A leaking balcony is one of the most common water problems in Sydney apartment buildings. It usually shows up as a stain or drip in the ceiling of the unit below, bubbling paint on the balcony soffit, or rust and cracking at the slab edge. This guide explains why balconies leak, how the source is found, and the usual repair options for strata buildings in NSW.
Why balconies leak
- Failed waterproofing membrane: the membrane under the tiles keeps water out of the slab. Once it cracks, comes away or wears out, water gets through even if the tiles look fine.
- Door sills: water often gets in where the balcony meets the sliding door, especially where the membrane was not turned up behind the sill or the sill sealant has failed.
- Drainage: blocked outlets, or a floor that falls towards the door instead of the drain, leave water sitting on the balcony.
- Grout and tile joints: cracked grout lets water under the tiles, where it sits on the membrane and finds any weak point.
- Balustrade fixings: posts and brackets fixed through the membrane can let water in around each fixing.
- Slab edge and soffit: water that reaches the steel in the slab edge causes rust stains and spalling, known as concrete cancer.
Signs to look for
- Stains, drips or mould on the ceiling below the balcony
- Bubbling or flaking paint on the balcony soffit
- White powdery deposits (efflorescence) on tiles, grout or the slab edge
- Rust stains or cracks along the slab edge
- Drummy or loose tiles
- Water pooling on the balcony after rain
How the source is found
A ceiling stain rarely sits directly under the point where water gets in, because water can travel along the slab before it shows. A proper leak investigation usually combines:
- An inspection of the balcony, sills, drains and balustrade fixings, with photos.
- A check of the ceiling and soffit below with a moisture meter or thermal camera.
- Targeted water testing: wetting one area at a time, such as the drain, the door sill or the tiled floor, while someone watches below. See façade water testing.
Testing one area at a time is what separates a leak investigation from guesswork. It shows which repair is needed before money is spent.
Repair options
- Sealant and drainage repairs: replacing failed sealant at sills, junctions and fixings, and clearing or fixing outlets. Suitable when testing shows the leak is at a specific detail.
- Regrouting and tile repairs: can help where cracked grout is part of the problem, but they do not fix a failed membrane underneath.
- Membrane replacement: the tiles and bedding are removed, the slab is repaired and prepared, a new membrane is installed with upturns at walls and sills, and the balcony is re-tiled. This is the long-term fix when the membrane itself has failed.
- Slab edge and soffit repairs: concrete cancer repairs and repainting of the underside, which can often be done by rope access without scaffolding.
In Australia, waterproofing membranes for external above-ground areas such as balconies are covered by AS 4654.2. Waterproofing is its own licence class in NSW, so check the contractor holds the right licence before membrane work is booked.
Who pays for balcony leaks in a strata building?
In many NSW strata schemes the balcony slab and its waterproofing membrane are common property, which the owners corporation must maintain and repair under the Strata Schemes Management Act 2015. Some items, such as tiles, fixtures or works added by an owner, may be the lot owner’s responsibility, and some buildings have by-laws that change who looks after what. Check the strata plan and by-laws, and speak with the strata manager before work is booked.
If the building is relatively new, defects may also be covered by the statutory warranties in the Home Building Act 1989, which have time limits. Get advice early if you think the leak is a construction defect.
Common questions
Can a balcony leak be fixed without removing the tiles?
Sometimes. If testing shows the water is getting in at a sill, drain or fixing, a targeted sealant or drainage repair may be enough. If the membrane under the tiles has failed, the tiles usually need to come up so it can be replaced.
Why does the ceiling below only leak in heavy or windy rain?
Wind-driven rain reaches details that normal rain does not, such as door sills and balustrade fixings. Read more about leaks from wind-driven rain.
Can an upper-floor balcony be inspected without going through the unit?
The outside of the balcony, the slab edge and the soffit can be inspected by rope access. Water testing usually also needs someone inside the unit below to watch where the water appears.
Leaking balcony? Request a leak investigation or call 1300 926 176.
