Parts of a Roof: Complete Diagram and Glossary for Homeowners

Last reviewed: October 2026.

The 18 parts of a roof fall into four groups: 5 structural, 7 surface, 3 water management and 3 ventilation and penetration parts, including the drip edge that IRC R905 requires.

The Short Answer: 18 Essential Roof Terms

The 18 essential parts of a roof, grouped by function:

Structural framework (5): ridge, hip, valley, rafters or trusses, roof sheathing.

Surface elements (7): shingles, underlayment, drip edge, flashing, fascia, soffit, gable and rake.

Edge and water management (3): gutters, downspouts, eaves.

Ventilation and penetrations (3): ridge and soffit vents, skylights, chimneys and vent stacks.

The Structural Framework

The five framework parts carry the roof’s weight plus snow and wind loads (IRC R802 covers rafter and ceiling joist framing). For labeled names, see roofing terminology with pictures.

For style-specific framework discussion, see the dedicated style articles: gable roof, hip roof, gambrel roof, and mansard roof.

Ridge (the Highest Point)

The ridge is the highest horizontal line on the roof, where two opposing slopes meet.

On a gable roof it runs from one gable end to the other; a pyramid hip has no ridge.

In stick framing the ridge is a beam (glulam or LVL in cathedral ceilings); in a trussed roof it is where top chords meet.

The visible ridge has a ridge cap (special shingles or formed metal) and, if present, a ridge vent.

Common ridge failures: lifted caps after high wind, caps pulling away from field shingles, and damaged ridge vents that admit water.

Hip (Where Two Slopes Meet at a Corner)

A hip is the sloping line from a building corner up to the ridge, found on hip roofs and Dutch gable variants.

The hip rafter carries the jack rafters framed into it and is longer than a common rafter for the same run.

The hip cap, special shingles or formed metal, covers the hip line and tends to lift before field shingles. See hip roof for detail.

Valley (Where Two Slopes Meet Inward)

A valley is where two slopes meet at an inward angle, at cross-gable intersections or where a dormer meets the main roof. Valleys are the highest-leak-risk part of the roof.

A valley collects water from two slopes and channels it to the gutter, so a flashing failure there leaks fast.

Best-practice valley construction uses a 36-inch-wide self-adhered ice and water shield underlayment running the full length of the valley, followed by either a closed-cut shingle valley, an open metal valley, or a woven valley. The open metal valley is the highest-performing detail and is the standard for high-end residential and any home in a high-rainfall climate. See roof flashing for valley flashing detail.

Valley type	Detail	Leak risk	Best for
Woven valley	Shingles from both sides interlace	Higher (no metal liner)	Budget residential, low-rainfall
Closed-cut valley	One side shingles run through, other cut	Moderate	Mainstream residential
Open metal valley	Metal channel exposed in valley center	Low	Premium residential, all climates
California valley	Modified closed-cut variant	Moderate	West Coast residential

Rafters and Trusses

Rafters (sloped beams cut on site) or trusses (prefabricated triangles) span from exterior wall to ridge.

Trusses dominate new residential framing because they install in hours, are factory-engineered, and use less lumber for the same span.

Stick framing remains common for cathedral ceilings, where rafters double as the ceiling structure, and for renovations matching existing framing.

For span tables and the fink, scissor and attic truss types, see roof trusses.

Roof Sheathing

The roof sheathing is the wood panel surface installed over the rafters or trusses. Sheathing forms the working deck on which underlayment, shingles, and other roofing materials are installed. The standard sheathing material is 1/2-inch or 5/8-inch CDX plywood or OSB (oriented strand board).

Required thickness depends on the span rating stamped on the panel and the rafter or truss spacing (IRC Table R503.2.1.1(1)); heavier coverings such as concrete tile or slate need more.

Sheathing condition is a critical inspection point during any roof replacement. Soft or rotted sheathing has to be replaced before new roofing material is installed; our roofing cost per square page prices installed decking at $45 to $110 per 4 x 8 sheet.

For the complete sheathing discussion including material selection, spacing requirements, and rot detection, see roof sheathing.

The Surface Elements

Surface elements are everything on top of the sheathing: underlayment, flashing, the visible roofing material, and the edge and water management systems.

Shingles (the Visible Material)

Asphalt composition shingles are the most common residential roof covering in the United States; ARMA publishes quarterly shipment reports. “Shingle” technically means any small individual covering unit.

