Asphalt Shingles

Asphalt shingles are fiberglass mats coated with asphalt and ceramic granules. They’re the most common, cost-effective residential roofing material. More than 80 percent of all residential roofing applied in the U.S. is currently produced by the asphalt roofing industry. There’s a reason for that. They shed water, they’re available everywhere, and they don’t break the bank.

The decision that matters most is grade. There are three: 3-tab (budget, 15-20 years), architectural or dimensional (standard, 25-30 years), and luxury (premium, 30-50 years). Grade drives lifespan, and it drives how the roof holds up against wind and impact. In western Montana — where chinook gusts strip granules and ice dams pile up at the eaves — that matters more than the color you pick off the sample board.

How do you choose? Selection should prioritize your climate’s wind and impact requirements, long-term housing plans, and aesthetic goals. If you’re building a forever home in snow country, the math on a longer-lived shingle works out. If you’re flipping or staying short-term, the calculus changes. The shingle is one decision. The system underneath it is what actually keeps water out.

Grades, Sizes, and Estimating Your Order

The three grades stack up by lifespan and price tier. Here’s the breakdown.

Grade	Tier	Expected Lifespan
3-tab	Budget	15-20 years
Architectural / dimensional	Standard	25-30 years
Luxury	Premium	30-50 years

On sizing: asphalt strip shingles are typically 12” wide and 36” long with a 5” exposure. But that’s not the whole story anymore. Metric-size shingles, which have slightly larger dimensions, are being used in the U.S. market as well, and there are a number of new shingles with unusual sizes. Don’t assume. Individual manufacturers may have specific instructions for specific products, so review all instructions on or inside the product’s packaging before beginning.

Estimating material is straightforward. Measure roof area in square feet, divide by 100 to get squares, and add 10-15% for waste. That waste factor isn’t padding — valleys, hips, and starter courses eat material. Run short in September and you’ve lost a day waiting on the rest of the order.

ARMA lays out the selection factors plainly. The manual covers exposure and coverage, fire resistance, wind resistance, and aesthetics as the four things a buyer weighs. In this climate, wind and fire resistance move to the front of the line.

Installation and the Full Roofing System

The shingle is the visible layer, but it’s the last thing that goes on. You work from the bottom up, starting with the bottom-most layer of components. The asphalt shingles are the first line of defense against weather, but what’s underneath them really counts.

Here’s the sequence that makes a roof actually work:

Deck. Before installing any roofing materials, make sure the roof deck is smooth, properly fastened, dry, and free of gaps or holes. Fasten only to a proper deck — never over insulation. Insulation does not have adequate nail-holding ability, so shingle damage or blow-off may occur, and the wind classification of the installed system may be affected. Asphalt shingles should only be fastened to deck surfaces such as plywood and oriented strand board, or other surfaces acceptable to the manufacturer.

Drip edge. The first material installed at the eave, it provides a clean edge and protects the lower edge of the roof deck by preventing water from wicking back up before it leaves the roof. Drip edge goes under the ice and water at the eaves and on top of the ice and water and underlayment on the rakes.

Ice and water shield. This is not optional in Montana. This thin, self-adhering membrane installs over the drip edge, and is a wise roofing system component that is likely required by your local building code in cold climates. Get the coverage right: to be fully effective, it should extend up the roof to a point at least 24” inside the vertical extension of the interior side of the wall. These membranes work because their rubberized asphalt coating seals around the shanks of the overlying shingle fasteners, adding an extra degree of water-shedding protection. That’s what stops ice dam backup from finding its way into your living room.

Underlayment. Next comes the underlayment, which can be either asphalt-saturated felt or a synthetic — both offer protection beneath the shingles. Owens Corning’s guidance ties it to slope: underlayment for slopes 4:12 and greater, with special low-slope treatment for 2:12 to under 4:12.

Valleys. In cold country, go open metal. Consider open metal valleys in cold weather — woven and closed-cut valleys require shingles to be bent, which may result in shingle damage. The recommended flashing material is 28-gauge galvanized metal or an equivalent corrosion-resistant, non-staining material (check local codes).

