Floor joist question - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 04-22-2011, 03:59 PM Thread Starter
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Floor joist question

Not exactly a hobby question, but one that will entail woodworking as a solution.

One of the joists in my crawlspace rotted out - the previous owner stuck a jack under the beam and left it for me to deal with. So I'm gonna deal with it, but am not sure how to approach the fitting. The joist is a 2 1/4" x 10" rough cut doug fir beam. If i wanted to fit a 4x6 support column to the beam, I'd have to carve a channel in the 4x6 to fit the joist - at least a 2" deep channel, preferably 4" channel so that I can run a bolt through the assembly to tie them together. I can't use standard structural ties because the joist isn't a "standard" width - they didn't use 2x10's, they used rough cut 2x10's.

Am I talking about hand sawing the channel, then drilling out the interior, then using a chisel to clean up the channel? I don't want to just toenail the joist and support column together if I can create a stronger joint by cradling the joist with the support column
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post #2 of 10 Old 04-22-2011, 04:35 PM
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scab patch

put a 2x10 on the side then screw and bolt this should be stronger than first joist. Carll
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post #3 of 10 Old 04-22-2011, 04:39 PM Thread Starter
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Oopsie...

I just re-read what I posted...

I stated it wrong. The support column for the joist rotted out, so the previous owner replaced it with a floor joist jack.

The crawlspace used to have a river of water running through it (hey this is western washington), and the bottom of the support column must have turned to mush from standing water. Fortunately he had the forethought to install a french drain to cure the water problem - but for some reason thought it would be perfectly fine to leave a rickety column jack in place of that rotten column board.
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post #4 of 10 Old 04-22-2011, 04:46 PM
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Joists vs beams

Well you posted while I was typing so I understand it better now!

It's confusing because you use the terms interchangeably. They are different . The flooring sits on the floor joists. the joists sit on the support beam. Beams run horizontal, columns and posts run vertical.
Quote:
One of the joists in my crawlspace rotted out - the previous owner stuck a jack under the beam and left it for me to deal with. So I'm gonna deal with it, but am not sure how to approach the fitting. The joist is a 2 1/4" x 10" rough cut doug fir beam. If i wanted to fit a 4x6 support column to the beam, I'd have to carve a channel in the 4x6 to fit the joist - at least a 2" deep channel, preferably 4" channel so that I can run a bolt through the assembly to tie them together. I can't use standard structural ties because the joist isn't a "standard" width - they didn't use 2x10's, they used rough cut 2x10's.

Generally speaking when a joist rots, you "sister" it on both sides with similar width boards.
When a beam rots, you build a temporary header to support the joists and replace the beam.
When a post rots out you build a temporary post away from the original, remove the rotten one and replace it. Or, if the temporary one works, fits and makes sense, leave that in place. A screw jack or hydraulic bottle jack will prove invaluable.

Your question is then...Do I leave the column jack in place or replace it with a post?

I'd build up a raised portion of concrete or use a solid block and then put my new Pressure Treated post on that. I'd dunk the whole end in a buck of used motor oil overnight as well, or spray it with automotive undercoating and let it dry.

I have done this numerous times, kinda fun in a way. When you hear creaking noises and the lever on the bottle jack gets hard to push you know you've got some weight on top. I have worked with a lot of steel beams and steel posts, but the temporary ones were made of 2"x 10" s in a box form and the jack sat on a stack of plywood on top. If you are not comfortable doing this, better to have an "expert help" or do the entire job. BTW I have 3 automotive jacks, 4 bottle jacks, including a 20 ton, several screw jacks, and a 5 ft HD Off Road truck jack. Hydraulics are GREAT! bill

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 04-22-2011 at 04:53 PM.
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post #5 of 10 Old 04-22-2011, 06:22 PM Thread Starter
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I'm comfortable working around the equipment, but it's a little creepy - kneeling on drainage pebbles listening to the boards creak and groan as the joist is raised ever so slightly to remove the now seriously bowing column jack (or lally jack/lolly jack/screw jack). I can just see myself slowly raising the joist, then <CRACK!!!> and find myself pinned under the rubble that used to be my living room.

