Parts of a Roof: Every Component Named and Explained

A pitched roof is built in layers: a frame and deck, water barriers, metal at the edges, shingles across the field and over the ridge, and flashing wherever the roof meets a wall, chimney, valley or pipe. A low-slope section, such as a porch, garage or addition roof too flat for shingles, swaps the shingles for a membrane and adds parts of its own, named in their own section below. Once you know each part’s name and where it sits, the part names on an estimate or inspection report map onto your own house.

The diagram below stacks the layers of a pitched shingle roof from the outside in. The sections that follow name each part in the order a roof is built, with a link to the page that covers it in depth. For questions beyond part names, find your roof decision and the page that answers it.

PITCHED SHINGLE ROOF: LAYERS FROM THE WEATHER SIDE INWARD

  OUTSIDE
  ridge cap ............ caps the peak and the hips
  field shingles ....... overlapping courses, eave to ridge
  starter strip ........ first course along the eave
  flashing ............. at walls, chimneys, valleys and pipes
  underlayment ......... sheet layer over the whole deck
  ice barrier .......... self-adhered strip at the eaves, where required
  drip edge ............ metal along eaves and rakes
  roof deck ............ plywood, OSB or boards
  rafters or trusses ... the sloped frame, meeting at the ridge
  INSIDE (attic)

  At the eave, the drip edge and ice barrier can lap in either order;
  the product instructions decide.

ROOF EDGES SEEN FROM OUTSIDE

  ridge ...... the horizontal peak line
  hip ........ a sloped outside corner where two planes meet
  valley ..... a sloped inside corner where two planes meet
  eave ....... the lower, level edge, where a gutter hangs
  rake ....... the sloped edge at a gable end
  fascia ..... the vertical trim board along the eave
  soffit ..... the underside of the overhang

The Structure: Rafters or Trusses, Ridge, and Deck

Rafters are the sloped framing members that run from the wall to the peak. Trusses do the same job as factory-built triangles, with a top chord along the slope and webs inside. The ridge is the peak line where opposing slopes meet.

Ceiling joists or rafter ties run level across the attic and tie the bottoms of opposing rafters together. A City of Phoenix code interpretation on ceiling joist alterations explains that opposing rafters push against each other at the ridge and that ceiling joists or rafter ties resist that outward thrust; collar ties higher up are not part of that load path. If an estimate mentions cutting any of these, ask for an engineer’s review.

The roof deck, also called sheathing, is the layer of plywood, oriented strand board (OSB) or boards nailed over the frame. Everything above it is fastened into it. FEMA’s Wind Retrofit Guide (P-804, April 2023) points out that many existing roofs have deck panels thinner than 15/32 inch, and it reports trusses lifted off exterior walls in Hurricane Ida. Both findings point the same way: the connections between frame, deck and walls matter, not only the roofing. Deck materials and replacement are covered in roof decking, and fastener rules in roofing nails.

The Water Barriers Under the Shingles

Over the deck, the first layers are there for the water that gets past the shingles. Underlayment is the sheet layer over the whole deck, a second line of defense if water gets past the shingles. Asphalt-saturated felt and synthetic sheets are the two categories you will see on quotes; their types and product specifications are compared in roof underlayment.

The ice barrier, sold as “ice and water shield” or self-adhered membrane, is a sticky, rubberized sheet laid at the eaves and in other spots where ice dams or slow water are likely. The ASTM D1970/D1970M-25 specification covers these self-adhering sheets for ice dam protection. Where code requires one and how far it must reach are in ice and water shield.

The Roof Edges: Eaves, Rakes, Drip Edge, Fascia, and Soffit

Where the deck ends, the edges take over. The eave is the lower, level edge of a roof plane, where water leaves the roof. The rake is the sloped edge at a gable end. How far each edge should reach past the wall, and what a deeper one exposes, is covered in roof overhangs and eaves.

Drip edge is the bent metal flashing along those edges that carries water off the roof and away from the fascia. DOE calls for it on both eaves and rakes in its Building America guide to asphalt shingle roofs; whether your code requires it is covered in drip edge.

The fascia is the vertical trim board fastened to the ends of the rafters along the eave, and gutters hang from it. The soffit is the horizontal underside of the overhang, and a vented soffit is where outside air enters the attic. Both are explained in soffit and fascia, and the gutter connection in gutters and downspouts.

The Field and the Top: Starter, Shingles, Hips, and Ridge Cap

The starter strip is the first course along the eave, installed under the first visible row so the edge has sealant and full coverage; the same DOE guide has it overhang the drip edge by 1/4 to 3/4 inch, or by no more than 1/4 inch, with the shingles above it, on a roof built to the IBHS FORTIFIED standard.

Field shingles are the overlapping courses that cover the main surface. Each course’s exposure is the part left visible, and the offset staggers the joints between courses; both values come from the manufacturer’s instructions.

Hips are the sloped outside corners where two roof planes meet, and the ridge cap is the row of cap shingles that covers the peak and the hips. Starter and cap products are compared in starter strips and ridge caps. On some roofs, snow guards are fastened across the field to keep snow from sliding off in one mass; see snow guards.

