What Are Asphalt Shingles?

What asphalt shingles are made of

Each shingle starts as a thin mat of glass fibers. The Asphalt Roofing Manufacturers Association (ARMA), the shingle makers' trade group, describes it as a mat "composed entirely of glass fibers of varying lengths and orientations" ³. The mat is the shingle's skeleton. It gives the shingle strength and keeps its shape.

The mat is then coated with asphalt, the same sticky black material used in road paving but refined for roofing. The asphalt is what keeps water out. On top of the asphalt, the factory presses a layer of crushed mineral granules.

The granules give the roof its color, and they shield the asphalt from the sun. Sunlight breaks down bare asphalt, so the granules are a big part of how long a shingle lasts.

Older shingles used a mat of paper and wood fibers, called an organic mat. ARMA notes that fiberglass mats arrived in the 1960s and that shingles in the United States are now mainly fiberglass-based ³.

If a house has a very old roof, it may still have organic shingles, and that matters if a roofer plans to lay new shingles over them.

Most shingles also have a strip of factory-applied sealant on the back or front. The sun warms it after installation, and it glues each row to the row below.

This seal is a large part of how the shingle resists wind, and it is why the wind rating depends on the seal actually forming ⁴.

How a shingle roof keeps water out

A shingle roof works like overlapping fish scales. Each row covers the nails and the top part of the row below it.

Water landing on the roof runs over the exposed part of each shingle and onto the next one down, until it drips off the edge into the gutter.

No single shingle has to be watertight on its own; the overlap does the work.

That is why shingles need enough slope. On a flat or nearly flat roof, water moves slowly, can be pushed uphill by wind, and can sit long enough to creep under the laps.

The code sets the lowest slope for shingles at 2 in 12, which means the roof rises 2 inches for every 12 inches it runs across ¹. Our roof pitch guide explains how to read that number.

Under the shingles there are more layers. The roof deck is the wood sheathing, and the code says shingles must be nailed to a solidly sheathed deck ¹.

On the deck goes underlayment, a water-resistant sheet that is the backup if water gets past the shingles. In cold climates, a self-adhering ice barrier goes along the eaves. At the roof edges sits drip edge metal.

The shingles are only the top layer of a full roofing system.

The diagram shows the stack from the top down: the shingles shed most water, and the layers under them catch what gets past.

Types of asphalt shingles

ARMA groups shingles into two main shapes ³. "Luxury" or "designer" shingles are a marketing tier of laminated shingle, not a separate standard.

Sources: [3]

Worked example: reading the shingle line on a quote

Here is how one real product's published data maps onto the questions you should ask. The figures are from IKO's own sheets for its Dynasty laminated shingle ⁷ and its conformance bulletin ⁶. They are an example of how to read a line, not a product recommendation.

If your quote says only "architectural shingles, 30-year", none of these lines can be checked. Ask the roofer to write the brand and product line, then read the data sheet yourself. One roofing square is 100 square feet, which is how bundle counts are usually figured.

Where asphalt shingles are used

Asphalt shingles are used on sloped roofs of houses, garages and small buildings.

They suit gable roofs, hip roofs and most roof shapes with a slope of 2 in 12 or steeper ¹.

They are a poor fit for flat or very low-slope roofs, where membranes such as modified bitumen or single-ply sheets are used instead.

They can be used on very steep roofs too. The code says that on slopes over 21 in 12, shingles must be fastened by the maker's approved method ¹. Steep roofs often need extra nails or hand-sealing because the sun may not warm the sealant enough, and gravity pulls the shingles down.

They also go on over an old roof in some cases. ARMA says shingles can often be laid over an existing roof, but not over hard or brittle materials, uneven surfaces, or decks that are warped or rotted ³.

The code caps a roof at two layers; once there are two, the old layers must come off before a new roof goes on ¹.

Benefits of asphalt shingles

• Widely made and stocked, so most roofers install them and parts are easy to match later.
• Light enough for most house framing, unlike tile or slate, which may need a structural check.
• Many colors and looks, from flat three-tab to laminated shingles that copy slate or shake.
• Most products carry a Class A fire rating when installed with underlayment ⁶.
• High wind classes are common: IKO, for example, reports D7158 Class H testing on its shingles ⁶.
• Single shingles can be replaced after storm damage without redoing the whole roof.