That jack has to go, last time I looked it was bowing, at the time I didn't think too much of it, but now that i've thought about it - it's obviously about to go.

Still, I feel like I'm building a an old-time barn or something - get out the saw to cut the channel, use the augur to remove the material, use the chisel to smooth the sides. All I need now is a beetle mallet to pound the replacement post into place.
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post #6 of 10 Old 04-22-2011, 06:53 PM
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Quote:
Originally Posted by klr650 View Post
I'm comfortable working around the equipment, but it's a little creepy - kneeling on drainage pebbles listening to the boards creak and groan as the joist is raised ever so slightly to remove the now seriously bowing column jack (or lally jack/lolly jack/screw jack). I can just see myself slowly raising the joist, then <CRACK!!!> and find myself pinned under the rubble that used to be my living room.

That jack has to go, last time I looked it was bowing, at the time I didn't think too much of it, but now that i've thought about it - it's obviously about to go.

Still, I feel like I'm building a an old-time barn or something - get out the saw to cut the channel, use the augur to remove the material, use the chisel to smooth the sides. All I need now is a beetle mallet to pound the replacement post into place.
The idea is to replace what's there. I wouldn't sister the thing. You would need 2 2x's to do the exchange. I wouldn't use any oil on it, as it seems to make sense, but oil may soften the end.

Use the second 2x as a fitted support to keep the elevation constant. Cut it to length to fit on top of a wood block. To install this temporary support you may have to tap it in place with a sledge hammer. Having it on a block will make it easier to set in place and to remove it when the final support goes in.

I would use a pier for the bottom to sit on whatever is there. Cut the first 2x to fit the height from the pier to the beam/floor joist above. Once you have fastened the column, remove the second 2x.

This is not a difficult repair. I'm not a structural engineer, and if you feel a bit hesitant to make this repair, do a "Google" search, or get some advice from a qualified structural engineer.








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post #7 of 10 Old 04-23-2011, 10:53 AM Thread Starter
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I see what you're saying, you're suggesting using two posts, one just to lift it up, the second as the actual final replacement. I was gonna use a bottle jack or second lally jack for that purpose.

It's gonna be a tight fit no matter what, so my idea of making the support column cradle the joist for a stronger end-product might be unrealistic in that sense that I'd never be able to wedge it into place.

The replacement column will be a ground contact rated pressure treated lumber, so oiling won't be necessary.

the calcs don't bother me, I'm a mechanical engineer. The difficulty is in translating what's on paper to real-world application. I like to get a reality check from people who have had to do this so I don't blunder into doing something that looked good on paper.

I appreciate the responses, you've all been a big help.
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post #8 of 10 Old 04-23-2011, 11:43 AM
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What's the ground like under the house? If you have had water running there it might be soft. Will there be frost under the house? In either case I would make sure there is a solid ground for the column. Dig a hole to remove soft soil, fill it with gravel and make a concrete slab to place the column on. The column I would make of three 2x6's (the one in the middle 2-1/4x6 to fit the beam). Jack up the beam a hair more than needed, insert the column and lower the beam.
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post #9 of 10 Old 04-23-2011, 11:48 AM
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Excellent advice from all. Well done
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post #10 of 10 Old 04-23-2011, 02:48 PM Thread Starter
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Quote:
Originally Posted by Longknife View Post
What's the ground like under the house? If you have had water running there it might be soft. Will there be frost under the house? In either case I would make sure there is a solid ground for the column. Dig a hole to remove soft soil, fill it with gravel and make a concrete slab to place the column on. The column I would make of three 2x6's (the one in the middle 2-1/4x6 to fit the beam). Jack up the beam a hair more than needed, insert the column and lower the beam.
Attachment 23764
Thanks for the pic, that's what I was thinking about doing, just probably the hard way instead...

As for the ground - in that I'm in luck, the post that rotted out was right where they decided to put the french drain - the ground under the new post block is pea gravel. So in that I won't have to worry about water, settling, or frost.
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