Installing Warped Joists


Old 08-25-04, 11:55 PM
Ted Crocker
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Installing Warped Joists

As part of a 1930's kitchen remodel which has uncovered some sagging and broken 2 " x 4" ceiling joists in need of replacement, I just received my order of select grade, 24' x 2" x 10" Doug fir to be used for new ceiling joists in my attic, but some have over an inch of bow. They will ultimately span 21' from an exterior kitchen wall to an inner, load bearing wall (over the kitchen and dining room), with an extra supporting (non load bearing) wall between the two rooms located 8'7" in from the exterior wall. This extra wall does not have piers located directly under it, but rather >5" offset, so it is not considered load bearing by our building department. I was therefore required to install joists sufficient to span the entire 21' width. We have lathe and plaster ceiling remaining over the dining room which is not to be disturbed. The two load bearing walls and the intermediate wall will serve as the anchor points for the new joists.

I'm obviously concerned about having a level ceiling/floor. How much warp is acceptable over such a span? I believe it is proper to install all joists with the crown up, but for those joists with the worst bow, it might be easier to install at the exterior wall and the intermediate wall, bow down, then, using a cripple wall in the attic at the other end, leverage the raised end down using wedges, before nailing. I'm not sure that I could add enough weight to the center of the beam to press it down level and nail it to the intermediate wall if I installed the joist bow up. If I do one that way, should I do all that way? Any suggestions?

Last edited by Ted Crocker; 08-26-04 at 12:04 AM. Reason: Clarity
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Old 08-26-04, 06:41 PM
Join Date: Aug 2004
Posts: 1,150
You have the right idea and it is a common practice to straighten wood with nails, because nails move wood.
Remember, you're talking about a 1" crown in 21', which probably does not occur exactly in the middle, you have nailing at 8' 7", which is about 1/3rd which is less than 3/8th's.
Just make sure that your layout is correct and put your weight on it and nail with 3-16D's.
You're than loading it with ceiling material.
Old 09-01-04, 02:32 PM
Join Date: Sep 2003
Posts: 344
I would keep the bows up, so the ceiling doesn't look like it's sagging.

You will likely find the bows will be minimized when the joist is supporting itself.

Alternate the 'good' joists with the 'bad' joists, don't group them together.

You will likely find your partition holding up the 'good' joists a bit, and the 'bad' joists floating over the partition wall.

If nails aren't doing the trick, you might need to use 12" timber screws to pull the joists down to the partition wall top plate. If this is the attic floor and you plan to deck it, decking it with 3/4 ply and screwing it all down will go a long way to minimizing the joist variances. Screw into the 'low' joists, pull them up and then see how it all looks.

I don't agree with the inspector's total discounting of the wall due to a minor offset; cantilever construction is an accepted technique. A structural engineer most likely would have won a debate with the inspector and you might not have needed to use 2x10s. If this ceiling is the attic floor, a lot depends on what you said was the attic plan.

Most of this 'problem' will be minimized as construction proceeds.

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