End lap (metal roofing)
End lap is the overlap where two metal roof sheets meet end-to-end. AS 1562.1 minimums by pitch: 150 mm above 10 degrees, 300 mm at lower pitches.
Ask Chalkline about this →An end lap is the overlap where two metal roof sheets meet end-to-end along the slope of the roof. End laps are needed on roof runs longer than the maximum available sheet length (typically 12 m to 21 m off the truck; sometimes longer on bespoke order). The end lap is the most weather-exposed joint detail on a long sheet roof: if it’s the wrong length or unsealed at low pitch, water finds its way through.
Minimum end lap under AS 1562.1:
| Roof pitch | Minimum end lap | Sealant |
|---|---|---|
| > 10 degrees | 150 mm | Not required (gravity sheds water) |
| 5 to 10 degrees | 300 mm | Sealant strongly recommended along the lap line |
| < 5 degrees | 300 mm + sealant | Sealant required (capillary action above lap minimum) |
The pitch is measured at the roof slope, not at the angle of incidence. AS 1562.1 sets these as minimums: manufacturer install guides for specific profiles (Trimdek, Klip-Lok, Custom Orb) may specify more.
Why the pitch matters. Above 10 degrees, gravity drains water down the sheet faster than capillary action can wick it back up under a lap. Below 5 degrees, capillary creep pulls water uphill against gravity; even a long lap will leak without sealant.
Detail rules:
- Position the end lap over a purlin or batten. Unsupported end laps flex and the lap line opens under wind load.
- Sealant is butyl-based (not silicone). Butyl stays flexible long-term; silicone hardens and cracks within years on exposed roofs.
- Sealant bead is laid between the sheets before they’re brought together, not after. The sandwich compresses the bead into a continuous seal.
- Fix through the lap into the purlin per the manufacturer’s fixing schedule. Generic fixings into a non-purlin location are a defect.
- Don’t over-tighten at the end lap; deformation around the screw head creates a path for water entry. Screws into rubber-washered washers should compress the washer but not crush it.
Common end-lap defects:
- Too-short lap because the rafters were spaced without accounting for sheet length. Fix: order longer sheets or accept the cost of re-doing.
- Unsealed low-pitch lap that leaks during the first heavy storm. Often shows as a wet patch in the ceiling below the lap line.
- Lap not over purlin: lap flutters in wind, eventually opens. Refixing with a strap or short purlin can salvage; full re-lay is sometimes needed.
- Wrong sealant chemistry: silicone hardens and shrinks; reseal with butyl.
For builders. Plan the sheet length at quote stage:
- Measure the roof run and order sheets to span without an end lap if possible. Custom-length sheets to 21 m are typically only a small cost premium.
- Where end laps are unavoidable, locate them at a purlin and detail per the manufacturer system.
- For low-pitch roofs, build sealant cost into the quote; it’s a meaningful line item on a large area.
Also known as: sheet end lap, endlap, end overlap.
Category: Materials / metal roofing / installation.
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Last updated: 2026-05-14. Verified: 2026-05-14.