Roofing Glossary — 100+ Terms Defined

Plain-English Definitions for Every Roofing Term You Need to Know

Plain English. No Jargon.

This glossary covers 86+ roofing and exteriors terms across structural components, materials, installation terminology, insurance vocabulary, building codes, and warranties. Use the letter index below to jump to a section, or individual term anchors for deep links.

A

ACV (Actual Cash Value): The depreciated value of a roof at the time of a loss. An ACV policy pays what the roof was worth — not what it costs to replace it. A 15-year-old roof with an expected 25-year life may receive only 40% of replacement cost. Contrast with RCV. How ACV vs RCV affects your claim→
Alligatoring: A cracking pattern in roof coatings or built-up roofing membranes that resembles alligator skin. Caused by UV degradation and thermal cycling. Indicates the coating has lost elasticity and requires replacement or recoating.
APP (Atactic Polypropylene): One of two modifier types used in modified bitumen roofing. APP-modified membranes are typically torch-applied and offer excellent UV resistance. Contrast with SBS.
Architectural Shingle: A laminated asphalt shingle constructed from two or more layers bonded together, creating a dimensional profile. Also called dimensional shingles or laminate shingles. More durable and visually interesting than 3-tab shingles. Architectural shingles in St. Louis→
ASTM D-3462: The ASTM International standard specification for asphalt shingles made from glass felt. Compliance indicates the shingle meets minimum weight, tear strength, and weathering requirements. Premium shingles typically exceed this standard.
Assignment of Benefits (AOB): A contractual arrangement where a homeowner transfers insurance claim rights to a third party — often a contractor. The contractor then negotiates and settles the claim directly. Carries significant risk for homeowners. Never sign an AOB without legal review. Insurance claim fraud red flags→
Attic Ventilation: The system of intake (soffit vents) and exhaust (ridge vents) that allows air movement through the attic space. Proper ventilation prevents heat and moisture buildup that degrades roofing materials and contributes to ice dam formation. Roof ventilation systems→

B

Blister: A bubble or raised area in a roofing membrane or shingle caused by trapped moisture or air. Blisters weaken the membrane and should be evaluated by a roofing contractor before they crack and allow water infiltration.
BUR (Built-Up Roofing): A low-slope commercial roofing system consisting of alternating layers of bitumen and reinforcing fabric (ply sheets), topped with aggregate or a cap sheet. One of the oldest modern roofing systems; provides excellent redundancy through multiple plies.

C

Cedar Shake: A roofing or siding product split from western red cedar logs. Natural wood texture, good insulation value, and a distinctive aesthetic. Requires fire treatment in most municipalities and periodic maintenance. Lifespan 20–30 years with proper care. Cedar shake roofing in St. Louis→
Chimney Flashing: The metal flashing system sealing the joint between a chimney and the roof plane. Consists of base flashing (step flashing against the chimney sides), counter flashing embedded in mortar joints, and saddle flashing (a cricket) behind wide chimneys. A leading source of roof leaks when failed.
Class 4 Impact Rating: The highest impact resistance rating under UL 2218, assigned to shingles that survive a 2-inch steel ball drop test without cracking. Class 4 shingles often qualify for homeowner insurance discounts in Missouri and Illinois. Class 4 impact-resistant shingles→
Code Upgrade: A roof replacement may trigger building code requirements for upgrades not present on the original roof — such as drip edge on all eaves and rakes, ice and water shield at eaves, or additional attic ventilation. Code upgrade costs are sometimes covered by insurance as a line item.
ColorPlus Technology: James Hardie's factory-applied finish for fiber cement siding. Baked on at the factory under controlled conditions. Carries a 15-year limited warranty covering peeling, chipping, and fading. Outperforms field-applied paint in UV resistance.
Counter Flashing: Metal flashing embedded in masonry (chimneys, parapets) that laps over base flashing to divert water. Usually cut into mortar joints and sealed. Separate from base flashing so each piece can be replaced independently.
Cricket (Saddle): A peaked ridge structure built behind a chimney or other roof projection to divert water around it. Required by building code on chimneys wider than 30 inches on most slopes. Prevents the 'dead valley' water accumulation that leads to leaks.
Cupping: A shingle defect where the edges curl upward, creating a concave appearance when viewed from the side. Caused by differential drying between the top and bottom mat layers, typically from moisture imbalance. Indicates shingles nearing end of life.
Curling: A shingle failure mode where the shingle bends upward at the edges (cupping) or at the tab tips (clawing). Both indicate thermal stress or moisture cycling damage and signal the need for evaluation.

