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Guide

Parts of a Roof

By Muhammad Tayyab Updated Published

Every part of a roof has a name, and knowing them makes contractor estimates far easier to read. This is the full anatomy, from the deck up.

A roof is built in layers: structural framing (rafters or trusses), decking or sheathing, underlayment, then the roof covering. The named edges and joints are the ridge, hip, valley, eave and rake, and the vulnerable transitions are protected by flashing.

Structural layers, bottom to top

These are the layers that exist on every pitched roof, in order from the framing outward.

How a roof is built up, in section A slice through a sloped roof at its lower edge. From the inside out the layers are Rafters or trusses, structural framing. Decking, plywood or osb sheathing. Underlayment, felt or synthetic. Shingles, the weather surface. At the eave the rafter ends are closed off by the fascia board, the soffit panel spans from the fascia back to the wall and carries the intake vents, a metal drip edge turns water off the deck, and the gutter hangs from the fascia to catch it. Wall Rafters or trussesDeckingUnderlaymentShingles Fascia Soffit Drip edge Gutter
Drawn at a 6/12 pitch. The order matters: every layer sheds water onto the one below it, which is why underlayment goes on before the covering and the drip edge tucks under the shingles but over the fascia.
Rafters or trusses
The structural skeleton carrying the roof load down to the walls. Rafters are cut on site and leave attic space open; trusses are engineered and delivered complete.
Decking (sheathing)
Sheets of OSB or plywood fastened across the framing to form a solid surface. Typically 7/16" at 16-inch rafter spacing, 5/8" at 24-inch. Replacing decking is priced per sheet.
Underlayment
A water-resistant layer over the decking, beneath the covering. Synthetic has largely replaced felt because it is lighter and does not tear as easily. See what replacing underlayment costs.
Ice and water shield
A self-adhering waterproof membrane at eaves and valleys. Required by code in cold climates to stop ice dams from forcing water back under the shingles.
Roof covering
The visible layer: shingles, panels, tile or membrane. It is the wear surface, and it is only as good as the layers beneath it.

Edges and joints

These are the named lines on a roof. Contractor estimates quote most accessory materials against them.

The five named lines of a roof: ridge, hip, valley, eave and rake A plan view of an L-shaped roof. The main block runs left to right and is hipped at its left end and gabled at its right. A narrower wing projects downward from the middle. The ridge is the high line along each block. Two hips run at 45 degrees from the left corners to the end of the main ridge. Two valleys run at 45 degrees inward from the corners where the wing meets the main block and meet at the head of the wing ridge. Eaves are the outer edges that carry gutters, and rakes are the sloped edges at the gable ends. Ridge Hip Valley Eave Rake Eave Rake
Plan view. On a roof where both slopes are equal, every hip and valley runs at exactly 45 degrees, which is why the wing's ridge starts where its two valleys meet. The wing is narrower than the main block, so its ridge sits lower and dies into the main slope rather than joining the main ridge.
Ridge
The horizontal line at the top where two slopes meet. Covered with ridge cap shingles and usually where the exhaust vent runs, so it is where ridge vents go. Compare the vent types.
Hip
An external angled line where two slopes meet, sloping down to a corner. Hips need cap shingles like ridges and increase waste because every course cuts into them.
Valley
An internal angle where two slopes meet, channelling water down. The highest-volume water path on the roof and one of the most common leak sites, which is why valley repair comes up often.
Eave
The lower edge, usually overhanging the wall. Carries the gutter and the soffit intake ventilation.
Rake
The sloped edge at a gable end. Trimmed with rake board and finished with drip edge.

Trim, flashing and drainage

Most leaks begin here rather than in the field of the roof, which is why these components matter out of proportion to their cost.

Fascia
The vertical board closing off the rafter ends along the eave. Carries the gutter and is the first thing to rot when gutters overflow.
Soffit
The horizontal underside of the overhang. Usually vented, providing the intake air that makes attic ventilation work; see the cost of soffit vents.
Drip edge
Metal flashing along eaves and rakes that directs water into the gutter and away from the fascia. Code-required and inexpensive.
Step flashing
Individual L-shaped pieces woven into the courses where a roof meets a vertical wall. See roof flashing types. Continuous flashing in that position is a common and serious defect.
Counter flashing
Flashing set into a chimney or wall that laps over the base flashing, so water cannot enter the joint from above. Failure here means chimney flashing repair.
Boot (pipe flashing)
The rubber-collared sleeve sealing around a plumbing vent. The rubber perishes in 10 to 15 years and is one of the most common causes of a roof leak, and one of the cheapest kinds of flashing repair.

Put this to work

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Frequently asked questions

What are the main parts of a roof?

From the bottom up: framing (rafters or trusses), decking, underlayment and the roof covering. The named edges are ridge, hip, valley, eave and rake, with fascia, soffit, drip edge and flashing completing the assembly.

What is the difference between a hip and a valley?

Both are lines where two roof planes meet. A hip is an external angle that sheds water away from it; a valley is an internal angle that collects water and channels it down.

What is the difference between fascia and soffit?

Fascia is the vertical board at the edge of the roof that the gutter attaches to. Soffit is the horizontal panel underneath the overhang, usually vented to provide attic intake air.

What is drip edge and is it required?

Drip edge is metal flashing along the roof edges that directs water into the gutter instead of behind it. It is required by the International Residential Code and is one of the cheapest components on the roof.

Where do most roof leaks start?

At penetrations and transitions rather than in the open field. Chimney and wall flashing, plumbing vent boots, valleys and skylight curbs account for the large majority of leaks. <a href="/guides/roof-flashing/">Each flashing type</a> is named for where it sits.

What is a roof rake?

The rake is the sloped edge of a roof at a gable end, running from eave to ridge. It is also the name for the long-handled tool used to pull snow off a roof from the ground.