NRCA Metal Flashings cheat sheet

Copper: solders and brazes readily, develops a protective patina; runoff stains light masonry and accelerates corrosion of zinc and aluminum below it.

Stainless steel Type 304 is standard for flashing; Type 316 resists chlorides and coastal salt spray better at higher cost.

Aluminum forms a self-healing oxide film but is amphoteric: it corrodes in both acidic and alkaline conditions and must not contact copper, brass, or bare steel.

Zinc (alloy to EN 988 / ASTM B69) requires a minimum slope near 1:12 in many details, needs ventilation beneath, and must be isolated from copper, lead, and steel.

Lead is used for its malleability and acid resistance but is heavy, low strength, and toxic; it is incompatible in contact with fresh lime mortar and copper.

Terne and terne-coated stainless carry a lead-tin alloy coating; galvanized steel (G90, G115) is the low-cost baseline but has the shortest service life.

Kynar 500/PVDF coil coatings on steel and aluminum resist chalking and fading; cut edges and field-formed bends expose bare metal and need touch-up.

Dissimilar metals ranked on the galvanic series: anodic metals (zinc, aluminum, mild steel) corrode when coupled to cathodic metals (copper, stainless) in moisture.

Sheet metal gauges differ by metal: copper is specified by ounce weight (16 oz = 0.0216 in), steel by gauge number, zinc by thickness in mm.

Bend allowance = (π/180) × bend angle × (inside radius + K × thickness); set back the flat pattern accordingly before cutting.

Minimum bend radius varies by temper: soft copper and lead bend tight, while hard-temper aluminum and stainless crack and need larger radii.

Soldering copper uses 50/50 or 95/5 tin-antimony with an acid or rosin flux; joints must be clean, tight-lapped, and flux residue removed to prevent corrosion.

Brazing and welding of stainless require shielding gas (TIG) or low-hydrogen processes; galvanized steel welding demands fume extraction and zinc coating repair.

Fasteners must match or be isolated from the flashing: copper nails for copper, aluminum or stainless for aluminum, and neoprene or EPDM washers under exposed heads.

Sealants: use low-modulus neutral-cure silicone or polyurethane at moving joints; do not rely on sealant as the primary water barrier in concealed laps.

Cleat spacing and lap dimensions follow SMACNA guidance; typical standing-seam and cap-flashing cleats are spaced 12 in on center maximum.

Gutter sizing follows rainfall intensity and roof area; the rational method Q = C × I × A converts to flow, and manufacturer tables set gutter cross-section.

Downspout capacity: one 3 in round leader handles roughly 1,000–1,200 sq ft of roof at 1 in/hr rainfall; rectangular leaders are sized by equivalent area.

Expansion joints in long gutter runs use slip joints or expansion-joint covers; allow roughly 1/8 in movement per 10 ft of run for copper.

Scuppers and overflow provisions are required where parapets can pond water; secondary drainage must be independent of the primary system.

Conductor heads and leader strainers keep debris out; concealed leaders inside walls need cleanouts and must not be embedded in masonry without sleeves.

Gutter hangers: strap or bracket spacing is typically 24–36 in on center, closer in snow-load regions, and must permit thermal movement.

Splash blocks and downspout discharge must direct water away from foundations; below-grade leaders need footing drains, not direct soil discharge.

Vent stack and pipe flashings: use a two-piece assembly with a base flange and a counterflashing collar; the base laps over the roof membrane and the top clamps the pipe.

Curbs for skylights and equipment must be a minimum of 8 in above the finished roof, higher in snow country, with a wood or metal nailer and an inside cant.

Chimney flashings use base, step, cap, and counterflashing components; masonry chimneys need a reglet cut or a surface-mounted counterflashing.

Skylight curbs require a continuous metal cap and a weep path; condensation gutters inside the curb prevent interior water staining.

Equipment supports must not penetrate the membrane without a curb; pipe supports and strut stands need flashing collars or pitch pans with gravel stop.

Pitch pans are a last resort: fill with compatible sealant or gravel, inspect and replenish, and prefer a manufactured boot where the pipe is round.

Lead or soft-metal flashing is used at round penetrations and where movement occurs; the top edge must be turned into a reglet or clamped.

Through-wall flashing must lap shingle-style, with the upper piece over the lower, and extend to the exterior face with a drip.

Reglets: cut or cast a minimum 3/4 in deep groove and set flashing with a sealant or lead wedge; stainless or copper spring-lock reglets are common.

