Example Joist Selection
So here’s how you’d select a typical TJI floor joist from the span tables. Let’s assume we’re going to have a 15 foot span (fairly typically with a 30 ft wide house). Let’s also assume we want a very stiff floor so I’ll choose L/480 deflection criteria and 20 psf dead loading. I’ll also assume we’re going to frame the joists at 16 inches on center.
I’ve highlighted several key columns in the L/480 Span Table as you can see above. First off I’ve decided I want to try and use 11-7/8 inch deep joists (most standard size). Secondly I’m using the columns for 20 psf dead load fround on the right side of the table. Now all I did was pick the lightest (I’ll explain this below) TJI in the 11-7/8 inch depth that has an allowable span greater than my design of 15 ft. As you can see I’ve highlighted the TJI 110 (left column) that has an allowable span of 17′-8″ for a dead load of 20 psf and a deflection criteria of L/480.
The second column in the table identifies the TJI size for a given depth. The sizes range from lightest (110) to heaviest 560. Once you’ve selected a size be sure to check with our local supplier. Some of the sizes in the span tables are not always available. If that’s the situation, just pick the next biggest size and go with that.
Follow Standard Construction Details
Be sure you follow all of the recommended construction details in the design manual. The details ensure safety during and after construction. The details also help you build the floor to eliminate floor noises and performance issues.