Installing asphalt shingles

Asphalt shingles will improve the look of any roof. But they won't last forever. In fact you can expect problems to crop up after 15 to 20 years. For example, shingles may start to break, wrinkle or lift. These are signs that the time has come for you to re-roof.
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1. Remove the old shingles
2. Install the membrane and flashing
3. Snap a reference line
4. Install the first row
5. Start the second row
6. Cover the valleys
7. Work around the chimney and vents
8. Cover the ridge and hips
9. Finishing
10. Glue the shingles
11. Special precautions

1. Remove the old shingles

Before starting to install new shingles, you'll need to remove all the old shingles and nails using a square shovel or roofer’s shovel (a special square shovel with teeth and a bent handle).

Once you've removed the old shingles, inspect the plywood panels underneath, which should be at least ½" (12.5 mm) thick, making sure that every sheet is firmly attached to the roof framing. Don't hesitate to add more nails if need be, and fill any obvious gaps with sealer.

2. Install the membrane and flashing

To prevent leaks and ice dams, install a metal drip cap along the perimeters of the roof and eaves before laying sheets of self-adhesive bituminous membrane or 50-lb felt paper on perimeters and openings, vent pipes and chimneys. For added protection, you can also cover the entire surface of the roof with 15-lb felt paper.

Install the chimney and vent flashings. Prepare membrane sheets for these areas by cutting slits large enough to insert the flashing and allowing an extra 12" around all the edges.

To cover a valley (the hollow where two sections of roof meet), place a 36" strip of self-adhesive membrane down the centre of the valley, so that approximately 18" of membrane covers each side. Then install the flashing the length of the valley.

3. Snap a reference line

Install shingles from the bottom of the roof upwards. To determine the location of the first row, trace a chalk reference line 5-10" (12-25 cm) from the lower framing header of the roof, depending on the type of shingles you are using, bearing in mind that the first row of shingles will overlap the eaves by approximately 3/8" (10 mm).

4. Install the first row

The first row should be installed “feet up”, meaning that the notched ends of the shingles must be pointing upwards from the roof edge. The shingles should line up with the reference line. Be sure to nail them at least 6" (15 cm) from the framing header. Use four nails per shingle and drive them 1" (25 mm) from the sides and ½" (13 mm) above each notch. Drive the other nails 12" in. (30 cm) apart along the lower framing header. It's important not to drive nails through the self-sealing strip. Furthermore, nails must be straight and flush with the surface of the shingles. This starter row must overlap the roof edges by approximately 3/8" (10 mm).

5. Start the second row

Start the second row at the same place as the first, but now install it “feet down”, having trimmed half a tab so that the joints are staggered. Always align the lower edge of the shingles with the top of the notches on the preceding row before nailing. Repeat this operation for every row. You can install up to five rows at a time. To give shingles good support at the peak of the roof, fold the shingles from the last row over the peak and nail them down on the other side.

The second row must also overlap the roof edge by approximately 3/8" (10 mm). Both layers (steps 4 and 5) finish the roof’s bottom edge.

6. Cover the valleys

Cut the shingles to fit the angle of the valley and bevel-cut their top corners to minimize the risk of water seepage. Seal with a layer of plastic cement. Drive in the nails at least 6" from the centre of the valley and seal the joint with plastic cement.

7. Work around the chimney and vents

Install the self-adhesive membrane sheet that was cut to allow an extra 4" up the sides of the chimney and a 12" edge around it on the roof. Next, install the flashing and seal the joints with plastic cement. Cut and lay the shingles to form a neat line around the chimney. Apply plastic cement to seal the joints and improve their water-tightness. To work around a vent, you can simply cut the appropriate-sized hole in the shingle, nail it down and then glue it in place with plastic cement.

8. Cover the ridge and hips

When the visible part of the shingles arrives at 5 5/8" from the top of the roof, it’s time to prepare for the last stage: finishing the ridge. Fold over the top of the shingle and nail it down on the opposite side of the ridge. Do the same on the other side of the roof.

To finish the ridge, cut three-tab shingles into three equal pieces. Then cut the upper corners of each piece at 45 degrees. Trace a chalk line 6 ½" from the ridge along either side. Starting from the end of the ridge that faces the prevailing wind, fold each piece of shingle along the centre so that half of each piece covers each side of the ridge. Then nail the shingle into place on both sides, 1" from the ridge and 6" from the bottom of the visible part of the shingle. Install the shingles so that each one overlaps the last, with 5 5/8" of shingle visible.

Repeat this process for the roof hips.

9. Finishing

When all the shingles are in place, use a metal ruler and utility knife to cut the overlapping edges.

10. Glue the shingles

For additional protection against the elements, glue down the shingles on each edge of the roof and those along the top, using plastic cement.

11. Special precautions

As with most construction projects, it's important to check with your local authorities if a permit is required. At the same time, you should enquire as to how best to dispose of the old shingles.

Try to get help from at least three other people if you can; working on a roof is quite a challenge!

High levels of dust, strong winds, and certain other weather conditions can reduce the efficiency of the self-sealing strips.
Asphalt shingles are popular because they are relatively easy to install. There are many different grades of shingles, but we recommend you invest in shingles that are guaranteed for at least 20 to 25 years.
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