Lap length
Lap length is the overlap where two reo bars or mesh sheets splice so load transfers continuously; short laps fail in bending and are a common pre-pour fail.
Ask Chalkline about this →Lap length (or lap) is the distance two reinforcing bars, or two mesh sheets, must overlap where they join so the load transfers continuously through the splice. Reinforcement comes in finite lengths; where one bar or sheet ends and the next begins, they overlap by the lap length so the steel acts as one continuous run. Lap too short and the splice fails in bending, the bars effectively pulling apart under load.
Lap length is a structural calculation, not a rule of thumb. The engineer specifies it (to AS 3600 for engineered elements), and it depends on the bar diameter, the concrete grade, and the cover. For deemed-to-satisfy residential slabs, NCC 2022 Housing Provisions clause 4.2.11 sets minimums:
| Reinforcement | Minimum lap |
|---|---|
| Bars up to 12 mm | 500 mm |
| Bars over 12 to 16 mm | 700 mm |
| Trench mesh | 500 mm |
The engineer’s drawing may require more; where it does, follow the drawing.
Short laps are a common pre-pour failure. The certifier checks lap lengths against the drawings before the pour, and a failed inspection pushes your pour date and your concrete booking. Tie the laps properly so they do not pull apart when the concrete is placed, and lap mesh sheets rather than butting them per the steel fixer’s setout. See reo reinforcement.
Also known as: Lap, splice length, overlap.
Category: Concrete reinforcement / Detailing.
Related
See also
References
- AS 3600:2018 Concrete structures, Standards Australia (verified 2026-05-08)
- ABCB NCC 2022 Housing Provisions clause 4.2.11 (verified 2026-05-08)
Last updated: 2026-05-30. Verified: 2026-05-08. Quarterly review for currency.