Installing Asphalt Shingles

Before you can begin laying down shingles, the roof has to be prepped properly, and your geographic location has a lot to do with what preparation is appropriate. If you are in a part of the country that is prone to ice dams, code requires you to install ice protection membrane a certain distance up the roof (Q&A, “Ice Dam Membrane at Eaves”, Feb/18). The code also requires drip edge along the eaves and rakes of the roof (Code’s Eye View, "Drip Edge and the IRC," May/18); integrating the drip edge with the underlayment can be a challenge to get right (Q&A, “Drip Edge and Ice Barrier,” Mar/18).

Starter course. Regardless of style, shingle installation always begins with a “starter course.” Manufacturers make shingles especially for this application, but often they just recommend cutting off the exposed part of the shingle and nailing the leftover part of the shingle onto the roof with the edge of the shingle either flush with the drip edge or extending 1/4 inch past.

Offset patterns. Asphalt shingles are installed in alternating courses known as an offset pattern. There are two common variations for offset patterns for three-tab shingles: straight-up and staggered (see illustrations, below).

With the straight-up pattern, the shingles vary half the width of the tab from course to course in a straight line up the roof. With this method, the butt joints of the shingles align every other course, and that alignment means a greater possibility that wind-blown rain can get driven under the shingles and cause leaks.

While this method is frequently used, the butt joints align every other course, which doesn't provide much protection from wind-blown water. Also, the cutouts align every other course, which can cause premature weathering of surface granules.
Tim Healey While this method is frequently used, the butt joints align every other course, which doesn't provide much protection from wind-blown water. Also, the cutouts align every other course, which can cause premature weathering of surface granules.

A staggered pattern - one in which each course of shingles steps over a given distance from the course below - can provide better protection for the roof. The most common of these staggered patterns is half-tab, where the tabs align every other course and the butt joints align every seven courses, reducing the chances that wind-blown rain can find its way through.

A half pattern (also called half-tab or sixes) staggers each course with a 6-in. offset (half a tab width for metric shingles). Butt joints are better protected from water migrating horizontally, but cutouts still align every other course.
Tim Healey A half pattern (also called half-tab or sixes) staggers each course with a 6-in. offset (half a tab width for metric shingles). Butt joints are better protected from water migrating horizontally, but cutouts still align every other course.

Other staggered patterns—4-inch and 5-inch—give the roof a more random look from the ground.

A 4-in. offset keeps cutouts separated by two courses, and butt joints align every ten courses. But the short lap doesn’t provide enough protection in wet climates, or in areas with severe freeze-thaw cycles.
Tim Healey A 4-in. offset keeps cutouts separated by two courses, and butt joints align every ten courses. But the short lap doesn’t provide enough protection in wet climates, or in areas with severe freeze-thaw cycles.
Here, the courses are offset by 5 inches between courses. The pattern looks more random from the ground, and helps hide shingle irregularities. The cutouts align only every eight courses, so runoff is less likely to cut channels into the shingle granules. Butt joints also align every eight courses, providing good protection from wind-blown rain.
Tim Healey Here, the courses are offset by 5 inches between courses. The pattern looks more random from the ground, and helps hide shingle irregularities. The cutouts align only every eight courses, so runoff is less likely to cut channels into the shingle granules. Butt joints also align every eight courses, providing good protection from wind-blown rain.

For more information on installing three-tab shingles, the Asphalt Roofing Manufacturers Association (ARMA) has just updated its Good Application Guide for Three Tab Shingles.

Architectural-style shingles should be staggered according to the manufacturer’s recommendations that come with each bundle. Following those instructions ensures that the laminated tabs of shingles in successive courses don’t align. Typically, the instructions have you remove a certain specific width of shingle for successive courses. Unlike the three-tab shingles, the architectural-shingle courses don’t stagger evenly, but with the manufacturer’s directions, the sections that are cut off can be used to start courses above in the sequence.

The installation pattern for laminated, or architectural-style, shingles is determined by the manufacturer to prevent the tabs or cutouts in the shingles from aligning course to course. The cutoffs are designed to be used as starter shingles for courses farther up the roof. In this example, the 6-inch and 11-inch cutoffs are used to start the fourth and fifth courses. With this strategy, the butt joints align every six courses.
Tim Healey The installation pattern for laminated, or architectural-style, shingles is determined by the manufacturer to prevent the tabs or cutouts in the shingles from aligning course to course. The cutoffs are designed to be used as starter shingles for courses farther up the roof. In this example, the 6-inch and 11-inch cutoffs are used to start the fourth and fifth courses. With this strategy, the butt joints align every six courses.

Asphalt shingles have an asphalt sealing strip above the tabs. After shingles are installed, the sun’s heat melts these strips to adhere the shingles above.

Nailing. Driving the nails that hold a shingle on the roof is one of the first things to practice and get right. Start by selecting nails that have a head at least 3/8 inch wide and that are long enough to penetrate 3/4 inch into the roof deck. (Most manufacturers will specify a minimum-length nail, so read that shingle wrapper.)

Drive the nails so that the head is flush with the shingle surface (see Properly Driven Nails, below). Nailing depth is especially critical when you are using a pneumatic nailer, which can drive roofing nails at different depths depending on how solid the material is below the shingle. Adjust the pneumatic nailer’s air pressure to drive the nails flush with the shingle surface when nailing into the sheathing between rafters. As you work the gun, keep an eye on the depth of the nails. When a nail hits framing, it might not penetrate deeply enough, and you will need to drive it flush to the shingle surface by hand. But if the nailer is adjusted for driving nails into the framing, then there may be a tendency to overdrive the nails. Underdriven nails can be finished by hand, but overdriven nails can damage the shingle and have to be pulled out.

