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Sistering Floor Joists on Cantilevered Sliding Door

Sistering Floor Joists on Cantilevered Sliding Door

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Old 08-16-14, 07:41 PM
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Sistering Floor Joists on Cantilevered Sliding Door

I have uncovered 10 years of water/termite damage beneath a cantilevered sliding door during the residing of the house which is 20 years old. I just removed a cement slab deck that was butted up against the house above the sill plate. There was a thin piece of flashing between the cement and the sheathing. Thus the damage. It is a two story house. There are 6 joists that are 2" x 10" x 15' that span back to the main beam in the middle of the house. The overhang is 2' x 7' wide and it is just one floor. The joist on the far left corner is doubled, obviously to bear the weight on the outermost corner. They are tied together by a 2" x 10" below the face of the slider. I need to sister a joist on that outside left corner. The damage on the outer two joists has left nothing for me to nail sheathing to in order to continue with the siding. The damage on the outer two joists runs back to the sill plate as you can see in the picture. I have cut out the first section on the left, not shown in this picture, and I think I would be able to run a full 15' back to the center beam of the house from the outside, but I do not have enough clearance to twist the new joist to sister it properly on edge. I am about 1/8"-3/16" shy. The joists have obviously compressed somewhat over the years. I would have to run that off the 2" x 10" to fit it in there. I could notch the sill plate, or I could notch the joist, but I am afraid of losing the integrity of the new joist. Do I even need to run it back the full 15' or would 4' to 6' of sistering be sufficient? Should I try and jack a two story house to run the 15'? Some ideas would be appreciated. Thanks.
 
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Old 08-17-14, 07:02 AM
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You can use a circular saw to cut a bevel on the top and bottom. Basically removing the offending corner that prevents you from rotating the joist to the vertical position. You should not do this in the area where the joist rests on a beam or the foundation since you are cutting away the load bearing surface. The other option is to jack up the house or simply pound the snot out of the joist until you can hammer it up to vertical.



Running the new joists back to the beam in the center of the house would be best. I have never sistered a cantilever like you have so I'm just guessing at this point. If you don't do full length sisters I'd make the non-cantilevered length of the joist at least three times the length of the cantilever. So, if your overhanging 2' I'd want to have at least six feet on the other side meaning a 8' sister. And, I'd through bolt the joists together with 1/2" bolts every 2' on the other (non-cantilevered) side.
 
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Old 08-17-14, 07:22 AM
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I also forgot to mention that there is another joist an inch to the left of the double damaged ones, so I am not too worried about the integrity there. I did plan to use 1/2" bolts with washers on both sides. Also, take a look at the damaged joists. They all appear to have damage on the bottom. Do i need to cut out the damage, or just leave it and sister on to what has strength?
 
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Old 08-17-14, 09:35 AM
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Since the bearing surface of the existing joists is damaged I would not cut the corners off the sister joists in that area. I'd probably jack just enough to get the new joists in without having to trim them for height.

I would leave the damaged portions of the existing joists. It's more work to cut it out.
 
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Old 08-17-14, 09:46 AM
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OK, but is it alright to trim the corner at the top portion that would be sitting beneath the sub-floor if need be to get the sister section in there? Similar to how you suggested I trim the corner the length of the 15' earlier in this post?
 
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Old 08-17-14, 04:34 PM
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The top edge has the sub flooring along it's full length so cutting a corner off the top is generally not a big deal. The bottom, especially where you have a point load like resting on a beam you really want to keep all the wood bearing surface.

In reality though I don't bother with trimming the corners off of joists when sistering. I just get a bigger hammer and pound them until they stand upright.
 
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Old 08-17-14, 06:41 PM
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They are tied together by a 2" x 10" below the face of the slider
I was just reading through this. The rim joist mentioned above can be totally removed and replaced without any temporary structural support.

or I could notch the joist, but I am afraid of losing the integrity of the new joist
Notching a joist 3/16" will not effect integrity at all. You have 6 each 2 x 10's over 7', supporting a 2' cantilever.

If you can't stand them upright by pounding them in, as Dane said, notch bottom slightly where joist will bear on foundation. The tighter, the better, but some trimming may be called for.

I like to look at cantilevered wall as an entire unit. It has support from other joists, sheathing and other components.
 
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Old 08-23-14, 10:57 AM
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I have sistered four joists. I sistered the outside edge joist 16' back to the center beam. The other three I only sistered back 8' as the damage was not that bad. I pretty much just needed something to nail to from the outside beneath the slider and it's only a 2' overhang. I plan on using 1/2" bolts with washers. What should the pattern be? 2' apart, top and bottom? 2' apart just in the middle? Staggered? Thanks for your help.
 
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Old 08-23-14, 11:19 AM
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A typical nailing schedule would call for 2 16d nails (top and bottom), 16" on center.

Nailing schedules do not specify bolt patterns, so just a guess but 24" on center, top and bottom.

You don't really need bolts, the fact that you sistered the joist provides the additional strength and nailing area you wanted. Nails have very good shear value, but shear value doesn't factor in this situation much.
 
 

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