How to Measure for Snap Lock and Nail Flange Standing Seam Metal Roofing Panels

Standing seam looks clean from the street, but how do you measure for it? A couple of small details at the edges decide whether your order fits.

We make two standing seam profiles: Snap Lock Standing Seam with Striations (hidden clip) and Standing Seam with Nail Flange (a flat panel with a nail flange). Both are 24 gauge, Grade 50 steel, and both cover 16 inches per panel. The good news is that you measure for them the same way, so this one guide covers both.

Roofing with something else? We have separate guides for Tuff Rib Ag and Commercial PBR.

Tuff Rib Ag is mostly installed on 2x4 wood purlins 24 inches apart, and PBR on steel purlins 48 inches apart. Either can also go over plywood, but those are the common cases.

Standing seam is almost always installed over solid sheathing: plywood, OSB, or ZIP-system-type panels. So instead of starting from the truss or rafter, you measure from the edges of the sheathing.

These are concealed-fastener panels, so there are no exposed screws on the roof. Clips or fasteners sit at each panel joint, and the next panel covers them. At the bottom, the drip edge is fastened to the sheathing, and the lower edge of each panel is hemmed (folded tight) around the lip of the drip edge. That hem holds the bottom edge tight with no exposed fasteners. For more on how these systems differ, see standing seam vs. exposed fastener.

At the ridge: Keep the plywood back from the peak by 1 to 1.5 inches at most on each side. Measure from the center of the ridge pole, or from where the top chords of the truss meet. Two inches is too much for this profile. The panels are installed flush with the top edge of the plywood, so they do not go past it and do not stop short of it.

There is one caveat. If you have a very large ridge pole in a rafter setup, such as a double ridge pole about 3 inches wide, 1.5 inches on each side would completely block venting. In that case you will likely need a custom, larger ridge cap. For a standard truss or a single ridge pole, 1 to 1.5 inches works.

At the eave: The plywood normally runs to the outside edge of the fascia board. It does not overhang the fascia, and it is not set back from it.

Measure from the top edge of the plywood down to the bottom edge of the plywood. Then add two things:

• 1 inch for the drip edge lip. Our drip edge has a lip that extends 1 inch past the plywood.
• 1 inch for the hem. The lower edge of the panel folds back underneath around that lip.

Panel length = plywood length + 2 inches

If you want to cross-check with framing numbers, the plywood length is roughly the top chord (or rafter) length, plus the fascia thickness, minus the 1 to 1.5 inch ridge setback.

Your plywood runs 12 feet from the ridge edge to the eave edge.

• Plywood length: 12 feet = 144 inches
• Plus drip edge lip: 1 inch
• Plus hem: 1 inch
• Panel length: 146 inches, or 12 feet 2 inches

Standing seam covers 16 inches per panel, much narrower than the 36 inches of Tuff Rib Ag or PBR, so you will have more panels.

Measure the roof rake to rake. The drip edge also runs up the rakes, and it is the same drip edge used at the eave. The panel at each end hangs out 1 inch over the rake drip edge. The overlap rib on that panel is cut off, and the extra inch is folded around the drip edge. So add 1 inch on each side.

Panel count = (rake-to-rake width + 2 inches) ÷ 16 inches, rounded up, plus 1 to 2 extra panels

Because the end panels are trimmed and folded, the simple count falls short. Always add at least one more panel, and sometimes two.

Your roof is 24 feet from rake to rake.

• Width: 24 feet = 288 inches
• Plus 1 inch per rake (2 inches): 290 inches
• 290 ÷ 16 = 18.125, which rounds up to 19 panels
• Add 1 to 2 extra panels for the trimmed end panels: 20 to 21 panels

Each of those panels would be 146 inches long, using the length from the first example.

The ridge on standing seam works differently from Tuff Rib Ag and PBR, which use foam or mesh closure strips under the ridge cap. Here there is no foam closure between ribs. Instead, a Z-bar is installed between the ribs at the top of each panel. For 16 inch wide panels, the Z-bar pieces are 16 inches wide. They fasten through the panel into the plywood below.

The Z-bar is also how the ridge cap is attached. Because this is a concealed-fastener system, the Z-bar is fastened to the roof and the ridge cap snaps over it. Which Z-bar you use depends on whether you want the ridge to vent:

• Non-venting: A standard solid-metal Z-bar closes off the gap and keeps out rain and snow. It does not let the ridge breathe. Use it when you do not want venting, for example when the building has gable vents, or when spray foam insulation is against the underside of the roof deck.
• Venting: The Snap Z-Enclosure is a perforated Z-bar with mesh behind the perforation. Air passes through the perforation and mesh to the outside, while the perforation and mesh keep rain and snow out of the ridge. Use it for most attic applications, and for cathedral-type ceilings with fiberglass insulation and proper baffles or vents against the underside of the plywood, since that cavity needs to breathe.

Either way, the 1 to 1.5 inch setback stays. It is there for venting or fit, and also for thermal movement. Steel expands and contracts with temperature, and panels installed touching on a cold day can push into each other in summer heat.

The large ridge pole caveat from above still applies. With a double ridge pole about 3 inches wide, you will likely need a custom, larger ridge cap.

We make trim to order, in standard or custom profiles, in standard lengths of 10 and 12 feet. Ten feet is the most common, and 12-footers are used only where 10s would create too much waste.

To count pieces, add up each trim run, divide by 10 feet, and round up. For the 24-foot-wide roof above, drip edge along both eaves is 24 + 24 = 48 feet, which is 5 pieces of 10-foot drip edge (50 feet). The rakes need drip edge too, so add those runs as well. A deeper trim guide is coming soon.

• Round up on panel counts, and add the extra end panels described above
• Add a spare panel or an extra piece of trim for mistakes or damage
• Order extra fasteners so a job is not held up for a few pieces

With a 24 to 48 hour turnaround on stock-color coil*, a small top-up order is easy if you come up short.

*24–48 hour turnaround applies to stock coil colors only. Custom colors may take longer.

A good request includes:

1. Snap Lock Standing Seam with Striations or Standing Seam with Nail Flange (or tell us about the building and we will help you choose), and color
2. Plywood length for each roof plane, and rake-to-rake width, or your measurements and a sketch
3. Trim list: the total length per trim type (or the piece count), and whether you need standard or custom profiles
4. Photos of the roof or building
5. Delivery address or pickup plan, and your timeline

The hem and rake folds depend on exact plywood dimensions. We recommend having your contractor or installer confirm the measurements before you order. Whoever is doing the install, whether that is a subcontractor, a contractor, or a DIY homeowner, should verify the panel lengths, because they know exactly how they will install it.

We deliver across New England, New York, and New Jersey, or you can pick up at our shop in Westfield, MA. That is our only location.