● Building code

Balcony waterproofing upturn height. Not always 150 mm.

11 Nov 20261 min readFORSPEC Technical Team

The short version

The external membrane standard requires the upturn to be high enough that water, including wind-driven water, cannot get over it. It gives no single figure.
Its guide runs from 40 mm in the calmest wind class to 180 mm in the most severe.
The height is measured above the finished surface, not above the slab.

150 mm is the figure most people carry in their heads. On a sheltered ground-floor terrace it is more than the guide asks. On an exposed tower balcony it may not be enough.

What the standard says

The requirement: High enough above the finished surface that water cannot get over, wind-driven water included
The guide: 40 mm to 180 mm, by the wind class of the site
Where water is held back: Above the overflow level
Planters: At least 100 mm above the soil or fill

Three mistakes this causes

Measuring from the slab. Tiles, bed and screed can use up 50 mm or more. Measure from the finished surface.
Guessing the wind class. It comes from the engineer or the building approval, not from the suburb.
Treating the NCC 2025 step-down as the upturn. The 70 mm step in the slab at a door is a concrete level. The membrane upturn is still measured above the finished surface.

At the door

Where the levels leave no room for an upturn at a door, the standard's answer is to take the membrane under the sill and drain it. The sub-sill flashing is part of the membrane system, so it is drawn and installed with the membrane, not left to the window installer.

Roof and parapet details are in the drawings library.