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 ?
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
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.
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.
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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