On a roof slope of 12/12, and with 2x10 pine rafters 24 feet long, and on 16" oc can shorter boards say (a 16' and a 12' be spliced to get the 24 foot long rafter?
Do you know of a section of the code or building practice book that addresses this question and offers guidence?
Don't know code allows but I know it can and has been done. I have a couple rafters in one of my outbuildings that has been spliced that way for length. What they did was nail the two together (bottom angled nailed) and sistered the joint with 3 feet of same size lumber on BOTH sides so one and a half feet of the sisters was on either side of the splice joint like a bandaid. That was done quite awhile ago and it seems to have worked as its still standing. If I was to do that now though I'd use some Simpson metal ties to lock them together and then sister. I don't know the number but they are flat pieces of metal with teeth on them used for mending ... and then I would still sister. Those metal mending plates DO come in different sizes depending on the size wood you are adjoining and you would need one of the Longer ones to mend a 2X10. Your hardware store would know what size for the need. I think the way the code reads is that joints (splices) like that SHOULD be supported by wall or over a beam. Code likes the splices well supported.
To modify and work on rafters does require a permit though.
Splicing or sistering another alongside is a common method.
Another way that allows for the use of lighter rafters, or just simply if the lengths are greater than the available timber is to use under-purlins.
Whichever way you go, collar ties could also stiffen up the area of the joints.
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