Square
A unit of roof area equal to 100 square feet of roof surface. Dividing the surface area by 100 gives the number of squares. Most common asphalt shingles are packed so that three bundles cover one square.
Glossary
A glossary of roof terms
Roof diagrams, inspection reports and quotes share a vocabulary that is rarely explained. These definitions describe each term as roofers in the United States generally use it. Local practice and codes vary, so ask whoever wrote your document if a term seems to mean something different.
Measurement
Size, slope and waste
Pitch
The steepness of a roof, written as inches of rise per 12 inches of horizontal run. A 6/12 roof climbs 6 inches for every 12 inches across. Some references call this measure slope, but on most quotes and diagrams pitch means rise over a 12-inch run.
Pitch factor
The number a footprint is multiplied by to get the surface area at a given pitch. Steeper pitches have larger factors: 1.118 for 6/12, 1.202 for 8/12 and 1.414 for 12/12. Roof pitch and roofing squares explained shows how it is worked out.
Footprint
The area of a roof section measured flat, as if seen from directly above, with the slope ignored. Overhangs are included when the footprint is measured from above. Multiplying a footprint by its pitch factor gives the surface area.
Plane
One flat section of roof surface, bounded by ridges, hips, valleys or edges. Also called a facet. A simple gable roof has two planes, and a complex roof can have dozens.
Waste factor
A percentage added to the measured roof area to cover shingle material lost to cutting and fitting. Often about 10 percent on simple roofs and 15 percent or more on roofs with many hips and valleys. Starter strip and ridge cap are ordered separately, by the linear foot.
Takeoff
The list of quantities a contractor prices a roofing job from: squares, waste, edge lengths, flashing, penetrations and materials. It is usually a working document, though a homeowner can ask to see it. Also called a material takeoff.
Roof shape
Lines, edges and ends
Ridge
The horizontal line at the top of a roof where two sloping planes meet. It is covered with ridge cap and often carries a ridge vent.
Hip
The sloping line where two planes meet at an outside corner, with water running away from the join on both sides. Hips are covered with cap shingles, like a ridge.
Valley
The sloping line where two planes meet at an inside corner, so that water from both runs toward the join. Valleys carry a large share of a roof's water and are lined with valley flashing or protected with membrane and shingles.
Eave
The lower, level edge of a roof plane, where gutters are usually attached and where the roof commonly overhangs the wall.
Rake
The sloping edge of a roof at the end of a gable, running from the eave up toward the ridge.
Gable
The triangular section of wall at the end of a roof with two sloping sides, framed by the two rakes. A gable roof has this shape at one or both ends.
Wall line
On a roof diagram, a line marking where a roof plane runs into a vertical wall, such as the side of a dormer or a second story. Its length tells an estimator how much step or apron flashing the job needs. Codes also use the phrase exterior wall line, meaning the line of the house's outside walls beneath the roof.
Penetration
Anything that passes through the roof surface, such as a plumbing vent, an exhaust fan, a skylight or a chimney. Each one needs its own flashing or pipe boot, so takeoffs and quotes usually count them.
Roof edge
Trim, starter and caps
Fascia
The vertical board along the roof edge that covers the ends of the rafters. Gutters are typically fastened to it.
Soffit
The finished underside of the roof overhang, between the fascia and the wall. Vented soffit panels often serve as the air intake for attic ventilation.
Drip edge
An angled metal strip installed along eaves and rakes. It directs water away from the fascia and, at the eaves, into the gutter, and it protects the edge of the decking.
Starter strip
The first course of shingle material laid along the eaves, and often the rakes, under the first full row. It seals the edge and covers the gaps between shingles in that first row. It is ordered by the linear foot.
Ridge cap
Shingles made or cut to bend over ridges and hips, covering the joint where two planes meet. It is ordered by the linear foot of ridge and hip.
Flashing
Where the roof meets something else
Step flashing
Small L-shaped pieces of metal woven in with each course of shingles where a sloping roof runs along a side wall or the side of a chimney. Each piece overlaps the one below it.
Counter flashing
A second layer of metal fixed to a wall or set into a chimney's mortar joints. It covers the top edge of step or apron flashing so water cannot run behind it. Also written counterflashing.
Apron flashing
A continuous strip of metal where the top of a roof plane meets a vertical wall, and along the downhill face of a chimney. Also called headwall flashing.
Valley flashing
Metal or membrane lining a valley to carry water down the join. In an open valley the metal stays visible, and in a closed valley shingles cover it.
Chimney flashing
The set of flashing where a chimney passes through the roof: apron flashing along the downhill face, step flashing up the sides, counter flashing set into the mortar joints over both, and a cricket or a metal back pan on the uphill side.
Chimney cricket
A small peaked structure built on the uphill side of a chimney. It splits water and debris around the chimney instead of letting them collect behind it. Codes commonly require one on wider chimneys. Also called a saddle.
Kickout flashing
A short angled piece at the bottom of a roof-to-wall joint, where the roof edge ends against a wall. It turns water into the gutter instead of letting it run down behind the siding.
Skylight flashing
The flashing around a skylight, usually a kit made by the skylight manufacturer for that model. A kit typically combines a sill piece at the bottom, step flashing along the sides and a head piece at the top.
Pipe boot
A flashing collar that seals the roof around a plumbing vent pipe. Many have a metal or plastic base with a rubber seal around the pipe, and others are made entirely of lead or another metal. Rubber seals crack in the sun, so pipe boots often need replacing before the shingles do. Also called a vent boot.
Layers and work
What lies under the shingles, and how it is replaced
Decking
The structural layer of panels or boards fastened to the rafters or trusses, usually plywood or oriented strand board. Older houses may have plank decking. Also called sheathing.
Underlayment
A water-resistant layer laid over the decking beneath the shingles. Asphalt-saturated felt is the traditional underlayment and is still used; many roofs now use synthetic underlayment.
Ice and water membrane
A self-adhering waterproof membrane, often sold as ice and water shield, laid along eaves and often in valleys. Where ice dams are a known risk, codes commonly require it from the eave edge to at least 24 inches inside the exterior wall line. Also called an ice barrier.
Ventilation
The flow of outside air through the attic, usually in through soffit or eave vents and out through ridge or roof vents. Balanced ventilation limits the heat and moisture that shorten shingle life and cause condensation.
Ridge vent
A vent that runs along the ridge, usually covered by cap shingles, that lets warm, moist air out of the top of the attic through a slot cut in the decking. It works with intake vents at the soffits or eaves, and it is ordered by the linear foot of ridge.
Tear-off
Removing the existing roof covering down to the decking before installing a new roof. It exposes the decking, so damaged sections can be found and replaced.
Overlay
Installing new shingles over one existing layer instead of tearing it off. Also called a recover or layover. Codes generally do not allow an overlay where two layers already exist, and an overlay hides the decking from view.
Spot these parts from the ground
Most of the parts above can be seen from the yard, from an upstairs window or through binoculars. Do not climb onto the roof to find them, and stay well away from a storm-damaged roof.
See the terms in context
The roof diagram guide shows where ridges, valleys, planes and pitches appear on a drawing, and the flashing guide explains why the joins matter so much.