Nails for attaching shingles need to have a head at least 3/8 inch in diameter. Drive nails so that the head is flush with the surface of the shingles. Underdriven nails will not anchor the shingles properly and can damage the overlapping shingles; overdriven nails damage the surface of the shingle; and crooked nails break the surface of the shingle and can damage the overlapping shingle as well.
Tim Healey Nails for attaching shingles need to have a head at least 3/8 inch in diameter. Drive nails so that the head is flush with the surface of the shingles. Underdriven nails will not anchor the shingles properly and can damage the overlapping shingles; overdriven nails damage the surface of the shingle; and crooked nails break the surface of the shingle and can damage the overlapping shingle as well.

When nails are underdriven, they are left with the head sticking up above the surface. This scenario leaves the shingle unsecured and able to move on the shaft of the nail. Underdriven nails are also apt to damage the overlapping shingle over time.

When nails are overdriven, they break the structure of the shingle. This can lead to a blow-off, or a shingle that slips down the roof. A shingle nail driven at an angle does not secure the shingle evenly and damage to the shingle is inevitable.

Nail placement. Normal nailing for three-tab shingles in areas of the country not subject to high winds is a nail driven above each cut out and 1 inch in from each end. These nails should be in a line below the adhesive strip and above the cutouts. For high-wind applications, the number of nails increases to six, with two nails above each cut out. Additionally, some manufacturers recommend dabs of roofing cement under the corners of each tab for added adhesion in high-wind areas.

For nailing three-tab shingles in areas not subject to high winds, drive a nail above each cutout as well as nails 1 inch in from each end. Nails should be driven in the horizontal band below the sealing strip and above the cutouts.
Tim Healey For nailing three-tab shingles in areas not subject to high winds, drive a nail above each cutout as well as nails 1 inch in from each end. Nails should be driven in the horizontal band below the sealing strip and above the cutouts.
In high-wind areas, drive two nails above each cutout as well as nails at both ends of the shingle. Manufacturers may also recommend dabs of roof cement under the tabs to help adhere the tabs in place.
Tim Healey In high-wind areas, drive two nails above each cutout as well as nails at both ends of the shingle. Manufacturers may also recommend dabs of roof cement under the tabs to help adhere the tabs in place.
When installing laminated (architectural) shingles in normal areas, drive nails 1/3 and 2/3 of the way across each shingle, and at the ends.
Tim Healey When installing laminated (architectural) shingles in normal areas, drive nails 1/3 and 2/3 of the way across each shingle, and at the ends.
In high-wind areas, drive two nails at the 1/3 and 2/3 distance across each shingle, and drive a nail at each end. If it's recommended by the manufacturer, apply dabs of roofing cement along the bottom edge of the shingle.
Tim Healey In high-wind areas, drive two nails at the 1/3 and 2/3 distance across each shingle, and drive a nail at each end. If it's recommended by the manufacturer, apply dabs of roofing cement along the bottom edge of the shingle.

One thing to note is that asphalt shingles come in stacked bundles with a cellophane strip on the underside of the shingle to keep the shingles from sticking together. Whether or not to remove this strip has been the source of some controversy over the years. According to the folks at ARMA, once the shingles are installed it is not necessary or desirable to remove the strips. As long as the cellophane strip is still attached to the underside of the shingle, it can remain in place without affecting the performance of the shingle. However, if the cellophane adheres to the adhesive strip on top of the shingle instead, it must be removed for the adhesive to function properly.

Straight and Parallel

Before you begin to install the shingles, it’s a good idea to check the roof measurements. Measure from the ridge down to the drip edge at both ends of the roof. Those measurements should be close (within 1/2 inch); any difference much greater than that and you will have to take corrective action, and you should bring this condition to the attention of the person in charge.

The strategy for keeping the courses straight is the same for all styles of shingles. Start by snapping a chalk line for the first full course at the eaves. Measure from the line to the drip edge to confirm that the first course will be either flush with the drip edge or extending over by no more than 1/4 inch.

Next, complete the initial group of five or six courses across the roof from rake to rake. At both ends of the roof, again measure down from the ridge to the top of the cutouts in the top course. Ideally, those measurements should be the same (or very close) at each end. If not, mark the longer of the measurements at both ends and snap another chalk line between the marks. That line then becomes the guide for the bottom of the next course. Repeat this procedure every half-dozen courses or so; adjusting the courses intermittently will keep the exposure of the shingles running parallel.

Cutting Shingles

When cutting shingles, always cut from the back. Rarely do the shingle courses end precisely on the half-tab distance. Don’t just let the shingles hang over the rake and then trim them all at once at the end. This can result in a ragged edge along the rake while creating a lot of waste, as usable parts of shingles fall to the ground.

A better strategy that doesn’t require a lot more time is to cut shingles individually to complete each course. You don’t need to measure this distance and transfer it to the shingle. Just set the shingle (or usable scrap) in line to the rake, and make a nick with a razor knife at the top edge of the shingle. Then flip the shingle over to make the cut.

Use a scrap of plywood as a cutting board to avoid cutting and damaging the installed shingles. To keep the rake lines as straight and smooth as possible, use a framing square to guide your cut. Or, use the top corner of a fresh shingle as a square straightedge, making sure the razor knife doesn’t slice into this guide shingle.