+- Woodnet Forums (https://forums.woodnet.net)
+-- Thread: I need to sister a rafter. Am I on the right track? Updated (/showthread.php?tid=7361569)
Pages:
1
2
I need to sister a rafter. Am I on the right track? Updated - chrisntam - 03-15-2021
A fallen tree branch struck the roof last year, breaking a rafter at my mom's house. 2 x 6 rafters, roof is about a 5/12 or 6/12 pitch, comp roof now, it had wood shingle roof on it in the past, so it has 1 x 4 sleepers across the rafters and plywood decking atop that.
My plan is to jack it jack up slightly to get the belly out of it then bolt a new 2 x 6 along side the damaged one, going about 3 or 4 feet each way from the crack. 1/4" bolts ok? What hole size? Make the bolts tight in the hole or allow for a little slack? I'll use fender washers to spread the load of the bolt and nut on either side of the 2 x 6s.
I'm also thinking I'd like to toe nail one end of the sister rafter into the hip rafter, it's obviously a compound cut, but I have no idea of what angles to use. The roof is about a 5 or 6/12 pitch. I have a 10" compound miter saw, I think it's big enough to cut the 2 x 6. Any idea of what angles to use? Maybe this is not needed....
Any other tips or tricks I'm missing on this repair? It's over a garage that's floored, I can't think of a more convenient place to do a rafter repair.
Thanks in advance!
[attachment=34120]
[attachment=34122]
Sistered it this morning, construction adhesive and 2 2 x 6s along with structural screws. The sag is out of the roof. I think the repair will hold. Thanks for the advice.
[attachment=34604]
RE: I need to sister a rafter. Am I on the right track? - MT Woodworker - 03-15-2021
It broke at a weak point
As you said I would remove the belly then glue, screw, and bolt in sisters to both sides
Maybe larger than 1/4 inch though
A starting point
RE: I need to sister a rafter. Am I on the right track? - DieselDennis - 03-15-2021
You're on the right track, but don't waste brain cells overthinking it. Remember a sole 2 x 6 is supposed to suffice as the rafter, and the part that's not cracked is still holding up the roof, as is the two rafters beside it.
Biggest thing is finding something on the ceiling to jack against. Probably lay down a 2x flat over 3-5 joists. Center this 2x where the jack will be when you start jacking. Attach this flat 2x to the joists below. I'd probably use decking screws, just because I have some handy. I generally don't like hand hammering things in the attic. Have had experience with this cracking the drywall below.
Place your jack on the flat 2x and underneath the crack in the joist. Start jacking until the rafter is straight again. Get your sister 2 x 6 and attach it to the cracked rafter. Again, I'd probably just use 3" decking screws (and plenty of them) because they're handy to me. If I was going for bonus points, I'd glue it. If I were going for bonus points and extra credit, I'd get a 2 x 4 and attach it to the side of the cracked joist and the side of the flat 2x installed earlier. If I were going to try to clep the class, I'd get a 2 x 4, stand one end on the flat 2x, and beat the other end underneath the broken/sistered rafter until it was sufficiently tight, then toe screw it is on the flat 2x and the rafter. If I were going to try to clep the class and never take the teacher again, I'd go through the trouble of marking out the angles (by holding the 2 x 4 in the approximate position and dragging a pencil along the back), and cutting them to fit before I attached the support 2 x 4 to the flat 2x and the rafter with Kreg HD pocket screws.
Judge how well this job goes by how many trips you have to make up the ladder.
RE: I need to sister a rafter. Am I on the right track? - MT Woodworker - 03-15-2021
And remember, any curve, belly in the sistered rafters goes up to minimize any future sag
RE: I need to sister a rafter. Am I on the right track? - TDKPE - 03-15-2021
If it were me, I'd probably just glue and screw as close to the sill as possible without getting nuts, and up near the crack but on the low side of it, with a few sprinkled in between if you like, with the new rafter flush with the old rafter at the top. No idea if the new one is exactly the same depth as the old one, which is why I would use the top, which is flat against the sleepers. Once it's set up, jack up the free end near the ridge until it's flush like other bottom half and glue and screw it also.
The load on the screws is all shear, and a group at the bottom, top, and both sides of the crack will fix what's broke, but a few extra in the space between won't hurt.
RE: I need to sister a rafter. Am I on the right track? - crokett™ - 03-16-2021
Glue and screws is all that is needed, and the screws are just there to clamp things together. Bolts are not. If glue is used it is better than bolts. The screws are there ala Norm "just until the glue dries". Once the construction adhesive dries, the wood will fail before it does. I might support the the ceiling from the garage floor before I started jacking up the rafter, but that's probably overkill.
RE: I need to sister a rafter. Am I on the right track? - chrisntam - 03-16-2021
Wood glue or construction adhesive?
And thank you for all the advice, it is appreciated!
FTR, it's on a short hip, I don't think there will be much jacking force needed to bring it back in line.
chris.
RE: I need to sister a rafter. Am I on the right track? - srv52761 - 03-16-2021
Remember, the goal is to transfer the load to the sister.
As TDKPE mentioned:
- The force at any screw will be shear. If you do not glue the sister then consider structural screws (I would use those whether I glued or not).
- The forces on the rafter when the load is app!ied will be compression and tension on the edges. The center of the rafter and sister will be in equilibrium. If you expect any screws to help transfer the load, make sure they are in the top and bottom third of the sister and rafter.
RE: I need to sister a rafter. Am I on the right track? - tomsteve - 03-16-2021
2 by whatever the rafter is .span 4-6 feet both sides of the break .double( on 2 by 6) or triple row of nails every 12".
ive nailed the sistering rafter one side of the break then used a 2 by 4 (resting on a 2 by 6 spanning a couple of ceiling rafters) to wedge and drive the other side of the rafter back into place. i think that will be easier than trying to use a jack. i think it will move easier than youre thinking. theres not much weight on the roof there and the broken rafter isnt all jacked up.
a speed square will get the numbers needed to make the compound cut at the top but i dont think its necessary.
RE: I need to sister a rafter. Am I on the right track? - joe1086 - 03-16-2021
I did a fair amount of joist sistering on a bathroom remodel intending to glue/screw them. Take a flat edge to your damaged rafter to see how flat it it is. Most of my 30 year old joists were cupped and screws wouldn't pull the the faces together.
+1 on the structural screws.