How to Find a Roof Truss for a Roof Bracket

Place your extension ladder against the side of the house, and look upward, under the eaves. Here, you'll see the soffit covering the bottom of the overhang. If practical for your application, remove one of the soffit panels, pry the edge of the soffit, or look through the soffit vents to locate the end of the truss extension. When you locate it, drive a small nail upward into the center of the truss, leaving about 1/2-inch of nail exposed.

Tie the end of your string to the nail, then throw the string over the rooftop and down the other side. Repeat the truss-finding and nailing procedure on the corresponding truss extension on the other side of the building, but do not tie the string to it. Instead, climb up onto the center of the roof-top. Have your assistant wrap the string around the second nail, and pull it tight. Pull up on the center of the string where it crosses the roof peak to free it of snags. Have your assistant tie and tighten the string when you've straightened it.

Repeat this procedure with every fourth roof truss. Now, measure the center-to-center distance between each roof truss visible from the soffit panels. Then transfer your measurements to the rooftop with a grease pencil, using your strings as reference lines.

Test your reference marks with deadblow hammer-taps to the roof-top; preferably, directly on the wood, under the shingle, if you can pry a shingle up far enough or if you've yet to lay shingle down. You should hear a hollow, drum-like boom over the open spaces, and a solid thud when you hit a truss. Alternately, this method will work if you can't locate truss extensions under the soffit, or don't have extensions. However, the hammer method can be a bit inaccurate for mounting purposes, so it's best used as a back-up to double check marks between your reference strings.