HAAG Roof Inspector cheat sheet

Slope is rise over run expressed as X:12; slope ratio = rise ÷ 12. Roofs below 3:12 generally require a full underlayment system and are treated as low-slope by most shingle manufacturers.

Asphalt shingle minimum slope is typically 2:12 with double underlayment; 4:12 and steeper may use a single layer. Always confirm the specific manufacturer's published installation instructions, which govern over generic rules.

Attic ventilation balance rule: total net free vent area (NFVA) is split roughly 50/50 between intake (soffit/eave) and exhaust (ridge/static). Net free area is the vent's stated NFVA, not its gross opening size.

Ice dam control: ice barrier membrane is required along eaves in cold climates, extending from the eave edge inward to at least 24 inches past the interior line of the exterior wall.

Flashing failure points on residential roofs: step flashing at sidewalls, counterflashing at chimneys, valley metal, pipe boots, and kick-out flashing where a roof meets a wall above a lower roof.

Fastener rules for asphalt shingles: nails must penetrate at least 3/4 inch into solid decking or through the deck; high-nail placement (above the nail line) is a common cause of shingle blow-off and is a defect.

Decking: minimum 5/8-inch plywood or OSB is common; gaps between panels of 1/8 inch allow expansion. Soft, delaminated, or rotted decking must be replaced, not covered.

Valley types: open metal valley, closed-cut valley, and woven valley. Closed-cut and woven are not permitted on slopes below the manufacturer's stated minimum for those methods.

Low-slope commercial roofs are defined as less than 3:12 (some codes use 2:12 as the membrane threshold); steep-slope is 3:12 and above. Membrane selection follows slope, not just building type.

TPO and PVC are thermoplastic single-ply membranes joined by hot-air welding; EPDM is thermoset and joined with adhesive or tape. Weld seams are tested with a probe or seam tester, not by visual inspection alone.

Modified bitumen is applied in plies (often base plus cap sheet) by torch, hot-mop, or self-adhered methods. Torch application requires a fire watch and is restricted near combustibles.

Built-up roofing (BUR) consists of alternating layers of felt and bitumen topped with surfacing (gravel, cap sheet, or coating). Ply count and surfacing determine the membrane's durability and warranty class.

Roof drains and scuppers: primary drainage plus secondary (emergency) drainage is required by code on most commercial roofs. Ponding water is a defect when it persists more than 48 hours after rain.

Insulation attachment: mechanically fastened, adhered, or ballasted. Ballasted systems rely on paver or aggregate weight and require a perimeter zone with additional ballast for wind uplift resistance.

Roof curbs, expansion joints, and penetration details require a minimum 8-inch curb height above the roof surface for many HVAC units, and flashing height is measured from the finished roof surface, not the deck.

Recover vs. tear-off: a recover adds a new membrane over the existing roof; most codes limit to one recover and require tear-off when the existing roof is wet, blistered, or already has two layers.

Wind pressure on a roof is proportional to the square of wind speed (dynamic pressure q = 0.00256 × V² in psf at standard conditions). Doubling wind speed quadruples the pressure.

Roof zones for wind uplift: field, edge, and corner. Corner zones see the highest uplift coefficients, edge zones next, field lowest. Damage patterns follow these zones.

Uplift is negative pressure: wind flowing over a roof creates suction that pulls the covering upward. Missing shingles or membrane are often torn, not pushed in, and creased or flipped tabs indicate uplift.

Fastener pull-through and shiner (missed nail) patterns are the leading causes of wind blow-off on shingle roofs. Shiner nails and high nails are installation defects, not storm damage.

Wind-borne debris causes impact damage (dents, punctures, granule loss). Impact marks on metal or membrane, and granule displacement on shingles, are documented with close-up photos and measurements.

Membrane billowing and seam peel on single-ply roofs are wind damage indicators. Check seam edges for peeling, and check perimeter edge metal for lifting, fastener withdrawal, and deformation.

Direction of damage helps establish wind direction: shingles torn from the windward edge and creased toward leeward, or edge metal bent in the direction of flow. Document with orientation notes.

Wind speed estimation from damage is approximate; use a damage indicator scale (such as a roof-covering damage scale) alongside weather data rather than relying on visual estimates alone.