Starter, shingles, then hip and ridge. Complete the underlayment and valley flashing before the field shingles go on.

On nailing — this is where warranties live or die. For most asphalt shingles, a minimum of four nails is required per full-size strip shingle. Select nails long enough to penetrate at least ¾” (19 mm) into the roof deck; if the sheathing is less than ¾” thick, use nails long enough to penetrate through it at least 1/8” (3 mm). Nails are not to be underdriven, overdriven to break or cut into the shingle, or driven crookedly. And always match the manufacturer’s pattern — follow the specific installation instructions of the shingle manufacturer to ensure the intended performance and compliance with building codes.

A note on slope: the maximum slope ARMA considers suitable for normal asphalt shingle application is 21:12. Steeper than that, and you’re into special cement-spot methods.

Cold-Weather Handling and Ventilation

Montana’s building season is short, and a fair amount of roofing happens in cold conditions. Handle accordingly. Use caution handling bundles in cold weather, as they may crack or break apart — choose an installation temperature where the shingles are flexible enough to install, since asphalt shingles become less flexible as temperature decreases. The fix is simple: for best results, store shingles indoors to keep them warm prior to application.

The sealant strip is the other cold-weather catch. Most asphalt shingles include thermally activated asphalt sealant that bonds the shingles together after application, and sealing time varies with slope, orientation, and sun exposure. In the cold, that bond may not happen on its own. To provide improved protection from wind blow-off in very cold weather, asphalt shingles can be hand-sealed with an approved asphalt roofing cement or other adhesive acceptable to the manufacturer. Skip that step before a chinook event and you’ll be picking shingles out of the yard.

Ventilation is what keeps ice dams from forming in the first place and what protects the shingle warranty. Most vent system manufacturers recommend a soffit/ridge venting ratio of between 50 and 60 percent, with an air space of 3/4-inch (19 mm) suggested as a minimum and 1.5-inch (38 mm) or wider preferred. Adequate intake airflow must also be provided for proper ventilation dynamics. Intake low, exhaust high — that’s the principle that moves heat and moisture out before it melts snow into an ice dam.

One more for high-snowfall sites: certain regions receive very high snowfall amounts requiring snow and ice removal from the roof, and extreme caution must be taken so the shingles are not damaged by shovels, scrapers, or foot traffic. A roof rake used carelessly will strip granules and shorten the life of the roof you just paid for.

Frequently Asked Questions

How long do asphalt shingles last? It depends on the grade. 3-tab shingles run 15-20 years, architectural or dimensional run 25-30 years, and luxury shingles run 30-50 years. Cold-climate freeze-thaw and UV exposure tend to push real-world lifespans toward the shorter end of those ranges.

How much material do I need to order? Measure your roof area in square feet, divide by 100 to get the number of squares, and add 10-15% for waste. Complex roofs with multiple valleys and hips lean toward the higher waste figure.

What size are standard asphalt shingles? Strip shingles are typically 12” wide and 36” long with a 5” exposure, though metric-size shingles with slightly larger dimensions are also used in the U.S. market. There are also a number of new shingles with unusual sizes, so check the packaging for the specific product.

Why is ice and water shield such a big deal in cold climates? Ice dams. The membrane’s rubberized asphalt coating seals around the shanks of the shingle fasteners, adding an extra degree of water-shedding protection. It’s a wise roofing system component and is likely required by local building code in cold climates. When melted snow refreezes at the eave and backs water up under the shingles, this layer is what keeps it out of the deck.

Can I nail shingles right over rigid insulation? No. Insulation does not have adequate nail-holding ability, and shingle damage or blow-off may occur if shingles are attached to it. Fasten only to deck surfaces such as plywood or oriented strand board, or another surface acceptable to the shingle manufacturer.

How many nails per shingle? A minimum of four nails per full-size strip shingle for most asphalt shingles, though some shingles and conditions require a different number — always follow the specific installation instructions of the shingle manufacturer. High-wind regions may call for more.

Should I install in winter? You can, but handle the shingles right. Store them indoors to keep them warm before application, and hand-seal with approved asphalt roofing cement for improved wind protection in very cold weather. Cold shingles crack when handled roughly.