new rafters on old house

Hello, Please excuse me if this is an ignorant question. I'm thinking about replacing the roof on an old house (ridgeboard, rafters etc). I'm not sure the yet if the house is square. I would like to cut all the rafters ahead of time, but am worried that the bird's mouth cut may be too short or long because of an out of square condition. My question is: is there a common way to correct once the rafters have been cut? Maybe recut and shim or ? Thanks, Paul
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Why?

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PaulS wrote:

Measure the existing rafters to see how much they vary.
--
Art

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PaulS wrote:

There's a term for rafters that have been mis-cut - blocking.
Cutting rafters does not take a very long at all, so you wouldn't be saving very much time. The odds of you making a mistake, an expensive mistake, cutting them ahead of time is fairly high.
If you're replacing the roof, take off the old one and then measure the top plates for level, square and straightness. Then cut the new rafters.
R
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if not, squareness is not really an issue with rafters. it affects the rake overhangs and the roof if you are using three tab shingles or steel, but not really the rafters. what you are looking for is straight, parallel, level walls (within tolerance).
I do agree with rico that it is probably not wise to cut your rafters ahead of time. my standard operating procedure is to cut one or two rafters and try them out to make sure I have things right before I commit. you could cut all your plumb cuts on top ahead of time if you want. I suppose you could even go so far as to cut a pair of patterns. then when you have the old roof off, you can try them out (without having to start scratching your head with a rafter table book or calculator or whatever) and if they fit, quickly cut the rest.
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Thanks, I agree with you and RicodJour that it would be safer to cut a test pair after the roof is off. I guess I was just thinking about moving as fast as possible before rain. Maybe I should think about some tarps. Paul

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Don't.
Set up the ridge using temporary props and cut each as you go.
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Seems to be a lot of hand wringing over this.
Back in the days where you had to lay out rafters with a square, I would always cut a pair and try them. There's nothing to stop you from nailing a couple blocks on a wall and try the pair there. That's assuming you know the span and if you don't, I would stop right there and hire someone else.
With rafter books now days, it's hard to be wrong as long as you can read a tape.
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