NRCA Metal Shingle cheat sheet

Metal shingles are formed from coil stock; common substrates are galvanized steel (G90/G60 coating weights), Galvalume (AZ50/AZ55), aluminum, and copper; each has different corrosion and coastal suitability rules.

Minimum steel thickness for metal shingles is typically 26 gauge (0.018 in) to 24 gauge (0.024 in); aluminum is commonly 0.024–0.032 in; thinner panels dent and oil-can.

Panel profiles fall into two families: interlocking stamped shingles (horizontal courses) and modular panels that mimic slate, shake, or tile; each has its own exposure, sidelap, and endlap requirements.

Finish systems: Kynar 500/Hylar 5000 (70% PVDF) for architectural colors, SMP/polyester for economy; PVDF holds color and chalk resistance better, and coastal salt exposure demands PVDF plus appropriate substrate.

Fasteners must be manufacturer-listed and matched to substrate: self-drilling screws with EPDM or neoprene washers for wood, gasketed screws for steel purlins; mixing fastener types voids warranties.

Fastener corrosion class (e.g., 410 stainless, 304 stainless, hot-dip galvanized) must match or exceed panel metallurgy; copper panels require stainless or copper fasteners to avoid galvanic attack.

Published manufacturer data govern: exposure, minimum slope, fastener spacing, clip spacing, and wind-uplift ratings (e.g., Miami-Dade/Texas Department of Insurance listings) are product-specific and must be used over generic rules of thumb.

Metal shingles are considered a 'through-fastened' or clip-fastened system depending on product; clip systems allow thermal movement while direct-fastened systems require slotted or oversized holes.

Warranty tiers (finish vs. substrate vs. weather-tightness) differ; installation defects such as overdriven fasteners or wrong underlayment typically void weather-tightness coverage.

OSHA 1926.501(b)(13): employees on steep roofs (slope >4:12) must use fall protection; roofs 50 years old or less with slope ≤4:12 may use a warning line plus guardrail/monitor option, but metal shingle roofs are steep-slope work.

Fall protection options: guardrail systems, safety net systems, personal fall arrest systems (PFAS), or a combination; warning lines alone are not acceptable on steep slopes.

PFAS anchor points must support 5,000 lb per worker (or be designed by a qualified person with a 2:1 safety factor); anchorage, connectors, and lifeline must be inspected before each use.

Full-body harness with shock-absorbing lanyard or self-retracting lifeline; calculate total fall distance including free fall, deceleration distance, and a 3-ft safety margin above the lower level.

Ladder setup: extend 3 ft above the eave, 4:1 slope, secured at top; metal roofs are slippery - use roof brackets or a roof jack system with planks for working platforms on steep slopes.

Metal shingles and panels have sharp edges and burrs; cut-resistant gloves, safety glasses, and long sleeves are baseline PPE; coil and panel edges can slice through leather gloves.

Electrical hazards: metal roofing conducts; maintain 10-ft minimum clearance from energized overhead lines (per OSHA), and use non-conductive ladders near electrical sources.

Weather and wind: stop work when wind, rain, frost, or ice makes footing unsafe; metal surfaces become dangerously slick when wet or dusty from metal shavings.

Tool safety: use grounded or double-insulated power tools, keep cords off walk surfaces, and never leave fasteners or cutoffs on the roof where they create trip/slip hazards.

Deck must be sound, flat, and dry; replace rotted sheathing, re-nail loose boards, and correct sagging before installing underlayment or panels.

Minimum decking for metal shingles is typically 15/32-in or 7/16-in OSB or nominal 1-in wood boards, per manufacturer; some products require solid sheathing with no gapping beyond 1/8 in.

Deck fasteners must be flush or countersunk; protruding nail heads telegraph through underlayment and metal, causing oil-canning and premature wear.

Ice dam protection: an ice barrier membrane (self-adhering) is required at eaves from the eave edge to a point at least 24 in inside the exterior wall line (IRC R905.1.2), and in valleys.

Underlayment for metal shingles is typically a high-temperature synthetic (e.g., 30-lb felt equivalent or heavier) or a peel-and-stick membrane; some manufacturers require a slip sheet or separator to prevent sticking and allow movement.

Overlap underlayment per manufacturer (commonly 4–6 in side laps, 6–12 in end laps) and run it horizontally, lapping upper courses over lower courses to shed water.

Valleys and penetrations receive extra underlayment: a minimum 36-in-wide strip centered in the valley (18 in each side) or a W-rolled valley lining, per manufacturer.

Ventilation path: underlayment must not block soffit or ridge vent openings; maintain a clear air path from eave to ridge.

Fasten underlayment with cap nails or manufacturer-approved fasteners at prescribed spacing; staples alone may not meet wind or code requirements.

Establish a level chalk line at the eave and a plumb reference line at the rake or center; metal shingle courses are laid to level lines, not to the deck edge, because deck edges are rarely square.

Compute exposure and course count: divide the rafter length (or slope length) by the manufacturer's published exposure; adjust the top course or eave starter to avoid a partial course at the ridge.

Starter course: install the manufacturer's starter strip or eave trim first; the starter sets the first course height and must be level around the entire perimeter.

Horizontal alignment is maintained with chalk lines every course; vertical alignment is maintained by measuring from a fixed plumb line at intervals, not by trusting panel edges.

