Lay the Shingles
After all the prep work, the shingling itself is mostly repetitive. Each bundle of shingles has basic installation instructions on the packaging.
The most common shingle is the “three-tab,” so called because it has two slots cut into one edge. Shingles are sold by estimated longevity, 20-year, 25-year, etc. Twenty-five-year shingles are a tremendous value because they offer quality look and durability. To estimate how many shingles you’ll need, multiply the length times the width of your roof to find the total area in square feet. A”square” of shingles equals 100 sq. ft. of coverage. Divide your roof area by 100, and then add 10 percent for waste, to get the number of squares you need.
4. Make the starter row by cutting the three tabs off a regular shingle and nailing the remainder so it all overhangs the edge of the roof by about 3/8 in. The adhesive left on the lower edge will bond the tabs of the first row of full shingles. Use a utility knife and straightedge for the cuts, and cut from the smooth backside.
5. Begin the shingling pattern in either of two ways: For roofs less than about 25-ft. long, start the first row with a full shingle in one corner and work upward along the rake edge. Cut 6 in. off the first shingle in the next row, lay it over the first, nail it, and work upward in a pyramid fashion. Then go back to the bottom row and step a series of full shingles all the way up, adding another row on top. Continue to work diagonally across the roof.
The second method is a little more complicated, but it takes into account that shingle sizes aren’t precise. By the time you reach the other side of a wide roof, the alignment of the cutouts running up the roof will noticeably waver. For a better appearance, some pros begin wider roofs near the middle. This method requires stretching a measuring tape from one rake edge toward the middle to a distance that’s an even multiple of three (like 1 ft., 15 ft., etc.) and subtract 3 in.
At this point snap a chalk line up the roof (parallel to the rake) and snap a second line 6 in. closer to the rake. These reference lines should be used to keep the cutouts aligned. Lay the first row of shingles toward the rake edge starting from one line. Then stagger the second row 6 in. and run it to the rake as well. Offset each row 6 in., again building a pyramid. Most shingles have small slits spaced every 6 in. along the top edge to aid in alignment. As shingles are added, use two lines as a reference to keep the cutouts aligned.
Lay each shingle so that the lower edge just covers the top of the cutout on the shingle below, leaving the 5-in. tab exposed. Cutouts vary, so snap horizontal chalk lines the entire length of the roof about every three rows to use as guides which help to keep the rows running straight. Nail the shingles just below the self-sealing adhesive about 1 in. from each end and directly above the two cutouts. Always let the last shingle in each row overhang the rake edge. Then cut the ends all at once with a “hook blade” utility knife.
Create the Valleys
6. Valleys are the main channels for diverting water so they need special attention. Use the type of valley recommended by your building inspector. To make an “open” valley, lay a 24-in.-wide preformed galvanized steel valley over the strip of asphalt flashing, nailing the metal along its edges to hold it in place . Next, snap a pair of chalk lines (beginning at the top) 3 in. from the center, and angling wider about 1/8 in. per foot of valley. As your rows of shingles reach the valley, trim each shingle along this line and glue it down with a 3-in. band of roofing cement. Remember to trim off the top corner of each shingle so water isn’t diverted underneath. “Woven” and “closed” valleys are also common in many regions .
Finish the Ridge
7. Fold the shingles over the top and nail on a row of ridge shingles once you have reached the ridge. Make the ridge shingles by cutting the regular shingles into thirds. Cutting them off at a small angle improves their appearance. Lap them, leaving only the tab exposed and nail them 1 in. from their edge just below the adhesive. Snap a chalk line along the ridge to keep the row perfectly straight, and use longer roofing nails that will penetrate the sheathing 3/4 in.
Flashing Part 2: Roof Penetrations
Leaks generally occur in two areas: where a pipe or chimney pokes through the roof or where the shingles butt against a wall. These areas can be kept watertight by bending and installing special metal flashing to divert water away. The most common metals are 26-gauge galvanized steel and aluminum, both of which can be purchased in 10-in. rolls. (Important: don’t use aluminum around concrete, mortar or other cement products since they will make it corrode. Both weather to a dull gray color.) Tip: If you want the flashing to blend with your house color, purchase it from a steel siding dealer who offers sheet metal in several baked-on colors.
Flashing a Dormer
A dormer usually requires two types of flashing. The flashing along the front wall consists of a 10″-wide sheet of galvanized steel bent down the middle. Slide it up under the siding and building paper and nail it along the bottom edge every 8 in. Sometimes you have to remove trim boards so you can bend the end of the flashing up around the corner. You might have to pull nails from the lowest siding board to place this flashing properly.
8. Complete the corner by cutting a 10″-long piece off the 10″-wide roll. Fold it at a right angle, and slip it under the siding going up the roof. Cut and bend it around the corner 3 in. Apply a silicone caulk along the backside to seal the corner.
9. Lay the next row of shingles to within 1/4 in. of the wall, covering the flashing. But don’t nail the last shingle within 5 in. of the wall, since you want to avoid penetrating the flashing. Then, slide another piece of flashing behind the siding, and nail it at its top edge. Cover it with the next row of shingles, and repeat the flashing and shingling by “stepping” up the side of the dormer.
Flashing the Chimney
Flashing the chimney (or any masonry wall) is similar to flashing a dormer, but has a few additional steps that take a lot longer. Plan on spending an entire day to do a complete, first-rate job (and remember to put up the scaffolding to provide safer footing).
10. Begin by placing the regular flashings as you did around the dormer. Since our front section extends 12 in. up the chimney and 4 in. down the roof, we had to buy additional 16″-wide galvanized steel. If there are no siding boards, you can’t slip your flashings under anything. Instead, chisel out mortar joints about 1 1/2-in. deep and slip a second type of flashing, called “cap” flashing, into the joints, bending them over to cover the regular flashings. Make one long cap flashing to cover the front and bend it 3 in. around the sides. Then, cut others 8- to 10-in. wide and step them up the chimney joints, overlapping the ones below by at least 3 in.
11. On the back or up-slope side of the chimney—where water, ice and debris can collect—construct a “saddle” or “cricket” from 2x4s and plywood, making its slope the same as the roof’s slope. If it’s small, cover it with galvanized steel flashing. If it’s larger, treat it like a small roof. Install valleys and shingle it. Continue the cap flashing around the corner and up the backside. Finally, remortar the joints to keep out water.
12. Flashing Pipes and Vents—Purchase special preformed metal and rubber pipe flashing that fits the pipe’s size. To install it, lay shingles until the colored surface is within 5 in. of the pipe. Then drop the flashing in place. Nail the flashing with two nails at the bottom and lap the next row of shingles over the metal edges as far as possible, being careful not to nail through those edges (see photo). Cover exposed nailheads with silicone. If old roof vents are rusted or beat up, replace them. Install them exactly the same way as pipe flashing. Tip: This is the ideal time to add more of these vents if your attic needs better ventilation.