1907 12x12 roof sagging

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Old 07-20-14, 06:19 AM
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1907 12x12 roof sagging

Hi all, first time here but not first rehab rodeo. Since each case can be unique here's mine. We bought a 1907 two and a half floor (first one was a 1909) that already has work well under way. The 12x12 roof sags from ridge to heel on unsupported 2x4s and on the side that has a perpendicular dormer the extra weight has split a valley rafter as well. I estimate the half way point sag at 1"-2" and the valley rafter sag about the same, pictures are coming. We plan to make the attic into a living space with knee walls and collar ties, insulation, heat and electrical service. The biggest question here is do we try to reduce the roof sag with jacks before framing, or frame as is and live with the appearance. Any advice will be helpful.
 
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Old 07-20-14, 08:40 AM
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You need to repair this. Finishing off the space and insulating it will result in an increased level of snow remaining on the roof for longer periods. The snow will be adding additional weight which, combined with the new interior finishes, may be just enough to result in a failure.

Jacking individual rafters is not really that big an operation. They should go up fairly easily. Make sure you build up a suitable base to distribute the load by running a few larger framing members, maybe 2x12's, laid flat over several ceiling joists. Establish a string line from end to end in the room and bring your rafters up to that point. Wherever you are planning a knee wall you should establish a mini beam for studs to rest on by doubling up 2x material and nailing a strong back to the back side which could be a 2x 8 to help stiffen the assembly and not impart a point load on the ceiling joists below.
 
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Old 07-20-14, 04:50 PM
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Thanks. I'm not too sure extra snow will be an issue. A previous owner had 8+ inches of loose insulation blown over the entire attic sub floor and there are some vents as well. However, I can't say if that caused the sagging as you described. I admit to being am leery of jacking as I have read many accounts of lower wall damage but so far have been pretty responsible about thinking things through and seeking good advice. If I do it I already envisioned plenty of jack load distribution as well as robust knee wall plates. This is a picture of the attic with the sagging rafters on the left, a bed of insulation, and some kind of raised walkway also insulated.
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