NRCA Modified Bitumen flashcards
NRCA Modified Bitumen · 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.
- SBS modifier
- Styrene-butadiene-styrene elastomer that gives modified bitumen rubbery, elastic behavior and high elongation, making SBS membranes suited to roofs subject to movement.
- APP modifier
- Atactic polypropylene plastomer that gives modified bitumen a more rigid, heat-tolerant compound, which is why APP membranes are commonly torch-applied.
- Polyester reinforcement
- Nonwoven polyester mat used as a membrane carrier; it provides high tear strength and elongation, making it suitable for roofs that experience movement.
- Fiberglass reinforcement
- Glass mat carrier that gives modified bitumen high tensile strength and dimensional stability but low elongation, so it is less tolerant of substrate movement.
- Granule surfacing
- Mineral granules applied to the top of a cap sheet to protect the bitumen compound from ultraviolet degradation and provide a walking surface.
- ASTM D6164
- Product standard for SBS-modified bitumen sheet using polyester reinforcement; it specifies physical properties such as tensile, tear, and low-temperature flexibility.
- Roll storage rule
- Store rolls upright on pallets, protected from standing water and direct sun; heat deforms SBS rolls and wet or dirty rolls contaminate laps.
- Deck deflection limit
- Low-slope membrane roofs are designed so the deck deflects no more than L/360 of the span under design load, verified before membrane installation.
- Steel deck minimum
- Roof steel deck is typically minimum 22 gage, fastened to supports with side laps stitched or fastened per the deck manufacturer's span table.
- Vapor retarder placement
- Installed on the warm side of the insulation, continuous and sealed at laps and penetrations, to limit moisture migration into the roof assembly.
- Minimum roof slope
- New low-slope roofs are designed for positive drainage at a minimum of 1/4 in. per foot, or 2 percent, toward drains or scuppers.
- Ponding water definition
- Water that remains standing on the roof surface more than 48 hours after rain, indicating inadequate slope, deflection, or blocked drainage.
- Base sheet attachment
- Base sheets are fastened by mechanical fasteners and plates, hot asphalt, cold adhesive, or torch, using the method approved for the deck and wind load.
- Typical lap widths
- Modified bitumen ply sheets typically use 3 in. side laps and 6 in. end laps, but the membrane manufacturer's printed instructions always govern.
- Shingle-fashion ply layout
- Each ply is installed lapping over the previous ply so water drains over the laps, with end laps staggered between plies to avoid buildup.
- Hot asphalt temperature
- Built-up and modified systems typically use asphalt heated to about 400 to 440 degrees Fahrenheit at the kettle, never above its flash point.
- Overdriven fastener
- A fastener set below the deck surface or with a crushed plate; it is a defect that reduces uplift resistance and must be replaced.
- Torch lap indicator
- A continuous bead of molten asphalt visible at the lap edge shows the sheet was heated enough to bond; glossy or charred compound indicates burnout.
- Hot asphalt embedding
- The membrane is laid into a mopped or applied layer of ASTM D312 Type III or IV asphalt at proper temperature, then broomed to remove air.
- Cold adhesive application
- Adhesive is applied with a notched trowel or spray, allowed to reach open time, and the sheet is rolled in; laps may need lap adhesive or sealant.
- Self-adhered application
- Substrate is primed and dried to touch, release film is removed progressively, and the sheet is pressed with a weighted roller for full contact.
- Sheet orientation
- Granule-surfaced cap sheets face up for UV protection, while sanded or film-surfaced sides face down to receive the bonding bitumen.
- Base flashing height
- Wall base flashing typically extends a minimum of 8 in. above the roof surface, terminated in a reglet, counterflashing, or termination bar.
- Termination bar spacing
- Fasteners through a termination bar are spaced at a maximum of 12 in. on center, with a sealant bead applied over the fastener heads.
- Pitch pan use
- A flanged metal pan set in membrane adhesive or hot asphalt and filled with sealant, used for clusters of pipes and irregular penetrations.
- Drain flange stripping
- The drain flange is set in adhesive or hot asphalt, clamped by the strainer, and stripped with a reinforcing ply at least 6 in. wide.
- Hot-work permit
- A written authorization required before torch or hot asphalt work, specifying fire watch, extinguisher, combustible clearance, and post-work monitoring.
- Combustible clearance
- Combustible materials within 35 ft of torch work must be removed or protected, and combustible decking or insulation must be shielded.
- Fire watch duration
- A fire watch remains on site during torch work and for at least 1 hour after the last torch is shut off, unless local code requires longer.
- Fishmouth repair
- An open lap or fishmouth is cut back to sound membrane and patched with new membrane extending at least 6 in. beyond the cut.
- Blister repair
- The blister is cut open, the area dried, and a patch installed extending at least 6 in. beyond the cut; widespread blistering may require replacement.
- Fire classification
- Roof assemblies are rated Class A, B, or C under ASTM E108 or UL 790; Class A is often required where the roof is over a combustible deck.