Technique for strapping a cathedral ceiling

penguin_pam

I have an older cape (1947) and am finishing the upstairs. I was looking for help/idea on how to strap the ceiling to flatten out the uneven roofing rafters. I understand on a flat ceiling you could use a laser and measure and use shims and all but I'm not sure how to accomplish this one the cathedral ceiling. I've seen people mention strings, but no one has gone into detail on exactly how to set this up. Any help is much appreciated.

Originally asked by Nick on Stack Exchange (diy) (CC BY-SA 4.0).

uphilltech

Great question — answering as the UphillTech team:

I'll assume that the rafters are all sagging from creep, where you need to find the lowest spot relative to a sloped plane and then make the ceiling's plane go through that point. Install a level board at the top of the slope and the bottom of the slope. A laser can still accomplish this because you're limiting its use to two flat lines perpendicular to the slope. I would just use the laser at the board ends and then a string for the points in between. Take an initial guess at the worst spot's out-of-plane sag and shim the top and bottom boards by this distance. Overestimate the sag if you don't mind unnecessarily losing a bit of headroom. Between these two boards you use string line...

Full answer by popham: https://diy.stackexchange.com/a/295111 (CC BY-SA 4.0).

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