COMMERCIAL ROOFING GLOSSARY REFERENCE

A reference glossary of commercial roofing terms for building owners and asset managers, written in plain language by owner-side roofing advisors.

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Reference

Commercial roofing carries its own vocabulary, and most of it is written for installers rather than the people who sign the checks. We built this glossary for building owners, REITs, asset managers, and facility executives who need to read a proposal, a condition report, or a warranty document and understand exactly what is being promised. The definitions below are grouped by category and written the way we explain them to our clients: plainly, with an eye toward what the term means for your capital plan and your risk.

Roof Systems

  • TPO (Thermoplastic Polyolefin) — A single-ply white membrane that is heat-welded at the seams. It is the most common low-slope system specified today, valued for reflectivity and competitive cost.
  • EPDM (Ethylene Propylene Diene Monomer) — A single-ply rubber membrane, usually black, with seams that are taped or glued. Known for durability and a long track record, though it absorbs heat.
  • PVC (Polyvinyl Chloride) — A heat-welded single-ply membrane prized for chemical and grease resistance, which makes it common on restaurants and manufacturing buildings.
  • BUR (Built-Up Roofing) — A traditional system of alternating layers of bitumen and reinforcing felts, topped with gravel or a cap sheet. Heavy, redundant, and long-lasting, often called a "tar and gravel" roof.
  • Modified Bitumen (Mod-Bit) — Asphalt membranes reinforced with polymers, applied in rolls by torch, hot asphalt, or self-adhesion. A durable evolution of built-up roofing.
  • SPF (Spray Polyurethane Foam) — A seamless foam sprayed in place that insulates and waterproofs at once, then protected by a coating. Excellent for irregular roofs but coating-dependent.
  • Metal Roof System — Standing-seam or through-fastened panels, typically on steeper slopes. Long service life but sensitive to fastener and seam detailing.
  • Green/Vegetative Roof — An assembly supporting plantings over a waterproofing layer, used for stormwater and energy goals. Adds weight and inspection complexity.
  • Ballasted Roof — A membrane held down by river rock or pavers rather than fasteners or adhesive. Common on older EPDM roofs and difficult to inspect without moving ballast.

Components and Assembly

  • Membrane — The waterproofing layer itself, whether single-ply, modified bitumen, or built-up.
  • Cover Board — A rigid board installed over the insulation and under the membrane to add puncture resistance and a stable substrate. Its presence often signals a quality assembly.
  • Insulation — The board stock (commonly polyiso) that provides thermal resistance and, when tapered, drainage slope.
  • Tapered Insulation — Insulation cut to varying thicknesses to create positive slope toward drains on an otherwise flat deck.
  • Roof Deck — The structural surface (steel, concrete, or wood) that everything else is built upon.
  • Vapor Retarder — A layer that limits moisture from inside the building from migrating into the roof assembly.
  • Flashing — Material that seals the membrane to penetrations, walls, and edges. The majority of leaks originate at flashings, not in the open field.
  • Parapet — The wall extending above the roof line at a building's edge. A frequent source of leaks where wall meets roof.
  • Coping — The cap, usually metal, that covers the top of a parapet wall to shed water away from it.
  • Cant Strip — An angled filler at the base of walls and curbs that eases the membrane transition and prevents sharp bends that crack.
  • Curb — A raised frame that mounts rooftop equipment such as HVAC units, requiring its own flashing.
  • Pitch Pocket (Pourable Sealer Pocket) — A small container filled with sealant around odd-shaped penetrations. A known weak point that needs routine refilling.
  • Reglet — A groove cut into a wall that receives and locks in the top edge of counterflashing.
  • Counterflashing — The upper flashing that overlaps base flashing to direct water away from the joint.
  • Walkway Pads — Protective surfaces installed along service routes to shield the membrane from foot traffic.
  • Termination Bar — A metal strip that fastens and seals the membrane edge against a vertical surface.

Drainage and Edge Details

  • Scupper — An opening through a parapet or curb that lets water drain off the edge, often into a downspout.
  • Internal Drain — A drain plumbed through the building interior, collecting water at low points in the field.
  • Overflow Drain — A secondary drain set slightly higher than the primary, providing backup if the main drain clogs.
  • Cricket — A small ridged structure built behind curbs or between drains to divert water and prevent ponding.
  • Gutter and Downspout — Edge collection and vertical conveyance, more common on sloped or metal roofs.
  • Drip Edge — Metal edging that directs runoff away from the fascia and into gutters.
  • Saddle — A raised diversion, similar to a cricket, guiding water around an obstruction.

