![]() Use two 12d toe nails one one side and and one on the other to firmly attach the rafter. Nail on a three foot collar tie every four foot to meet code requirements. ![]() Be sure to use rafter clips on every rafter not nailed into a ceiling joist. One size does not fit all, and one simple table will not do it for you either. All other data can be found in the 2012 International Residential Code Rafter Spans. In making your choice, consider how you will insulate your insulate your roof. Another option are 2 X 8 rafters spaced 24 inches o.c. The table states that 2 X 6 rafters spaced 16 inches on center (o.c) can span a maximum distance of 13 feet 5 inches. to arrive at an educated and engineered sale. Looking through the center of the table, we can find a couple of options. With time you may gain some experience and efficiencies at doing the analysis and making the judgements about possible options, but I think you pretty much have to do the inspection, etc. Rafters with ceiling doesn attached to rafters, ground snow last 50 Psf, dead loaded 20 Psf, deflection limit L/180. The following span table uses a moderate snow auflast of 50 Psf, but yours could be more or less. Now, you can start to make a current condition judgement, and start thinking about any excess rafter cap’y., or how to add some reinforcements, or how to distribute your new point loads to several rafters to meet your needs. Consult your on-site building code authorize to determine the snow load by your area. Is the roof sway-backed from years of permanent set and deflection, indicating too flexible a roof for the existing loads? Are the joints intact, not pulling apart, crushing or splitting, enough bearing area, properly cut and fitted, no rafter thrust problems at their bearings, etc. Probably, more importantly, look at the entire roof and all the important details for condition or defects and deficiencies. length and also a table of the axial load- biaxial moments - biaxial curvatures relationships for eccentric- ally loaded columns. To do what you are talking about the right way, you have to do an inspection of the/each roof system and measure sizes and spans. Hundred year old houses might have been made of any good local wood, ask some old contractors, restoration people, old lumber guys, not the kid at the bog-box. As suggested you can study the grading rules over the years, there are classes for becoming a lumber grader, which you could take. as a function of field measure sizes and spans and assumed species and grade. A span options calculator allows selection of multiple species and grades for comparison purposes. Joists and rafter spans for common loading conditions can be determined. It is also often expressed more a ratio of rise to run, or a fraction of the rise override that run. Performs calculations for ALL species and grades of commercially available softwood and hardwood lumber as found in the NDS 2018 Supplement. Stretch are common messured horizontally along the renter projection from the ridge to the outer corner for the supporting outside fence plate. Multiply the span given by the multiplier for the wind zone (low and medium 1.3) or (high and very high 1. Write your own spread sheet to do the required calcs. Span Tables for Wood Joists, Rafters and Carriers.
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