How much shrinkage in a 4x4 PT post

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  #1  
Old 03-25-14, 03:08 PM
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How much shrinkage in a 4x4 PT post

I am replacing a small section of the wall in the basement with a header and 4x4 PT posts. The posts that I bought at Home Depot does not seem fully dried yet. Since I want a tight fit to carry the floor joist above.

I will sandwich (2) 2x10's as shown in the red box.

Then I will frame with 2x4's on the left 2 arrows and use a Pressure Treated 4x4 for the right arrow. Will the 4x4 shrink too much to provide adequate support to the floor joist above? Or should I just use a 3 2x4's instead of the 4x4? Should I cut post 1/8 or 1/4" longer and force it in to accommodate for shrinkage?
 
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  #2  
Old 03-25-14, 03:44 PM
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First of all, your engineered floor joists are probably designed to span the area without having to provide for support at a intermediate area.

If the stairway wall is supporting a load bearing wall on the upper level and you want to provide the post to transfer that load then I would probably go with the three studs nested together or a LVL post or a steel column. The reason I would choose an alternate post is not so much due to longitudinal shrinkage ( nil in your situation), but more relative to the potential for twisting and turning in the post as it dries.

Ate you using a PT bottom plate? If so, the shrinkage across the thickness of the plate would probably be of greater dimension than the post.
 
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Old 03-25-14, 04:05 PM
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Looks like the floor joists terminate on this section of the wall.

It does not look like that wall is supporting a load bearing wall above. I was more concerned about any weight from traffic coming up and down the stairs and the landing right before the stairs.

The bottom plate will be an existing PT lumber, so hopefully all the shrinkage is done. Thanks, I will go with the three stud approach.

Cheers,
 

Last edited by Dudley Wong; 03-25-14 at 04:40 PM.
  #4  
Old 03-25-14, 04:06 PM
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Wood doesn't shrink much at all in length, only in width. At any rate, why use PT wood, and why use a 4x4? It will probably bow as it dries. (there's a reason framing lumber is kiln dried) Use a bottom plate (only) that is PT as Calvert mentioned. Use SPF lumber for the rest.

I also don't understand your drawing. Are you intending to cantilever your header and have no support on the right side?
 
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Old 03-25-14, 04:37 PM
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Yes, I want to cantilever the header and use the 2x10 to support the end of the double floor joint which is the top of the stair on the main level above.

In the original framing by the builder, he had a 2x4 PT stud on the end of the wall next to standard lumber. No moisture here, so not sure why.
 
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Old 03-25-14, 08:36 PM
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No framing inspector would approve a cantilevered header like that. I would suggest you come up with a new plan.
 
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