![]() ![]() This would require an engineer stamp and some real thought as to how to lift the beams into place and straighten the rafters as you install it. If I recall that is a system used in England a lot. The box is made of structural beams and the entire purlin beam is attached to the next beam as well as every rafter. A boxed purlin system at mid span of the rafters all the way around the inside of the roof can be built. I have seen an alternative, usually done when being built, but possible could be retrofitted. This is hard to do in an open span garage. ![]() You usually need a way to brace the purlins at not over 45 degree angle to the rafter and the braces have to transfer the load to the ground. It means straightening each and every rafter as you add the purlins (with a jack, usually the force applied 90 degrees to the rafter and you need to have a method of finding what straight is, easier done with the shingles off). I agree with purlins as a possible fix if you are saying that the roof is low in the middle. My assumption is since they will be lifting the rafters, they should be sized for roof/snow load, versus just for the rafter tie/drywall dead load? If so, i'm curious about the sizing of the beams. ![]() If not, any suggestions? I'd rather not involve an engineer if i can simply overbuild this enough. The first question is if you all think that's a workable solution. My thinking is that that wouldn't cause too much undo stress on the roof considering the new beams are taking the load off the ends, and allow the center of the shop to remain free of posts. I'd to remove the crooked hangers from the attic and replace with more vertical hangers to keep the rafter ties/ceiling joints from dropping too far in between the beams. The beam will likely be butt jointed over the posts for easier handling. The fewest i can get away with using a reasonably sized beam. Then place posts under the beam, either 3 or 4. To solve this, i'd like to add beams under each end of the rafter ties - either right at the joint with the rafter or slightly inboard, and jack up the rafter ties/rafters to remove the sag. The are a handful of hangers/struts in the attic to keep the rafter ties turned ceiling joists from sagging. There had been storage up there as well but that has been removed. The issue the rafter ties were raised at some point to a little less than a third the rafter length, and ties were drywalled and attic insulated. It's double gabled with 12/9 pitched roof and 32x24 footprint. this garage is only 5 years old,why someone didn’t use trusses i’ll. If your garage is 24 feet wide and has a 4/12 roof, the new rafter ties can be placed no more than 16 inches up from the plate without additional engineering. the rafters are currently 2×4’s 2 oc with no collar ties.there are rafter ties every 4 made with 2×6’s that are currently free spaning the 24 width and sagging. I'm working to solve some sagging rafters on a garage/woodshop. i have a 24 wide garage,4/12 pitch with comp shingles. New to the forum, thanks for having me here. ![]()
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