Poor balcony drainage is one of the leading causes of persistent leaks in multi-storey residential buildings. When water cannot drain freely from a balcony surface — because the falls are incorrect, the outlet is undersized, the threshold is too low, or the drain grate is blocked — it ponds and ultimately finds a path through the waterproofing system into the floor or ceiling below. Drainage problems compound over time, and what begins as a minor inconvenience can lead to significant structural damage, membrane failure, and internal water damage affecting multiple lots.

Atomic Projects approaches drainage upgrades as an integrated part of balcony remediation — assessing the full system, not just the outlet, and designing solutions that prevent recurrence across the life of the building.

How We Approach Drainage & Threshold Upgrades

• Hydraulic Assessment: Each balcony is assessed for existing falls (slope toward drains), outlet capacity, grate condition, and threshold height relative to the finished floor level. Water testing is used to identify ponding zones.
• Drain Upgrade & Relocation: Where existing outlets are inadequate, we core or saw-cut new drain locations into the slab, install proprietary drainage channels or puddle flanges, and connect to the existing stormwater system. All work complies with AS 3500.3 (Stormwater Drainage).
• Threshold Detailing: Balcony-to-internal floor thresholds are one of the most common leak points in residential buildings. We rebuild thresholds to ensure a minimum 50mm upstand above the waterproofing layer, with correct step-down transitions that are both watertight and compliant with accessibility requirements under AS 1428.1 where applicable.
• Screed & Fall Correction: Where drainage improvements alone are insufficient, we integrate screed and fall correction works to re-establish correct drainage gradients (minimum 1:80 for trafficable surfaces) before membrane and tile reinstatement.
• Expansion Joint & Perimeter Sealing: All joints around drains, thresholds, and perimeter upstands are sealed with movement-capable polyurethane or polysulfide sealants to maintain waterproof continuity at the most vulnerable points.

Frequently Asked Questions

Water pools on our balcony after rain — is this a drainage or waterproofing problem?

Often both. Ponding water indicates inadequate falls or a blocked/undersized drain. But persistent pooling also accelerates membrane deterioration and joint failure, so it's important to address both issues together. An investigation will determine whether re-grading the screed, upgrading the outlet, or replacing the membrane — or all three — is required.

What is a threshold detail and why does it matter?

The threshold is the junction between the external balcony surface and the internal floor. It's one of the most common leak entry points because it requires a waterproof upstand on the external side and a level or step-down transition internally. Poorly detailed thresholds — especially those where the membrane has not been taken up behind the door frame — are responsible for a large proportion of apartment water damage claims.

Can drainage upgrades be done without replacing the waterproofing membrane?

If the existing membrane is in good condition, it may be possible to upgrade just the outlet and threshold detailing without full membrane replacement. However, any penetration through the membrane for a new drain requires careful re-detailing and testing to maintain system integrity. We always recommend a leak investigation before scoping drainage-only works.

How do we manage drainage upgrades in an occupied building?

Balconies are staged to minimise disruption, with each balcony typically out of service for 3–5 working days during coring, screed laying, and membrane re-detailing. Temporary weather protection is provided where balconies must remain open to rain during cure periods.

Can Atomic Projects coordinate the full balcony scope including drainage, waterproofing, and tiling?

Yes. This is our preferred approach because integration across trades eliminates interface defects and simplifies strata contract management. We handle the complete scope from waterproofing through to tile reinstatement under a single contract.

Balcony drainage failures are preventable when the correct standards are applied from the start — and correctable when the full system is assessed and upgraded by a team that understands how each element interacts. Atomic Projects is a Class 2 Registered Builder with over 10 years of experience in balcony remediation across Sydney. Contact us to arrange an inspection and drainage assessment for your building.