Expert: Stephen Major - 8/21/2007

Question
I have an 8' span (interior catwalk) 7' wide.  I'm planning 16" centers so I expect 6 joists. Wanting to limit the visable profile, can I use 5" steel I beams (w5x19) instead of 2x8 douglas fir lumber.

Answer
Jim,

5" steel I beams are way too much for this small span.  If you are maintaining the 16 inch spacing, you could get away with a much smaller steel section, such as a 3 inch or 4 inch I-beam, C-channel or rectangular tube.  Ask your steel supplier, they can figure the minimum requirements from their sizing charts.  Use a design live load of 50 pounds per square foot.

You can also use 2x6 joists at 12 inches on center.  Be sure to glue and nail the plywood subfloor, and optionally do the same on the bottom with 1/2 inch plywood for a very stiff assembly.

--Steve Major