![]() ![]() For example, I am not sure, with 23 psf roof snow load, if I can use 20 psf live snow load table. Rafters are sized the same way as joists: Establish live load, dead load and deflection limits use the appropriate rafter table to determine acceptable Fb and. If not for the internet, that is what i'd done.:laughing:Īgain, thank you for all replies and would appreciate it if you will confirm or disagree with my steps. Other floor and roof loading conditions, a variety of species and other lumber. The second extent table is the same than an first, except e assumes a ground snow load of 50 Psf. Trusses must be designed for any special loading, such as concentrated loads. Thank you Seniorsitizen for a good laugh. The first span table is for roofs where the ceiling is not attached to the rafters (with no snow load), a live load of 20 Psf, a dead load on 20 Psf, and a deflection limit the L/180. Would you explain what those 2100 and 1.8 mean? wood roof framing in Section R80219 of the 2009 IRC which includes slope, span, and spacing location of all joints, required bearing widths design loads. 40ft x 12 480 ÷ 24 on-center 20 rafters + 1 21 rafters per side x 2 42 rafters. You’ll get the number of rafters needed for your roof. After getting the answer, add 1 for the ‘0’ rafter and multiply it by 2. This is just what I have (formula for hypotenuse of a triangle). 40ft x 12 480 (length in inches) ÷ 24 on-center 20 rafters. I used 2100f (1.8E) because it was the middle, which gave me max span of 14'1" for the rafter. 180 for deflection (no finished ceiling material) MSR lumber council table - I used the table specifying: This edition has been updated to the 2015 NDS Design Values. A companion Supplement to Span Tables for Joists and Rafters, Design Values for Joists and Rafters, tabulates allowable bending (Fb) and modulus of elasticity (E) design values for visually graded and mechanically graded dimension lumber. Ground snow load (necessary for roof snow load) by zipcode - mine is 30 psfĪbove info gave me 23.1 psf roof snow load (roof snow load calculator) It is referenced in the 2015 IBC and IRC. Also if anybody else was wondering, this is how I got some numbers. R502.3.1 Sleeping areas and attic joists.
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