Reinforcing Floor Joists - Pro Tips

REPAIRING A BOUNCY FLOOR BY SISTERING JOISTS

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A client recently asked us if we could reduce the “bounce feeling” in their bedroom floor.
Sistering | Doubling the Joists can solve a lot of problems like sagging, uneven, or strengthening undersized floor joists. Sistering adds structural integrity to damaged joists and can also be used to level old floors.
2-Methods of Sistering
Full length sistering is the strongest method, and my preferred method when possible. This method extends the entire length of the joist and has full bearing support at each end. This method requires a minimum of 1-1/2” to 3 inches bearing at each end.
An alternative to bearing is to install joist hangers from a wall or supported blocking.
Mending Plate or Scabbing:
In some remodeling situations, it is too difficult or impossible to get a sistered joist onto a bearing point. I find that in these situations using a mending plate or plywood scabs can help tremendously. A mending plate is typically a 2x joist section fastened to the old section of joist to strengthen it.

There are 2 rules of thumb when installing mending plates:
1. Install the sistered mending joist ⅔ the length of the original joist, this can also be used to fix joist sag.
2. Extend your repair 3 feet on either side of a damaged area. This method reinforces the damaged area, and the joist ends will be able to handle the additional weight of the sister.

“Plywood scabbing” is also an effective technique that allows you to add strength to and fix minor problems that are affecting floor joists. I often use construction adhesive and 8D ring shank nails or structural screws to fasten 3/4-inch plywood as scabs to both sides. When scabbing I try to use the full 8-foot rip of plywood or the longest length that will fit.
8 Steps on Sistering the Entire Floor

1. Remove Plumbing, Wiring, Cross-Bracing and Other Obstructions
First step is to remove any blocking, wiring, plumbing, or HVAC in your way.
2. Measure and Cut the New Joist
If you are running the sistered joist the same length as the old joist, use that joists measurement. If you are sistering a partial joist, use the ⅔ rule if possible.
Pro Tip:
To ease fitting, we cut a 20-degree bevel of the top edge of the joist [1/2’ in and ½” down] this helps the joist slide past the subfloor and into place.
Ensure your new joist has at least 1-1/2” to 3’ of bearing.
3. Install The Joist
Slide the new joist “crown up,” into the space and tilt it up. The goal is to ensure the sistered joist sits snugly against the old joist. If the old joist has sagged, you may have difficulty getting a full-sized sister joist to fit.
If you cannot fit the sistered joist against the old due sagging, you can jack up the old joist to create room.
Pro Tip:
If installing a partial joist, you’ll also need to jack up the old joist to level and then sister the repair to that.
4. Jacking
I position a 6-ton hydraulic jack under the old joist and on top of a board spanning several floor joists. This support board helps spread the downward pressure weight of the jack to the floor below. I fasten two 2×4’s together to make a simple jack post. I then slowly jack the sag out of the old joist in order to get the new joist against the old joist. Jacking too fast can cause wall cracks above and it’s always best to jack slowly and not too much.
After lifting the cracked joist, I used a 3-pound hammer to move the new joist into position.

5. Level Vs Flat
Level is not always achieved but certainly desired. Flat is usually the consolation prize to level, in old houses. We used a combination of strings, levels, and a rotary laser to attempt to get the bottoms of our new joists level. We consider all of this information and raise or lower the jack post as needed. We also sometimes trim the joist bearing edge to assist in in fitment.
6. Fastening
To attach the new joist to the older one, we installed a series of 3-inch Fasten Master Head-LOK structural lag screws in a “W” pattern. Once secured, we released the jack pressure and remove the jack.
7. Install Solid Blocking
The last step is to install solid blocking perpendicular to the joists. Solid blocking helps to transfer weight to adjacent joists. We snap a midspan line, cut our blocks a hair stronger acts as stronger than the space, and tap them in with a hammer.
Install the blocking in a straight ling [not alternating] for the strongest connection.
8. Strap The Ceiling
The last step is to install 1x3 ceiling strapping 16” on-center to the ceiling joists. Strapping is fastened with two 8D ring-shank nails per joist. It seems that strapping is an N.E. kind of thing, but I like it for two reasons.
1. Strapping can be easily shimmed to level out the ceiling
2. Electrical wiring can easily be snaked in the ¾” space for future wiring running, like adding recessed lighting

#FloorRepair #ReinforcingFloorJoist #LevelingFloors #SisteringFloors

[duanecartwright]

Somebody give this man an award for effective communication. Explaining succinctly is a real talent and this guy has it..

