A
- Actual cash value (ACV)
- An insurance settlement that pays replacement cost minus depreciation. On an older roof, the ACV payment can be well below the cost of a new roof.
- Adhered system
- A single-ply roof in which the membrane is glued to the insulation or cover board across its full surface, rather than fastened at the seams. Fully adhered roofs tend to resist wind flutter and hail well.
- Approved applicator
- A roofing contractor a manufacturer has authorized to install its systems and offer its warranties. Extended manufacturer warranties are only available through approved applicators.
B
- Ballast
- Loose stone or concrete pavers laid over a membrane to hold it in place instead of fasteners or adhesive.
- Base flashing
- The membrane or sheet that turns up from the roof surface onto a wall, curb or parapet to seal the transition.
- Blister
- A raised bubble in a roof membrane, usually caused by trapped air or moisture. Small, intact blisters are often monitored; cracked or growing blisters need repair.
- Built-up roof (BUR)
- A multi-ply roof made of alternating layers of bitumen and reinforcing felts, finished with gravel or a smooth coating. See built-up roofing.
C
- Cap sheet
- The top, often granule-surfaced, layer of a built-up or modified bitumen roof that protects the plies beneath from UV and weather.
- Coping
- The metal cap that covers the top of a parapet wall and sheds water away from the wall.
- Core cut
- A small sample cut through the roof to show its layers and confirm whether the insulation is wet. Cores are patched the same day.
- Counterflashing
- Metal flashing set into or attached to a wall that overlaps the top of the base flashing, keeping water from getting behind it.
- Cover board
- A thin, dense board installed between the insulation and the membrane. It protects the insulation from foot traffic and hail and gives the membrane a firm surface.
- Cricket
- A small sloped area, usually built with tapered insulation, that diverts water around a curb or toward a drain.
- Curb
- A raised frame that supports rooftop equipment or a skylight and lets the roof membrane be flashed up and around it.
D
- Deck
- The structural surface the roof system sits on, typically steel, concrete or wood on commercial buildings.
- Depreciation
- The reduction in value an insurer applies to a roof based on age and condition. Recoverable depreciation is the portion an insurer may pay once the work is completed, depending on the policy.
E
- Edge metal
- The metal trim at the perimeter of a low-slope roof that secures the membrane edge. It must be designed and tested to resist wind.
- EPDM
- Ethylene propylene diene monomer, a synthetic rubber single-ply membrane, usually black, with taped seams. See TPO vs EPDM.
- Expansion joint
- A flexible joint in a roof that lets sections of the building move independently with temperature changes without tearing the membrane.
F
- Field of the roof
- The open, flat area of a roof away from edges, corners and penetrations.
- Flashing
- Any material used to seal the roof where it meets a wall, edge, curb or penetration. Most leaks start at flashings.
- Flood coat
- The heavy top layer of bitumen on a gravel-surfaced built-up roof, into which the gravel is embedded.
H
- Hail-rated assembly
- A roof system tested and rated for resistance to hail impact. Some manufacturer warranties cover hail up to a stated size when the roof is built to a specific specification.
- Heat welding
- Joining thermoplastic membranes such as TPO with hot air so the seam fuses into one continuous sheet.
I
- Induction welding
- A method of attaching single-ply membrane in which special plates under the membrane are heated by an induction tool, bonding the membrane to the plates without penetrating fasteners through the sheet.
- Infrared moisture survey
- A thermal scan, usually done in the evening, that finds wet insulation under a roof membrane. See infrared roof moisture surveys.
- Insulation
- Rigid boards beneath the membrane that slow heat flow. Polyiso is the most common on commercial roofs; required thickness is set by the energy code.
L
- Low-slope roof
- A roof with little pitch, commonly called a flat roof, that relies on a continuous membrane rather than overlapping shingles or panels to keep water out.
M
- Mechanically attached
- A single-ply system held down with screws and plates, usually placed in the seams, rather than adhesive.
- Membrane
- The waterproof sheet that forms the top layer of a low-slope roof, such as TPO, EPDM or modified bitumen.
- Modified bitumen
- Asphalt modified with polymers and reinforced, installed in rolls by torch, hot asphalt, cold adhesive or self-adhesion. Often used as a two-ply system.
