Parts of a roof: every layer from the deck to the ridge.

From the street a roof looks like one surface. Up close it is a stack of parts, laid in a set order, each one covering a weak spot in the one below it. When one part fails, the parts around it are left doing a job they were never built for, and that is usually where a leak begins.

This guide takes the parts in the order a crew installs them on a Texas shingle roof, from the wood deck to the ridge, then the gutters. For most parts we give the minimum rule from the International Residential Code, the model code Texas cities adopt as their residential building code. If you are holding two bids, keep our guide to comparing roofing estimates open beside this one.

Under everything sit the rafters or trusses, the timber frame that gives the roof its shape. Nailed across them is the deck, also called the sheathing: sheets of plywood or oriented strand board (OSB). The code's rule for a shingle roof is short: asphalt shingles must be fastened to a solidly sheathed deck, with no gaps for a shingle to bridge.

Nobody can see the deck until the old roof comes off. Years of small leaks soften it, and a soft sheet will not hold a nail, so on a replacement we look at every sheet once it is bare and swap out the bad ones before anything goes on top.

What to check. A per-sheet decking price on the quote, and a photograph of the bare deck before it is covered. On our jobs the production manager sends you that photograph.

The first metal on the roof is the drip edge, a bent strip along the lower edges of the roof, called the eaves, and the sloped edges at the gable ends, called the rakes. It makes rain fall clear of the fascia board instead of curling back under the roofing and into the wood.

The code requires a drip edge at the eaves and rakes of a shingle roof, with pieces overlapping at least 2 inches and reaching at least 2 inches back onto the deck. The underlayment goes over it at the eaves and under it at the rakes, so water running down the slope always lands on top of the metal. Our roofs get new drip edge along every edge.

Over the deck goes the underlayment, the roof's second line of defense. The Asphalt Roofing Manufacturers Association puts it plainly: shingles should not be laid straight onto a wood deck. When wind lifts a shingle or a storm drives rain sideways, the underlayment keeps the water off the wood.

There are three families of it: asphalt-saturated felt, lighter synthetic sheets, and self-adhered membrane, often sold as ice and water shield, which seals around each nail driven through it. On a Mammoth roof, Igloo Shield™ ice and water shield goes at the eaves, in the valleys and around penetrations, and Pelt Felt™ synthetic underlayment covers the rest of the deck. Our roof underlayment guide compares the three and what the code asks of each.

Shingles go on from the eave upward, each course lapping the one below so water runs over a joint and never into one. The first course is a starter strip with a line of sealant that glues down the edge of the first visible course, and starter strips run up the rakes too, because the edges are where wind gets under a roof first.

The code sets the minimum for the nails: galvanized steel, stainless steel, aluminum or copper, with a shank of at least 12 gauge and a head at least 3/8 inch across, long enough to go 3/4 inch into the deck. Each strip shingle takes the number of nails its maker specifies and never fewer than four. We drive six ring-shank nails into every shingle, two more than that floor.

A shingle also carries a wind class from one of two ASTM tests, and the code matches the class a house needs to its design wind speed. Makers add conditions of their own: CertainTeed's 2026 shingle warranty raises its wind coverage only when its own starter strips run along the eaves and rakes and its matching caps cover the hips and ridge.

Flashing is the metal, and sometimes rubber, that seals the places where the roof is interrupted. The code lists them: wherever the roof meets a wall, wherever it changes slope or direction, and around every opening. When we trace a leak from the attic it is usually a pipe boot, a flashing, a vent or a nail pop, and all but the last are joints like these.

• Step flashing climbs the side of a wall or chimney in short bent pieces, one for each course of shingles, tucked under the siding above it. The code wants each piece at least 4 inches up the wall and 4 inches onto the roof.
• Kickout flashing sits at the foot of that run, where an eave meets a wall, and turns the water out into the gutter. The code requires flashing there to divert water away from the wall; without it, water runs down the face of the wall, and too often into it.
• Chimney flashing wraps the chimney. On a chimney more than 30 inches wide the code adds a cricket, a small peak built on the uphill side so water splits around it instead of pooling behind it.
• Pipe boots seal the plumbing vents. Cheap rubber cracks in the sun, and a cracked boot is one of the leaks we find most often, so every boot on a new Mammoth roof is the Double Tusk™ Pipe Flashing System.

