How a Roof Works
Lesson 1. The Parts of a Roof, Named
At a Glance
- The ridge is the top. The eave is the bottom edge
- A valley is where two slopes meet and water collects
- Flashing is the metal at every joint, and it leaks first
- The deck is the wood. Everything else sits on it
The Outline of the Roof
| Part | Where It Is |
|---|---|
| Ridge | The horizontal line at the very top |
| Hip | An outside corner running down from the ridge |
| Valley | An inside corner where two slopes meet |
| Eave | The lower edge, usually over the gutter |
| Rake | The sloped edge at the gable end of a roof |
| Gable | The triangle of wall under a rake |
| Dormer | A window structure poking out of the roof |
Valleys matter more than the rest of this list. Two roof planes worth of water go down one channel, so a valley moves more water than anywhere else on the roof and fails more often.
What Is Actually Stacked Up There
A roof is five or six layers, built from the wood outward.
- Rafters or trusses, the frame holding everything up
- The deck, usually plywood or oriented strand board, sometimes old plank boards
- Ice and water shield, a sticky waterproof membrane at the eaves and valleys
- Underlayment, a sheet covering the rest of the deck
- Starter course, drip edge and the field of shingles
- Ridge cap and ventilation at the top
When an estimate says it includes new underlayment, that is layer four. When it says ice and water shield, that is layer three, and how far up from the eave it runs is the number to ask about.
The Parts Under the Edge
Look up under the overhang at the edge of your roof. The board facing you, the one the gutter is screwed to, is the fascia. The surface above your head, the ceiling of the overhang, is the soffit.
The soffit usually has vents in it. Those are where air enters the attic, and blocking them is the most common ventilation mistake there is.
The Word Square
Roofing is sold by the square. One square is one hundred square feet of roof surface, which is a ten foot by ten foot patch.
An average two story house in Davenport is between eighteen and thirty squares. This is the unit every roofer prices in, so once you know your square count you can compare any two bids honestly.