Sistering basement joists?

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  #1  
Old 05-07-09, 09:43 PM
J
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Sistering basement joists?

Hello,
1880's colonial, 2 story, balloon frame. All the joists ends where they sit on the sill plate have rotted. House is currently supported by header beams and 15 jack posts on the effected side. Sort of like this



Now we have removed all the brick on the effected side because it was crumbling. I want to sister all the joists full length. It's 12 ft span and the current joists are 2x8. They actually measure 2"x 7 3/4" and some 2"x 7 1/2".

My problem is that the header beam has sunk into the joists about 1/4 on some of the joists, and these no way to slide a joist by the header beam to get it in place. Would it be alright to cut 1/4 - 1/2" off of the depth of a 2x8 used for sistering?

Also when sistering like this, do I have to use glue? What exactly does glue do for me when Im putting 3-4 16d nails every 16"?

Thanks!
Joe
 
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  #2  
Old 05-08-09, 10:07 AM
G
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I would put spacers only under the existing joists before I jack them up. Then, when sistering, you have ample room to install new ones.

I wouldn't cut any of the joist unless it is at the bearing points, then replace the 1/2" with plywood, or a hardwood.

The tension and compression is in the top and bottom 1-1/2" of the joists, you would be reducing the size of the joist to a smaller one if you cut much out. Be safe, G
 
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Old 05-08-09, 01:08 PM
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Thanks again GBR, house is already up though. Foundation removed. I MAY be able to jack the individual joists up enough to add metal plates under them.. maybe.
 
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Old 05-08-09, 01:51 PM
B
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How soon will the concrete wall be in place. It might provide the load bearing you need to temporarily support the rest of the beams while you install the sisters.

If your picture is correct, consider a shot sister on one side from the temp beam to the new wall. There will be space above the wall to work because you will need a sill plate or two. Support on the short sister as you remove the temp beam and add the new joists/sisters on the other side. They will not fit well as the floor will have a bow in it. Once all are in place, re-install your temp beam and jack the new joists/sisters into place, leaving the short sisters where they are.

Food for thought
Bud
 
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Old 05-08-09, 05:50 PM
J
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Bud, cool idea. that may be a viable alternative!
 
  #6  
Old 05-08-09, 06:06 PM
B
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They actually don't have to be short, as long as they can fit over the temp beam. So the short section could be the 7 1/2" or whatever you want and the rest could be less to get it in place over the temps.

Bud
 
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