Snap-Lock Metal Roofing Panel Installation Guide

Snap a chalk line parallel to the eave approximately 24 inches from the roof edge. This line will serve as your baseline reference.

Select a datum point on the alignment line near the gable edge. From this point, create a 12-foot arc extending toward the ridge.

Measure 9 feet along the alignment line from the datum point and mark a reference point. 

From the reference point, create a 15-foot arc until it intersects the 12-foot arc. Snap a chalk line from the datum point through the arc intersection. This establishes a square alignment line for the first panel.

Where valleys are present, establish valley centerlines before panel installation. Since underlayment may conceal these locations, clearly mark valley alignment lines to ensure proper placement of valley flashing and adjacent panels.

The first panel controls the alignment of the entire roof system. Verify all measurements befoe installation. Even minor alignment errors at the starting point can compound across the roof and affect panel appearance, flashing fitment, and overall installation quality.

The framing square method is a quick and effective way to establish a straight starting point for panel installation. Begin by

establishing a straight reference line along the eave. After eave flashing has been installed, position the first panel and use a

framing square to verify the panel is square to the eave and alignment line.

Once properly aligned, secure the panel with temporary fasteners at the top and bottom. Install the next panel and verify

alignment before proceeding with the remainder of the roof.

Verify the first panel remains square to the eave. Check the distance between the panel edge and gable edge throughout the roof length. Minor variations can typically be accommodated by gable trim. Significant out-of-square conditions may require ripping the first or last panel to maintain a straight appearance.

In situations where the roof is substantially out of square, custom trim or alternative flashing details may be required.

Prow roofs require additional layout attention due to the angled roof geometry. Establish the centerline and verify all dimensions before panel installation.

Install the first panel using a verified reference line. Confirm alignment at both the eave and prow before installing additional panels. Panels may require field trimming to maintain consistent panel spacing and visual alignment.

The accuracy of the first panel is critical, as any alignment error will be amplified across the roof surface.

Before installing full-length panels, verify panel alignment at the eave, confirm panel spacing is consistent, check that the panel remains square to the established reference line, and make adjustments early to avoid cumulative alignment issues.

When properly aligned, the first full-length panel will establish the reference for the remainder of the roof system.

Hip roofs present unique alignment challenges and require careful planning before installation. Establish the centerline of the roof and install a reversing strip or center reference point. Begin installation from the center and work outward in both directions while continuously verifying panel spacing and alignment.

An alternative method is to begin with a longer panel positioned near the center of the roof area. Verify alignment using either the 3-4-5 Triangle Method or Framing Square Method. Install the remaining panels working back toward the shorter roof sections.

The S3 Metals Reversing Strip allows Snap-Lock panels to be installed in opposing directions from a common centerline. This method is most commonly used on hip roof applications to maintain panel balance and alignment, but it may also be used on other roof configurations where installation from a center reference point is preferred.

Locate and mark the centerline of the roof section using either the 3-4-5 Triangle Method or the Framing Square Method.

Snap a straight chalk line perpendicular to the eave. The accuracy of this line is critical, as it will serve as the reference point for aligning the panels on both sides.

Position the reversing strip along the centerline and fasten it securely to the roof deck using approved wafer head fasteners spaced 18" to 24" on center.

Position the first panel so the female locking rib engages the lip of the reversing strip.

Pull the panel firmly into position and fasten the panel according to S3 Metals installation requirements.

Verify alignment before proceeding with additional panels.

Install the next panel in the opposite direction, engaging the female locking rib over the corresponding rib of the previously installed panel.

Apply firm downward pressure until the panel is fully seated and locked into position. Secure the panel using the recommended fastening method.

Continue installation outward from the centerline while periodically checking panel alignment.

The reversing strip allows installers to work from the center of the roof toward both edges, helping maintain balanced panel layout and reducing alignment issues on complex roof designs.

Before using a reversing strip, verify that all panels, accessories, and flashing details are compatible with this installation method. Improper use may affect panel fitment, appearance, and overall system performance.

At the top of each panel, create the required relief cuts at both panel edges as shown in the applicable detail drawings. After making the cuts, use an approved bending tool to turn the panel pan upward slightly beyond 90 degrees.

The upended section acts as a water stop, helping prevent moisture intrusion at the upper termination of the panel system. Seal all exposed openings created by the upend process with an approved sealant to maintain a weather-tight assembly.

At the eave end of the panel, trim the corner of the fastening flange as shown in the detail drawings. This trim improves appearance and allows proper fitment of adjacent trim and flashing components.

For roof slopes below 3:12, additional panel preparation may be required to improve water management at the eave.

Using an approved bending tool, form an open hem by bending the panel pan downward and back underneath itself at the eave end. This detail helps reduce the potential for water wicking or siphoning beneath the panel. When using this method, allow additional panel length as required to accommodate the hem detail.

As an alternative, a slight downward bend may be formed at the eave end of the panel to create a drip edge. This detail encourages water to shed cleanly away from the panel edge and eave flashing.

S3 Metals recommends a minimum roof slope of 3:12 for Snap-Lock panel systems. Projects with roof slopes below 3:12 should be reviewed prior to fabrication to ensure appropriate panel preparation, flashing details, sealant requirements, and installation methods are incorporated into the design.

Before installing panels, verify that all required roof preparation has been completed. This includes installation of the approved underlayment, eave flashing, valley flashing, gable flashing, and any other trim or flashing components required for the specific roof design.

Carefully verify all roof dimensions. Roofs are rarely perfectly square, and minor dimensional differences from one end of the roof to the other are common.

