Parts of a Roof, Explained for Baltimore Homeowners

What each part of your roof does, what usually goes wrong with it, and what to call it when you call us about a problem.

I'm often up on a roof, so a text usually reaches me fastest, but call anytime.

What are the parts of a roof?

A pitched roof is built in layers. From the bottom up, it has rafters or trusses, the roof deck, ice and water shield, drip edge, underlayment, a starter strip and shingles. Flashing seals the chimney, walls and valleys. Pipe boots seal vent pipes. Ridge vents, soffit vents, fascia and gutters move air and water off the house.

What does each part of a roof do?

Every roof term from A to Z, what it does, and what usually goes wrong with it. The orange number matches the diagram. Each part has its own link, so you can send it to someone or come back to it.

What are the parts of a slate roof?

A slate roof is built in layers too, but with different parts. From the bottom up, it has rafters, wood board sheathing, a copper drip edge, a cant strip, felt paper, a doubled starter course and the slate. Copper nails hold each slate, and copper flashing seals the chimney, valleys and vent pipe.

1. Rafters: the frame that holds the roof up. Slate is heavy, so the frame has to be sound.
2. Board sheathing: solid wood boards nailed across the rafters. Older homes have boards, not plywood, and rotted boards get replaced with boards of the same thickness.
3. Copper drip edge: sends water off the roof edge and into the gutter.
4. Cant strip: a wood strip along the eave that tilts the first row of slate so it lies at the same angle as the rest.
5. Felt paper: 30 lb or heavier felt under the slate. It cushions the stone and backs it up, but the slate is what keeps the house dry.
6. Starter course: a doubled first row at the eave, so every joint is covered from the first row on.
7. Slate: natural stone, laid in rows with a headlap of about 3 inches over the row two below.
8. Copper slating nails: two per slate, set so the slate hangs on the nail instead of being pinned down tight.
9. Slate hook: a small copper hook that holds a replacement slate in place, so one broken slate can be swapped without tearing up the rows around it.
10. Snow guards: small copper guards set in staggered rows above the eave so snow melts off slowly instead of sliding off all at once.
11. Copper step flashing: one piece tucked in with each row of slate where the roof meets the chimney or a wall.
12. Copper apron flashing: covers the low side of the chimney where the roof runs into it.
13. Copper counterflashing: set into the chimney mortar and laps over the flashing below it.
14. Copper pipe flashing: a copper sleeve around the plumbing vent, in place of the rubber boot a shingle roof uses.
15. Open copper valley: a copper lined channel where two slopes meet, with the slate cut back along each side.
16. Slate ridge (saddle ridge): slates lapped over the peak. Some roofs use a copper ridge roll instead.
17. Soffit: the underside of the roof overhang.
18. Fascia: the board at the roof edge that holds the gutter.
19. Gutter: catches water coming off the roof. On slate roofs it is often copper, to match the flashing.
20. Downspout: carries water away from the house.

How a slate roof differs from a shingle roof

• Slate is nailed, not glued down. There are no sealant strips like on asphalt shingles.
• The slate itself often outlasts the flashing and nails by decades. Most slate leaks come from worn flashing, broken slates or old rusted nails, not the stone.
• A broken slate can usually be replaced on its own with a slate hook or a copper nail and a copper bib, which is why a slate roof is usually worth repairing.
• Roofing tar and caulk on slate are a short fix that makes the next repair harder.
• Flashing, nails and gutters stay one metal, usually copper, so they don't corrode each other.

What is under roof shingles?

Under the shingles are the layers that keep water out when a shingle fails. Along the edge there's a starter strip, then synthetic underlayment over the whole roof, ice and water shield at the eaves and valleys, metal drip edge on the edges, and the plywood or OSB roof deck nailed to the rafters.

From the bottom up: Rafters or trusses → Roof deck (sheathing) → Drip edge → Ice and water shield → Underlayment → Starter strip → Shingles

What is roof flashing?

Roof flashing is bent metal that seals the spots where the roof meets something else, like a chimney, a wall, a skylight, a valley or a vent pipe. Shingles can't seal those joints by themselves, so flashing laps over and under them and steers water past the gap.

Kinds of flashing: Step flashing, Chimney flashing, Counterflashing, Valley, Pipe boot (plumbing vent).

What goes wrong: a lot of the leaks I find start at flashing, not out in the middle of the shingles. The usual causes are counterflashing that has pulled out of the mortar, rusted step flashing, a cracked pipe boot, or a joint that someone patched with tar or caulk instead of fixing the metal. I repair flashing on shingle, slate, metal and flat roofs. Roof flashing repair

What is the difference between fascia and soffit?

