Dealing with Crowned Floor Joists?

Started by rwalter, June 20, 2005, 12:17:49 PM

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rwalter

June 20, 2005, 12:17:49 PM Last Edit: June 21, 2005, 07:22:29 AM by rwalter
Hello Everyone,

I a have a question. first off my experience in framing floor joists is limited to only framed a few small floors on a couple of sheds. I have never before had to deal with much of a crown issue. I am wondering on a larger span, like 18-20 feet how much crown on a floor joist is allowable before you reject the piece of wood?  Certainlly the wieght of the floor and building will help correct some of the crown. I am aware that the crown side is up when you frame it and that similar crowned pieces should be adjacent to it but on that size span how much variation is tolerable from joist to joist? I will be cutting joists this coming weekend, I cut a few this past weekend but haven't nailed them in place yet. The spacing on my joists are 12" OC, the span is just over 18 feet and the joist size is 19.4 feet.  I was thinking of laying a masons string above the rim joists at a level point and measuring the distance at the center of the joist from the top of joist  to the string. Then writing that distance on each joist and matching the joists up with similar joists measured crowns and then try to taper the crowns down to level joists. Any suggestions, tips or comments would be appreciated. Thanks

JRR

#1
June 20, 2005, 02:50:26 PM
I'm in the middle of a covered porch project and also dealing with joists with varying "crowns".   I failed to do any preplanning and now am "shimming" like crazy trying to get a level and flat floor.

My plan for "next time" goes like this:
1.  Select the "most crowned" joist and install it first .... in the center of the floor area if possible.
2.  The top of this joist becomes the "bench mark" for height.
3.  Install all other joists so that their high spots match the bench mark elevation.

This should yield the best match and minimize, or eliminate, the shimming required.

Jimmy_Cason

#2
June 21, 2005, 09:24:35 AM
Out of 32- Pressure Treated 2x10x 20ft floor joists, I had only two that I could not use. They where about 3/4" crowned. But the crown only started to become a crown in the last 5 feet. Two grown men standing on them could not get them to level out.

My biggest problem with the floor joists was the size of the boards.  I had some vary as much as 1/2" from one two the other. Shims, Shims, and More shims. If I had two do it again I would find the smallest size and trim them down on a table saw a few times on both sides to match the smallest joist.

glenn-k

#3
June 21, 2005, 09:37:18 AM
Rather than run that big ole board through the table saw, you could just mark the bearing points out and trim them to the size of the smallest joist with a skill saw.  Seems like it might be easier. ???

If you only had a few small ones it seems that shims would still be the way to go.  Or you could go 1/2 way - trim the big ones- shim the small ones - leave the average ones.

Decisions- decisions- decisions ::)

Jimmy_Cason

#4
June 21, 2005, 09:53:41 AM
QuoteRather than run that big ole board through the table saw, you could just mark the bearing points out and trim them to the size of the smallest joist with a skill saw.  Seems like it might be easier. ???
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