Membrane upstand termination (flat roof, balcony)
Membrane upstand termination is the AS 4654.2 detail: 150 mm minimum upstand, cap-flashing lap, primer compatibility. Wrong = water tracks back to the wall.
Ask Chalkline about this →Membrane upstand termination is the process of terminating a flat-roof or balcony waterproofing membrane at a vertical upstand, almost always at a parapet, penthouse threshold, or door reveal. Under AS 4654.2:2012 Appendix A (called up by the NCC Volume Two H2D8 external-waterproofing provisions), the upstand must be at least 150 mm high above the finished water level, with a continuous cap or counter-flashing lapping back over the membrane. Get the height, the lap, or the primer wrong and water tracks behind the cap and into the wall.
The AS 4654.2 rule
- Minimum upstand height: 150 mm above the finished water level (typically the finished waterproofing surface plus any tile / topping). Higher where wind-driven rain or a step-up detail dictates.
- Membrane dressed up the upstand face and mechanically terminated at the top with a horizontal termination bar, sealed termination, or capping detail.
- Counter-flashing or cap flashing lapping back over the membrane termination by a designed distance, preventing water from getting behind the membrane top edge.
- Primer compatibility between the membrane and the substrate (parapet face) is critical; a missed primer step halves the bond.
The detail in sequence
- Build the upstand structurally. The parapet or kerb to design height, faced with the substrate the membrane manufacturer’s spec calls up (typically primed FC sheet, masonry, or treated formwork).
- Prime the substrate per the membrane data sheet. Wrong primer = no bond.
- Dress the membrane up the face to the full 150 mm minimum (or greater per detail). Roll out, set with the manufacturer’s roller, ensure no voids or fish-mouths.
- Terminate the top edge with the specified termination bar / sealed lap / capping detail.
- Install the cap flashing or counter-flashing lapping back over the termination by the designed distance, mechanically fixed to the substrate above.
- Seal the cap-to-substrate junction so wind-driven water can’t get behind the cap.
Common failure modes
| Failure | Cause | Fix |
|---|---|---|
| Water tracking down inside wall | Upstand too short (less than 150 mm); or cap-flashing lap wrong | Increase upstand height; redo cap detail to designed lap |
| Membrane lifting from upstand | Primer missed or wrong; substrate dirty | Strip back, re-prime to spec, re-bond |
| Cap flashing lifting at corner | No mechanical fixing into substrate above | Add stainless fasteners through cap into substrate |
| Ponding at upstand foot | Fall not designed; topping made level | Re-set fall away from upstand at floor finish |
For a builder
- Measure twice before topping goes down. The 150 mm is from the FINISHED water level (over any topping / tile), not from the bare substrate. A topping that’s deeper than planned eats into the upstand.
- Brief the topping contractor. A tiler who doesn’t know the upstand height limit will sometimes build up the topping right to the cap-flashing line, leaving zero upstand.
- Don’t accept a substituted membrane mid-pour. The primer-and-membrane system is brand-specific; substituting one element breaks the system warranty.
Try it
(Compliance Checker app placeholder, future Chalkline embed for membrane-upstand inspection checklist.)
Related
See also
Last updated: 2026-05-29. Verified: 2026-05-29. Quarterly review for currency.