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shazapple 10-04-2012 02:05 PM

Sistering to a sagged rafter
I am putting a dormer on my 1.5 story house, and am at the point where I have to sister the rafters on each side of the opening. The house is over 100 years old, so there is about 1" of sag in the middle of the 14' rafters (not bad considering!)

What is the easiest way of dealing with this? The rafters are true 2x6 so could I take a 2x8 and scribe it to fit the curve? Jacking it straight wouldn't be an option as the sag probably happened before the ceiling / rafter ties were installed (probably about 70 years ago). Any help would be appreciated!

mae-ling 10-04-2012 03:19 PM

Why not sister and straighten all rafters that are in this area?

I guess scribing a 2x8 would work.

Do you have a permit or need one? that may effect what you can do. ask your inspector if applicable. Notice your in Atlantic Canada. My wife is a Newfie.

hand drive 10-04-2012 08:48 PM

In situations where ripping the width of the framing lumber will not compromise the strength of the lumber- I will measure the width that needs to come out at the center of the piece and pop a chalk line from center outward to both ends of the piece, making a long V cut .
Also, with the crown of the piece of lumber facing down it will form more (sister) to a sagging framing member though I think there is more deflection strength with the crown facing upward.
Just buy lumber with a 1" crown in it, not hard to find these days :)

mae-ling 10-04-2012 10:12 PM


Originally Posted by hand drive (Post 1023974)
Just buy lumber with a 1" crown in it, not hard to find these days :)


Gary in WA 10-06-2012 10:07 PM

I doubt your 2x6 roof framing would meet your required energy code for insulation thickness... never rip a piece of lumber to compensate for ?, fig. #3: why not frame it larger and furr down the rest of the rafters to match?


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