Limits of asphalt shingles

• They need slope. Below 2 in 12 the code does not allow them at all ¹.
• The wind rating only holds if the shingles are nailed right and the sealant bonds. Shingles laid in cold weather may not seal until it warms up.
• Granules wear off over time. Once bare asphalt is exposed to the sun, the shingle ages faster.
• Hail can crack or bruise them, and a hail rating is a lab test, not a promise for every storm ⁸.
• They are not a great fit for very hot, flat or low-slope areas such as porches tied into a main roof at a shallow angle.
• ARMA says a roof more than 20 years old is a prime candidate for reroofing, so plan for replacement in the long run ³.

What drives the cost of an asphalt shingle roof

• Roof size, counted in squares of 100 square feet, plus waste for cuts at hips and valleys.
• Shingle tier. Laminated shingles cost more than three-tab, and luxury or impact-rated lines cost more again.
• Pitch. Steeper roofs need more safety setup and go slower, which raises labor.
• Tear-off. Removing one or two old layers adds labor and disposal. A third layer is not allowed, so tear-off may be required ¹.
• Deck repair. Rotted sheathing found after tear-off is usually priced per sheet.
• Underlayment and ice barrier. Low slopes need double underlayment, and cold areas need an ice barrier at the eaves ¹.
• Accessories. Starter strip, ridge caps, drip edge, flashing and vents are often separate lines.
• To turn these drivers into a number for your house, use the roof cost calculator or the cost guide.

How a crew installs an asphalt shingle roof

This is what you should see on a typical reroof. It is not a do-it-yourself guide. Roof work is a fall risk, and a licensed roofer should do it.

1. The old roofing comes off down to the deck, unless an approved overlay is planned.
2. The deck is checked, and soft or rotted boards are replaced. Shingles need a solid deck ¹.
3. Drip edge goes on at the eaves, then the ice barrier where required, then underlayment over the whole deck.
4. On slopes from 2 in 12 up to 4 in 12, the underlayment is doubled ¹.
5. A starter strip goes along the eave so the first row is sealed.
6. Shingles go on in rows from the bottom up, each with the nails the maker and the code call for, placed where the maker shows.
7. Flashing goes in at walls, chimneys and valleys, then hip and ridge caps finish the peaks.
8. The crew cleans up nails and debris, and the building department may inspect the work.

Caring for an asphalt shingle roof

• Look at the roof from the ground once or twice a year and after big storms. Binoculars help. Do not walk on it.
• Check the gutters for granules. Some loss right after installation is normal; heavy loss on an older roof is a sign of wear.
• Keep gutters clear so water does not back up under the first row of shingles.
• Trim branches that rub the roof or drop debris on it.
• Look in the attic for daylight, stains or damp insulation, which can point to a leak.
• Keep attic vents open. ARMA describes attic ventilation as the free flow of outside air under the roof deck, and it helps the shingles and the deck last ³.

Warning signs and common failures

• Bald spots where granules are gone and black asphalt shows.
• Curling or cupping at shingle edges, often from age or poor attic ventilation.
• Missing or lifted shingles after wind, often where the sealant never bonded or nails were placed too high.
• Cracks or soft dents after hail.
• Dark streaks, which are often algae; they are mainly a looks issue but worth checking.
• Leaks at flashing around chimneys, walls and vents, which is where many shingle roofs first fail.
• If you see these, a roof inspection will tell you whether a repair or a new roof makes more sense.

Treat each sign as a reason to get the roof looked at, not as proof of what is wrong.

What the building code requires

These rules come from Section R905.2 of the 2021 International Residential Code, read as adopted in Maryland. Most states adopt the IRC, often with changes, so your local building department's edition is the one that applies.

Fire class is set separately. Under R902, Class A, B or C roofing is required where local law designates it, or where the roof edge is less than 3 feet from a lot line ¹. Many fire-prone areas require Class A.

Sources: [1] [2]

The three ratings printed on every bundle

The code says shingle wrappers must be labeled with the wind classification ². The trade group NRCA explains the wind classes this way ⁴:

The D7158 classes assume a building 60 feet tall or less in open or suburban terrain; outside those limits an engineer must check them ⁵. A wind class describes a tested shingle, not your roof: it only holds if the nails and sealant match the test.

Sources: [4] [8] [5]

Asphalt shingles vs other roof coverings

Slopes are from the IRC Chapter 9 sections for each covering ¹. Weight terms are general. For a side-by-side look at your house, try the roof material selector or read the roofing materials guide.

