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Roof Purlin Repair advice

marrahb | Posted in General Questions on
I have a roof purlin that is pretty badly split in numerous areas and while I was debating on sistering it myself, I think I’m going to leave it to the professionals and have put it out to bid. The only question I have is what the proper repair should be?
Would it be sistering with same size wood, or using 3/4 plywood on the front and back along with construction adhesive and lag bolts or headlock etc? Or with how badly it is split just all out replacement?
I want to make sure it is done right, and anything to look out for when getting bids is what I am aiming for.
If the link works, I have a PDF of the type of construction my roof has (seems non typical for the area), pictures of the splits as well.
What contributed to this I believe is the previous high heat in the space (crystalized sap around) and then I’m sure a high load was put on the roof when reroofed (was done at sale of house as a condition of sale). They put a ton of vents on the house so I don’t see this becoming an issue again in the near future.
Located in Washington state House built in 1970

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  1. Expert Member
    BILL WICHERS | | #1

    It might be easiest to just replace that bad purlin, but another board could be installed alongside with the original left in place. The original though is bad enough that I don't think sistering is really sufficient, since there isn't enough of the original to reliably connect the new piece to.

    Normally you would glue a new piece alongside ("sistering"), with nails or screws to secure it while the glue cures. I like to use screws instead of nails, since the screws act like clamps to draw the pieces tightly together to get a good glue joint. Note that ideally you want screws that have 1.5" of unthreaded shank so that they can spin freely in the new piece while they screw into the old piece. I just don't think there is enough of the old piece left to grab onto, and my guess is it will split more if you try to screw into it.


  2. marrahb | | #2

    That's one of the things that I was thinking about was just putting another board on the opposite side with another in the middle to fill in the gap. I agree it is pretty far gone to try and push the pieces back together and salvage the original. Lol sorry for the crude picture, but attached of what I was envisioning.

  3. marrahb | | #3

    Thanks all for the help. I decided to hire a structural engineer to detail the repair, then I'll shop around GC's who can execute it (assuming it's outside of my expertise).

  4. Deleted | | #4


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