(1/11*0.71) = 2.87 for hardwood, slightly better than half of R5
These R values are all for 1" thick wall; yours might be about 3.5" for 2x4, 5.5" for 2x6
Yes I am well familiar with the insulation properties of wood. the point is 1/2 of the heat is not lost through the 2" wide space between the insulation panels. That's all. Its not that inefficient. If one would use metal frame studs, then you can reduce the heat loss even further. I think we have digressed from the OP topic.
According to the math I just did, almost half the heat is lost through the 1.5" wide space between insulation batts.
It is that inefficient. Or, fiberglass insulation is that good, approaches point of diminishing returns.
Since OP wanted to avoid losing heat through the walls, I pointed out that a thermal break to block heat through the studs could insulating value. Polyurethane is 4x better than wood, so a 1" layer over a 4" thick wall would cut loss through wood in half, reducing loss through wall (if no windows) by 25%.