Chapter 10 Floor Framing 259 many builders use 5/8″ or 3/4″ plywood. Plywood subflooring is applied much like OSB, with the long dimension of the sheet perpendicular to the joists and the end joints staggered. Use 8d nails or 1 5/8″ screws spaced 6″ along edges and 10″ along intermediate members. Plywood intended for subflooring has tongue-and-groove edges, similar to that found on OSB flooring. Subfloor underlayment panels are available for joists or beam spacing of 16″, 20″, 24″, or 48″. Maximum support spacing is stamped on each panel. A 3/4″ thickness is used for 24″ O.C. spacing. Be sure to follow the instructions supplied by the manufacturer. Pro Tip Material specifications and application procedures for subflooring are provided in a booklet published by APA—The Engineered Wood Association. 10.8 Estimating Materials To estimate the number and size of floor joists on a job, first check the plan and determine the lengths that are needed. Be sure to allow sufficient length for full bearing on girders and partitions. Average resi- dential structures require several different lengths. To determine the number of joists needed for spacing 16″ O.C., multiply the length of the wall that carries the joists by 3/4, then add one. For 24″ O.C. spacing, multiply the length of the wall by 1/2. Also, add extra pieces for doubled joists under partitions and trim- mer joists at openings. If solid wood joists are being used, add extra pieces for headers at openings. If the floor is to be framed with I-joists, add LVL according to the plans for headers at openings. Note the follow- ing example: No. of joists = length of wall × 3/4 + 1 + extras The sizes and numbers of joist headers will be the lengths of the foundation sections on which they rest. The depth of the band joists will be the same as the adjoining floor joists. Your estimate should include the cross-sectional size and the Goodheart-Willcox Publisher Figure 10-44. Applying construction adhesive for a glued floor system. A 1/4″ wide bead of adhesive applied to the top of the joist is sufficient. Two beads are applied where panel ends butt. Goodheart-Willcox Publisher Figure 10-45. Use a maul and protective strip of wood to close up the tongue-and-groove joints in subfloor- ing. Leave a 1/8″ gap all around. Goodheart-Willcox Publisher Figure 10-46. Fasten the glued subflooring with mechanical fasteners before the adhesive sets. A power screw gun avoids stooping and speeds the operation. Copyright Goodheart-Willcox Co., Inc.