I have a wooden roof.

I need to drill though it from above, and hit the beams exactly in order to attach something.

The edges of the roof are not straight, and it is impossible to find out where the wooden roof begins, so using a tape measure to find the beams will be extremely difficult.

Does modern technology provide a tool with which I can find the position of the beams through the roof?

I'm thinking about a two-part gadget where one part can tell when it is close to the other part or something.

The roof is about an inch thick.

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  • 1
    Are the beams steel? How about a metal detector?
    – Doresoom
    Aug 24, 2014 at 14:44
  • 1
    Perhaps a magnet? Or if those aren't steel, a pair of magnets.
    – Dan D.
    Aug 24, 2014 at 15:54
  • So what did you end up doing?
    – Handy Man
    Sep 1, 2014 at 14:47

4 Answers 4


Use a long, small diameter drill bit from below and drill all the way through the beam and the roof. To prevent water intrusion, fill the hole with silicone caulk from above prior to making your attachment, then simply patch the beam from below with wood putty or spackle and paint/stain to match. enter image description here

  • 4
    Be sure to find the hole while the bit is in it, or have something long and brightly colored you can stick up through the hole - it can be remarkably difficult to spot a small hole when you don't know exactly where to look.
    – Ecnerwal
    Aug 24, 2014 at 20:50

I use a pocket compass. Place a neodymium magnet on one side and scan the wall on the other. Gets within an inch or two on a thick wall 🧭 takes a little practice for the first few times


My first thought was to suggest a stud finder, but since I don't know the material on the roof i'll suggest a Wall scanner.

Bosch carries a professional model called D-Tech150, here is a video of how it works.

There are cheaper alternatives such as this

If all else fails, a hammer and a good set ears should help you locate the beams.

Note: I have no personal experience with the wall scanner, but everything I've read indicates this is the type of solution that will help you locate the beams.


Decide the best location for the item on the roof. Drill a hole from the top. Add additional blocking for support below. Paint blocking to match.

Alternatively, locate one of the joists relative to the edge of a door or window opening. Using squares, plumb lines and levels create a station point for reference on the roof. Offset to the desired joist from the station point.

Establishing additional station points and triangulating will improve accuracy or find errors in measurements.

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