[ablodneyget]

Hi folks,

Due to some rot damage along the bottom edges (up to 3" up) on several of the joists under my house, I have sistered all the joists with one fresh 2x10 each and bolted them together with Flatloks. (Root cause of the damage has long since been remedied.)

I had to knock out the mid-span cross blocking to get the sisters in, and now I'd like to reinstall blocking to further stiffen the floor. (It's very solid but I can still feel deflection 8 feet away when someone walks on the same joist I'm standing on. They don't feel like they move together.) Since the joists are all doubled-up now, I can't end nail through the 3" of lumber, but could toe nail or use brackets. I'd like to do whatever gives me the strongest connection; if toenailing, I'd pre-drill to avoid splits and then hammer by hand, since I don't have a nail gun.

I'm also considering using Simpson brackets such as the L70 or A34, show here. The A34 brackets would be installed two at each end of each piece of blocking, one top and one bottom--basically one on each corner. The L70's (7" long) would be installed one at each end, halfway up. I might use structural screws to make installation easier since I can easily zip them in with an impact driver.

Some of the old joists are rotted out for the bottom couple inches, so I won't always be able to fasten the blocking super close to the bottom at both ends. Where the blocking meets the new lumber I can fasten anywhere I want and would aim close to the corners (maybe an inch and a half from top and bottom) for stability.

Any thoughts on which approach would give the stiffest connection? The cost doesn't isn't an issue with the brackets. The main cost is my time and effort and I'd like to make this the best I can.

Thank you!

A.

 

[Nealtw]

Any or all your plan will work the blocking is really about keeping the joists standing straight up and down so they can take all the weight they are rated for.
So when you have all of that done add a 2x4 on the flat across the center the same direction as the blocks. In order for the floor to sag, that 2x4 has to stretch to allow it.

 

[ablodneyget]

Any or all your plan will work the blocking is really about keeping the joists standing straight up and down so they can take all the weight they are rated for.
So when you have all of that done add a 2x4 on the flat across the center the same direction as the blocks. In order for the floor to sag, that 2x4 has to stretch to allow it.

Any or all your plan will work the blocking is really about keeping the joists standing straight up and down so they can take all the weight they are rated for.
So when you have all of that done add a 2x4 on the flat across the center the same direction as the blocks. In order for the floor to sag, that 2x4 has to stretch to allow it.

I wanted to follow up, especially for the benefit of anyone else doing a similar project.

• I cut blocking to fit snugly and installed with one L70 bracket on each end of each block. Some of the blocking creaked and popped when someone walked across the floor.
• I then tapped shims between the blocks and the joists where I saw any clearance. This snugged them up considerably and quieted most of them.
• Toe nailing 2 x 12D on the sides opposite the brackets helped a bit more, but there were still some blocks that made noise.
• What really made the difference was a liberal bead of polyurethane (Loctite PL-3) on each joist face before installing the blocking.

In a retrofit situation, it's very hard to get everything to fit perfectly snug. The adhesive provides lubrication to reduce installation effort, the shims tighten the fit at all four corners of each block, the brackets transfer vertical load and provide a backstop to aid in installation, and the 12D nails are probably overkill since the adhesive does all the work after curing.

Here's the procedure:

• Cut blocking to fit snug. This required some trial-and-error since some of the joists were in and out a bit from nominal alignment.
• Smear a bead of polyurethane adhesive on joist faces.
• Gently tap/slide blocking into position, held by friction. (Adhesive acts as a lubricant, making it easy to adjust the position.)
• Install two L-brackets, one on each block end, between the block and joist, using Simpson SDS screws.
• Identify any areas with clearance between block and joist and tap in wood shims for a tight fit at all four corners.
• Drive nails at 45 degrees into joist opposite the brackets.

The difference in the overall stiffness and quietness of the floor system is impressive. I'd be happy to upload a picture of the installation if anyone is interested.

A.