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The top plate is rotten and needs replacement, because of roof leaks. I want to replace about a six foot stretch. Is it even possible to push the roof edge up half an inch so as to do this? I have an auto floor jack in mind and some 4x4s.

EDIT: Picture added enter image description here

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  • For better answers, please post a photo Commented Jan 29 at 5:27
  • There are top plate constraints dictated by the code that you should be aware of, see IRC R602.3.2. There's nailing schedule stuff under IRC R 602.3. You might create another question on how to properly patch in the new top plate. Images will be necessary to avoid a recitation of the code.
    – popham
    Commented Jan 29 at 5:40
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    It does not need to be a 1/2", a 1/4" is plenty. It will be difficult to do over a short area. The roof sheathing will be reluctant to let you go the 1/4" as it is. If you plan to repair a 6' section. jack up over a 10' or better if you can. Realize you will need to arch the plate, not simply deadlift one section. @popham is correct. The joints in the plates should be separated 4'. There are ways to do less lap with metal straps. Look it up. Usually it is a strap 1 1/2" wide by 24" long. They are made by various companies. Longer is better.
    – Jack
    Commented Jan 29 at 6:30
  • Jack, what do you mean by arch the plate, and not just deadlift?
    – drt33ts
    Commented Jan 29 at 19:54
  • @drt33ts, he means that you want to lift the roof into a smooth curve. That stands in contrast against a jump from 0" lift to 1" lift, a chain of 1" lifts, and then a jump back to 0" lift at the end. With great powerful lifting ability comes great responsibility. If you were using, say, a 15" pry bar to lift things, then you would be forced to incrementally lift things and avoid the possibility of breaking stuff. You forgot the @, so Jack didn't hear you unless he's following your question.
    – popham
    Commented Jan 29 at 23:03

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Installing a header for a window is a very similar problem to yours. Search YouTube for "install header for window". Most videos will implement some pattern for shoring up the ceiling while the studs get reconfigured. If your floor joists are I-joists or trusses, then abort and question the conventional wisdom. A concentrated load over an I-joist could damage it. They're relatively delicate, where I would want something like 18" long chunks of 4x4 running parallel to the I-joists and above them to distribute the load better than a 3-1/2" bottom plate could manage. And a concentrated load that misses a floor truss's panel point (where the top chord gets stiffened by truss members from below) could easily overwhelm the floor truss.

Creating a temporary wall is a nice cheap method in my opinion. If you have roof rafters, then offset the temporary wall to the interior by 2 feet or so. If you have roof trusses, then maybe take a 1 foot offset. If the 1 foot is too tight for you, then put the temporary wall below the closest truss panel point (where the bottom chord gets braced by truss members from above), but within reason. A temporary wall for trusses should be within, say, 5 feet of the exterior wall, as it's stressing your floor joists with the roof's load. Locate each temporary stud directly above a floor joist and use a double top plate. Needless to say, I hope, you shouldn't do this when there's 15 psf of snow on the roof.

To jack up the roof, go to each stud/joist location, and use a pry bar and shims or wedges at these locations to lift the roof just enough to unstress the exterior wall. Move on to the next location if the current one has gotten too stiff, working back and forth along the line until the exterior wall is unstressed. 1/2" is way too much lifting and will damage things. One of those 15" flat pry bars with the 90 degree bend at the end works well. Putting the bend under the bottom plate over a joist and pulling sideways will generate the best lift.

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  • Building the temporary wall 1/4" taller than the existing wall, then banging it into place should gently and evenly lift the roof by the required 1/4".
    – FreeMan
    Commented Jan 30 at 15:40
  • @FreeMan, this answer didn't survive the subsequent image post. I see a rafter with no tie. I think I see a hip rafter coming in at a 45 (when viewed in plan). But that would be really strange without a wall coming in at 90 and with a hip roof's typical arch action. I figure it must have a post at the other end, but I still don't know what's going on for sure. With how unresponsive the guy is, I'm pessimistic.
    – popham
    Commented Jan 30 at 17:30
  • @popham I'm sorry, life pulled me away. The diagonal piece is a valley rafter. To the left of it the roof slopes down to the exterior wall. To the right the slope is at 90° to the first, hence the other diagonal piece just behind it, which is the rake for the latter part of the roof. The water came in where it ran down both roof facets to accumulate in the valley, in which previous owners never installed any flashing.
    – drt33ts
    Commented Mar 19 at 18:20
  • @popham Your response is full of useful info I'll have to walk through. I do not have I-joists underneath but solid 4x6s, parallel with the wall. I was afraid to stress the floor even so and built a temporary support wall above the joist, which placed it about a yard away from the wall. For the valley rafter I hope to hold it up with a vertical 4x4 banged into place, but I haven't got there yet as I'm not yet ready to pull out the rotten top plates. Figuring out how to cut them.
    – drt33ts
    Commented Mar 19 at 18:25
  • @drt33ts, I only see 2 rafters in your image. One of them looks untied. The other, the valley rafter, looks like it could possibly be tied. If there's a substantial connection between the valley rafter and its intersecting ceiling joist, then it's important to maintain that substantial connection. And you should consider putting shoring below the floor joist that runs under your temporary wall. It depends on the size of the floor joists, but 24" spacing between 2x4 posts sounds plenty sufficient.
    – popham
    Commented Mar 19 at 19:08

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