Where Leaks Start: Valleys, Flashing, Crickets, and Penetrations

Junctions, where the roof changes direction or meets something else, are where water has more chances to get behind a layer than anywhere in the open field. How many junctions a house has depends on its shape; gable, hip and other roof shapes lists each shape’s weak points.

A valley is the sloped inside corner where two roof planes meet, carrying water from both. HUD’s Residential Rehabilitation Inspection Guide lists valleys and gutters clogged with debris among the things an inspector looks for. Valley methods are compared in roof valleys.

Flashing is sheet metal or membrane that bridges a joint so water stays on the outside. Step flashing is woven in piece by piece where a roof slope runs along a sidewall. A kickout is the angled piece at the bottom of that run; in a federal guide to step and kick-out flashing, its job is to turn the water off the wall and into the gutter. See roof flashing for all types and kickout flashing for that one detail.

At a chimney, base flashing is worked into the shingles where the roof meets the masonry, and counterflashing is set into the masonry and laps down over it; see chimney flashing. A cricket, or saddle, is a small peaked section built on the uphill side of a wider chimney to split water around it; when one is required is covered in chimney crickets.

Penetrations are anything that pokes through the roof: plumbing vent pipes sealed with a rubber or metal pipe boot, exhaust vents, and skylights. Boots and their failure points are covered in roof pipe boots.

The Air Path: Intake Vents, Exhaust Vents, and the Attic

Attic ventilation is outside air moving through the space directly beneath the roof deck.

Intake vents let air in low, at the soffit or along the eave. Exhaust vents let it out high: a ridge vent runs along the peak under the ridge cap, while box vents, turbines and gable vents are individual openings. The types are compared in roof vent types, and the attic ventilation page explains how intake and exhaust work as one system.

The attic itself is part of the roof system. Its floor insulation, its air leaks from the house below and its vents together decide how warm and how damp the underside of the deck gets.

Low-Slope Roof Parts: Membrane, Seams, Edges, and Drains

Below 2:12, the minimum slope for shingles in the code text quoted in flat roof materials, a roof section needs a continuous waterproof layer instead of overlapping pieces. The frame and deck underneath play the same role as on a pitched roof; the parts above them change.

• Membrane: the continuous waterproof layer over the whole surface, such as EPDM rubber, TPO or PVC sheet, modified bitumen or built-up roofing. The systems are compared in flat roof materials.
• Seams: the joints where membrane sheets overlap and are bonded on site with tape, adhesive or heat welding. The sheet comes from a factory; the seams are made on your roof.
• Flashings at walls, curbs and pipes: membrane or metal carried up where the roof meets a wall, a curb under equipment or a pipe, so water stays on the outside of the joint.
• Edge metal: the metal trim that closes the membrane at the roof’s perimeter.
• Insulation boards and tapered insulation: boards under the membrane; tapered boards are cut to a gradual pitch to build slope toward the outlets.
• Crickets: on a low-slope roof, built-up sections that divert water around obstructions.
• Drains, scuppers and gutters: the only exits for water. A drain sits in the roof surface, and a scupper is an opening at the roof edge that lets water out to a gutter or downspout; how ponding develops when these fail is covered in flat roof drainage.
• Ballast: on some membrane roofs, stone or pavers that hold a loose-laid sheet down by weight; EPDM rubber roofing compares it with adhered and fastened sheets.
• Coating: a liquid-applied surface layer over some membranes, or over spray foam in place of a membrane; see roof coatings and spray foam roofing.

Where on the Roof Is Your Problem?

Hold the estimate or report beside the diagram and place each named part on your own house. Then match where the symptom shows up to the parts that live there:

• At an edge (eave or rake): drip edge, starter strip, fascia, soffit, gutters and, in cold climates, the ice barrier.
• In the field: shingles, nails, underlayment and the deck below.
• At a junction: valleys, step and kickout flashing, chimney flashing, crickets and pipe boots.
• At the top: ridge cap and ridge vent.
• On a low-slope section: membrane, seams, edge metal, flashings at walls and curbs, and drains or scuppers.
• In the attic: deck underside, ventilation and the air leaks below it.

Open the page for the part your symptom points to. If the paperwork uses a contract, insurance or rating term rather than a part name, look it up in the roofing glossary.

Here is that method applied to four lines from an inspection report. The lines are invented, written the way such reports often read.

Each line now has a place on your own house and a page to read next, which is all the report needs from you before you ask a roofer to price the work.

This guide is general information for U.S. homeowners, not legal, insurance, tax, or engineering advice. Codes, laws, and policy terms vary by location and change over time; confirm details with your local building department, your insurer, or a licensed professional.

Sources

• FEMA P-804 Wind Retrofit Guide for Residential Buildings, Federal Emergency Management Agency
• D1970/D1970M-25 Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection, ASTM International
• Asphalt Shingle Roofs, U.S. Department of Energy Building America Solution Center
• Residential Rehabilitation Inspection Guide, U.S. Department of Housing and Urban Development
• Step and Kick-Out Flashing at Roof-Wall Intersections, U.S. Department of Energy Building America Solution Center
• Ceiling Joist Alterations Interpretation (TRT/DOC/00341), City of Phoenix Planning & Development Department