Joist span - InspectionNews

wayne soper · #1 (**permalink**) 05-18-2007, 09:39 AM

I'm thinking the span is too great here but not sure of exact length required for joists without support beam below.

David Banks · #2 (**permalink**) 05-18-2007, 10:21 AM

I took seminar by Journal of Light Construction and deck builder told us this as rule of thumb.
1/2 span plus 2 equal joist size.(16 inch on center)
If you have 14 foot span divided by 1/2 equals 7. Plus 2 equal 9. You need a 2x10.
2x12 no longer than 16 feet.
Lots of variables but not a bad rule of thumb in the field.
I also have table if you have the span and joist size.

Frank Kunselman · #3 (**permalink**) 05-18-2007, 01:08 PM

It would be helpful to know both the joist span and the unsupported span of the deck edge beam as well as the size of the members.

For example: a 12 ft joist span with an 8 ft span on the edge beam, a dbl 2x10 #2 SYP would be sufficient considering a 40psf live load.
The same joist span with a 10 ft edge beam span would require a dbl 2x12 #2 SYP.

The size and span of supporting edge beams, headers and girders is all dependent on the live load and total load per LF exerted on the beam.