Masonry Magazine July 2011 Page. 29
Component Weight Calculation
Component | Weight (lb/ft²) | x Fraction of Wall | x Specific Heat | = HC
------- | -------- | -------- | -------- | --------
8 Partial Grouted CMU | 46.00 | 1.00 | 0.21 | 9.66
2x4 Wood Studs | 9.30 | 0.15 | 0.33 | 0.46
R-11 Batt | 0.25 | 0.85 | 0.30 | 0.06
5/8" Gypsum Board | 2.60 | 1.00 | 0.26 | 0.68
Total HC = 10.86
under "mass walls" in the body of the table for above-grade walls. Area weighted averaging of U-factors is allowed for compliance under Section 1322. Note that footnote 1 of Table 13-1 (Climate Zone 1) still permits an exposed, partially-grouted concrete masonry wall to comply when the ungrouted cores are filled with foam, rigid inserts, or poured insulation. Also, note that the previous minimum heat capacity value of 9.0 has been changed to either 7.0 or 5.0 as discussed previously.
There has been some confusion regarding the calculation of heat capacity values to meet the "mass wall" definition of the Washington code. To determine the heat capacity of a wall assembly simply take the weight per square foot of the wall layer and multiply it by the material's specific heat. Then add the values together if there is more than one layer. The calculation can be structured in tabular form as shown below.
The heat capacity values in Table 1 include common single-wythe masonry walls as found in Table 10-9 of the code. In addition, values for brick veneer and a masonry
There's been confusion as to calculating heat capacity values to meet the "mass wall" definition of the Washington code.
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July 2011
MASONRY 27