Conditions and Failures

  • Ponding — Standing water that remains more than 48 hours after rain. It accelerates membrane aging and signals inadequate slope or clogged drains.
  • Blistering — Raised pockets where the membrane has separated from the substrate, usually from trapped moisture or vapor.
  • Alligatoring — Surface cracking that resembles reptile skin, typical of aged asphalt and bituminous surfaces.
  • Splitting — Tears in the membrane from thermal movement, substrate shifting, or stress concentration.
  • Fishmouthing — An open, gaping seam edge that has lifted and no longer lies flat.
  • Membrane Shrinkage — Contraction over time, common in older EPDM, that pulls flashings and stresses seams.
  • Punctures — Penetrations from foot traffic, dropped tools, or debris that compromise the waterproofing layer.
  • Delamination — Separation between layers of the assembly, such as a membrane lifting from its cover board.
  • Saturation — Water-logged insulation beneath the membrane, which loses thermal value and adds weight and rot risk.
  • UV Degradation — Breakdown of exposed materials from sun exposure, gradually embrittling membranes and coatings.
  • Open Seam — A weld or adhesive joint that has failed and allows water entry.

Warranties and Coverage

  • Manufacturer Warranty — Coverage issued by the membrane manufacturer, distinct from the contractor's labor warranty.
  • Contractor (Workmanship) Warranty — The installer's guarantee against defects in their labor, typically shorter than the manufacturer term.
  • NDL Warranty (No Dollar Limit) — A manufacturer warranty with no cap on repair cost for covered defects, the strongest common form.
  • Material-Only Warranty — Covers the product but not the labor to install or repair it, leaving the owner exposed to labor cost.
  • Prorated Warranty — Coverage that declines in value over the term, so later claims pay less.
  • Pre-Existing Conditions Exclusion — Language that voids coverage for problems traceable to issues present before the warranty began.
  • Maintenance Requirement — A warranty condition obligating documented inspections and upkeep; failure to keep records can void claims.
  • Transferability — Whether a warranty can pass to a new owner on sale, often with a fee and a window. Critical in acquisitions.

Inspection and Testing

  • Infrared (Thermographic) Scan — A nighttime survey using thermal imaging to find heat signatures of trapped moisture beneath the membrane.
  • Nuclear Moisture Survey — A grid survey using a meter that detects subsurface moisture, used to map wet insulation.
  • Electronic Leak Detection (ELD) — A method using electrical current to pinpoint breaches in the membrane, including low-voltage and high-voltage techniques.
  • Flood Test — Temporarily flooding a roof area to confirm watertightness, common on plaza decks and new installations.
  • Core Cut — A small sample removed through the assembly to verify layers, confirm construction, and check for moisture.
  • Pull Test — A field test measuring fastener or adhesion strength to the deck.
  • Roof Condition Assessment — A documented evaluation of remaining service life, defects, and recommended actions that anchors capital planning.

Capital and Process

  • Roof Asset Management — A program of inspection, repair, and budgeting that treats the roof as a tracked asset rather than a reactive expense.
  • Reserve Study — A forward projection of major repair and replacement costs used to fund a capital reserve.
  • Remaining Service Life (RSL) — The estimated years a roof can perform before replacement, the single most useful number for budgeting.
  • Re-Cover (Overlay) — Installing a new membrane over the existing one, permitted when the deck is dry and codes allow only one overlay.
  • Tear-Off — Full removal of the existing system down to the deck before rebuilding, required when the assembly is saturated.
  • Roof Coating (Restoration) — A fluid-applied layer that extends the life of a sound roof and can renew certain warranties, but is not a fix for a failing assembly.
  • Capital Expenditure (CapEx) — A roof replacement or major project carried as a depreciable asset rather than an operating expense.
  • Scope of Work — The detailed description of materials, details, and methods in a bid, which is where comparable pricing lives or dies.
  • Owner's Representative (Advisor) — An independent party who specifies, inspects, and oversees work on the owner's behalf, with no stake in selling the installation.