Seattle Roofing Contractor
Solar Tubes, Gutters and Skylights. Installations and Repairs
(425) 774-0806

Key Roofing Terms

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Caulk: To fill a joint with sealant, mastic or asphalt cement to prevent leaks.

Chalk line: A line made on the roof by snapping a taut string or cord dusted with chalk. Used for alignment purposes.

Class “A”: The highest fire-resistance rating for roofing as per ASTM E-108. Indicates roofing is able to withstand severe exposure to fire originating from sources outside the building.

Class “B”: Fire-resistance rating that indicates roofing materials are able to withstand moderate exposure to fire originating from sources outside the building.

Class “C”: Fire-resistance rating that indicates roofing materials are able to withstand light exposure to fire originating from sources outside the building. 

Closed cut valley/California Valley: A method of valley treatment in which shingles from one side of the valley extend across the valley while shingles from the other side are trimmed two inches from the valley centerline. The valley flashing is not exposed.

Closed soffit:  Underside of an overhang that is finished.

Coating: A layer of viscous asphalt, aluminum or emulsion applied to the outer roof surface to protect the roof membrane.

Color-through: During manufacturing, the color is mixed throughout the roofing material to become an integral part of it. When the product is cut, the affected area shows the same color as the surface.

Concealed nail method: Application of roll roofing in which all nails are driven into the underlying course of roofing and covered by a cemented, overlapping course. Nails are not exposed to the weather.

Condensation: The change of water from vapor to liquid when warm, moisture-laden air comes in contact with a cold surface.

Chimney flashing: That portion of the flashing attached to a vertical surface to prevent water from migrating behind the base flashing.

Chimney counter flashing: L flashing installed at the base of the chimney to make the roof deck water tight.

Course: A row of shingles or roll roofing running the length of the roof.

Coverage: Amount of weather protection provided by the roofing material. Depends on number of layers of material between the exposed surface of the roofing and the deck; i.e., single coverage, double coverage, etc.

Cricket: A peaked saddle construction at the back of a chimney, skylight or wall to prevent accumulation of snow and ice and to deflect water around the chimney.

Cutout: The open portions of a strip shingle between the tabs.

Deck or Decking: The structural “skin” of a roof over which roofing in felt paper or base sheet is applied. Most new homes have decking made of plywood. There are four main types of decking commonly used on residential roofing projects:

  • Plywood: Plywood is strong, durable, and light. It comes in many grades with ratings from A to D. Use only exterior grade plywood for decking. The thickness of plywood depends on the spacing of the rafters.
  • OSB: Oriented strand board (OSB) is cheaper than plywood, but not as strong as plywood, and does not hold nails as well as plywood. One side has a slip resistant coating and should be placed facing up.
  • Tongue and groove 2×6: If a roof will be seen from the inside (no ceiling installed), tongue and groove is used. It is a wood decking that provides great insulation with the use of rigid roof insulation in moderate climates. Also, the boards can be painted or stained on the inside to match the interior. 
  • Skip/Split Sheathing: Skip sheathing is used alone or in combinations with solid sheathing for installation of shakes. Skip sheathing allows air circulations under the shakes by using 1×4 or 1×6 boards that are evenly spaced so that air can move under the shake roof.


Dormer: A framed small roof that projects through the sloping plane of a roof.

Double coverage: Application of asphalt roofing such that the lapped portion is at least two inches wider than the exposed portion, resulting in two layers of roofing material over the deck.

Downspout: A pipe for draining water from roof gutters.

Drip edge: A non-corrosive, non-staining material used along the gable, rakes or edges to allow water run-off to drip clear of underlying construction.

Dutch lap method: Application of giant individual shingles with the long dimension parallel to the eaves. Shingles are applied to overlap adjacent shingles in each course as well as the course below.

Eaves: Outside overhang of a flat or pitched roof.

Edging strips: 4×36 roofing shingles nailed along eaves and rakes to provide secure edges for re-roofing with asphalt shingles.

Exposure: Portion of the shingle exposed to the weather. Exposure is measured from the butt of one shingle to the butt of the next.

Feathering strips: Tapered wood filler strips placed along the butts of old roofing or sheeting to create a level surface when re-roofing over existing wood shingle roofs. Feathering strips are also called horse feathers.

Felt: Tar paper or felt paper. Available in 15 or 30 lbs. A flexible sheet that is saturated with asphalt and used as an underlayment. 

Fiberglass mat: An asphalt roofing base material manufactured from glass fibers.

Flashing: Pieces of metal, rubber, lead or plastic used to prevent seepage of water into a building around any intersection or projection in a roof such as vent pipes, skylights, chimneys, adjoining walls, dormers and valleys. Galvanized metal flashing should be minimum 26 or 28-gauge. There are 4 main types of flashing used in residential roofing systems:

  • Valley flashing: This flashing is used in open valleys of the roof. Most often leaks are found in the valley flashings due to flashing that is nailed that is not trimmed far enough from the valley.
  • Plumbing vent flashing: Plumbing vent flashing prevents rainwater from running into holes cut for pipes penetrating through the roof. This flashing is sold according to the size of the vent pipe and the roof angle. Roof flashing is installed over the roofing and under the roofing above it. 
  • Lead flashing: When working with tile roofs, lead flashing is used. In the case of a plumbing vent flashing, the lead flashing is actually molded to the shape of the tile’s surface. Then the top of the lead flashing is covered by the next tile to prevent water from seeping under the flashing.
  • Step flashing: When a chimney or dormer wall intercepts the slope of the roof, step flashing is used. Step flashing is usually a metal piece that is bent in the middle, so that one end lays on the roof, and the other against the vertical wall of the dormer or chimney.


Flashing is one of the most important elements of the roof because it seals the seams and joints of the roof–the locations where leaks are most likely to occur. Often, flashing is not maintained well, or installed correctly in the first place. Check for the following signs that your flashing needs maintenance or repair: 

  • Rusting of metal flashing
  • Excess leaves and debris in valleys or metal flashings of the roof (can lead to rusting and corroding of the metal)
  • Prolonged exposure to the elements such as moisture, UV rays, climate changes–especially when asphalt compounds or caulking material is used. Look for cracks, loss of elasticity and delamination.


In many cases the flashing can be cleaned and then repaired, relaminated or repainted (even in the case of rust). In other cases, the flashing may need to be replaced.

Flashing cement: An asphalt-based cement used to bond roofing materials. Flashing cement is also known as mastic.

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