D

Dead Valley: A roof valley that terminates at a flat or low-slope area with no outlet, causing water to accumulate. A significant leak risk. Requires specialized flashing and often a drainage solution. Common on complex residential roof geometries.
Deck (Roof Deck): The structural substrate over which roofing materials are installed. Typically OSB (oriented strand board) or plywood. Must be structurally sound and free of soft spots, delamination, or rot before new roofing is installed.
Deductible (Recoverable): Some insurance policies include a 'deductible waiver' or recoverable deductible provision. Regardless, a homeowner is always responsible for their deductible — any contractor claiming to waive or absorb it is engaging in insurance fraud.
Depreciation: The reduction in a roof's value due to age, wear, and condition, used by insurers to calculate ACV payouts. Under RCV policies, the withheld depreciation is released as a second payment after work completion.
Dimensional Shingle: See Architectural Shingle.
Downspout: The vertical pipe that carries water from the gutter to the ground. Should discharge at least 4–6 feet from the foundation via downspout extension or underground drain. A leading cause of basement water intrusion when too short or clogged.
Drip Edge: An L-shaped metal flashing installed along all eaves and rakes that directs water off the roof edge and into the gutter rather than onto the fascia. Required by IRC on all new roofing installations.

E

Eave: The lower horizontal edge of a roof that overhangs the exterior wall. Ice and water shield is typically required at the eave (the first 3–6 feet of the roof plane) to prevent ice dam water infiltration.
EPDM (Ethylene Propylene Diene Monomer): A synthetic rubber roofing membrane used on low-slope and flat commercial roofs. Available in black or white, typically 45–90 mil thickness. Excellent lifespan (40+ years with proper maintenance), flexible in cold temperatures. EPDM roofing in St. Louis→

F

Fascia: The horizontal board running along the lower edge of the roof, to which gutters are attached. Typically covered with aluminum fascia wrap for protection from moisture. Rot in the fascia board indicates gutter overflow or improper drip edge installation.
Fiber Cement Siding: A composite siding material made from cement, sand, and cellulose fiber. Dimensionally stable, rot-proof, pest-resistant, and Class A fire rated. James Hardie is the dominant fiber cement brand. Fiber cement siding in St. Louis→
Flashing: Sheet metal (typically galvanized steel or aluminum) installed at roof intersections, penetrations, and transitions to prevent water infiltration. Includes step flashing, valley flashing, chimney flashing, and counter flashing.
FORTIFIED (IBHS FORTIFIED): A building certification program from the Insurance Institute for Business & Home Safety that grades homes for wind and hail resistance. FORTIFIED Roof designation requires impact-resistant shingles and specific installation details. Can lower insurance premiums.

G

Gable: The triangular wall section at the end of a pitched roof, between the two sloping planes. A gable vent provides attic ventilation at the gable end but is less efficient than ridge-and-soffit systems.
Gable Vent: An opening at the gable end of a roof for attic ventilation. When present with ridge and soffit vents, gable vents can short-circuit airflow patterns and reduce ventilation effectiveness. May need to be sealed when a balanced ridge-soffit system is installed.
GAF Certified: GAF's manufacturer certification for roofing contractors, requiring installation training and insurance compliance. Authorizes the contractor to issue Silver Pledge and Golden Pledge enhanced warranties. Note: GAF Master Elite is a separate, higher designation. GAF certification details→
Golden Pledge Warranty: GAF's highest warranty tier. Provides up to 25 years of non-prorated workmanship coverage and 50-year non-prorated material coverage. Only available through GAF Certified contractors. GAF warranty tiers→
Granule Loss: The shedding of mineral granules from asphalt shingles. Some granule loss is normal early in a shingle's life. Accelerated granule loss from hail impacts or UV degradation exposes the asphalt mat and accelerates failure. Visible in gutters after a hail event.
Gutter: A trough attached to the eave that collects and channels roof runoff to downspouts. Seamless gutters (formed on-site from continuous aluminum coil) are superior to sectional gutters in leak resistance.

H

Hip: The inclined external angle formed by the intersection of two adjacent roof planes. A hip roof has four planes meeting at a central ridge point.
Hip Cap: Pre-cut ridge cap shingles applied along hip lines. Must overlap properly to prevent water infiltration at the hip intersection.
Ice Dam: A ridge of ice that forms at the eave when heat escaping through the roof deck melts snow, which then refreezes at the cold eave overhang. Dammed water backs up under shingles and infiltrates the structure. Prevented through proper insulation, ventilation, and ice and water shield.
Ice & Water Shield: A self-adhering underlayment with a rubberized asphalt backing that seals around fasteners and at cuts. Required at eaves by IRC and at valleys as a best practice. The primary defense against ice dam water infiltration.
IRC (International Residential Code): The model residential building code adopted (with local amendments) by Missouri and Illinois. Sets minimum requirements for roof construction including decking, underlayment, ice and water shield, ventilation, and flashing.

