Sistered Floor Joists

[Skip Erwin]

I ran across this today. It's floor joists that are approximately 8 feet long made from 2 floor joists approximately 4 1/2 feet long. Where the two pieces of floor joist meet they aren't nailed together or have one or two nails! The joists are supporting a bathroom tub.

My question is can floor joists be spliced or sistered properly? If so, how might it be done? All I can find in my code book is "floor joists can't be spliced".

[Richard A. Hetzel]

That's RIDICULOUS! Let me see if I can find it in the code...I know it says somewhere that joists must be a single piece...

[Richard A. Hetzel]

R502.2 Design and construction. Floors shall be designed and constructed in accordance with the provisions of this chapter, Figure R502.2...

Figure R502.2 clearly shows joists of a single piece spanning the full distance between supports.

Joists may also be deisgned and constructed in accordance with AF&PA/NDS, which is American Forest & Paper Association / National Design Standard, andI'm sure something in there requireds a single piece also.

In my opinion, joist splicing, if possible at all, must be engineered, and just slapping a few nails through two pieces ain't engineered.

[Jon Randolph]

Those are not sistered they are spliced and should be replaced with full spanning joists or a suitable support, including columns and girders, built underneath.

A sistered joist is a joist that spans the entire distance and has another equally sized joist attached along side a length of it to strengthen a damaged portion of the original joist or to provide additional stiffness and support if the sisters both span the entire distance.

Those spliced joists will fail if a heavy load (tub full of water) is placed above them.

[Skip Erwin]

Thanks for clearing up "sistered". It amazes me that someone went to all the trouble to install the joists (incorrectly) and doesn't even nail them together.
I wonder what would happen if a 400 pound lady was in the tub above?

[Christopher Currins]

What you have is definitely wrong. They should be overlapped more and supported with beams. One approved "sistered" design that I know requires using metal plates, similar to this http://www.sabrefix.co.uk/downloads/splice_plate.pdf

[Jon Randolph]

I had to go back and look at the pic again. You are right, they are not nailed together. What is keeping them in place?

Do you have a wider shot of the area?

[Skip Erwin]

I don't have a wider shot. Sorry.

[Kenton H. Shepard, CMI]

One or both sides may be cantelevers, which doesn't make them right but might explain why the tub is not already lying on the floor of the crawspace on top of broken joists. Also, the subfloor is probably helping to hold things in place.

[dhelm]

In general, a sister must span from bearing point to bearing point. Most sistered joists I see do not do this. Also, in areas where certain WDI exist, sistering new wood to infested wood is a no no.

[Jon Randolph]

Originally Posted by dhelm

in areas where certain WDI exist, sistering new wood to infested wood is a no no.

Why? That is a good way for contractors to ensure repeat business.

[dhelm]

In Western Washington, the most common, and destructive, WDI is the wood borer Anobiidae. It only requires a moisture level of 13 percent. New wood against infested wood becomes infested wood.

[Frank J. Carey]

Thats pretty bad. I am assuming that it is cantilevered somehow as Kenton said or they would have to have nailed it to the subfloor after putting the subfloor on? Put a glue lam under that with a few columns and you will be fine. Oh and toenail the floor joists to the beam after the columns are in place...palm nailer works great in tight spots like that.

[Frank J. Carey]

Just looked a little closer...the joists coming from the left are PT. I assume they are from a porch or deck that would reinforce the cantilever theory. Still would feel a little better if the joists were at least nailed...

[Richard A. Hetzel]

If they are cantilevered, it's a mighty long cantilever for sawn lumber joists...it looks to be in excess of four feet, which leads me to believe they aren't cantilevered, or if they are, they're surely not engineered.