Floor Joists Span Chart for 2012 IRC

The floor Joist span chart and building code requirements are based on data from the 2012 International Residential Code using number 2 lumber.

Types of Floor Joists

Joists for use in residential framing applications fall into two different categories; tree sawed and engineered. This page focuses on the tree sawed variety. Kiln dried number 2 Pine is the most widely used material. It is relatively inexpensive and is widely available. It is available in sizes that will work for joists from 2 x 8 x 8′ to 2 x 12 x 24′. There are limits on how far these boards can span. 

Floor Joist Span Chart for 40 lb Live Load

Floor Joist Span Chart for 30 lb Live Load 

Floor Joist Building Code Requirements

The best way for a joist to transfer its load is for it to stack. This simply means for it to rest directly on top of another framing member like a drop girder, a wall, or a pressure treated mud sill. There is some criteria the joists must meet according o the 2012 International Residential Building Codes.

• The joist must have a minimum of 1 1/2″ riding on the wall or beam.
• If the joists are lapped, then they must be lapped at least 3″.
• Maximum end notches for 2 x 8, 2 x 10, and 2 x 12 respectively are 1 13/16″, 2 5/16″, and 2 13/16″.
• Use an approved hanger or a 2 x 2 ledger strip on flush beams for spans greater than 12′.
• When framing openings, use header and trimmer joists. Double any header over 4′ and any trimmer joists with a header attached within 3′ of its bearing.
• Use a minimum of 3 8d nails for toe nailing to girder or sill.
• Use a minimum of 3 10d nails for face nailing and lap joints.

Be aware that these spans and code requirements are taking things to the absolute limit. In a practical application it is a good rule of thumb to not use 2 x 8’s at all, never span a 2 x 10 over 14′, never span a 2  x 12  over 20′, and use as many nails as possible without damaging the wood.