My house was built in 1978 and has one attic rafter that has a crack, I’m going to scab/sister a board on either side and then attach it with 4” structural screws, I plan to also use a glue so that I have a mechanical and chemical bond.

Should I use wood glue/Gorilla Glue or construction adhesive/Liquid nails for the glue part of my project??
Or does it not really matter and flip a quarter to determine which adhesive to use?

Thank you

I'd use the clear gorilla glue in a caulk tube. It's really good stuff I use it often. I'd sandwich the cracked rafter rather than sister it.

No matter what project I work on, I use the strongest glue possible unless there is a possibility I might have to take it apart. Construction Adhesive would be my choice.

I use titebond III for cabinet/furniture construction.
I’ve done experiments gluing up boards edge to edge. With the titebond, the wood always breaks somewhere besides the joint.

I would lag some steel to it. A piece of six flat bar with some lags or better yet bolt through with 3/8 bolts. It may be over kill but it will hold.

I’d just scab a 2x4 on it with a few screws and let it bump.

Tire bond 3 is the best wood glue I’ve ever used. I’m not sure what you mean by sister board. I would scab both sides and the bottom. Any idea why it cracked in the first place?

I agree with the Titebond III.

Those construction screws you are talking about, if it's a #22x4 in 1.5" thick Southern Pine, each have a shear capacity of about 400 pounds. So you are probably going to be good without the glue.

I would extend reinforcement members at least 12" past the crack on each end.

Keep in mind that rafter is only supporting the contributory area of that one rafter, which would be half the distance between it and the nearest two rafters. So let's say that the rafters are 16" apart and the length is 20'. That's a worst case area of 26 square feet of contributory area. Apply a load of 30# per square foot including live load and dead load and you are only talking about that single rafter supporting a total load of 780 pounds.

So you should be good to go.

Thank you for the engineering explanation.

I'd just screw a board on either side and use carraige bolts every 2 to 3 feet secure it. I dont like adhesives

I would nail the boards on instead of screwing them. Screws do not have any ductility, so I personally wouldn’t use them for that application.

ductility...I learned a new word. Guess that's why I can answer electrical questions and not carpentry ones.

What 000buck and Irish said. Now if its a corner jack for a hip roof or something, I'd do more. Regular old rafter, a scab will do, but always extend it well beyond the break.

Build a hog through with a couple 8' 2x4s. Screw it centered on the cracked rafter and then to the other rafters they cross. Glue is not the answer X

Whatchutalkinboutwillis?

Duct tape that thing!

I know that regular construction and deck screws don’t have much shear strength but this is what I was going to use.
Advertised as replacing a 3/8” lag.
https://www.homedepot.com/p/FastenM...ews-Black-12-Pack-FMHLGM412-12/202268269

Make sure you drill a hole at the very end of the crack to prevent it from running, before you scab it.

Regardless of how you do it , if you wanta glue wood Titebond is the glue to use.

Ductility is a material’s ability to bend without breaking. Important for applications facing high wind load like a roof or exterior wall.