How to overlap metal roofing: lap each exposed-fastener panel by at least one full rib on the side (the side lap) and 6 to 12 inches on the end (the end lap), run a continuous bead of butyl tape between the mating surfaces, and drive the fasteners through the rib high points. The exact end lap and whether sealant is mandatory both track the roof slope and the panel maker’s instructions. Below is what actually keeps the seam dry.
By The Roofing Brief Team. Last reviewed August 2026.
How much should metal roofing overlap?
Overlap exposed-fastener metal panels by one full rib on the side lap and 6 to 12 inches on the end lap. Steeper roofs (6:12 and up) can use the 6-inch minimum end lap because water clears fast. Low-slope roofs between 3:12 and 1:12 need 8 to 12 inches and a sealed lap, because water moves slower and has more time to wick under the seam.
The side lap covers the outside rib of the lower panel with the outside rib of the upper panel. On a 5-rib panel that is a single interlocking rib; on corrugated sheet it is 1.5 to 2 corrugations, roughly 3 to 4 inches. Standing seam is different: it has no exposed end lap or screwed side lap, since the ribs join with a snap-lock or a mechanically seamed joint. See snap-lock versus mechanical seam panels for that distinction.
| Panel type | Side lap | End lap | Fastener location |
|---|---|---|---|
| R-panel / ribbed (36″) | 1 full rib (about 3-4 in) | 6-12 in by slope | Through rib high points |
| Corrugated (26″) | 1.5-2 corrugations | 6-12 in by slope | Through corrugation crowns |
| Standing seam (16″) | Mechanical seam, no screws exposed | Continuous, no end lap | Concealed clips |
Side lap vs end lap: what each seam does
The side lap is the vertical seam between two panels sitting next to each other across the roof. The end lap is the horizontal seam where an upper panel overlaps a lower one as you run up the slope toward the ridge. Both must shed water downhill, so the upper element always sits on top of the lower element, never the reverse.
Side laps carry most of the wind-driven rain exposure, which is why the overlapping edge faces away from the prevailing wind. End laps carry the gravity load of sheeting water and are the seam most likely to leak on a low slope, which is why sealant matters more there.
What is the minimum slope for lapped metal panels?
The International Building Code sets 3:12 (3 units vertical in 12 horizontal) as the minimum slope for lapped, non-soldered metal roof panels installed without applied lap sealant, per IBC Section 1507.4.2 and the matching IRC provisions. With sealant applied at the laps per the manufacturer’s instructions, the same code allows a minimum slope down to 1/2:12, which is about a 4 percent slope.
In plain terms: at 3:12 and steeper, most exposed-fastener profiles can be lapped dry without a mandatory sealant bead because gravity clears the water. Between 3:12 and 1/2:12, code and nearly every panel manufacturer require a continuous row of butyl tape or a compatible lap sealant along the full overlap. Always confirm against the specific panel’s published instructions, because the warranty follows those, not the code minimum.
| Roof slope | End lap | Lap sealant | Code basis |
|---|---|---|---|
| 6:12 and steeper | 6 in typical | Optional on most profiles | Above IBC 3:12 minimum |
| 3:12 to 6:12 | 8-10 in | Recommended | At/above IBC 3:12 minimum |
| 1/2:12 to 3:12 | 10-12 in | Mandatory (butyl + lap seal) | IBC 1507.4.2 sealed-lap allowance |
| Below 1/2:12 | Not permitted | Use a membrane system | Below code minimum for lapped panels |
How to overlap metal roofing panels step by step
Overlapping panels is a repeatable sequence: set the first panel true, lap the side, seal and lap the end, then fasten through the high points. Each step below stands on its own so you can check your work panel by panel.
- Start on the downwind side and set the first panel square. Begin at the end of the roof opposite the prevailing wind so every later side lap faces away from that wind. Square the first panel to the eave and ridge before fastening, because every panel after it references this one.
- Lap the side by one full rib. Set the next panel so its outside rib covers the outside rib of the panel already down. On corrugated sheet, overlap 1.5 to 2 corrugations. The lap should sit flat with no gap that daylight shows through.
- Run butyl tape before closing an end lap. Where an upper panel meets a lower one, lay a continuous bead of butyl tape across the top face of the lower panel first, then set the upper panel into it so the tape compresses into a gasket. Do not stretch the tape thin; keep it full width.
- Overlap the end lap 6 to 12 inches by slope. Use 6 inches only at 6:12 and steeper. Use 8 to 12 inches from 3:12 down to 1/2:12, where a sealed lap is also required. Position the lap so a fastener line will pass through it.
- Fasten through the rib high points, never the valleys. Drive #12 self-tapping screws with bonded EPDM washers into the ribs so water in the flat pans never sits against a screw hole. Seat each washer until it is snug and the rubber just bulges; do not overdrive and dimple the panel.
- Space the fasteners to the panel schedule. A typical exposed-fastener schedule places about 5 panel screws plus 1 lap screw per screw line at panel ends, and 3 panel screws plus 1 lap screw per line on interior panels, with lap screws 12 to 18 inches on center. Follow the maker’s screw layout for the exact pattern.
