NRCA Metal Shingle common mistakes
NRCA Metal Shingle · Understand the traps and how to avoid them.
Treating metal shingles as interchangeable with asphalt shingles when selecting underlayment, fasteners, and clips, rather than pulling the specific manufacturer's installation manual and checking the approved component list for that exact product profile.
Candidates study generic steep-slope roofing practice and assume the principles transfer; each metal shingle system has proprietary clips, gauges, and underlayment requirements, and exam questions are written to the product-specification level.
What to do instead
For each product family, memorize the manufacturer's required underlayment type, fastener type and length, clip spacing, and minimum slope. Practice answering 'what does the manufacturer require' rather than 'what is typical practice.'
Skipping or misapplying fall protection planning on steep-slope metal roofs, e.g., assuming a roof anchor is acceptable without verifying it is rated for the slope, or forgetting that metal shingle surfaces and new panels are slippery and require guardrail or personal fall arrest systems rather than relying on roof jacks alone.
Candidates conflate residential asphalt-roof practice with metal roofing and underestimate that OSHA-style fall protection triggers at low heights and that metal surfaces behave differently underfoot.
What to do instead
Learn the fall-protection hierarchy (guardrail, safety net, personal fall arrest, warning line) and the trigger heights and slope thresholds. Know anchor ratings, lanyard and harness inspection, and that roof brackets must be installed without damaging the metal panels.
Installing underlayment without a proper ice dam protection membrane at the eaves, or lapping underlayment the wrong direction and amount, and failing to account for high-temperature metal roofs that require a specific high-temp underlayment rather than standard felt.
Candidates memorize 'ice and water shield at eaves' but not the specific eave-to-eave extent, the high-temperature requirement for metal, or the correct lap orientation and headlap for the slope.
What to do instead
Memorize the ice dam membrane extent (typically from the eave to at least 24 inches inside the warm wall line, and per local code), the high-temp underlayment requirement for metal, and the correct lap orientation and amount by slope. Practice slope-based lap tables.
Starting the first course without establishing a true, square reference line, then chasing misalignment across the roof, resulting in racked courses, uneven exposure, and visible shingle edges that do not line up at hips and valleys.
Candidates focus on individual shingle placement and underestimate how a small out-of-square start compounds across a large roof plane, especially where the deck or eave is not square.
What to do instead
Always snap a chalk line square to the ridge or a verified reference, check diagonal measurements, and dry-lay the first course. Learn to correct for out-of-square decks by adjusting the starter rather than the field.
Fastening metal shingles with the wrong fastener type, length, or location, e.g., using nails instead of the specified screws, overdriving or underdriving fasteners, or placing fasteners in the wrong part of the shingle so thermal movement is restricted or the shingle is not held down.
Candidates apply asphalt-shingle nailing habits (four nails in a pattern) to metal, where fastener placement is engineered and often in a specific clip or slot to allow movement.
What to do instead
Memorize the manufacturer's fastener schedule: type, length, thread, washer, number per shingle, and exact location (e.g., in the clip, in the slot, at the overlap). Learn to set the driver clutch so the fastener seats without dimpling the metal.
Detailing valleys, hips, and ridges with generic flashing or by cutting and lapping shingles without the manufacturer's specific valley metal, hip and ridge caps, or without maintaining the required clearance and lap for the metal system.
Candidates rely on generic flashing knowledge and do not realize that metal shingle systems have proprietary valley, hip, and ridge components and specific lap and clearance requirements to accommodate thermal movement.
What to do instead
Study the manufacturer's detail drawings for open and closed valleys, hip and ridge, and sidewall and headwall. Memorize required clearances, lap dimensions, and which components are field-fabricated versus factory-supplied.
Ignoring thermal movement by rigidly fastening panels at every point and butting shingles tight, rather than allowing the specified expansion gaps and slip joints, leading to oil-canning, buckling, or fastener fatigue.
Candidates think of metal as static and apply tight-fit carpentry instincts; thermal expansion of metal is significant over a roof length and must be designed for.
What to do instead
Learn the coefficient of thermal expansion concept, the manufacturer's required gaps at panel ends and at penetrations, and where slip joints or oversized holes are required. Practice calculating expansion over a given roof length.
Failing to balance intake and exhaust ventilation, or installing vents without accounting for the metal roof's specific venting components and the air channel above the underlayment, leading to condensation and moisture problems.
Candidates treat ventilation as a generic attic concern and miss that metal roofs need a continuous air path, correct net free area, and compatible vent types that do not compromise the roof's weathertightness.
What to do instead
Memorize the 1:150 and 1:300 ventilation ratio rules, the requirement for balanced intake and exhaust, and the manufacturer's approved vent components. Understand how the underlayment and air channel interact with venting.
Performing a final inspection by walking the roof and looking only at surface appearance, missing fastener seating, clip engagement, underlayment laps, flashing laps, and clearance at penetrations that are hidden once shingles are installed.
Candidates equate inspection with a visual pass and do not know the sequence of hold points where hidden work must be verified before it is covered.
What to do instead
Learn the hold-point inspection sequence: deck, underlayment, ice dam membrane, flashing, and fastener/clip engagement before covering. Know what to check at each stage and how to document it.
Answering code-compliance questions from memory of generic residential code without distinguishing which requirements come from the model code, which from the manufacturer's instructions (which are code-enforceable), and which are local amendments.
Candidates blur the hierarchy of code, manufacturer instructions, and local amendments, and exam questions test whether they know that manufacturer instructions are part of the code-required installation.
What to do instead
Study the code sections governing metal roofing and steep-slope installation, learn that manufacturer instructions are referenced and enforceable, and practice identifying which source governs a given requirement. Review common local amendments for ice dam and wind uplift.