Southern yellow pine rafter span tables3/15/2024 ![]() Normally the joists would just tie into the main beam perpendicularly, but I'm trying to make use of lumber that's left over from other projects. ![]() The beams that run perpendicular are triple 2x10x12 #1 graded pine. The long beams with 45 degree braces are double 3x10x16. Here's a Sketchup design I drew up tonight for the proposed loft. ![]() You probably have to add some margin for error so you can't go all the way to 16', but you get the idea.Īround here you would have to use graded lumber with a stamp for that. Then what kind of joist system you need to span 16' at 40 lbs/sf. Next step is to figure out what kind of post and footing you need to carry 8,000 lbs. That means the post at each end of each beam is carrying 8,000 lbs. Since the beam is 12' long that means just over 32', or 16' on each side of the beam. If the beam is between two walls the walls will hold half the load, so you can actually support 400 square feet with each 12' section of beam. If your floor is built to hold 40 pounds/square foot that means you can support just under 200 square feet of floor. If you are sistering two you can double that to 7922lbs. Reading all the way over to the right gives a capacity of 3961 lbs. On page 83 it has 12' span, and the fifth entry is 3x10. The table doesn't go up to 16 feet (which might tell you something) but let's look at 12. In the second table we'll use the column for 2000 psi, the rightmost column. The first table says it has a bending strength of 2156.25 psi. Let's say you're using Eastern White Pine. In beam applications, sistering doubles the bearing capacity for a given span. You can get bending strengths here: Maximum Span Calculator for Joists & Rafters This table has 3x10 beams: To use this table you need to know your species of wood, and it's bending strength (Fb). You calculate the load by figuring out how many square feet of floor the beam is supporting, and how many pounds per square feet that floor is rated for. For that application there are two parameters, the span and the load. It sounds like you may be thinking of a beam to support floor joists. Sizing of a header depends upon the load on the bearing wall. I think of a "header" as a piece that goes over an opening in a bearing wall to carry and spread the load, so I'm having trouble picturing what you're doing.
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