- Inspect the seam and the sealant. Check that every end lap is fully bedded in butyl, every side lap is tight, and no screw sits in a pan. Confirm the sealant is continuous with no skips before moving up the slope.
Which way should the overlap face?
The overlapping edge should face away from the prevailing wind so wind-driven rain blows over the seam instead of into it. Install panels working against the prevailing wind: start on the downwind end of the roof and move upwind, so each new panel’s side lap tucks behind the one already fastened relative to the wind.
Getting this backward is a common reason a technically correct lap still leaks in a storm. If the exposed edge points into the wind, pressure pushes water uphill under the lap past the fastener line. The rule is one line: laps shingle downhill for gravity and downwind for pressure.
Do you need sealant on metal roofing overlaps?
Sealant is mandatory on low-slope laps and strongly advised on end laps everywhere. Below 3:12, code and manufacturers require a continuous butyl tape or lap sealant at every overlap. At 3:12 and steeper, many profiles are approved to lap dry, but a butyl bead at end laps is cheap insurance against the seam that fails first.
Use butyl tape between the mating metal surfaces, not a bead of caulk smeared over the outside of a finished seam. Butyl stays flexible and moves with the panel, which matters because metal expands and contracts with temperature. For where the tape goes and why exterior caulk fails, see butyl tape for metal roofs, and for the movement it has to survive, metal roof thermal movement.
Common overlap mistakes that cause leaks
Most overlap leaks trace to a handful of repeatable errors, not to the panel itself. Fixing these at install is far cheaper than chasing a stain later.
- Screws in the valleys. Fasteners in the flat pan sit where water collects; every hole becomes a wick. Drive through the rib high points instead.
- Too little end lap on a low slope. A 6-inch lap at 2:12 lets slow-moving water back up under the seam. Match the lap to the slope table above.
- Exterior caulk instead of bedded butyl. Surface caulk cracks and peels within a few seasons; the seal belongs between the surfaces, compressed by the fasteners.
- Overdriven screws. Crushing the EPDM washer or dimpling the panel breaks the seal and pools water. Seat until the washer just bulges.
- Lap facing into the wind. The overlapping edge must point downwind, or wind-driven rain is pushed under the seam.
DIY vs hiring a pro
Overlapping panels on a simple gable at 4:12 or steeper is within reach for a careful DIY installer who follows the panel schedule. Low-slope roofs, complex hips and valleys, and any job where the warranty depends on certified installation are better handed to a contractor who does it daily.
The break point is usually slope and complexity. At or above 3:12 on a straight run, the risk is manageable. Below 3:12, where sealed laps and exact fastener torque decide whether the roof leaks, the cost of a redo outweighs the labor saved. Panel coverage math also matters for ordering; see metal roof panel widths and coverage before you buy, and screw pull-out strength for how fastener choice holds the whole system down.
Frequently asked questions
How much should metal roofing overlap on the side?
Side laps should cover at least one full rib of the panel below. On a 5-rib R-panel that means the outside rib of the upper panel sits over the outside rib of the lower panel. On corrugated sheet, overlap 1.5 to 2 corrugations, roughly 3 to 4 inches. The lap should lie flat with no visible gap before you fasten it.
How many inches do you overlap metal roofing on the end?
End laps run 6 to 12 inches depending on slope. Use 6 inches at 6:12 and steeper, where water clears quickly. Use 8 to 12 inches on low slopes between 3:12 and 1/2:12, and add a continuous butyl or lap sealant bead there. Always confirm the exact figure against your panel manufacturer’s published instructions.
What is the minimum slope for lapped metal roofing?
IBC Section 1507.4.2 sets 3:12 as the minimum slope for lapped, non-soldered metal panels without lap sealant. With sealant applied at the laps per the manufacturer’s instructions, the minimum drops to 1/2:12, about a 4 percent slope. Below 1/2:12, a lapped panel system is not permitted and a membrane roof is the correct choice.
Which way should metal roof panels overlap?
Panels overlap downhill for gravity and downwind for wind pressure. Start installing on the downwind end of the roof and work against the prevailing wind, so each side lap’s exposed edge faces away from the wind. This keeps wind-driven rain blowing over the seam rather than being forced underneath it.
Do you have to use sealant on metal roof overlaps?
Below 3:12, sealant is required by code and by manufacturers at every lap. At 3:12 and steeper, many profiles are approved to lap dry, but a butyl tape bead at end laps is inexpensive protection. Use butyl tape bedded between the metal surfaces, not exterior caulk over a finished seam, because bedded butyl flexes with the panel’s thermal movement.
Where do the screws go on overlapping metal panels?
Drive fasteners through the rib high points, never the flat valleys where water collects. Use #12 self-tapping screws with bonded EPDM washers. A common schedule is about 5 panel screws plus 1 lap screw per line at panel ends and 3 panel screws plus 1 lap screw per line on interior panels, with lap screws 12 to 18 inches on center. Follow the panel maker’s exact layout.