Locating roof trusses below the deck for sleepers

Morning people.

The goal of this job is to re-roof, but also make the structure more energy efficient by adding ventilated overhanging soffit to the new eaves.

I need to accurately locate roof trusses below a roof deck with underlayment so I can screw down 2x4 sleepers set vertically on top of them. These sleepers will hang over, or extend past the outside wall 18" to create space for the ventilated soffit. I’m concerned if the sleepers is not exactly over the truss, the screws may glance off, pull out or split the existing truss. This home is in Iowa which is known straight line winds and tornado’s.

I doubt any stud finder would work accurately through 1/2" plywood and underlayment. Any suggestions?


Find the end of the truss/rafter at the ridge then find it at the eaves & snap a line from the eave to the ridge.


Thanks Axiom. I can find all the trusses at the peak because were going to remove one row of plywood to blow in more insulation, and also leave a 4" gap to help remove moisture. But the truss tails over the bearing wall are hidden because there is no fascia board. After tear off, the deck seams will reveal those truss tails, but the other two trusses will be hidden, and I’m not sure if I trust the folks who built it to have placed the trusses exactly on 16" centers.

Try the unscientific way. Tap on the sheathing with your hammer and listen/feel. Then drive a nail to confirm.