The three asphalt shingle categories are 3-tab (the cheapest, 15 to 20 year service life), architectural or dimensional (the mainstream, 20 to 30 year service life), and premium impact-rated (Class 4 hail rating, 30 to 40 year service life).

Non-asphalt options include cedar shake, slate, metal shingle, synthetic slate, and clay or concrete tile, each with different install rules and costs.

Material	2026 cost per sq ft installed	Service life
3-tab asphalt	$4.50 to $6.50	15 to 20 years
Architectural asphalt	$5.00 to $8.00 (per our 2026 roofing cost report)	20 to 30 years
Impact-rated asphalt	$7.50 to $11.50	30 to 40 years
Standing seam metal	$11.00 to $18.00	50 to 70 years
Cedar shake	$13.00 to $22.00	30 to 40 years
Slate	$22.00 to $40.00	75 to 100 years
Concrete tile	$11.00 to $18.00	50+ years

For the deep material comparison, see metal vs asphalt shingle roof.

Underlayment (the Secondary Water Barrier)

Underlayment is the secondary water barrier between sheathing and shingles, catching water that gets past them in wind-driven rain or ice damming.

The two main underlayment categories are felt (traditional asphalt-saturated paper) and synthetic (engineered polymer materials). Felt is cheaper and has 100 years of installation track record. Synthetic is lighter, more tear-resistant, more UV-stable for extended dry-in periods, and substantially more expensive.

Self-adhered ice and water shield is a specialty underlayment used in critical areas: along eaves (to prevent ice dam damage), in valleys, around penetrations, and around skylights. IRC R905.1.2 requires an ice barrier where Table R301.2 records a history of ice forming along the eaves, running from the eave to at least 24 inches inside the exterior wall line, and 36 inches along the slope on roofs 8/12 or steeper (2021 Seattle Residential Code chapter 9).

For the felt versus synthetic decision in detail, see felt vs synthetic underlayment.

Drip Edge (the Eave Protection)

The drip edge is metal flashing at the eaves and rakes that sends runoff clear of the fascia and into the gutter.

Without a drip edge, water wicks back under the shingles onto the fascia, causing rot and paint failure.

IRC R905.2.8.5 requires a drip edge at the eaves and rake edges of shingle roofs, overlapped at least 2 inches, extending 1/4 inch below the sheathing and 2 inches up the deck, and fastened at no more than 12 inches on center (2021 Seattle Residential Code chapter 9).

For full drip edge installation detail, see drip edge.

Flashing (Around Chimneys, Walls, Vents)

Flashing is metal sheet, typically aluminum, copper or galvanized steel, sealing joints at chimneys, walls, valleys and plumbing vents.

Flashing failure is among the most common leak causes because an error in bend, lap direction or sealing opens a leak path.

The four primary flashing types are:

Step flashing. Used at a vertical wall; individual pieces interleave with each shingle course for a layered seal.

Counter flashing. Used over step flashing at a masonry wall; set into a mortar joint, it laps over the step flashing.

Apron flashing. A single piece of L-shaped flashing at the lower side of a chimney or wall projection.

Cricket or saddle flashing. A small peaked structure behind a chimney that diverts water around it.

For the complete flashing detail breakdown, see roof flashing.

The Eaves: Fascia + Soffit

Eaves are the lower roof edges that overhang the walls; the visible parts are the fascia (vertical board) and soffit (underside panel).

The fascia is the board to which gutters are attached. It runs along the entire perimeter of the eave. Fascia is typically 6-inch or 8-inch nominal lumber (1×6 or 1×8) or composite trim board, painted or finished to match the trim color of the home.

Soffits (vinyl, aluminum or wood) close the underside of the overhang; most include perforated panels or vent strips for attic air intake.

For full fascia material and replacement detail, see fascia board. For soffit ventilation strategy, see soffit vents.

Component	Material options	2026 cost per linear foot replaced
Wood fascia	Pine, cedar, composite	$8 to $18
Aluminum fascia	Coated coil over wood	$10 to $22
Vinyl soffit (perforated)	PVC vented panels	$7 to $14
Aluminum soffit (perforated)	Coated aluminum vented	$10 to $20
Wood soffit	Plywood with vent strips	$8 to $16

Gable and Rake (the End-Wall Edges)

The gable is the triangular end wall; the rake is the sloping roof edge above it, finished with rake trim.

Gables and rakes appear on gable, gambrel and hybrid roofs; hip roofs have hips at the corners instead.

The rake is exposed to side wind, a common site of rot and wind damage; hurricane uplift can lift the gable-end overhang.