Counterflashing laps the base flashing a minimum of 4 in and must terminate in a reglet or be surface-mounted with a sealant bead at the top.

Coping covers the parapet wall and must have a drip on both faces, with concealed clips or cleats allowing thermal movement.

Weep holes or vents in the wall above through-wall flashing allow moisture to escape; space them 24–32 in on center.

Cavity wall flashing must integrate with the air/vapor barrier and the weep system; end dams at terminations prevent lateral water migration.

Parapet terminations: cap flashing must slope to drain, and the wall under the coping needs a continuous air barrier to avoid condensation.

Base flashing height above the roof surface is typically 8 in minimum, with a 4 in minimum vertical lap over the membrane.

Edge metal must be fastened at the drip edge with cleats or a nailed termination bar; fasteners spaced 6–12 in on center depending on wind uplift.

Drip edges need a minimum 1/4 in standoff or a kick-out to shed water clear of the wall and fascia.

Gravel stops retain ballast and provide a finished edge; they must have a continuous cleat and a sealed lap at corners.

Roof-to-wall transitions use a cant strip or fillet at the base; the flashing must not bridge a gap or be stretched across a change in plane.

Termination bars clamp the membrane edge and are sealed; use a compatible sealant and stagger fasteners to avoid a continuous split.

Wind uplift ratings for edge metal come from code-referenced test standards; the edge metal, fasteners, and substrate must be evaluated as a system.

Galvanic corrosion requires an electrolyte, an anode, a cathode, and electrical contact; removing any one stops the cell.

The greater the potential difference on the galvanic series, the faster the anodic metal corrodes; copper coupled to aluminum is a severe pair.

Isolate dissimilar metals with a barrier: bituminous coating, EPDM or neoprene tape, plastic washers, or a stainless fastener with an insulating sleeve.

Runoff is a hidden path: copper above zinc or aluminum carries dissolved copper ions and causes pitting even without direct contact.

Fasteners are the most common failure: use stainless or hot-dip galvanized fasteners compatible with the flashing, and never bare steel into copper.

Electrolytic corrosion is accelerated by chlorides, acids, and standing water; keep joints dry and sloped to drain.

Graphitic corrosion of cast iron and dezincification of brass occur in aggressive soils and waters; specify resistant alloys in these environments.

IBC Chapter 15 governs roof assemblies; flashing requirements reference ASTM and SMACNA standards and manufacturer installation instructions.

Fall protection: OSHA 1926.501 requires guardrails, nets, or personal fall arrest at 6 ft above a lower level in construction.

Hot work for soldering and brazing requires a permit, a fire watch, and clearance from combustibles; soldering near membrane needs a heat shield.

Lead exposure: cut, wash hands, and use respiratory protection when grinding or abrading lead-coated metals; do not eat or smoke in the work area.

Ladder and roof access: secure ladders, use roof jacks or staging, and never stand on a cleat or gutter as a step.

Manufacturer instructions control warranty: fastener type, spacing, sealant, and substrate preparation must match the published installation manual.

Material safety data sheets for fluxes, sealants, and coatings must be on site; acid flux is corrosive and requires eye and skin protection.

Expansion joints in metal roofing and flashing accommodate thermal movement: allow roughly 1/8 in per 10 ft of copper run.

Overflow scuppers must be sized to pass the design storm flow and be located at least 2 in above the primary drain or roof low point.

Secondary drainage must be independent of the primary system and discharge to a visible location so blockage is noticed.

Expansion-joint covers use a sliding lap with a sealant or a formed bellows; the joint must allow movement in all directions.

Ponding occurs when the roof slope is less than 1/4 in per foot; overflow provisions must be sized for the ponding depth.

Drainage calculations use the 100-year, 1-hour rainfall intensity for the site; check local amendments to the plumbing code.

Scupper and overflow openings must be protected with a screen or grate to prevent debris blockage.

Gutter sizing follows rainfall intensity and roof area; the rational method Q = C × I × A converts to flow, and manufacturer tables set gutter cross-section.

Downspout capacity: one 3 in round leader handles roughly 1,000–1,200 sq ft of roof at 1 in/hr rainfall; rectangular leaders are sized by equivalent area.

Expansion joints in long gutter runs use slip joints or expansion-joint covers; allow roughly 1/8 in movement per 10 ft of run for copper.

Scuppers and overflow provisions are required where parapets can pond water; secondary drainage must be independent of the primary system.

Conductor heads and leader strainers keep debris out; concealed leaders inside walls need cleanouts and must not be embedded in masonry without sleeves.

