Metal coping is the cap that sits on top of a parapet wall, shedding water away from both faces. When it's installed correctly it's invisible — water drains cleanly and the wall stays dry for decades. When it's installed incorrectly, water infiltrates behind the roofing membrane, down the wall cavity, and into the building. This guide covers the full installation sequence, the critical dimensions, and the details that fail most often in the field.
Understanding the Coping Profile
A parapet coping cap has three functional parts:
- Top flat — the horizontal face that spans the full wall width, with slope built in to shed water
- Exterior face leg — drops down the outside of the wall, typically 2½" to 4", with a hemmed drip edge at the bottom
- Interior face leg — drops down the interior (roof-side) face, typically 2½" to 3½"
The top flat should have a minimum 1/8" per foot slope toward the roof side. This keeps water from ponding on top and directs it toward the roof drain system rather than over the exterior face.
Spec note: SMACNA recommends a minimum 1/8" per foot cross-slope on coping. For walls wider than 18", consider increasing to 3/16" per foot to ensure drainage at the center of the cap.
Key Dimensions to Measure Before Ordering
| Dimension | What to Measure | Notes |
|---|---|---|
| Wall width | Top of parapet, face to face | Measure at multiple points — walls are rarely perfectly uniform |
| Exterior face height | From top of wall to desired drip edge termination | Minimum 2" below top of wall finish |
| Interior face height | From top of wall down to top of roofing membrane | Must overlap membrane termination by at least 2" |
| Linear footage | Total run of parapet requiring coping | Measure and add 5–10% for corner pieces and waste |
| Corner angles | Interior and exterior corner angles in degrees | Most are 90°, but mitered corners require custom pieces |
Cleat System
Coping caps are not fastened directly through the top — that would create fastener penetrations on the most water-exposed surface. Instead, they are held in place by a continuous cleat system.
How Cleats Work
A continuous metal cleat (typically the same gauge and material as the coping) is screwed to the top of the parapet wall along each face. The coping cap snaps or locks over the cleat hem, holding the cap down without any through-fasteners in the top flat.
Cleat Fastener Spacing
Fasten the cleat to the substrate at maximum 12" on center. In high-wind zones (ASCE 7 exposure C or D, or coastal locations), reduce spacing to 6" on center. Use appropriate fasteners for the substrate — wood screws for blocking, concrete anchors or powder-actuated fasteners for CMU.
Wind uplift: Parapet coping has a large surface area exposed to wind. In any location with design wind speeds above 90 mph, verify cleat spacing against local code requirements. Many failures happen because standard 12" spacing is used in high-wind locations that require 6".
Cleat Material
Use the same alloy as the coping to prevent galvanic corrosion. Steel coping gets steel cleats; aluminum coping gets aluminum cleats. Never attach aluminum coping to galvanized steel cleats without an isolation membrane — the contact point will corrode.
Joint Details
Coping sections are typically fabricated in 10' lengths. Joints between sections are the most common source of leaks and must be detailed correctly.
Slip Joint (Expansion Joint)
Standard joints should be designed as slip joints — one section telescopes under the next by 1½" to 2". This allows thermal expansion without buckling or opening the joint. The overlap direction should shed water: the upstream section laps under the downstream section.
Joint Sealant
Apply a bead of polyurethane or silicone sealant inside the overlap before sliding sections together. Do not fully bed the joint in sealant — a single bead on each side allows expansion while sealing the water path. Over-sealing locks the joint and causes buckling.
Fixed Points
One section per run should be fixed (screwed through the coping into the wall) to control the direction of thermal movement. All other sections should float. Without a fixed point, thermal movement is unpredictable and joints can migrate until they open.
Corner Pieces
Corners require either factory-fabricated mitered corners or field-formed pieces. Factory corners are more consistent and watertight. Field-formed corners are acceptable for inside corners but problematic for outside corners, where water concentrates.
- Outside corners: Use factory-fabricated 90° corner caps. They wrap continuously around the corner without seams at the peak water concentration point.
- Inside corners: Either factory corners or a properly lapped field joint with sealant.
- Non-90° corners: Require custom-mitered pieces. Field-mitering is imprecise — order custom from the fabricator with the measured angle.
End Caps and Terminations
Every open end of a coping run needs a closed end cap. End caps are typically field-fabricated from the same material, or ordered as matching pieces. They should be set in sealant and mechanically fastened to prevent uplift.
Where coping terminates at a roof penetration, wall, or parapet step, flash the termination with a counterflashing piece that laps over the coping end and integrates with the wall waterproofing system.
Common Installation Mistakes
- Through-fastening the top flat. Any screw through the top flat creates a water path. Use cleats — they exist for this reason.
- Insufficient interior leg overlap on membrane. The interior leg must lap at least 2" over the roofing membrane termination. Less than 2" and capillary action can pull water under the coping in driving rain.
- Joints lapped the wrong direction. Always confirm that upstream joints lap under downstream sections relative to water flow.
- Skipping the fixed point. Without a fixed fastening point, the coping will migrate at joints over seasonal temperature cycles and eventually open gaps.
- Wrong material combination. Aluminum coping on a steel substrate (or the reverse) without galvanic isolation will corrode at contact points within 2–5 years.
Ordering Custom Coping with the Right Dimensions
The most common ordering mistake is specifying only the wall width. A complete coping order requires: wall width, exterior face leg height, interior face leg height, material (gauge and coating), linear footage, number and type of corners, and whether end caps are needed. Missing any of these leads to back-and-forth with the fabricator that adds days to the lead time.
Trimgy's drawing canvas lets you lay out the exact coping cross-section — wall width, leg heights, hem type — see the developed width before ordering, and get a confirmed price with freight included. Draw your coping profile now →
Frequently Asked Questions
What is the correct cleat spacing for metal coping installation?
SMACNA specifies continuous cleats fastened at 12 inches on center maximum for standard wind exposure conditions, and 6 inches on center in high-wind zones (coastal areas or regions with design wind speeds above 120 mph). Cleats should be the same material and gauge as the coping cap to prevent galvanic corrosion. The coping cap locks over the cleat rather than being fastened directly through the top flat — this allows for thermal movement and keeps fasteners out of the weather.
How much should metal coping sections overlap at joints?
SMACNA recommends a minimum 3-inch overlap at coping joints, with the lapped joint oriented so the upslope piece laps over the downslope piece. At corners, factory-fabricated mitered corner caps are preferred over field-cut corners. The joint should be sealed with a polyurethane or modified silicone sealant compatible with the coping material, applied as a bead under the overlap — not as a surface-applied cap bead that can fail and allow water to track under.
What is the minimum gauge for metal coping on a parapet wall?
Per SMACNA Architectural Sheet Metal Manual, 7th Edition: for steel coping with a face dimension up to 12 inches, the minimum gauge is 24 ga. For coping with face dimensions over 12 inches, 22 ga. is recommended. For aluminum, the minimums are .032 inches for caps under 12 inches and .040 inches for wider caps. Lighter gauges increase the risk of oil-canning, wind uplift, and long-term fatigue at the bend lines.
Do I need inside corners or outside corners fabricated separately?
Yes. Inside and outside corners on parapet walls are the most complex coping detail. Factory-fabricated corner caps — mitered or box corners — are strongly preferred over field-cut corners. Field-cut corners require skilled sheet metal work to achieve a watertight result; factory corners are fabricated from a single piece with no exposed joints at the corner. When ordering coping through Trimgy, note the number and type of corners so the fabricator can include matching corner pieces.