Those using this on-line calculator assume all liability and hold PLIB harmless from its use. Neither PLIB nor its members assume any responsibility for any particular design prepared from this on-line calculator. Based on building codes, a 2×6 can span anywhere from 2’-1 to 20’-8 depending on the affecting factors. Other span tables are based on the guidance given in BS 5268-7.1 which is a uniformly distributed load of 1.5kN/m² for spans greater than 2400 mm and 3.6 kN load per metre width of floor for spans less than 2400 mm to ensure that very small joist sizes do not result from the calculations for smaller spans. The distance a 2×6 can span is determined by the species, grade, location, use, load, and spacing. Chapter 8 also provides requirements for the application of ceiling finishes, the proper ventilation of concealed spaces in roofs (for example, enclosed attics and rafter spaces), unvented attic. Joists must bear directly on beams, girders, ledgers, or load bearing walls or be supported by hangers or framing anchors. PLIB believes the information generated by this calculator is accurate and conforms with design standards referenced by U.S. A general rule of thumb for joist span is 1-1/2 times a board’s depth in feet, however, it’s not that simple. Allowable span tables are provided to simplify the selection of rafter and ceiling joist size for wood roof framing and cold-formed steel framing. General Notes for Floor, Rafter, and Ceiling Span Tables ables are based on M-29, Southern pine design T values (see page 2). 17 and/or the National Design Specification (NDS) Supplement published by the American Wood Council for adjustment factors. For other service conditions or load conditions, see paragraph 200 a-l in WCLB Standard No. Example: In the rafters span table below, the highlighted cell (13-0), indicates that 2' x 8' Douglas Fir joist, with a level of 2, spaced 24' apart, can have a best span of 13 feet - 0 inches (13-0) if developed for a live load of 20 psf, and dead load of 20 psf. Multiply the span given by the multiplier for the wind zone (low and medium 1.3) or (high and very high 1.1) to calculate the extended span for the wind zone chosen. In calculating the design values, the change in strength and stiffness that occurs as lumber dries has been taken into consideration as well as the reducing in size that occurs when unseasoned lumber shrinks. Choose the rafter size and the spacing intended and read off the permitted span. The typical on-center spacing, according to the International Residential Building Code (IRC), is 12, 16, 19. Note: The design values shown in the table are for normal load duration and dry service conditions and are applicable to lumber surfaced either unseasoned (S-GRN) or dry (S-DRY or KD).
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