WAC 51-11-1009   Section 1009 Mass.  


     1009.1 General: Tables 10-9 and 10-10 list default mass values for concrete masonry construction. Calculations are based on standard ASHRAE values for heat-storage capacity as listed in Standard RS-1, Chapter 25.


     Thermal capacity of furniture is ignored, as is heat storage beyond the first four inches of mass thickness. All mass is assumed to be in direct contact with the conditioned space. Concrete separated from the heated volume by other materials must multiply the listed concrete mass value by the result of the following formula:


     Ln(R-value) x (-.221) + 0.5

     Where:

          Ln = Natural log

     R-value = R-value of material covering concrete


Note: All default values for covered concrete slabs have been adjusted according to this procedure.

     1009.2 Mass Description: Mass is divided into two types: Structural and additional.

     Structural Mass: Includes heat-storage capacity of all standard building components of a typical residential structure, including floors, ceilings, and interior and exterior walls in Btu/ft2 • °F of floor area. It also assumes exterior wall, interior wall and ceiling surface area approximately equals three times the floor area.


     Additional Mass: Includes any additional building material not part of the normal structure, which is added specifically to increase the building's thermal-storage capability. This category includes masonry fireplaces, water or trombe walls, and extra layers of sheetrock. Coefficients are in Btu/ft2 • °F of surface area of material exposed to conditioned space. The coefficient for water is Btu/°F • gallon.


     1009.3 Component Description: Light frame assumes one inch thick wood flooring with five-eighths inch sheetrock on ceilings and interior walls, and walls consisting of either five-eighths inch sheetrock or solid logs. Slab assumes a four-inch concrete slab on or below grade, with five-eighths inch sheetrock on exterior and interior walls and ceiling, and with separate values for interior or exterior wall insulation. Adjustments for slab covering is based on R-value of material. Additional mass values are based on the density multiplied by the specific heat of the material adjusted for listed thickness.


TABLE 10-9

HEAT CAPACITY
  Partial Grout Solid Grout
8" CMU 9.65 15.0
12" CMU 14.5 23.6
8" Brick 10.9 16.4
6" Concrete NA 14.4


TABLE 10-10

DEFAULT MASS VALUES
Structural Mass M-value Btu/ft2 • °F floor area
 
Light Frame:  
Joisted/post & beam floor, sheetrock  
walls and ceilings 3.0
Joisted/post & beam floor, log walls,  
sheetrock ceilings 4.0
 
Slab With Interior Wall Insulation:  
Slab, no covering or tile, sheetrock walls and ceilings 10.0
Slab, hardwood floor covering, sheetrock walls and ceilings 7.0
Slab, carpet and pad, sheetrock walls and ceilings 5.0
 
Slab With Exterior Wall Insulation:  
Slab, no covering or tile, sheetrock walls and ceilings 12.0
Slab, hardwood floor covering, sheetrock walls and ceilings 9.0
Slab, carpet and pad, sheetrock walls and ceilings 7.0
   
Additional Mass M-Value: Btu/ft2•°F surface area
Gypsum wallboard, 1/2 inch thickness 0.54
Gypsum wallboard, 5/8 inch thickness 0.68
Hardwood floor 1.40
Concrete/Brick, 4 inch-thickness 10.30
Concrete/Brick, 6 inch-thickness 15.40
 
Btu/°F•gallon
Water, 1 gallon 8.0




[Statutory Authority: RCW 19.27A.020, 19.27A.045. 04-01-106, § 51-11-1009, filed 12/17/03, effective 7/1/04. Statutory Authority: RCW 19.27A.025, 19.27A.045. 01-03-010, § 51-11-1009, filed 1/5/01, effective 7/1/01; 98-03-003, § 51-11-1009, filed 1/8/98, effective 7/1/98. Statutory Authority: RCW 19.27A.020 and 1990 c 2. 91-01-112, § 51-11-1009, filed 12/19/90, effective 7/1/91.]