How to find rafter tails when covered by soffit?

Question

I'd like to repair some hanging gutters by drilling some new gutter hangers into rafter tails, but it's already fully assembled with fascia trim and soffit covering the outside, how do I locate the "hidden" rafter tails precisely to drill into them?

Answer 1

On my house, the fascia is covered in aluminum trim with vinyl soffit underneath. Since the AL soffit trim is very light, it's held on by trim nails that go through every 3rd valley in the soffit (per instructions) which is more than sufficient and gives no indication of where the rafter tails are.

A strong magnet slid along the vertical face of the fascia might pick up where the nails are that hold the wooden sub-fascia to the rafter tails, so that might be worth a shot. Once you find one, the next one should be 16" or 24" either side. Of course, there may be variations in spacing depending on roof-line changes, age of house, skill of previous DIYers, etc.

Additionally, some of my sub-fascia is 1x dimensional lumber, while some of the new work had 2x dimensional lumber used for the fascia. (I think my contractor used what he had on hand instead of making an extra run to the lumberyard.) If you can determine that you have 2x lumber for your sub-fascia, that will be more than sturdy enough to hold up your gutters without worrying about hitting a rafter tail behind.

Answer 2

I ended up drilling holes in the fascia that points inward and upward and sticking a wire in those to triangulate the location of the rafter tails. Video. After beating on the roof with a mallet first for approximate location, a few feet up above the gutters.

Another option: drill small holes in soffit, probe with wire, as shown in a video from a comment by mopac85.

You could also use a chiptoolz thing and drill a hole through a low row of shingles to find it. I'd recommend lifting up the shingles first though so hole isn't exposed.

Wire idea of stake flag from comments.