Minimum roof slope by code
2% (¼” per foot) for drainage on low slope roofs.
Intensive Green Roof
A green roof with soil directly on the roof, kept relatively flat, capable of supporting larger plants.
Extensive Green Roof
A green roof using independent soil trays, requiring a minimum 2% slope, often supporting lightweight plants.
Intentionally Ponding Roofs / Blue Roofs
A roof system designed to deliberately collect and store rainfall, often required in places like NYC for water catchment.
Max Slope of Low Slope Roofs
Roofs with less than 2 inches per foot slope (2:12 or 17%), relying on continuous, flawlessly installed membranes to handle slow drainage.
Bituminous Roofing Membrane
A family of roofing membranes containing asphalt.
Multi-Ply / Built-Up Roof (BUR)
A bituminous roof membrane made of a roof deck, rigid insulation, asphalt, cover board, alternating layers of asphalt/felt, and a protective coating.
Modified Bitumen (Mod Bit)
A bituminous membrane containing chemical polymers that improve wear and resistance.
Single-Ply Roofing Membrane
Roofing membrane consisting of factory-manufactured sheets rolled out onto the roof.
EPDM Membrane
A single-ply membrane made of thermoset rubber, with glued or taped seams (not heat-welded).
Fluid-Applied Membrane
A membrane sprayed or mopped into place, best for difficult locations with complex geometries.
Steep Slope Roofs
Roofs with slopes more than 2:12 (17%) that shed water via gravity using small overlapping units like shingles.
Back-up Drains
Secondary drains placed higher up that will work if the primary drain is blocked, often equipped with an alarm or draining to a visible location.
Roof Scupper
A drainage opening that releases water off the roof through the side of a parapet, often acting as a backup drain.
Drain Strainer
Part of a roof drain that prevents clogging; must be twice the area of the drain pipe.
Drain Hub or Sump
The recessed collection area of a roof drain system.
Pitch Pan
An oversized hole for a roof penetration filled with pourable sealant to create a curve; prone to leaking over time.
Cone-Shaped Boot
A mechanical seal for roof penetrations, preferred over chemical seals like pitch pans.
Cricket
A small pitched element used to geometrically divert water around an obstruction on both steep and low-slope roofs.
Roof Joints
Intentional gaps allowing roofing membranes to expand and contract.
Cant Strip
A beveled strip (typically wood) used to ease the transition between a horizontal roof deck and vertical wall (45 degrees) to prevent membrane cracking.
Counter-Flashing
Flashing that laps over the main flashing, allowing the roof membrane to be changed without removing the coping or main flashing.
Flashing
Waterproof material placed over the top of wall transitions to shed water.
Coping
The protective cap sitting on the very top of a wall to shed water.
