The Scourge of Under-sized Joists

Joist – the large beams that give the strength to your floor system.

Scourge – A source of widespread dreadful affliction and devastation such as that caused by pestilence or war.

Okay, okay, that's probably an overstatement, but it makes the point:

Never, never skimp on joist sizes to try to save money. In fact, I strongly urge you to go up to the next larger size from what is recommended.

My story for today is really heartbreaking.

I've been installing all the stained woodwork in a (roughly) 2 million dollar custom home (that's a really nice home here in the inland Southeast). It's a really quality structure on a lake, full of very high-grade elements and fixtures. This did not surprise me, because I had reason to know that the homeowner has made his fortune in commercial construction. It shows.

But one thing started bothering me. Whenever I would set a cabinet against an exterior wall, it would sit flat against the floor but lean away from the wall. This is a tell-tale sign that the joists are bowing down, thus making the floor-to-wall angle greater than 90 degrees. After a few incidences of this, I went into the basement and was shocked to see…

Twelve-inch Joists (I-joists, to be more specific for those of you who would care).

Later in the day, I asked the framing contractor about this. He said that, in a meeting before construction began, the owner had decided — against his recommendations — to go with 12″ joists instead of the 16″ joists called for in the plans. This is in a rural area where framing inspections are not an issue.

He did it to save a little money.

His experience led him to believe that it wouldn't be a problem.

The scary thing is that at this point the house is nowhere near being “fully loaded”.

Then there's the question of what time and moisture fluctuations will do to joists under that amount of stress.

Please learn from this man's mistakes. If you have the option, go up to the next size on your joists. You'll thank me.