A valley is the channel where two slopes meet and pour their water together. It carries more water than any other part of the roof, so it gets its own lining under the shingles. The code allows two ways to build one. An open valley leaves a strip of metal showing down the middle, over a lining at least 24 inches wide. A closed valley runs the shingles across the joint, over a lining of smooth roll roofing at least 36 inches wide or a self-adhered membrane.

We lay Igloo Shield™ in every valley either way, and where we build an open metal valley the membrane goes underneath it.

The ridge is the top line of the roof and a hip is the sloping line where two slopes meet on an outside corner. Both are capped with thicker shingles made to bend over the joint, and the ridge usually carries the attic's exhaust vent.

The attic needs air coming in low, through soffit or eave vents, and leaving high, near the ridge. The code sets the total vent opening at 1/150 of the attic floor area, or 1/300 when 40 to 50 percent of it sits high on the roof within 3 feet of the ridge and the rest sits low. The shingle maker cares too: CertainTeed's 2026 warranty cuts coverage to ten years, with no early full-coverage period, on a roof deck it judges inadequately ventilated. Our attic ventilation guide explains the balance, and the ventilation calculator gives a starting number for your attic.

Pitch is written as rise over run: a 6:12 roof climbs 6 inches for every 12 inches it runs across. The code allows asphalt shingles only on slopes of 2:12 or steeper, and between 2:12 and 4:12 it asks for a double layer of underlayment, because water drains slowly off a shallow slope and wind can push it back up under the shingles. A flatter roof than 2:12 needs a low-slope system, such as the membranes on our flat roofing page.

Pitch also moves the price: the cost guide lists a steep pitch among the things that push a quote up.

Gutters finish the roof's drainage, and in much of Texas they matter more than they get credit for. The Blackland Prairie, which runs from north of Dallas south to San Antonio, holds about 1.5 million acres of Houston Black clay, a soil the Texas Water Development Board describes as highly expansive: it swells when it is wet and shrinks when it dries. Where soils like that are known, the residential code asks for a controlled way to carry roof water to the ground at least 5 feet from the foundation walls.

By the National Association of Home Builders' estimates, aluminum gutters last about 20 years and copper ones more than 50. Before we hang new gutters we check the fascia and the drip edge they will hang from. More on our gutters page.

Take a two-story Texas house with a covered back porch under its own shallow roof at 3:12, tucked against the wall of the upper floor. Here is every part on that one small roof, in the order it goes on.

1. Drip edge along the porch eave and its open rake, each joint overlapped by 2 inches or more.
2. Two layers of underlayment, because 3:12 is below 4:12: a 19-inch strip at the eave, then 36-inch sheets, each overlapping the one below by 19 inches. A single layer of self-adhered membrane is the other method the roofing manufacturers' association names for this slope.
3. A starter strip along the eave and the rake, then the shingles, each with the maker's full count of nails.
4. Step flashing up the wall, one piece for every course, each at least 4 inches by 4 inches, with the siding lapped over it.
5. A kickout at the bottom of the wall, where the porch eave meets it, turning the water into the gutter.
6. A gutter along the porch eave, with a downspout that empties well away from the foundation.

Skip the kickout and water can run behind the siding at that corner for years. Use one layer of underlayment instead of two and wind-driven rain under the shingles reaches the deck. Neither mistake shows from the yard.

• The deck: a price per sheet, and photographs of the bare deck.
• The underlayment: the product named, where the membrane goes, and two layers or membrane under 4:12.
• The flashing: new step flashing, kickouts, pipe boots and chimney flashing, nothing reused.
• The nails and the vents: how many nails per shingle, and intake and exhaust sized to your attic.
• The gutters: kept or replaced, and where the downspouts empty.