Stud Spacing and Energy Efficiency
RosetteRemodeling
| Posted in Energy Efficiency and Durability on
How much better is a 2×6 24″ on center wall than 16″ on center? I know it can vary depending on a number of factors, but I was wondering if anyone can give me a rough idea of how much added energy efficiency you get from moving from 2×6 16″ on center to 24″ on center for exterior walls. Thanks!
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Replies
ASHRAE, the folks who authored Manual J, assume 25% framing factor for 16" spacing and 22% framing for 24" framing. Fiberglass 2x6 insulation is R19, wood is 1.25 per inch or R6.9.
At 25% framing factor, your U-factor is 75%*1/19+ 25%*1/6.9= 0.076 which is equivalent to R13.2.
At 22% framing factor, your U-factor is 78% */19+ 22%*1/6.9= 0.073 which is equivalent to R13.7.
You get about a 4% increase in R-value. Using rock wool at R21 instead of fiberglass, at 16" spacing, gives an increase of 5%.
That's all assuming cavity insulation only, correct? If you add continuous insulation, as now required by codes in cold climates, the difference would be even less.
Ekotrope has a great free online tool to help compare and understand the effective R-values of different assemblies: https://www.ekotrope.com/r-value-calculator
Thank you both for the great info!