Cathedral Celling Rafter Repair
I bought a house that had roof damage 20-30 years ago due to a fire and someone repaired it years ago before we owned the house. We gutted the room in question and discovered they used joist hangers to secure the 2×12 rafters to the cathedral ceiling on the side of the exterior wall. I’m not a fan of how they did this. They did not push the joist hangers tight to the rafter before nailing in some of the hangers so there is a gap there. Because of this gap they rarely placed nails between the hangers and the rafters. They also did a poor job cutting the angle of the end of the rafter. Also there would have to be a triple or more top plate to be able to support the hanger.
I’ve thought of the following ideas:
1. Build an interior support wall to support the rafters. There is a window on that wall which would present some issues due to the additional depth.
2. Sister the joists, use double joist hangers, add additional top plates under the current top plate and support with jack studs.
I’d hate to cover this up without fixing it correctly. Hopefully you have better ideas that I do. Thanks.
GBA Detail Library
一千年建筑细节的集合organized by climate and house part
Replies
If you can access the top, you can go with a top flange joist hanger. These can sit on the exiting top plate and the rafter can hang bellow without support.
https://www.strongtie.com/topflangehangersssl_solidsawnlumberconnectors/lbaz_hanger/p/lbaz
Joist hangers aren't as strong when they're sloppy like that. The worst I've seen is when there is a gap in the lower saddle part, which defeats the point of the joist hanger for the most part. I have on ocassion stuffed some 2x2 in in such a case to help, but it's far from idea.
Sloppy sides aren't as bad, but tension will cause the hanger to deform more under load, which is a Bad Thing. The hangers Akos linked to are better, since the forces keep the hanger in tension even if the sides splay out a bit.
I had a somewhat similar issue in a part of my own home that I renovated several years ago. The joist hangers were attached to a ledger, but the ledger was nailed through 1/2" polyiso! It wasn't tight against the framing! You could SEE the nails sagging under the load. My solution there was to plast a piece of 2" (2x2x1/8) structural steel angle under the ledger, bolting it into every stud along the wall with a 1/2" bolt and also bolting it into the edge of the ledger. This made a sort of shelf for the ledger to rest on.
I'm still a bit nervous about that bracket, and I'm planning to open up the wall again and build in an additional LVL header and some vertical supports to transfer the load down to the foundation.
One of the downsides of being an engineer who works with failure analysis a lot is you see potential failures everywhere. When you find structural issues in your house, you start seeing visions of things like your 4 year old daughter under that roof when there is a heavy snowfall (~5,100 pounds of snow load in my case). Then you start thinking about beefing up the structure a whole lot more.
My advice when you find anything you believe to be structurally deficient is to not take ANY chances, and beef things up as needed. You can bring in an engineer to consult on exactly how much you need to beef things up, but don't skimp. Strucural issues are serious.
In your particular case, I'd be a bit concerned with the beam/header/ledger the joist hangers are hanging on too, since it looks to be two seperate pieces. Note also that depending on the design of the roof, you might need those rafters to be able to handle some tension, in which case you don't want to trust face nails in the ledger -- you need screws/ledger bolts, something that can't pull out in tension. You have to make sure those forces all transfer through the structure correctly too so that you don't just make things fail somewhere else.
Bill
Thank you Akos. Are the LBAZ made to allow for an upward angle of about 10 degrees? Or would it just be a slight improvement over what is currently there. I do worry about that point load.
Thanks Bill. The studs in the house have balloon framing. This room is on the second floor. You are correct that the ledger is really just a double top plate consisting of two 2x4's. The piece of wood between 5 and 6 inches on the measuring tape is just a piece of lathe. Should I use some sort of mending plate or structrual screws to join the double top plate?
Adding another ledger like you did on your house is interesting. I wonder if I could do something similar without removing the joist hangers forcing me to build a temporary support wall.
You can just build underneath the existing joists so that the joists rest on top of the new beam. You end up with a similar arrangement to how joists would set on top of a header over a door frame. Ideally you want to preload the new beam a little bit so that it shares the load with the existing framing. If you use a big LVL as the beam, and screw it into the existing framing in addition to some new jack studs to support the ends, you end up with a pretty solid assembly without having to do things like biuld temporary support wall since you never disassemble anything -- you're just adding more.
Bill
Bill, did you cut a bird's mouth in existing rafters at an angle to fit the new beam so they meet up perfectly?
不,我没有把任何东西因为我不想weaken anything. I rammed the new beam up as tight as possible, shimmed as needed, then cut the jack studs a wee bit too long and pounded them into place too (to "preload" things). I don't remember a lot of effort with shims, so I'm thinking things were pretty even and I didn't have to shim things much. I DID jack up the roof prior to beefing things up though, since we had some sagging in the middle. That extra step might explain why things lined up rather well.
BTW, to jack things up for straightening, I put a temporary beam made of a doubled up 2x6 under the central maybe 2/3 of the roof, then jacked it up with two jack posts until things were even measured against a chalk line I snapped earlier. Once that was done, we put in the extra structural support to hold everything in place in the straight position. I have had no further sagging issues since doing all of that.
Bill
I just went up there again and noticed a crack developing due to the weight of to end of the rafter against the top plate. Any idea if I need a full 16' sister to repair that crack?
That crack isn't what I'd expect to see based on excessive loading, my guess is it was cracked like that when it went in -- or at least had a weak spot that opened up later. It wouldn't hurt to sister up a new one if you are concerned though.
That ledger looks undersized. As I mentioned earlier, DO NOT take any chances with the structure. Structural failures can and do kill people. If you have some structural weirdness going on, it's probably worth having an engineer come out and take a look. A consult isn't usually very expensive -- it's getting sealed plans drawn up that cost big(ish) money.
Bill
You size a structural member according to loading (usually dead load and snow for a rafter) and according to the span. You can do this from whatever code you are using in that area, or engineers/designers have programs that will show a pass/fail for members.
I agree with Bill, get somebody out that knows things. An engineer or an experienced contractor from the local area. They can have a look, come up with a plan, and you can complete the work. Maybe they will also see something that you are missing.