Notching a Joist

By Bud Coburn

When remodeling it sometimes require for a joist to be notched to move plumbing.  The following should be followed to maintain the structure and strength of the joist.

Residential Code book, which is probably on a reference shelf at your local public library. It shows exactly what you can do to a sawn-lumber joist without weakening it.

Here’s what it says about notching: No notches in the center third of a joist; and in the ends where you can cut notches, they can’t be any deeper than one-sixth the actual depth of the joist or any wider than one-third its depth. In your 7-1/2-inch-deep joist, that means the notch can’t be any deeper than 1-1/4 inches or any wider than 2-1/2 inches; too small for a drain pipe.

The code is more forgiving about drilled holes. They can’t be any closer than 2 inches from the edges of the joist, and their maximum diameter is one-third the joist’s depth. In ­other words, you’re allowed to drill a 2-1/2-inch hole, which should be just enough to accommodate your pipe.


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