![]() The lumber yard you called asked a very pertinent question. The following is posted soley in service to public safety.ĭupe posted important information relating to allowable spans for various sizes of standard 2x lumber. I don't know what code covers post and beam construction, but that's probably where you need to head. I think regular code doesn't list them because it's cover light wood framing, not heavy timber framing (post and beam). Also if these are sawn beams with no stampings on them, now that's a whole other issue. I would direct you to local building department. Engineered beams take this to an extreme and thus why something of the same dimensions has much higher ratings, they know what they got in that beam, so you can't use their numbers and apply to a sawn beam. The conservative nature makes sense both from simplicity but also when laminating multiple members you have a lower statistical chance of a bad flaw being in the same spot of the beam (one board could have a crack, the other doesn't vs one crack thru it all). So that is one place that touches on this. Now I would assume a 3圆 to be 2.5" thick vs 2 2byes which would be 3", so maybe some conservative nature. It list the same span values for the solid verses the build up. It has a few rows that call out 3圆 or 2 -2圆, 3x10 or 2 - 2x10, etc. ![]() There is an interesting table for deck beam spans. Joists supporting additional loads should be calculated by a competent person.So in IRC 2015, most tables for headers and such have a note below them saying to can interpolate for values between those listed. These span tables make no additional allowance for partitions or any other loads additional loads. BS 5268-7.1 was published before BS 6399-1 was amended to include the more onerous 1.4 kN imposed concentrated load, so the approach adopted for these span tables uses the recommendations given in BS 6399-1, however, both approaches do result in similar joist sizes being calculated. 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 floor joist span tables are based on the loadings given in the amended version of BS 6399-1 which is an imposed load of either a uniformly distributed load of 1.5 kN/m² or a concentrated load of 1.4 kN. Joists are to have minimum end bearing of 40mm. Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. Proprietary strutting is to be used in accordance with manufacturers recommendations. Solid timber strutting to be at least 38mm thick and be a minimum of three quarters of the joist depth. Joist spans over 4.5m - provide 2 rows of strutting at third span positions.Joist spans 2.5m to 4.5m - provide strutting at mid-span. ![]()
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