Gutter hangers: strap or bracket spacing is typically 24–36 in on center, closer in snow-load regions, and must permit thermal movement.

Splash blocks and downspout discharge must direct water away from foundations; below-grade leaders need footing drains, not direct soil discharge.

Vent stack and pipe flashings: use a two-piece assembly with a base flange and a counterflashing collar; the base laps over the roof membrane and the top clamps the pipe.

Curbs for skylights and equipment must be a minimum of 8 in above the finished roof, higher in snow country, with a wood or metal nailer and an inside cant.

Chimney flashings use base, step, cap, and counterflashing components; masonry chimneys need a reglet cut or a surface-mounted counterflashing.

Skylight curbs require a continuous metal cap and a weep path; condensation gutters inside the curb prevent interior water staining.

Equipment supports must not penetrate the membrane without a curb; pipe supports and strut stands need flashing collars or pitch pans with gravel stop.

Pitch pans are a last resort: fill with compatible sealant or gravel, inspect and replenish, and prefer a manufactured boot where the pipe is round.

Lead or soft-metal flashing is used at round penetrations and where movement occurs; the top edge must be turned into a reglet or clamped.

Through-wall flashing must lap shingle-style, with the upper piece over the lower, and extend to the exterior face with a drip.

Reglets: cut or cast a minimum 3/4 in deep groove and set flashing with a sealant or lead wedge; stainless or copper spring-lock reglets are common.

Counterflashing laps the base flashing a minimum of 4 in and must terminate in a reglet or be surface-mounted with a sealant bead at the top.

Coping covers the parapet wall and must have a drip on both faces, with concealed clips or cleats allowing thermal movement.

Weep holes or vents in the wall above through-wall flashing allow moisture to escape; space them 24–32 in on center.

Cavity wall flashing must integrate with the air/vapor barrier and the weep system; end dams at terminations prevent lateral water migration.

Parapet terminations: cap flashing must slope to drain, and the wall under the coping needs a continuous air barrier to avoid condensation.

Base flashing height above the roof surface is typically 8 in minimum, with a 4 in minimum vertical lap over the membrane.

Edge metal must be fastened at the drip edge with cleats or a nailed termination bar; fasteners spaced 6–12 in on center depending on wind uplift.

Drip edges need a minimum 1/4 in standoff or a kick-out to shed water clear of the wall and fascia.

Gravel stops retain ballast and provide a finished edge; they must have a continuous cleat and a sealed lap at corners.

Roof-to-wall transitions use a cant strip or fillet at the base; the flashing must not bridge a gap or be stretched across a change in plane.

Termination bars clamp the membrane edge and are sealed; use a compatible sealant and stagger fasteners to avoid a continuous split.

Wind uplift ratings for edge metal come from code-referenced test standards; the edge metal, fasteners, and substrate must be evaluated as a system.

Galvanic corrosion requires an electrolyte, an anode, a cathode, and electrical contact; removing any one stops the cell.

The greater the potential difference on the galvanic series, the faster the anodic metal corrodes; copper coupled to aluminum is a severe pair.

Isolate dissimilar metals with a barrier: bituminous coating, EPDM or neoprene tape, plastic washers, or a stainless fastener with an insulating sleeve.

Runoff is a hidden path: copper above zinc or aluminum carries dissolved copper ions and causes pitting even without direct contact.

Fasteners are the most common failure: use stainless or hot-dip galvanized fasteners compatible with the flashing, and never bare steel into copper.

Electrolytic corrosion is accelerated by chlorides, acids, and standing water; keep joints dry and sloped to drain.

Graphitic corrosion of cast iron and dezincification of brass occur in aggressive soils and waters; specify resistant alloys in these environments.

IBC Chapter 15 governs roof assemblies; flashing requirements reference ASTM and SMACNA standards and manufacturer installation instructions.

Fall protection: OSHA 1926.501 requires guardrails, nets, or personal fall arrest at 6 ft above a lower level in construction.

Hot work for soldering and brazing requires a permit, a fire watch, and clearance from combustibles; soldering near membrane needs a heat shield.

Lead exposure: cut, wash hands, and use respiratory protection when grinding or abrading lead-coated metals; do not eat or smoke in the work area.

Ladder and roof access: secure ladders, use roof jacks or staging, and never stand on a cleat or gutter as a step.

Manufacturer instructions control warranty: fastener type, spacing, sealant, and substrate preparation must match the published installation manual.

Material safety data sheets for fluxes, sealants, and coatings must be on site; acid flux is corrosive and requires eye and skin protection.