Fastening: place fasteners in the manufacturer's designated nailing/screw zone (typically the upper portion of the panel or the lock flange), never through the exposed face or in the water channel.

Fastener spacing typically ranges 6–12 in on center along the fastening flange, with additional fasteners at gable ends, ridges, and hips for wind uplift; follow the product's uplift listing.

Do not overdrive fasteners: the washer should be snug, not compressed past flat; overdriving deforms the panel, cracks washers, and creates leaks.

Thermal movement: clip-fastened systems allow panels to float; direct-fastened systems require slotted holes or oversized pilot holes so panels can expand and contract without buckling.

Stagger endlaps and sidelaps between courses as required by the profile; align panel locks fully engaged before fastening, and check each course for level before proceeding.

Valleys: open valleys use metal valley pans (typically 24 in wide, 12 in each side) under the shingles; closed valleys use a valley lining with shingle edges cut back to the valley centerline per manufacturer.

Valley metal must extend at least 12 in up each roof plane and be fastened at the upper edge only so it can move; do not fasten through the center of the pan.

Ridge and hip: use manufacturer's ridge cap or field-formed hip/ridge; hip flashing must lap over the shingle courses and be fastened on the concealed flange.

Sidewall flashing: step flashing (one piece per course) interleaved with the shingle courses, plus a counterflashing reglet in masonry; step flashing must lap the shingle below and be covered by the shingle above.

Headwall flashing: a single piece with a 4–6 in vertical leg and a 4–6 in horizontal leg, lapped over the top course and sealed with approved sealant; a cricket is required when a headwall width exceeds the manufacturer's threshold (commonly 30 in).

Eave and rake edge metal: eave trim or drip edge is installed under the underlayment at the eave and over the underlayment at the rake (or per manufacturer), with a drip leg that clears the fascia.

Penetrations: use manufactured boots or flashing plates matched to pipe diameter, set in sealant, with the upper flange lapped by the shingle course above; large penetrations require a curb with flashing.

Skylights and chimneys: flash with a curb, step flashing on sides, and a cricket/backer flashing on the uphill side; sealant alone is not a flashing.

Fastener and sealant rules: use only manufacturer-approved sealants (typically neutral-cure silicone or polyurethane) and place fasteners so they are covered by the next course where the profile allows.

Balanced ventilation: net free area (NFA) should be roughly equal at the eave (intake) and ridge (exhaust), typically 1 sq ft of NFA per 150 sq ft of attic floor area, or 1:300 with a vapor retarder and balanced vents (IRC R806).

Ventilation reduces condensation on the underside of metal panels and deck; without intake at the soffit, ridge vents cannot exhaust and moisture accumulates.

Thermal movement: metal expands and contracts with temperature; a 20-ft steel panel can move roughly 1/8–1/4 in over a 100°F swing (coefficient of thermal expansion ~6.5×10⁻⁶/°F for steel, ~13×10⁻⁶/°F for aluminum).

Clip-fastened systems accommodate movement by allowing panels to slide; direct-fastened systems rely on slotted holes, oversized holes, and fastener placement near the panel's fixed point.

Never fasten both ends of a long panel rigidly; fix at one point and allow movement toward the other end, or use the manufacturer's specified clip layout.

Condensation control: a vapor retarder on the warm side of the insulation, plus ventilation above the insulation, keeps the cold metal surface dry; metal roofing is a cold-deck system unless a thermal break is provided.

Thermal breaks (e.g., a rigid insulation layer or a separation sheet) reduce condensation and prevent the panel from conducting heat/cold into the structure.

Avoid trapping moisture: use breathable or properly lapped underlayment and do not sandwich the deck between two vapor-impermeable layers.

Ridge and soffit vent sizing must be confirmed against the manufacturer's and code requirements; undersized ridge venting is a common cause of attic condensation complaints.

Inspection sequence: deck condition and fastener flushness → underlayment laps and ice barrier → starter/edge metal → course level and plumb → fastener placement and engagement → flashing and valleys → ridge and vents.

Fastener inspection: check that every fastener is in the designated zone, driven straight, and snug (washer not crushed); overdriven or missed-fastener counts above the manufacturer's tolerance require repair.

Wind uplift compliance is verified against the product's listing (e.g., Miami-Dade NOA, TDI) and the required design pressure for the site; installation must match the listed fastener pattern exactly.

Code references: IRC Chapter 9 (R905.10 for metal roofing, R905.1.2 for ice barriers), IBC Chapter 15, and local amendments; manufacturer instructions govern where they are more restrictive.

Repair of a damaged shingle: remove fasteners, lift the course above, replace the panel, and re-fastener in the designated zone; do not patch with sealant alone on the exposed face.

Leak diagnosis: check penetrations, valleys, sidewalls, and fastener lines first; water often enters at a flashing lap and travels laterally along the underlayment before showing inside.

Cosmetic vs. functional defects: oil-canning, minor scratches, and color variation are often cosmetic; corrosion, loose panels, and lifted flashing are functional and warrant repair.

Documentation: photograph deck, underlayment, flashing, and fastener patterns before cover; retain manufacturer installation instructions and warranty documents for closeout.

Final inspection should confirm ventilation NFA, flashing heights, edge metal clearance, and that no fasteners penetrate the panel face or water channel.