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smata67 07-30-2012 08:38 PM

Will a Jack Post Lift?
The roof of a gable style shed is sagging a bit, maybe an inch, on the spine. Looking at it from the side, it bows in the middle. The shed is 10x10, shingled, and has 2x4 rafters with plywood gusset plates for support. The sag is due to the fact that one of the side walls blew out when a tree limb hit the roof. I've rebuilt the wall, but the rafters stick out over the stud wall at the middle, they are fine on either end (at the gable wall), this is due to the sag. So I'm thinking of putting a 2x8, 6' or so under the centerline of the roof, mounting two jack posts to hold it and gently raise the middle to get an even roof line again. At that point I'll add some ties to keep it from opening up and secure the rafters to the new all. There is some weight here, 1/2" plywood, 140sf of shingles, can a jack post be turned to get about 1" lift?

hand drive 07-30-2012 09:05 PM

Do you see visible splits in the rafter system from the impact? The problem with one 2x8 is that it will forecfully tilt when pressure is applied vertically against the grain while jacking against it. You will need a double 2x8 and possibly some added vertical ties to help vertically stabilize the beam while jacking, (usually done in the exterior wall system).

edit, just re read...
Are you jacking up to and against the plywood gussets ?

Duckweather 07-30-2012 09:19 PM

If you mean ridge board, the jacks will usually separate it from the rafters unless you pull the walls in at the same time. you could use come alongs to pull or if only one side wall is bowed out, a couple long spring boards. Long 2 x 6/8 staked to ground with the other end at the top of the wall. Bow it down as much as possible and nail the top to the wall. Then put a leg in the middle and work it toward the bottom with a bar. As it straightens out it pushes the wall in. Alternate from jack to springboard. Be careful and go slow springboards have an amazing amount of power.

Duckweather 07-30-2012 09:23 PM

Sorry I just re read that the springs would have to go against the rafter ends and the wall fasteners removed so the rafters slide on it. Or come along pulls on a beam attached to rafter ends.

smata67 07-31-2012 08:37 AM

1 Attachment(s)
I've attached a sketch that shows my issue. A coworker this morning suggested I use a bottle jack and I think he is right on. I plan on cutting a 30 degree cant in a 4x4, placing up against the rafters as shown at the low point of the roofline, it will be about 8' long (shed is 10' wide) jacking up an inch or so to level. This beam will tell me when I'm straight if it does not flex, as each end of the gable walls is in the correct position, the roof is just bowed in the center. Then I will install roof ties onto the rafters so it doesn't split out again and nail the rafters to the stud wall. Sound like a good plan? Or do I need to not be cheap and put up two 4x4 columns?

Duckweather 07-31-2012 08:59 PM

When you rebuilt the wall is it now shorter? If it is the same height and the rafters are further out in the middle of the wall, that point should be pushed or pulled back in. The ridge will go up at the same time. Just jacking the ridge seldom works. It usually separates the rafters, and if the rafters are now nailed to the wall, it will try to bow the wall in, unless there are no nails. Being only 10 feet long is your only chance it will work. I have done it many times on houses.

smata67 08-01-2012 05:00 AM

1 Attachment(s)
The new stud wall is the proper height. The rafters extend out beyond it about 1" at the middle of the wall, this dimension going to zero as one moves from the center toward the gable walls. I tried moving the rafters back by nailing a cross member and tapping, would not budge, but I'm going to try again after splitting that side of the roof into two parts, the break is not complete, there is about a 1' section at the ridge that is still somewhat intact. Still, when trying to tap those rafters back, you have the entire other side to work against, I'm pretty sure I have to go up. I'm counting on the rafters pulling back and falling into place as I raise the center, taking the bow out of it.

smata67 08-03-2012 02:12 PM

Done and worked good enough. Put a 4x4 on a car jack and selectively lifted from the opposite side of the damage as in my sketch, rafter scooted back into place, though 2 of them are still a bit long, perhaps 1/8". Once in the right place, I ran new screws in the gusset plates (previous ones were sheared) and added a tie to each rafter. Seems to be holding...

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