K

Kick-Out Flashing: An L-shaped piece of flashing installed at the terminus of a roof-to-wall intersection — where step flashing ends at the eave. Diverts water away from the wall surface. One of the most consistently missing details in improperly installed roofs.

L

LP SmartSide: Louisiana-Pacific's engineered wood strand siding product. Treated with zinc borate for pest and fungal resistance. Carries a 5/50 limited warranty when installed by a certified installer. LP SmartSide siding in St. Louis→
Low-Slope Roofing: Roofing systems designed for slopes below 2:12 (2 inches of rise per 12 inches of run). Standard asphalt shingles cannot be used below 2:12. Low-slope systems include TPO, EPDM, PVC, modified bitumen, and BUR.

M

Mat Exposure: The visible fiberglass or organic mat that underlies asphalt shingles, exposed when granule loss is severe enough to erode the asphalt layer. A shingle with mat exposure is at end of life and must be replaced.
Modified Bitumen: A low-slope commercial roofing membrane made from asphalt modified with polymer additives (APP or SBS). Applied by torch (APP), cold adhesive, or self-adhesion. More durable and flexible than BUR. Modified bitumen roofing in St. Louis→

O

OSB (Oriented Strand Board): Engineered wood panels used as roof decking. Made from compressed wood strands bonded with resin. Current standard for new construction. Vulnerable to delamination when repeatedly wetted — a good reason to maintain flashing and replace damaged sections promptly.
Owens Corning Preferred Contractor: Owens Corning's manufacturer certification requiring installation competency, insurance verification, and customer satisfaction standards. Unlocks OC's System Protection warranty tier. OC Preferred certification details→

P

Pipe Boot: A rubber or metal boot flashing that seals around plumbing vent stacks penetrating the roof. Neoprene pipe boots degrade in UV and typically need replacement every 10–15 years — a common source of slow leaks.
Pitch: The slope of a roof expressed as inches of rise per 12 inches of run (e.g., 6:12 = 6-in-12). Affects shingle selection (minimum slope requirements), ventilation design, and snow load considerations.
Public Adjuster: A licensed professional who advocates for the policyholder in insurance claims — not the insurance company's adjuster. Public adjusters charge a percentage of the claim settlement (typically 10–15%). Appropriate when claims are complex, denied, or significantly under-scoped.
PVC (Polyvinyl Chloride): A thermoplastic single-ply roofing membrane welded at seams with hot air. Highly chemical-resistant (appropriate for restaurant grease exposure), white reflective surface. Costs more than TPO but offers superior seam strength. PVC roofing in St. Louis→

R

R-Value: A measure of thermal resistance. Higher R-value = better insulation. Relevant to roofing in the context of attic insulation above the ceiling plane, which interacts with ventilation requirements under IRC.
Rafter: The inclined structural member running from the ridge to the eave that supports the roof deck. Defines the slope angle. In modern construction often replaced by pre-engineered trusses.
Rake: The inclined edge of a gabled roof running from eave to ridge. Drip edge on the rake prevents water from wicking back under shingles at the roof edge.
RCV (Replacement Cost Value): An insurance policy that pays the full cost to replace a damaged roof with like kind and quality, without depreciation. Under most RCV policies, the carrier pays ACV first and releases the depreciation holdback (recoverable depreciation) after work is completed. ACV vs RCV explained→
Ridge: The highest horizontal line of a roof, where two sloping planes meet. The ridge is where ridge vents are installed to exhaust hot and moist attic air.
Ridge Cap: Pre-formed shingle pieces or field-cut shingles applied to the ridge to cover the exposed joint. Must overlap properly to prevent water infiltration.
Ridge Vent: A continuous or segmented vent installed at the ridge that allows hot air to escape from the attic. Works in conjunction with soffit intake vents. The most effective exhaust ventilation for standard residential attics. Ridge vent systems→