Proper layout planning before installation can help minimize narrow panel conditions and improve the overall appearance of the finished roof.

When working on roofs that are out of square:

Consider adjusting panel layout, panel widths, or flashing details to maintain a balanced and professional appearance across the roof system.

Inspect all panels and accessories prior to installation. If any material appears damaged, defective, or incorrect, stop installation immediately and contact S3 Metals.

Installing damaged or defective materials may affect roof performance and may limit warranty coverage. S3 Metals must be given the opportunity to review and resolve any material concerns before replacement materials are provided.

Panels may be installed from left to right or right to left depending on project conditions and installer preference.

Determine the installation direction before preparing or installing the first panel.

Align the first panel with the established layout line at the gable edge. Position the panel to provide the required eave overhang specified in the applicable flashing details.

Apply sealant where required by the flashing detail and fasten the panel according to S3 Metals installation requirements. Verify the panel is square and properly aligned before proceeding.

Apply sealant where required by the applicable flashing detail.

Position the female rib of the next panel over the male rib of the previously installed panel. Engage the locking ribs and apply firm, even pressure until the panel is fully seated and locked into position.

Panels may be locked using hand pressure, foot pressure, or a non-marring rubber mallet as necessary. Always work from the eave toward the ridge while verifying proper engagement of the locking ribs.

Once the panel is fully seated and aligned, install the required fasteners. Continue this process for each successive panel, periodically checking panel alignment and roof layout to ensure a straight, consistent installation.

Proper alignment of the first panel is critical. Small alignment errors at the beginning of installation can become magnified as additional panels are installed across the roof.

Install panels with the required upend detail at the ridge or hip termination. Apply sealant at all exposed corners and panel openings as required.

Notch the hip or ridge cap as necessary to fit over panel ribs and maintain proper alignment. Use snips or approved cutting tools to create clean, accurate notches.

Allow the hip or ridge cap to overhang the lower edge a minimum of 1-1/2" unless otherwise specified by project requirements.

At hips, box and close the lower end of the ridge cap to match the roof angle and provide a finished appearance.

Overlap successive ridge cap sections a minimum of 2" to 3", working from the lower elevation toward the higher elevation. Apply sealant at all lap joints before fastening.

Fasten the hip or ridge cap using approved color-matched fasteners, stitch screws, or rivets as required by the application. Fasteners should be installed at each panel rib or as specified in the project details.

Secure valley flashing by fastening near the outer hem edge whenever possible. Fasteners should be spaced approximately 18"–24" on center along both sides. Seal all exposed fastener heads with approved sealant.

When joining valley sections, trim the hem back approximately 6" on each side of the overlapping section. Apply three continuous 1/4" beads of sealant between overlapping valley flashings.

Extend valley flashing over the ridge where required by project conditions.

Trim roof panels so they terminate a minimum of 4" from the centerline of the valley.

Remove all metal burrs and filings from cut panel edges immediately after cutting to help prevent corrosion and surface damage.

If panel crowning occurs near the valley, back-bend the panel or use an appropriate panel-ending tool to create a downward bend of approximately 30 degrees.

Apply butyl tape or a continuous 1/4" bead of sealant approximately 1" from the panel edge before installation.

For wide-valley applications, panel setbacks may be increased based on climate conditions and anticipated water flow. Position butyl tape approximately 1" from the panel end.

In areas subject to heavy snow loads, wider valley pans and increased clearance from the valley centerline are recommended to improve drainage performance.

Wide valley flashings should be considered for low-slope roof applications.

Apply a continuous bead of sealant along the top of valley flashing hems before panel installation.

Fasten roof panels through the valley fastening flange into the substrate as close to the hemmed edge as practical. Do not install panel fasteners through the water-carrying portion of the valley flashing.

Installation methods may vary based on roof design, panel profile, climate conditions, and applicable building codes. Buyer and installer are solely responsible for verifying proper installation methods. S3 Metals supplies materials only and assumes no responsibility for installation, field measurements, workmanship, or project performance.

These instructions apply to most standard skylight and chimney installations. Some applications may require custom flashing or additional installation measures. Always confirm the approved flashing requirements with the skylight manufacturer, as deviations may affect the product warranty.

A cricket may be recommended when water drains toward a curb wider than 24 inches or where debris is likely to collect. Crickets are custom-fabricated to fit the curb or chimney and are installed in place of the head flashing. The installation method for both components is generally the same.

Step 1: Working from left to right, cut to fit, bend, and install panel #1.

Step 2: Cut to fit, bend, and install panel Install additional panels as normal between panels #1 and #2, as needed to cover the width of the skylight/chimney opening.

Step 3: The next piece to install is head flashing #3. First, place a bead of skinning butyl sealant on top of panels #1 and #2 to prevent water from siphoning at the joint.  Next, cut and bend the head flashing to fit. The artificial ribs should be ½" high. Set and fasten the head flashing.

Working from left to right, cut panel #4 to fit, snap it into place, and fasten as normal.

Cut panel #5 to fit, install, and fasten as normal. Install additional panels between panels #4 and #5 as needed to cover the width of the skylight or chimney opening.

Install bottom flashing #6 using the same method as standard End Wall flashing. Next, install sidewall flashing #7 and #8 along each side of the curb to complete the skylight flashing assembly.

Use skinning butyl sealant at all joints and metal overlaps to help prevent water intrusion. Careful installation and attention to flashing details will directly affect the final appearance and performance of the system.

The information provided above is intended as a general installation guideline and is not the only acceptable method for flashing a skylight.