For style-specific gable detail, see gable roof.

Gutters and Downspouts

Gutters collect roof runoff along the eaves, and downspouts carry it to the ground and away from the foundation.

The standard residential gutter is 5-inch or 6-inch K-style aluminum, available in pre-finished colors. Half-round gutters are a premium option, often used on historic and high-end custom residential. Box gutters and built-in gutters are specialty options for certain architectural styles.

Seamless gutters are formed on site to the exact length needed and have no end joints, which eliminates the most common gutter leak point. They run about $2 to $5 more per linear foot than sectional gutters, depending on which HomeGuide guide you use (its aluminum gutter guide or its gutter installation guide).

Downspout sizing matters. A commonly cited rule is that a 2×3 inch downspout handles about 600 square feet of roof drainage area and a 3×4 inch downspout about 1,200 square feet. Undersized downspouts overflow during heavy rain events and cause water to spill at the eaves, undermining foundations and damaging landscaping.

For the complete gutter pricing and installation breakdown, see gutter installation cost.

Ventilation: Ridge + Soffit Vents

Attic ventilation lets air flow through the attic to remove moisture and heat, which extends shingle life and reduces ice damming.

The standard system pairs continuous soffit vents (intake) with a continuous ridge vent (exhaust); the thermal stack effect drives the flow passively.

IRC R806 sets net free vent area at 1/150 of the attic floor area, reduced to 1/300 when 40 to 50 percent of the vent area sits in the upper portion (at least 3 feet above the eave vents) or a Class I or II vapor retarder is installed. A 2,000 square foot attic therefore needs about 13.3 square feet of net free area at 1/150, or about 6.7 square feet at 1/300.

Alternatives include gable vents, turbine vents and powered attic ventilators; continuous ridge-and-soffit is the modern best practice.

For the complete attic ventilation breakdown including system selection and code compliance, see attic ventilation.

Penetrations: Skylights, Vents, Chimneys

Penetrations are anywhere something passes through the roof: skylights, plumbing stacks, exhaust vents, chimneys and electrical masts; each is a critical flashing detail.

Plumbing vent stacks are the most common penetration. Standard residential plumbing has 2 to 4 vent stacks penetrating the roof. The vent stack is flashed with a rubber boot (or a metal flange and storm collar in older homes) that seals around the pipe. The boot is the most failure-prone roofing component because the rubber material degrades over 10 to 15 years and cracks, allowing water to enter around the pipe.

Skylights are the second most common penetration in modern residential construction. Skylight flashing is provided as a manufacturer-engineered kit (head, sill and side flashing); VELUX is one maker that supplies kits matched to each model. Proper skylight installation requires the manufacturer’s kit, not site-fabricated flashing. For installation cost detail, see skylight installation cost.

Chimneys are the most failure-prone penetration. The flashing detail (apron at the front, step flashing on the sides, counter flashing into the mortar joints, and a cricket at the back if the chimney is wider than 30 inches) involves multiple critical components that must all work together. Most chimney leaks are flashing failures rather than chimney structure failures.

Penetration	Typical flashing type	Service life	Common failure
Plumbing vent stack	Rubber boot or lead flashing	10 to 15 years (rubber), 50+ years (lead)	Rubber cracking
Bathroom exhaust vent	Metal cap with flashing flange	15 to 20 years	Cap rust, screen damage
Skylight	Manufacturer kit (multi-piece)	20 to 30 years	Curb flashing failure
Chimney (masonry)	Step + counter + cricket	20 to 30 years	Counter flashing mortar joint failure
Chimney (metal)	Specialty manufacturer kit	20 to 30 years	Storm collar caulk failure
Service mast (electrical)	Boot flashing	15 to 25 years	Cracking around mast

Why Knowing These Helps Homeowners

The 18 parts are the vocabulary of every estimate, claim and inspection report, and they help in five situations.

Estimates: a line such as “replace 12 LF rake trim with PVC” can be verified, and missing flashing details can be questioned.

Claims: adjusters document “valley flashing damage” and “field shingle damage” separately, and they can be paid differently.

Inspection reports: pre-purchase and post-storm reports use these terms, so you can judge what is flagged and how serious it is.

Repair versus replace: a leak at field shingles is often a repair, at flashing sometimes either, and at the sheathing usually a re-roof.

Contractor selection: someone who can explain step versus counter flashing and their valley detail beats one who gives a single bottom-line number.

See how to choose a roofing contractor and learn.