Sources: [1]

Common misconceptions

Myth "Architectural" is a rating.

Reality It is a shape. Laminated shingles are thicker, but the wind, fire and hail classes come from tests listed on the data sheet.

Myth A 30-year or lifetime label is how long the roof will last.

Reality It names a warranty, which has its own terms. It is not a measured lifespan.

Myth Every shingle is impact-resistant.

Reality Hail ratings are optional. Only products tested to UL 2218 or FM 4473 carry a class.

Myth Shingles can go on any roof.

Reality The code does not allow them below a 2 in 12 slope.

Myth Laying new shingles over old ones is always fine.

Reality The code caps a roof at two layers, and ARMA warns against overlays on uneven, brittle or rotted roofs.

Myth A Class H shingle makes a Class H roof.

Reality Only if it is nailed and sealed the way it was tested. Poor nailing or a seal that never bonds undoes the rating.

Local rules and climate

The rules on this page come from the 2021 IRC. States and cities adopt the code on their own schedule and often amend it, so the edition at your building department is the one your roof must meet.

A reroof usually needs a permit, and the inspector checks the current code, not the one your house was built under.

Climate changes what you should ask for. In high-wind areas, the code ties the required wind class to the local design wind speed ², and makers often call for extra nails.

In cold areas, the ice barrier at the eaves matters. In hail areas, some insurers look for an impact class; IKO notes that its Class 4 certification is offered so owners can seek an insurance premium reduction, and is not a warranty ⁶. In wildfire areas, check whether your town requires Class A.

We do not list local rules here that we have not checked. Ask your roofer which code edition applies and what the inspector looks for on shingle roofs where you live.

What to ask your roofer about the shingles

• Which brand and product line are you quoting, and can I see its data sheet?
• What wind class is it, and does that meet the design wind speed here?
• Is it Class A fire rated as installed, with the underlayment you plan to use?
• Does it have a hail rating, and does my insurer give anything for it?
• How many nails per shingle will you use, and where will they go?
• Is this a tear-off or an overlay, and how many layers are on the roof now?
• What will you do if you find rotted deck boards, and how is that priced?

Keep going

• Roof replacementWhen it is time for a new shingle roof
• Roof repairFixing missing or damaged shingles
• Repair or replace?How to decide for an aging roof
• Roof life calculatorEstimate how much life your roof has left

Related terms

Architectural Shingles

Architectural shingles are asphalt roof shingles made from two or more layers bonded together, so each shingle is thicker than a flat strip shingle and gives the roof a textured, three-dimensional look.

3-Tab Shingles

A single-layer asphalt strip shingle cut into three tabs, giving a flat, uniform look. Most makers now sell mainly architectural shingles instead.

Impact-Resistant Shingles

Impact-resistant shingles are roof shingles that have passed a lab test in which steel balls or ice balls strike the shingle, and earned an impact class from 1 to 4, with Class 4 the highest.

Roof Underlayment

Roof underlayment is a sheet laid over the whole roof deck before the shingles or other roof covering go on.

Roofing Square

A roofing square is a unit of area equal to 100 square feet of roof surface, a 10-by-10-foot patch, and it is the unit in which shingles are sold and most roofing quotes are priced.

Drip Edge

Drip edge is a strip of bent metal flashing installed along a roof's eaves and rake edges that carries water off the edge of the roof and away from the fascia and the deck beneath.

Ice and Water Shield

Ice and water shield is a self-adhering, rubberized asphalt membrane laid directly on the roof deck under the roof covering, where it seals around nails and blocks water that ice dams or wind-driven rain push back under the shingles.

Roof Pitch

Roof pitch is the steepness of a roof, written as the inches it rises for every 12 inches it runs horizontally, so a 6/12 roof climbs 6 inches per foot.

Reroofing

Reroofing is the work of putting a new roof covering on a house that already has one, either by tearing the old covering off down to the deck (a replacement) or by laying the new covering over the old one (a recover, often called an overlay).

Also referenced from: Roofing System, Roof Pitch, Architectural Shingles, Impact-Resistant Shingles, Metal Roofing, Clay Tile Roofing, Wood Shakes, Composite Roofing, Solar Shingles, Drip Edge, Step Flashing, Valley Flashing, Pipe Flashing, Roofing Nails, Ridge Cap, Ridge Vent, Roof Wind Uplift, Roof Life Expectancy, Reroofing, Roofing Square, Roof Warranty, Manufacturer Warranty