Things You'll Need
Finding roof rafters from the top of the roof can be difficult, since regular stud finders have trouble penetrating the plywood, shingles or slate tiles covering the rafters. If you need to complete roof repairs, such as installing new shingles or tiles, you must know where the rafters are. Fortunately, there are several ways you can find roof rafters.
Measure the distance from the inside wall to the center of the first rafter inside the attic. In many cases, the rafters are exposed in the attic. Once you measure the distance from the wall to the center of the first rafter. Measure from the center of the first rafter to the center of the second rafter. Rafters are evenly spaced, so knowing how far apart they are gives you the ability to find the rafters while on the roof. Transfer the measurements to the roof. Start at the same end of the building and measure from the inside wall over to the first measurement. This marks the center of the first rafter. Measure over again. This measurement shows you the center of the second rafter. Repeat the second measurement until you reach the other end of the building.
Position yourself on the roof between the apex and the bottom edge. Tap the roof moderately with a rubber mallet or leather mallet as you work your way across the roof. When you hit a stud, you will hear a noticeable difference in the percussion sound. When you strike the rafter, the sound will be a dull thud with almost no reverberation. When you hit between the studs, the sound will be hollow with a small amount of reverberation.
Remove several shingles or tiles from the roof to minimize the distance a specialized "high-density" stud finder needs to look. High-density stud finders will see through the plywood and find the rafters inside the attic. These stud finders work the same way as normal stud finders but cost more. Hold the HD stud finder approximately 1 inch away from the roof surface and slide it across the roof. The finder beeps when it finds a stud.