How to Use Roofing Jacks

Select a mounting location for the roof jack that is directly over a rafter. Do this by accessing the underside of the roof in your attic and measuring the spacing of the rafters — usually 16 inches or 24 inches on center. Use these measurements to find rafter locations when you're on top of the roof.

Slide a pry bar under the tabs of the shingle directly over the desired mounting location of the roof jack. Loosen the tab and lift it carefully with the pry bar. Note that with some types of shingles — such as architectural shingles — you may have to lift the entire bottom edge of the shingle. Remove the pry bar.

Slide the upper end of the roof jack under the shingle that you have lifted until the bottom mounting hole in the jack is covered by the bottom of the shingle tab. Hold the jack in this position. Lift the shingle tab carefully to avoid creasing it, and drive a 2-1/2-inch roofing nail through one of the mounting holes in the jack.

Continue nailing through the remaining mounting holes in the jack until you have three nails that penetrate the rafter underneath. Note that the nail should not drive in easily, as this means that you have missed the rafter and gone only through the roof sheathing.

Try to move the jack from side to side. Add more nails to the remaining mounting holes in the jack if it moves, as this indicates it is not yet solidly mounted.

Add more roof jacks to the roof so they are installed in a straight row in the same fashion. Measure from the bottom edge of the roof to the jack to ensure they are all uniformly installed. Do not allow less than 48 inches of spacing in between each jack.

Adjust the angle of each jack by placing the notch in the movable part of the jack into one of the holes of the bottom of the jack. Make sure the horizontal top edge of the jack is as close to level and the closest adjustment it will allow. Note that it is better to have the top edge of the jack tilting slightly inward toward the roof than tilting away from the roof.

Lay a 2-inch by 10-inch inch plank of lumber across the top horizontal edges of several roof jacks. Use several boards to span all of the jacks installed, if necessary. Make sure there are not more than 8 to 12 inches of overhang on each board. Screw the boards to the jack through the mounting holes with 1-¼-inch wood screws.

Remove the jacks in the reverse order of installation.