Small Wood Roof Truss Repairs That Might Work When Both Top And Bottom Cords Are Damaged or Cut
The first thing to do is to cut the damaged part out and leave as much of the good wood as possible. If the rafter has termite damage that's going all the way through the rafter, it might be necessary to remove the whole rafter. Otherwise, just simply cut a section out.
If you see termites or wood rot, cut a little bit further. Greg also mentions that you will not be nailing the roof sheathing into the rafter unless you've removed the roofing materials. In some cases, the roof sheathing will hold up the roof rafter and has done single repairs using the roof sheathing. If not, put a support board underneath the rafter.
A 2x4, 2x6, or 4x4 would work depending upon how much weight there is on top of the rafter. It would be better to use a stronger board if you think a 2x6 will work but you're not sure. You can then go ahead and cut the roof rafter and install it on either side of the existing roof rafter. It shouldn't be that difficult to figure out how to cut the seat cut or to measure the distance from here to here by using one of the other rafters or by using the section you cut out of the existing rafter to trace the new seat cut.
The blocks on either side of the rafter will need to be removed because they're going to be a little bit shorter on one side and a little bit longer on the other side. If you leave the blocks in, it might make it difficult to install the new roof rafter. So again, the new rafter will go on either side of the roof rafter. Just make sure that you don't install any connectors on the side where you're going to be installing the new rafter.
Most of the time you're going to need to turn the roof rafter a little bit and sometimes you're even going to need to have a larger seat cut. It would not be difficult to cut the roof rafter to fit first and then see if it will slide in easy. If not, you might want to raise the existing roof sheathing or even try to raise some of the other sheathing around the area where the roof rafter might need a little more room to slide into place before making the seat cut a little larger.
After you're done, you can bolt it together. You could probably even nail it together, but Greg thinks for something like this it wouldn't be a bad idea to use some bolts, maybe some 3/8 in bolts and stagger them 16 in on center or put a few in and if it's strong enough leave it at that. These are only suggested repair methods and might not work on every project.
After that, you can install your blocks and you can always reuse one of the blocks that's going to be shorter. There is one more thing that you could have a problem with and that would be nailing the roof rafter to the top plate. For example, if you have a 2x4 rafter or a 2x6 rafter, it might be difficult to toenail the rafter into the top plate. In that case, you're going to need to use some type of hardware, such as a connector.