[melmartinez]

I'm in the process of sistering / scabbing a first-floor - which means I'm in the crawlspace and also dealing with the entire weight of both stories instead of just the 2nd floor. This video was useful - especially the tip about beveling a corner off the sisters to make it easier to hammer them into place. Wish I'd thought of that earlier. A tip not mentioned is that an oscillating tool with a tungsten blade (get a 3-pack) is extremely useful for quickly dealing with bazillions of existing nails and staples sticking through the subfloor and mis-nailed & sticking out of the existing joists. You want to cut those off so they don't interfere with the placement of the sister joists AND to save your head from getting poked in the brain while crawling around with your head up between the joists and under the subfloor.

[jamesfargo]

This video is incredible, the best ceiling reinforcement video I've ever seen. Every homeowner in America would benefit from taking 12 minutes to watch this instead of the crap on TV. Excellent information, to the point, and very clear with helpful video examples and demonstrations. Thank you sir, keep up the good work!

[anastasiabuss]

This was immensely helpful. We just bought an old farmhouse with some joists we’re concerned about. This was the most thorough and well explained video I’ve come across yet.

[inverness]

Holy cow! Best YouTube instructional ever made! Every question I had about my 1930s floor joist was answered in 11 minutes. Brilliant.

[raphaelteixeira]

I do not understand why you don't have millions of views in this video. The form of communication and making the content clear is incredible and very helpful.

[miked]

I had to work on my back in a tight crawl space for about four days re-enforcing a floor. Cutting full length sisters was not an option do to the tight confines. I was not able to get a full length ridged board under the crawl space so I ripped 3/4 treated plywood and sandwiched the 2x10 joists, glued, screwed, and carriage bolted . It worked like a charm and stiffened the floor up like I wanted.

[robbrundrett]

OK, OK, OK, I'M HOOKED ON THIS ROB KNOWS HIS STUFF. I'M A 64 Y/O LANDSCAPE CONTRACTOR THATS BUILT LOTS OF THINGS AND JUST LEARN SO MUCH FROM THIS VIDEO. GOD SPEED TO YA ROB.

[GVNSOLES]

You explained everything so perfectly and I feel so confident doing this project. I am a new homeowner and the floor joists are sagging in my kitchen. I am going to contact a specialist for guidance beforehand and I appreciate this video so much thank you.

[ExamineLife]

Very helpful, thanks so much! I've got a home where they did the room addition upstairs over the garage and they didn't provide adequate support for the joist under an interior wall in the upstairs addition. The floor is sagging. Install was in the mid 1980s. It's obvious I will need to remove the drywall underneath and get busy sistering those joists as well as jacking up that section. Great tip with the bevel for fit. Thanks for a very well done video.

[DennisMathias]

THIS is one of best presentations you've ever done.

[njreno]

As a Roofing Contractor, I like to watch programs on building and carpentry so that I can see what I am missing. The grind of roofing gets old and I sometimes think to myself, hey why not build garages and work your way up to homes. Then I wake up and realize that I love the freedom of being outside and not inside my customers home. Sometimes working inside is like walking on eggshells. You guys do great work and I enjoyed the video. Looking forward to some wood slivers this summer!

[billm]

Great tip on the 25 degree bevel. Thanks, Rob…

[fbtool]

Wow Thank you so much! I am a homeowner of a 1950's ranch style with a 2" x 12" x 12 ft termite damaged floor joist. (accessible in the unfinished basement) I'm trying to find someone to come sister it and it has been hard to find help. This video almost makes me want to do it myself. At least when I get someone to look at it I will have all the knowledge you have given me in this excellent video to help choose the right person for my job.Thank You!

[johnwealthy]

Great video!! I've lost sleep worried that my house is condemned. Now I have a solution!! Many thanks for sharing.

[turkeytrac]

As a recently retired carpenter, it's very refreshing to see someone building to best practices, bravo!

[levyrogers]

This is some of the best information on floor or ceiling repair I have heard of. Thank you from all of us DIYER. You have made our lives alot better my man. Wow!!

[sheldonpearo]

I am a carpenter and enjoy learning new ideas to fix things. I have a open mind and always learning knew thing's

[ts]

You can jack a joist by getting rid of the jack, and just making the strong back longer than the distance you need, a block between it and the temporary support plank on the floor can help it slide along. then just tap it into place with a sledge hammer. Unless you are lifting tons of weight it will go real easy, and you can be very precise. This saves the risk of kick back with the jack.

[waoh]

120ish year old house with logs for most of the framing…rot and termites have done their worst. Now I’m gathering good advice to fix my wife’s dream house. Thanks guys!