Energy Source Builder
What's in a Wall
When you put an R-21 batt in a wall you call it an R-21 wall. Of course, that's not right. The framing in the wall, which can make up as much as 30 percent of its area, reduces the wall's overall insulating value.
When the vast majority of walls were framed with lumber, the framing factor was a concern mostly to energy purists. Now, half a dozen wall systems compete for attention and each claims an R-value. The table below can help you compare the insulating value of several common wall types. The data from the table comes from several sources as indicated.
The R-values for steel framed walls were taken from an amendment to the current ASHRAE Standard 90.1 (commercial buildings) and currently in the final stage of approval for the residential building standard (90.2). Several research projects are currently underway to measure the impact of steel framing on insulating value. At this point there's little doubt that steel framing substantially degrades R-value.
#...Description.............Cavity Ins......Foam Sheathing.......Framing
1...Wood-Framed Wall............R-11............none.............2x4 (16 o.c.)
2...Wood-Framed Wall............R-11............R-5..............2x4 (16 o.c.)
3...Wood-Framed Wall............R-19............none.............2x6 (16 o.c.)
4...Wood-Framed Wall............R-19............none.............2x6 (24 o.c.)
5...Wood-Framed Wall............R-21............none.............2x6 (16 o.c.)
6...Wood-Framed Wall............R-21............none.............2x6 (24 o.c.)
7...Wood-Framed Wall............R-21............R-5..............2x6 (24 o.c.)
8...Steel-Framed Wall...........R-21............none.............2x6 (24 o.c.)
9...Steel-Framed Wall...........R-25............none.............2x6 (24 o.c.)
10..Steel-Framed Wall...........R-25............R-5..............2x6 (24 o.c.)
11..Foam Core Panel (3.5" EPS)..R-13............none.............none
12..Foam Core Panel (5.5" EPS)..R-21............none.............none
13..Ins. Conc. Form (Sheet) EPS foam............none.............none
14..Ins. Conc. Form (Block) Polyiso. foam.......none.............none
Sources:
Bonneville Power Administration
ASHRAE Standard 90.1g
Ecotope, Inc.
This article appeared in Energy Source Builder #34 August 1994 |
