NRCA Thermoplastic flashcards
NRCA Thermoplastic · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Thermoplastic membrane welding
- Hot-air or solvent fusion of overlapping TPO or PVC sheets into a continuous monolithic seam; nozzle temperature and travel speed must fully fuse both plies without scorching the reinforcement scrim.
- TPO membrane composition
- Thermoplastic polyolefin sheet with a reinforcing scrim sandwiched between two TPO plies; the scrim provides dimensional stability while the outer plies accept heat welding.
- PVC membrane substrate restriction
- PVC membrane must not contact asphalt or bituminous products because plasticizer migration and staining degrade the sheet; an approved separator is required over asphaltic substrates.
- Minimum heat-welded seam width
- Field seams are typically a minimum of 1.5 inches (38 mm) wide; the weld must show a continuous fused bead and resist separation without tearing the membrane.
- Probe test for seams
- A pointed tool is run along the cooled seam edge while still warm; a properly fused seam resists probing and any lifted edge reveals an unwelded void requiring repair.
- Peel test for seams
- A destructive field test where a seam sample is peeled apart; acceptable welds tear the membrane rather than separate cleanly at the weld interface, confirming full fusion.
- Mechanical attachment pattern
- Fasteners and plates are installed per wind-uplift design, with tighter spacing at perimeter and corner zones than the field; density follows the approved shop drawing.
- Termination bar detail
- A metal bar fastened over the membrane top edge with sealant, used at walls and curbs; it secures the membrane and prevents water from entering behind the flashing.
- Prefabricated corner flashing
- Factory-made inside and outside corner pieces welded into the flashing system; they replace field-fabricated seams at high-stress locations and improve watertightness.
- Pipe boot flashing
- A molded or fabricated membrane collar heat-welded around penetrations; the boot seals the pipe-to-roof junction and must be welded to the field membrane.
- Cricket and saddle
- Tapered insulation shapes that divert water around curbs and penetrations toward drains; they prevent ponding at obstructions and reduce seam stress.
- Roof slope for drainage
- Roofs are sloped to direct water to drains, commonly a minimum of 1/4 inch per foot; adequate slope limits ponding that accelerates membrane aging.
- Ponding water effect
- Standing water stresses seams and accelerates membrane degradation; drains and scuppers must be kept clear and slope must meet code to avoid chronic ponding.
- Wind uplift design
- Attachment layout is engineered for expected uplift forces; perimeter and corner zones experience higher suction and require denser fastening than the field.
- UV resistance of TPO
- TPO membranes resist ultraviolet degradation and ozone exposure, maintaining reflectivity and flexibility over time; this reduces cooling load and extends service life.
- PVC plasticizer migration
- Over time PVC plasticizers can migrate into adjacent materials, embrittling the membrane; compatible separators and substrates are required to preserve flexibility.
- Puncture resistance limitation
- Thermoplastic membranes have lower puncture resistance than modified bitumen; walkway pads are installed at service routes and HVAC access points to protect the sheet.
- Thermal movement accommodation
- Thermoplastic membranes expand and contract with temperature changes; terminations and flashings must allow movement without transferring stress to welded seams.
- Non-destructive seam testing
- Air-pressure or vacuum testing detects voids in welded seams without cutting; test pressure is held per manufacturer protocol and any drop signals a leak requiring re-weld.
- Warranty documentation
- Manufacturer warranties require documented seam tests, fastener pull-out values, and installation per published details; deviations can void no-dollar-limit coverage.
- Leak tracing method
- Water travels along deck and insulation; trace from the interior leak upward and outward, checking seams, penetrations, and terminations before opening the field.
- Insulation fastening
- Insulation is mechanically fastened or adhered over the deck before membrane installation; fastener type and pattern must match the deck and wind-uplift design.
- Hot-air welder temperature
- Heat-welding equipment typically operates with nozzle air temperatures around 350-600 °F; the correct setting depends on membrane thickness, ambient temperature, and travel speed.
- Scrim visibility indicator
- Visible scrim or thin spots at a seam indicate under-welding or scorching; both conditions weaken the seam and require repair before acceptance.
- Substrate cleanliness
- Membrane must be installed over clean, dry substrate free of dust, oil, and moisture; contamination traps voids in seams and prevents proper fusion.
- Counterflashing
- Metal flashing embedded in the wall or reglet that overlaps the membrane base flashing; it sheds water away from the termination and protects the top edge.
- Reflectivity benefit
- Light-colored thermoplastic membranes reflect solar radiation, lowering cooling loads and surface temperature; reflectivity is a performance attribute in energy codes.
- Ozone resistance
- TPO and PVC resist ozone and chemical attack better than many alternatives; this extends service life in industrial and coastal environments.
- Seam peel strength threshold
- Acceptable heat-welded seams typically reach peel strengths of 15-20 lbf/in or tear the membrane; values below this indicate incomplete fusion and require re-welding.
- Drain and scupper maintenance
- Clear drains and scuppers prevent standing water that stresses seams and accelerates aging; routine maintenance is part of long-term roof performance.
- Walkway pad installation
- Sacrificial pads are welded or adhered over membrane at service routes and equipment access points to absorb foot traffic and protect against puncture damage.
- Field seam layout
- Seams are laid out to minimize field welding and to align with attachment lines; proper layout reduces stress concentrations and simplifies quality control.