There is a wall section in this project with 4? thick interior polyurethane
spray foam inside the metal studs.
Since Table A9.2B of ASHRAE 90.1 does not provide the effective
insulation/framing layer R-Value for this type of insulation, how can one
calculate this value?
Your thoughts and suggestions would be highly appreciated,
Morteza
I would just pick the R-value for insulation (21, 25?) that best matches the R-value of 4 inches of polyurethane spray foam. The depth of the cavity doesn?t make much difference to the end result. If the R-value you?re aiming for isn?t 21, or 25, just interpolate using the numbers in the table. Note that small differences in the R-value don?t make much difference to the effective R-value as thermal bridging has such a strong effect.
?
Daniel Knapp PhD, P Phys, LEED AP
danielk at arborus.ca
Energy Efficiency Expert
Arborus Consulting
2-43 Eccles Street
Ottawa ON K1R 6S3
(613) 234-7178
I concur with Daniel 100%.
If you really want to run the math however for an odd case, look to Fundamentals (page 27.6 in the 2009 edition) to explore the ?Modified Zone Method for Metal Stud Walls with Insulated Cavities.?
~Nick
[cid:image001.png at 01D300AA.308F14C0]
Nick Caton, P.E., BEMP
Senior Energy Engineer
Regional Energy Engineering Manager
Energy and Sustainability Services
Schneider Electric
D 913.564.6361
M 785.410.3317
F 913.564.6380
E nicholas.caton at schneider-electric.com
15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States
[cid:image002.png at 01D300AA.308F14C0]
I agree with Daniel on this one.
If you wanted to go above and beyond, you could check out Table A3.3 in the section A tables of 90.1 since it has effective overall U-factors and R-values for different construction types and insulation applications ? to include steel framing @ 16 o.c. and 24 o.c.
You can select from the insulation R-values for each construction type and from there you can get the overall U-factor for the entire wall assembly which might also come in handy for any detail edits you might need to make.
There is also an R-value calculator online that will allow you to model each wall component and calculate the overall/composite R-value of the system. It might just be interesting to compare it to the ASHRAE 90.1 numbers in Section A tables or other values online.
Chris Baker
CCI Alliance of Companies
Fort Wainwright, Alaska
907-356-1681 (x105) office
907-750-4922 cell
Nathan, Daniel, Nick and Chris,
Thank you all for your helpful recommendations and guidance.
Morteza