As a plumber, I have to cut plenty of holes in roofs for vent pipes. One way to locate the spot for the hole is to hold a plumb bob over the vent pipe stub and then mark the vent’s centerline on the roof sheathing. But this can be cumbersome in a tight spot. I’ve found that a better way to locate my vent cuts is with a narrow-beam flashlight. As shown in the drawing, I place the flashlight atop a wood block over the vent stub. If I’m concerned about the flashlight shining straight up, I check it for plumb with a torpedo level. Held plumb, the light shows the way to my target.
F. X. Lowry, Somerville, MA
Edited and Illustrated by Charles Miller
From Fine Homebuilding #63
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Great suggestion! Here is an upgrade: use a laser pointer instead of a flashlight. This will eliminate 'light dispersion" with a target that gets larger with the distance. The laser pointer will highlight the exact center of the hole you need to drill. In addition, use a cheap 'laser level' which will ensure that the red laser dot is exactly square.
Mark Hays