Fascia is the flat board that runs along the roof edge, facing out, and the gutters hang on it. Soffit is the panel under the roof overhang, facing down, between the fascia and the wall. Soffit vents let fresh air into the attic. Both rot when gutters overflow or the drip edge is missing.

Air comes in through the soffit vents and leaves through the ridge vent, which helps keep the attic dry. When I replace rotted fascia or soffit, I also look at the gutter and drip edge above it, because that's usually where the water came from. Soffit and fascia repair

Where do the parts sit on a house?

What roofing materials are common in Baltimore?

Most Baltimore-area houses have asphalt shingles, either the older flat 3-tab kind or thicker architectural shingles. Rowhouses and porches usually have flat roofs: modified bitumen, rubber, or a coating. Older homes in the city and the north county often have slate, with copper or metal on bays, porches and flashing.

3-tab asphalt shingles

Flat, single-layer shingles with even cutouts. You still see a lot of them on homes reroofed in the '80s and '90s.

Typical lifespan: 15 to 20 years

What usually fails: Tabs crease and blow off in wind, the edges curl, and the granules wear off.

What I repair: I replace blown-off tabs and reseal loose ones. Matching an old 3-tab color can be hard, and I'll tell you up front if a patch will show.

Architectural shingles

Thicker, laminated shingles with a layered look. They're what most reroofs around here get now.

Typical lifespan: 20 to 30 years

What usually fails: Wind lifts them at the edges and ridge. Valleys, pipe boots and flashing usually wear out before the shingles do.

What I repair: I replace damaged shingles and ridge caps, and fix valleys, pipe boots and flashing.

Slate

Natural stone, split into thin pieces and nailed on one at a time. Common on older homes in the city and north county.

Typical lifespan: 75 to 100+ years, with the flashing redone along the way

What usually fails: The stone outlasts everything around it. Nails rust out and slates slide, slates crack when someone walks on them, and the flashing wears out first.

What I repair: I replace single broken or slipped slates and repair the flashing around them, without tearing off the rest of the roof.

Standing seam metal

Long metal panels joined by raised seams. Around here you see it on porches, bay windows and low slopes.

Typical lifespan: 40 to 60 years

What usually fails: Seams and fasteners loosen, sealant dries out where the metal meets a wall, and older painted steel rusts at scratches.

What I repair: I reseal and repair seams, fix flashing where the metal meets a wall, and patch small rusted spots.

Copper

Soldered copper sheet on bay roofs, valleys, flashing and gutters, mostly on older homes. It turns brown, then green, with age.

Typical lifespan: 60 years and up

What usually fails: Soldered seams crack as the metal expands and contracts, and valleys wear thin where leaves and water sit.

What I repair: I re-solder open seams and replace worn sections of copper flashing and valleys.

Modified bitumen (flat roof)

Asphalt-based roll roofing with a granulated surface. You see it on rowhouse, porch and addition roofs around Baltimore.

Typical lifespan: 15 to 20 years

What usually fails: Seams open up, the surface cracks from sun, and water sits where the roof doesn't drain.

What I repair: I repair open seams, flashing at parapet walls, and clogged drains and scuppers.

Rubber, EPDM (flat roof)

A single sheet of black rubber, glued or held down, with taped seams. Common on rowhouse and porch roofs.

Typical lifespan: 20 to 25 years

What usually fails: Seam tape lets go, the edges pull back, and it gets punctured by things left up there.

What I repair: I repair seams and punctures, reseal edges, and clear and reseal drains.

TPO (flat roof)

A white single-ply sheet with heat-welded seams. It reflects sun, so it shows up on newer flat roofs.

Typical lifespan: 7 to 20 years, depending on thickness and the install

What usually fails: Seams fail if they weren't welded right, and the edges and flashing are the weak spots.

What I repair: I repair seams, edges and flashing, and clear drains.

Cedar shake

Split cedar shakes. Less common around here, mostly on a few older or custom homes.

Typical lifespan: 25 to 30 years

What usually fails: Shakes split, cup and rot, especially in shade where moss holds water.

What I repair: I replace split or rotted shakes and repair the flashing. If a roof is too far gone for repairs, I'll say so.

Lifespans are typical ranges with normal upkeep, not promises. Shade, trees, attic airflow and how well the roof was put on all move the number. More on that in my roof lifespan guide and roof materials page.

What are the parts of a flat rowhouse roof?

A lot of Baltimore rowhouses have flat roofs, which really have a slight pitch toward the back or toward a drain. The parts are different from a shingle roof, and so are the problems.