S

SBS (Styrene-Butadiene-Styrene): One of two modifier types used in modified bitumen roofing. SBS-modified membranes have rubber-like flexibility, excellent cold-temperature performance, and are often self-adhering or cold-applied. Common in the St. Louis climate.
Scope of Loss: The insurance adjuster's documented list of covered damage and approved line items. The scope of loss is the basis for the claim payment. Discrepancies between the contractor's estimate and the scope of loss are addressed through the supplement process.
Sheathing: See Deck (Roof Deck).
Silver Pledge Warranty: GAF's mid-tier enhanced warranty. Adds a 10-year workmanship warranty on top of System Plus material coverage. Available through GAF Certified contractors. GAF warranty tiers→
Slate Roofing: Natural quarried stone roofing with a lifespan of 75–150 years. Extremely heavy — requires structural verification before installation. Repair requires matching the original quarry source for color and thickness compatibility. Natural slate roofing in St. Louis→
Slope: See Pitch.
Soffit: The horizontal surface under the roof overhang between the fascia and the exterior wall. Vented soffits allow outside air into the attic as part of the ridge-and-soffit ventilation system.
Soffit Vent: An intake vent built into the soffit panel. Outside air drawn in at the soffit travels up through the attic and exits at the ridge vent. Required for a balanced ventilation system.
Splash Block: A concrete or plastic pad placed under a downspout to direct discharge water away from the foundation. Low-cost, effective at preventing erosion and foundation water.
Square (Roofing Square): The standard unit of roofing material measurement. One square = 100 square feet of roof surface area. Roofing estimates, contracts, and invoices use squares as the primary unit. A typical 2,000 sq ft house may have 20–30 squares of roof.
Starter Strip: A specialized strip of modified asphalt shingle material installed at the eave and rake before the first course of shingles. Seals the bottom edge of the first full shingle course and prevents wind-driven rain infiltration. Required for manufacturer warranty compliance.
Step Flashing: Individual L-shaped metal pieces woven into courses of shingles at the intersection of a roof plane and a vertical wall surface. Each piece steps up with a shingle course, creating an overlapping waterproof barrier.
Supplement: An additional claim submission to an insurance carrier requesting payment for items missed in the initial scope of loss. Supplements are standard in the industry and are not disputes — they are corrections to incomplete documentation. How supplement claims work→
Synthetic Slate: A composite roofing material designed to replicate the appearance of natural slate at a fraction of the weight and cost. Products like DaVinci Synthetic Slate offer Class 4 impact ratings and 50-year warranties. DaVinci synthetic slate in St. Louis→
System Plus Warranty: GAF's baseline enhanced warranty, available through Certified contractors when a qualifying accessory system is installed. Typically provides 50-year non-prorated limited coverage on qualifying shingles. GAF warranty tiers→

T

3-Tab Shingle: The original asphalt shingle style, made from a single layer with three cutouts creating the appearance of three individual tabs. Lighter weight and lower profile than architectural shingles. Less common in new installations; largely replaced by architectural/dimensional shingles.
TPO (Thermoplastic Polyolefin): A single-ply white reflective roofing membrane welded at seams with hot air. The most widely installed commercial flat roofing membrane. ENERGY STAR rated in white; reduces urban heat island effect. TPO roofing in St. Louis→
Transferable Warranty: A manufacturer or workmanship warranty that can be transferred to a subsequent homeowner. Many GAF, Owens Corning, and CertainTeed warranties are transferable within a defined window (usually 30 days of sale) with a transfer fee. Warranty transfer details→
Turbine Vent: A wind-powered rotating exhaust vent. Less efficient than ridge vents in most configurations and requires wind to function. Not compatible with ridge-vent systems and typically not recommended for new construction.

U

UL 2218: The Underwriters Laboratories standard for impact resistance of roofing systems. Rates shingles from Class 1 (lowest) to Class 4 (highest). Class 4 shingles survive a 2-inch diameter steel ball impact test. Class 4 impact shingles→
Underlayment: A water-resistant or waterproof layer installed between the roof deck and the primary roofing material. Synthetic underlayment is the current standard; felt (15# or 30# felt) was the prior standard. Provides a secondary water barrier if the shingles are compromised.

V

Valley: The internal angle formed where two roof planes meet. Water from both planes concentrates in the valley — making it a high-velocity drainage zone and a common leak source when flashing fails.
Valley Flashing: Metal flashing installed in the valley to manage concentrated water flow. Open valleys expose the flashing; closed-cut and woven valleys use shingles over ice and water shield.
Vent Stack: The plumbing pipe penetrating the roof that vents sewer gas. Sealed with a pipe boot. Typically 1.5–4 inch diameter. A common leak source when pipe boot neoprene deteriorates.
Vinyl Siding: PVC siding panel in a wide range of profiles and colors. Maintenance-free, moisture-resistant, and affordable. Lower insulation value than fiber cement or wood alternatives unless insulated backing is added. Vinyl siding installation in St. Louis→

W

Wind Warranty: A manufacturer warranty provision covering shingle blow-off up to a specified wind speed. Standard limited warranties typically cover 60–110 mph wind. Premium shingles with enhanced nailing patterns can qualify for 130 mph coverage.

Terms, definitions, and code references on this page reflect general roofing industry usage and the Missouri/Illinois regulatory context as of 2025. Building codes are adopted locally with amendments — always verify specific requirements with your jurisdiction. For questions about how any of these terms apply to your specific project, contact Revolve at (314) 400-8006.

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