Rafter Span Table ?

[funflyer]

Hopefully there is a framer around who can answer a simple question regarding the rafter span table.

When it refers to "maximum rafter span", is that the span from wall to wall to include both rafters or just 1 rafter from ridge to wall?

Thanks.

 

[LB-1911]

How wide is the proposed structure and desired roof pitch ?

Once you have that

- go to -

http://www.oaklawnlibrary.org/documents/Speed Square Instruction Book 1983.pdf

 

[funflyer]

Thanks LB, the book looks like a lot of good info. However, I wasn't sure if the rafter span for a given size board was the entire length from wall to wall or from the ridge to the wall. I just learned from some carpenters on another forum that the span the table is referring to just the ridge to the wall span. The building is 20x20 with a 4/12 roof so according to the table for a light load 2x6s are required and for a heavy load 2x8s. I will go with 2x8.

 

[Falcon67]

Yep, joist span is ridge to wall - for a rafter. Not for a joist. Be sure you're looking at a table that matches the type of lumber you can purchase. A board isn't a board.

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

http://www.msrlumber.org/spantables.pdf

"The horizontal projected distance from face to face of supports in feet and inches defines the maximum spans provided in the tables. This represents the actual length of floor joists and ceiling joists. For sloping rafters, the span is also measured along the horizontal projection. The actual rafter length must be calculated based on the slope of the member."

 

[rburke65]

I didn't think a rafter went from wall to wall.....