Rafter sag question.

I have a roof about 50 years old with a 4:12 pitch and 2X4 common rafters. The problem is at the half way point between the ridge and the top plate on the wall there is about 3/4 of sag. (About 11 feet from ridge to the birdsmouth.)
What is the best way to take the sag out of these rafters? I worry that if I were to attempt to run a brace to the ceiling joist that this would in effect push the ceiling down.
Any ideas?
--

Roger Shoaf

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Roger Shoaf wrote:

Depends on what you're using the space for, why it's sagging, and whether you want correct the sag, or just arrest it.
Will just taking off all of the 9 layers of old shingles next time you re-roof do the trick? If you're not using the space, collar joists would probably work.
If you ARE trying to use the space then things get a little more complicated, but doable.
Or you could just let it sag.
--Goedjn
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on
if
if a brace would push the ceiling down, i think thats the next thing you need to fix. forget about the 3/4?(inch? foot??) sag in the roof....
randy
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an 11'-0" long rafter at 4 in 12 yields a 10'-5" horizontal span. A 2x6 at 16 inches on center No2 Douglas Fir will span 12'-1" horizontal. That means 2x4s are probably over stressed. It might be a good idea to remove the roof deck and sister straight 2x6s to the 2x4. It seems to me that applying force to straighten the existing 2x4s might split them or do other damage.
TB
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