Building a Garage - Applying Felt and Asphalt Shingles

Applying the Roofing Felt

Roofing felt acts as a waterproof barrier between the sheathing and the roofing material (shingles, etc.). We recommend using 15-30 lb. roofing felt. It is necessary to apply the roofing felt (tar paper) to a clean, dry surface immediately after the sheathing is completed to protect it from the weather.

If, however, this is not possible and the sheathing gets wet, allow it to dry for a few days before applying the felt so as not to trap any moisture that may cause damage to the sheathing. Felting applications vary according to the type of roofing so determine the proper application before beginning.

Most Common Mistakes

  • Applying felt to a wet surface.
  • Not overlapping the layers.
  • Not applying smoothly.


1. If you have chosen to apply a metal drip edge along the eaves, this must be in place before laying the felt. A drip edge is usually made of 26 gauge galvanized steel with a top flange of 3 to 4 inches that extends in from the roof edge.

2. In heavy rain or snow areas, we also recommend eave flashing, a strip of smooth or mineral faced roll roofing. This is cut to extend from the edge of the roof to a point 12 inches inside the wall line. Place the lower edge of the strip even with the drip edge.

3. The roofing felt is then applied in accordance with the type of roofing to be used. We will assume here that you are using asphalt shingles.

4. Snap horizontal lines on the roof sheathing to align the upper edge of the felt. Snap the first line at 35 and 5/8 inches above the eave. (The 36" felt should overlap the eave by 3/8".) Snap succeeding lines at 34 inch intervals, assuring a 2 inch overlap of each course.

5. The felt must be flush at the rake (side) edges, have 4 inch overlaps where two pieces are joined, and 6 inch overlaps on hips and ridges.

6. Ensure that the felt lies flat and smooth before securing it.

7. Tack the roofing felt down with 1/4" staples using an air compressor with a pneumatic stapler, a hammer-tacker, or a staple gun every 12 inches.

Applying Asphalt Shingles

Composite (asphalt) or fiberglass shingles is the most common roofing now in use. It is composed of asphalt impregnated paper with mineral granules coating the exposed surface. Numerous colors and styles are available to enhance the design of your garage.

Shingles are easy to install, require little maintenance and are easy to repair. Wind sealed shingles have an added dab of roofing cement under the bottom edge of each shingle. After these are installed and the roof is heated by the sun, the cement melts and sticks to the shingle below, increasing their effectiveness in high wind areas or on shallow sloped roofs.

Most Common Mistakes

  1. Leaving out the starter strip.
  2. Not keeping shingles aligned.
  3. Not overhanging shingles at eaves and rakes.
  4. Neglecting to stagger joints.
  5. Installing ridge shingles before hip shingles.
  6. Neglecting to keep hip and ridge shingles in a straight line.


1. If you are using a drip edge, the starter course goes on TOP of the drip edge at the eaves (bottom) and UNDER the drip edge at the rakes (sides). The starter course applied at the eaves is a standard row of composite asphalt shingles with three inches cut off the tab (bottom) ends. (You could also use a 9 inch wide strip of roll flooring.) These are installed in an inverted position. The tabs face the ridge, the wind seal is down, and the mineral surface is exposed to the weather.

2. Overhang the eave by 1/2 inch and leave a space of 1/16 inch between each shingle. Nail each starter shingle with four 12 ga. galvanized roofing nails placed three inches above the eaves - one inch and twelve inches from each end of the shingle.

3. The first full size course of shingles is installed DIRECTLY ON TOP of the starter course but with the tabs facing down towards the eaves. Nail the first and subsequent courses using four nails per shingle, placed 5 and 5/8 inches above the butt or bottom line (5/8" above the top of each cutout). Again, drive a nail one inch and 12 inches from each end.

4. To prevent the shingles from buckling, begin nailing each shingle from the end next to the previously laid shingle. Leave a gap of 1/16" between shingles. For the remaining courses, we recommend popping a vertical chalk line on the roofing felt every 36 inches and a horizontal chalk line every 10 inches. This will enable you to align the top and side edges of each shingle along a straight line.

5. The joints between the tabs must continue to be staggered. This means the joints (cutouts) must not be aligned in adjacent courses.

6. To do this, cut 6 inches off the first shingle of the second course at the rake (side) of the slope. Cut 12 inches (one full tab) off the third course, 18 inches off the fourth course, 24 inches (2 full tabs) off the fifth course, and begin the sixth course with just a 6 inch length of shingle. Repeat this sequence beginning with a full length shingle on the 7th course.

7. Once the flat planes of the roof have been shingled, you will need to apply the hip shingles, if you have a hip roof, which will be overlapped by the ridge shingles. Gable roofs will only have ridge shingles. These can be purchased prefabricated or can be cut from standard shingles - one 12 inch tab from a standard shingle, folded in the middle as shown in.

8. Pop chalk lines 6 inches on each side of the hip and/or ridge centerlines. These will be the guidelines for the edges of the shingles.

9. Start at the eaves of the hip, with a double layer of shingles, and work your way up to the ridge using the standard 5 inch exposure. Nail once on each side, 5 and 1/2 inches above the butt of each shingle. Where the hip intersects at the ridge, cut 4 inches up the center of a tab and nail this so that the uncut portion is nailed to the ridge and the 4 inch slit overlaps and is nailed to the top of the hip, covering the last of the hip shingles.

10. Begin applying the ridge shingles at the ends, working each end toward the center nailing a saddle tab where they meet. Nail the saddle in all four corners.

11. Cover any exposed nails with roofing cement and you are finished.