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Best way to attach joist sister to old joist [Merged threads]

Best way to attach joist sister to old joist [Merged threads]

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  #1  
Old 05-01-08, 08:05 AM
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Best way to attach joist sister to old joist [Merged threads]

I have a bathroom with some old joists that have a 24" span. Obviously this is way too long, and the old joists have some termite damage, so I would like to attach some sisters. I have never done anything remotely like this. Is it better to use framing nails, deck screws, or bolts to attach the sister? I have been considering buying a framing nail gun, but I don't really need it for more than this project, and $250 is a lot to spend if I can just attach the sister with 3" desk screws. But if it's better to nail it in, I don't mind buying the framing gun. I assume that whether I use screws or nails, they go in every 6" in a zigzag pattern (one at bottom of the joist, next near the top, etc)?

And what about bolts and washers? If these are better, do you just drill a hole with your drill then slide them in and tighten? What type of bolt do I get from Lowes?

Also, since my span is so large, should I do any cross bracing? The joists are 2x8, and I was going to get equivalent 2x8 for the sister. Do I need a sister on each side of the joist or just one? And lastly, someone else recommended joist hangers. Can you install these on a joist that is already in place instead of sistering?

Thanks for any help!
 
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Old 05-03-08, 04:50 AM
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Screws for the most part don't have the shear strength of nails or bolts. I would consider bolting the new members to the old. Installing cross bracing will help with squeaks and will help keep the members upright. I would use carriage bolts with a washer and nut, then just tighten them with a ratchet until the washer begins to imbed itself. Do this all along the length so you will have good strength. Adding double joist hangers at the ends of both joined joists is a plus and will help keep things in line.
 
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Old 05-03-08, 10:01 AM
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Thanks for the reply. Any special type of bolts I need, like galvanized? And do I just use a regular drill to drill the holes for them?
 
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Old 05-03-08, 10:04 AM
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Joists are too long to sister

Also, I have some joists that are 24" on center. I wanted to either sister some joists to them, or even better, put new joists between each pair that are already up for more strength. However I just measured them and the current joists are 17 feet long. There is no way I can maneuver a board that long under my crawlspace. Do I have any other options? Even though it won't be a strong, can I cut the new joists in two pieces, around 11 feet and 6 feet and then put a support post or something under the area where they meet?
 

Last edited by Spooksmcgee; 05-03-08 at 10:21 AM.
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Old 05-03-08, 10:24 AM
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If you can stand lower head room, you may be able to cut the length of the new joist in half & support them in the middle with a beam. What are the dimensions of the room.
11'6" x what with 2x8's on 24" spacing.
Cutting sisters in half as shown below will be your best alternative

______________________________________
_______________________________________Original
________________ ______________________ Sister
_______ ____________________ ___________Sister helper

Use construction adehesive
 
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Old 05-04-08, 09:59 AM
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Originally Posted by gejandsons View Post
If you can stand lower head room, you may be able to cut the length of the new joist in half & support them in the middle with a beam. What are the dimensions of the room.
11'6" x what with 2x8's on 24" spacing.
Cutting sisters in half as shown below will be your best alternative

______________________________________
_______________________________________Original
________________ ______________________ Sister
_______ ____________________ ___________Sister helper

Use construction adehesive
I didn't know you could use 2 sisters that way. That seems like a good way to go. So a sister cut in half in the middle, then a sister helper cut in thirds on the end? What is "head room?" The height of the crawl space? My dimensions of the bathroom are 11'x6'. Below are pictures of what I'm working with:








At first I tried using joist hangers, but the actual width of the joists are almost 2", so they are too big (unless I can use a double joist hanger for one joist and fill in the sides with scrap wood?

As you can see in the last picture, the joists are notched at the end so that they rest on the rim joist. I don't think this is done anymore, and it's caused a 10" crack where the notch is. The joist is also cutout about 5" in two places to give the drainage pipe room. So at it's weakest spot the joist is only about 3 or 4" thick.

I was thinking if I can't get a sister in there, one thing I could do would be to put a 6' long 4x4 pier in three places running underneath the 4 joists, and have jacks on either end of the pier to support it? This actually might also help me level out the adjoining wall, which is sagging a couple inches. My other thought is just to put some blocking or cross bracing in, and put 5 or 6 4x4 piers on top of concrete dek blocks underneath the joists at random spots. I just don't know since I've never done this before. Thanks again for the great advice!
 
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Old 05-04-08, 10:57 AM
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Can't use dek blocks for this. You should pour footings and build up from there. A good post and beam will suffice in this type situation. You don't have a crawl space, you have a snake space. How high is it to the bottom of the joists? 2 feet?
 
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Old 05-04-08, 11:12 AM
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What is wrong with Dek Blocks? Will they not support the weight? I've never poured footings before. How deep do they have to be? And do the footings need to be a certain height above the ground or can they be level with the ground?

You're right about my crawlspace. 2 feet would be awesome. It is 14" to the bottom of my joists. Most contractors and termite people will not work on my house due to the crawlspace size in relation to their weight.

Thanks for the quick reply!

Edit: I found this site - http://www.hammerzone.com/archives/f...t1/raising.htm

and think I pretty much want to do the same thing. I'm going to use two 6 ton bottle jacks and they're so cheap I don't mind leaving them there. Do I still need a concrete footing for the bottle jacks?
 

Last edited by Spooksmcgee; 05-04-08 at 11:46 AM.
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Old 05-04-08, 09:01 PM
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If you can block up under the two floor joist on each side using a 12" square pad on bottom with blocks up to the joist, you can the tear ou the two middle joist & run short joist at a 90 degree turn from the way they are now. Put them on 16" centers & use metal joist hangers. Block up under the two outside joist every 3 feet.
 
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