Metal Roof Installation Guide: What Happens From Tear-Off to Final Inspection

Fastener Patterns & Pull-Out
Seam Types and Why They Matter
Final Inspection Checklist

Metal roofing is one of the most durable and longest-lasting systems available for both residential and commercial buildings — but those performance characteristics depend almost entirely on the quality of installation. A standing seam panel system installed with correct seam engagement, proper clip spacing, and tight flashing details will outlast the building’s first mortgage. The same panels installed by a crew that cuts corners on underlayment, skips seam sealing, or uses mismatched fasteners will fail in the first severe hailstorm. This guide covers the installation sequence from substrate prep through final inspection, so you know what your contractor should be doing at every stage and what to ask when they’re not.

Metal roofing can be installed over several substrate types: plywood or OSB sheathing (typical on residential and wood-framed light commercial), steel structural deck (standard on commercial low-slope), concrete deck, and — in re-roofing applications — over existing asphalt shingles (where local code permits and the structure can support the additional load). Each substrate has different preparation requirements.

On a residential re-roof over existing shingles, the decision to strip or overlay depends on three factors: the number of existing shingle layers (most jurisdictions allow a maximum of two), the condition of the sheathing underneath (soft spots indicate rot or delamination that must be repaired before metal goes on), and the edge detail requirements of the specific panel system. Standing seam profiles that require a continuous eave cleat cannot be properly installed over a raised shingle edge — stripping is the right call in those situations regardless of what the shingle count allows.

On new construction over OSB or plywood, the key prep items are ensuring the sheathing is properly fastened (ring-shank nails or screws at 6-inch field spacing and 4-inch edge spacing per the structural drawings), all penetrations are framed, and the sheathing surface is level and free of high fastener heads that would telegraph through the panel. Metal panels are less forgiving than shingles — imperfections in the substrate read through to the panel surface and become visible from the ground.

Underlayment on metal is a category of its own. Traditional felt (15 lb or 30 lb) is not the right product under metal roofing because asphalt and metal have incompatible thermal movement rates — the asphalt can bond to the metal over time, restricting the thermal expansion and contraction that metal panels are engineered to accommodate. Specify a synthetic underlayment rated specifically for metal applications, with a non-woven face that won’t stick. On steep-slope applications, a self-adhering ice-and-water membrane at eaves (minimum 24 inches up from the exterior wall line, or per local code) is required in any climate with freeze-thaw cycles — which includes Dallas and points north.

The three dominant panel profiles in the residential and light commercial market are standing seam, exposed fastener (also called through-fastener or screw-down), and metal shingles. Each has a different installation method, a different performance profile, and a different cost structure.

Standing seam: Panels with a raised seam — typically 1.5 to 2 inches tall — that interlocks with adjacent panels. Fasteners are concealed within the seam, attached via a clip that allows the panel to float and expand longitudinally without buckling. Standing seam is the premium residential and commercial choice because the concealed fastener system eliminates the primary failure mode of exposed-fastener systems (gasket degradation at fastener penetrations). Installation requires trained crews and proper seaming tools — either a manual hand seamer for short runs and complex geometry, or a mechanical seamer (electric crimping tool) for long straight runs. Mechanical seaming is faster and produces a more consistent seam engagement than hand seaming on long panels.

Exposed fastener panels (R-panel, PBR panel, corrugated): Panels with a lower profile, fastened directly through the panel face with a self-drilling screw and EPDM-gasketed washer. Less expensive to install, faster to put up, and more forgiving of installer error than standing seam — but the fasteners are the system’s primary maintenance point. EPDM gaskets have a service life of 15–20 years; after that, gaskets harden, lose compression, and allow water intrusion at the fastener hole. Exposed-fastener systems are appropriate for agricultural buildings, secondary structures, and commercial applications where budget is primary and maintenance access is easy. On a primary residence or Class A commercial building, standing seam is the defensible specification.

Metal shingles: Stamped panels sized to mimic asphalt shingles, cedar shakes, or slate tiles. Installed in courses like traditional shingles. The fastener is driven through a nailing hem at the top of each panel, concealed by the overlapping course above — a concealed fastener system without the seaming complexity of standing seam. Metal shingles are the easiest metal product to install for a crew transitioning from asphalt, which makes them more widely available but also more often installed incorrectly by crews who don’t understand the interlocking geometry.

Fastener Patterns and Pull-Out Strength

Fastener selection and pull-out strength are the engineering foundation of any metal roof — particularly in high-wind regions. For exposed-fastener panel systems, the standard fastener is a #12 or #14 self-drilling screw with an EPDM washer, driven through the panel rib (not the flat) to minimize over-compression of the gasket. On 26-gauge panels, over-torquing the fastener by even one turn can deform the steel around the hole, create a stress riser, and cause cracking within a few thermal cycles. Torque-limiting drivers are not optional on metal roofing — they are a quality-control tool that competent crews use consistently.

