turally. This is true regardless of flooring type, but something to be especially aware of when the floor will be ceramic or stone tile. That’s because rigid, hard surface floor- ing materials are where concen- trated overloading of a wood frame structure might become visually apparent, in the form of cracks, due to their inability to bend. Baseline weights to factor into dead load To facilitate adequate structural design for tile and stone floors, the TCNA Handbook for Ceramic, Glass and Stone Tile Installation provides the approximate per square foot weight of tile, stone, and installation materials, individu- ally by material type (i.e., 1/2” thick cement board weighs 4 lbs. per square foot) as well as cumulatively by installation method (i.e., Method F144 weighs 8 or 10 lbs. per square foot, depending on whether 1/4” or 1/2” cement board is used). Using this information, located in Appendix B, building designers can arrive at accurate dead loads. Accurate dead load is impor- tant because dead load influenc- es the maximum span (length) of wood joist that can be used, per International Residential Code (IRC) guidelines. These guidelines provide maximum allowable joist span separately for an assumed dead load of 10 psf and 20 psf. Remember though, dead load is not just the flooring. So, while the separate span tables may be gen- erally used according to flooring type (e.g., follow guidelines for 10 psf dead load when lighter floor- ings like carpet will be installed, and guidelines for 20 psf dead load for tile and stone), one should not assume they apply in all situa- tions. Additional dead load could be present from other elements, causing total dead load to exceed 10 psf where a lighter floor finish will be installed or exceeding 20 psf where ceramic or stone tile will be installed. Not to mention, some tile and stone installation methods TECH TALK –––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Table 5: Backer Board and Wood Underlayment Panel Methods Method Backer Board or Wood Underlayment Weight (lbs. per sq. ft.) Mortar Under Board Plywood Underlayment Backer Board Radiant System Mortar Tile Bond Coat Ceramic Tile Stone Total Assembly* (Tile) Total Assembly* (Stone) RH130 15 ⁄32" Plywood 11 ⁄2 13 ⁄4 11 ⁄4 4 7 RH130 19 ⁄32" Plywood 13 ⁄4 13 ⁄4 11 ⁄4 4 7 RH135 1 ⁄4" CBU 1 2 13 ⁄4 11 ⁄4 4 10 RH135 1 ⁄2" CBU 1 4 13 ⁄4 11 ⁄4 4 12 RH135 1 ⁄4" Cementitious-Coated Foam 1 1 ⁄2 13 ⁄4 11 ⁄4 4 8 RH135 1 ⁄2" Cementitious-Coated Foam 1 1 ⁄2 13 ⁄4 11 ⁄4 4 8 RH135 1 ⁄4" Coated-Glass Mat Gypsum 1 11 ⁄2 13 ⁄4 11 ⁄4 4 9 RH135 1 ⁄2" Coated-Glass Mat Gypsum 1 2 13 ⁄4 11 ⁄4 4 10 RH135 1 ⁄4" Fiber-Cement 1 2 13 ⁄4 11 ⁄4 4 10 RH135 7 ⁄16" Fiber-Cement 1 21 ⁄2 13 ⁄4 11 ⁄4 4 10 RH135 1 ⁄4" Fiber Gypsum 1 11 ⁄2 13 ⁄4 11 ⁄4 4 9 RH135 3 ⁄8" Fiber Gypsum 1 2 13 ⁄4 11 ⁄4 4 10 RH135 1 ⁄2" Fiber Gypsum 1 23 ⁄4 13 ⁄4 11 ⁄4 4 11 F142 19 ⁄32" Plywood 13 ⁄4 3 ⁄4 4 7 F143 15 ⁄32" Plywood 11 ⁄2 11 ⁄2 4 7 F143 19 ⁄32" Plywood 13 ⁄4 11 ⁄2 4 7 F150 15 ⁄32" Plywood 11 ⁄2 11 ⁄4 4 7 F150 19 ⁄32" Plywood 13 ⁄4 11 ⁄4 4 7 F160 3 ⁄8" EG/LWP 11 ⁄2 11 ⁄4 4 7 F144 1 ⁄4" CBU 1 2 11 ⁄4 4 8 F144 1 ⁄2" CBU 1 4 11 ⁄4 4 10 F144 1 ⁄4" Fiber-Cement 1 2 11 ⁄4 4 8 F144 7 ⁄16" Fiber-Cement 1 21 ⁄2 11 ⁄4 4 9 F146 1 ⁄4" Coated-Glass Mat Gypsum 1 11 ⁄2 11 ⁄4 4 8 F146 1 ⁄2" Coated-Glass Mat Gypsum 1 2 11 ⁄4 4 8 F170 1 ⁄4" Fiber Gypsum 1 11 ⁄2 11 ⁄4 4 8 F170 3 ⁄8" Fiber Gypsum 1 2 11 ⁄4 4 8 F170 1 ⁄2" Fiber Gypsum 1 23 ⁄4 11 ⁄4 4 9 Appendix B of the TCNA Handbook is a compilation of material and system weights. Method F141 Stone weighs 23 pounds/square foot with a 1-1/4” mortar bed. 64 TileLetter | February 2019