N
- NDL warranty
- A "no dollar limit" manufacturer warranty that covers materials and labor for covered defects without a cap tied to the original roof cost. Terms and exclusions vary by manufacturer.
- NRCA
- The National Roofing Contractors Association, an industry association that publishes technical guidance, including the recommendation to inspect low-slope roofs at least twice a year.
O
- Overflow drain
- A secondary drain or scupper set slightly higher than the primary drain that carries water off the roof if the primary drain clogs.
P
- Parapet
- A wall that extends above the roof line at the edge of the building.
- Penetration
- Anything that passes through the roof, such as pipes, vents, conduit or equipment supports. Each needs its own flashing.
- Pitch pan
- A metal collar around an irregular penetration, filled with sealant. Also called a pitch pocket. Pitch pans need regular checks and refilling.
- Polyiso
- Polyisocyanurate, a rigid foam insulation board with facers on each side, the most common insulation on commercial low-slope roofs.
- Ponding water
- Water that stays on a roof well after rain or snowmelt. Ponding speeds membrane aging and can affect warranties.
R
- R-value
- A measure of insulation's resistance to heat flow. Higher numbers insulate better. Energy codes set minimum R-values for roof replacements.
- Recover
- Installing a new roof over an existing one instead of tearing it off. Only allowed when the existing roof is dry, sound and within code limits on layers.
- Remaining useful life
- The number of years a specific roof is expected to keep performing, used in reserve studies and capital plans.
- Replacement cost value (RCV)
- An insurance settlement basis that pays the cost to replace damaged property with new, subject to policy terms and the deductible.
- Reserve study
- A long-range plan that estimates when an association's major components, including roofs, will need replacement and how much to set aside. See HOA roof reserve planning.
- Restoration coating
- A liquid-applied coating that renews the surface of a sound, dry roof and can extend its life.
S
- Scupper
- An opening through a parapet or roof edge that drains water off the roof, often into a gutter or downspout.
- Seam
- Where two sheets of membrane overlap and are joined by welding, tape or adhesive.
- Single-ply
- A roof membrane installed as one layer, such as TPO or EPDM.
- Spray polyurethane foam (SPF)
- Foam sprayed onto the roof as a liquid that expands into a seamless, insulating layer, then protected with a coating. See spray foam roofing.
- Standing seam
- A metal roof with raised, interlocking seams between panels and concealed fasteners. See metal roofing.
T
- Tapered insulation
- Insulation boards cut with a built-in slope that direct water to drains on a flat deck.
- Tear-off
- Removing the existing roof down to the deck before installing a new one.
- Termination bar
- A metal or plastic strip fastened along the top edge of base flashing to hold it tight to a wall.
- TPO
- Thermoplastic polyolefin, a usually white single-ply membrane with heat-welded seams. See TPO roofing.
U
- Uplift
- The upward force wind places on a roof. Uplift design sets the fastening or adhesive pattern, especially at corners and perimeters.
V
- Vapor retarder
- A layer installed below the insulation that limits moisture moving up from inside the building, where it could condense in the roof.
W
- Walkway pads
- Protective pads laid on the membrane along routes to rooftop equipment, so service traffic doesn't wear the roof.
- Wet insulation
- Insulation that has absorbed water through a leak. It loses insulating value, adds weight and generally has to be replaced before a recover.
- Workmanship warranty
- The installing contractor's warranty covering how the roof was installed, separate from the manufacturer's material or system warranty.
Roofing glossary FAQs
What's the difference between a manufacturer warranty and a workmanship warranty?
A manufacturer warranty covers the roofing materials or the full system, depending on its terms. A workmanship warranty comes from the installing contractor and covers the installation itself. Most commercial roofs carry both.
Is a flat roof actually flat?
No. "Flat" roofs are low-slope roofs with a slight pitch, often created with tapered insulation, so water drains toward drains or scuppers.
What does "recover" mean in a roofing proposal?
Installing a new roof over the existing one. It's only appropriate when the existing roof is dry, sound and within code limits on the number of layers.
Why does my insurance estimate show depreciation?
Many policies reduce payment based on the roof's age and condition. Whether some of that depreciation is recoverable after the work is done depends on your policy. Your agent can explain your terms.