For standing seam with concealed clips, the clip itself is the structural fastener. Clips are attached to the substrate with two screws per clip (minimum) per the manufacturer’s FM approval. Clip spacing determines wind-uplift resistance — FM 1-90 approval (90 psf uplift) typically requires 12-inch clip spacing; FM 1-135 or higher requires 6-inch spacing or additional clip types. In DFW, Houston, and South Texas — where design wind speeds under ASCE 7-22 range from 115–130 mph depending on location — FM 1-135 minimum is the defensible specification on any commercial or high-value residential application.

Pull-out testing per ASTM E488 is the way to verify that your specific substrate (OSB type, thickness, and fastener pattern) delivers the required pull-out values at the clip locations. On lightweight steel deck, pull-out values for screw-attached clips can be substantially lower than on solid wood — a point that requires structural engineering review, not just a manufacturer’s spec sheet assumption.

Seam Types and Why They Matter

The seam is the most critical interface on any standing seam system. There are three seam types in common use:

Snap-lock seams: The two panel edges snap together under hand pressure. No mechanical seaming tool required. Seam height is typically 1.5 inches. Snap-lock is faster to install and appropriate for low-to-moderate wind zones on slopes ≥3:12. The limitation is seam retention force — under extreme uplift loading, snap-lock seams have lower resistance to seam disengagement than mechanically seamed profiles.

Mechanically seamed (single-lock): The seam is crimped 90° by an electric seaming tool. Single-lock crimping is suitable for most residential applications and moderate commercial applications. Seam retention is higher than snap-lock.

Mechanically seamed (double-lock): The seam is crimped 180° — folded over itself twice. Double-lock is the standard for commercial standing seam in hurricane and high-wind zones. It is significantly more resistant to seam disengagement under uplift than single-lock. FM-approved commercial systems in hurricane exposure categories typically require double-lock seaming.

The seaming tool must match the panel profile. Using the wrong tool on a panel — even a compatible profile from a different manufacturer — produces an inconsistent seam that looks fine on day one and fails under the first significant wind event. Verify that your contractor is using the manufacturer-approved seaming tool for the specific panel product being installed.

“We see seam failures on re-roofs where the previous contractor used a snap-lock panel in a zone that needed mechanical seaming. The insurance adjuster sees a ‘metal roof’ and assumes it’s better than shingles — but a snap-lock system installed in a 130-mph zone is not better than a properly installed shingle system. The seam type has to match the wind exposure.”

Flashing on metal roofing is where installations succeed or fail in the long run. The panel-to-wall transition, the ridge cap, the hip cap, valley treatment, and any penetration (pipe boot, curb, skylight) must be detailed to accommodate the thermal movement of the metal panels while maintaining a watertight seal. On a standing seam system, panels can move 1–3 inches longitudinally over a 40-foot run between summer peak and winter minimum temperatures — flashing details that are rigid and soldered will crack; details that use compressible sealant and sliding interfaces will last.

Ridge caps should be installed with a closure strip (foam or cellular) that fills the profile void at the panel top without restricting airflow in ventilated assemblies. The closure must compress fully against the panel without creating a stress point at the seam. Hip caps on standing seam require mitering the panels at the hip — a skill cut that separates experienced metal crews from shingle crews who picked up metal work as a side product.

Pipe boots on metal roofing are the single most common long-term leak source. The correct boot for metal is a lead or flexible flashing boot that conforms to the panel profile at the penetration, not a standard plumbing boot sized for flat shingles. Lead boots can be hand-formed to the panel profile on site; flexible EPDM boots work on moderate-pitch applications but may not maintain seal on steep slopes in freeze-thaw climates. Sealant at pipe boots should be non-hardening (butyl or silicone) — not acrylic caulk, which cracks within 3–5 years.

Final Inspection Checklist

Before accepting a metal roof installation, a thorough walkthrough should confirm:

Cut edges deserve a specific call-out. When metal panels are trimmed in the field — at hips, valleys, penetrations, or for length — the raw steel edge at the cut is exposed. Without treatment, this edge will rust within 2–3 years even on Galvalume or painted panels. Every field cut should be treated with the manufacturer’s edge sealant or color-matched touch-up paint before it’s covered by flashing. This is a 30-second step that almost never appears on a punch list but costs homeowners significant aesthetic damage when it’s skipped.

For more on selecting the right metal system for your project, see our comparison of metal roofs vs. asphalt shingles, or explore the full range of metal roof types available for residential and commercial applications.

Pro Exteriors installs standing seam, exposed fastener, and metal shingle systems across Texas, Colorado, Kansas, and Missouri. Every installation uses manufacturer-approved seaming tools and follows FM approval clip spacing — because that’s what your warranty requires.

Types of Metal Roofs: Standing Seam, Corrugated, and Metal Shingles Compared

Metal Roof Cost Guide: What to Expect Per Square Foot in 2026

Metal Roof vs. Asphalt Shingles: Which Is the Better Long-Term Investment?

For the service page this article supports, see metal roofing.