Terrace House Stormwater Design in NSW: Zero-Lot & Easement Guide

Terraces: Maximum Density, Minimum Room for Drainage

Terrace housing is back in favour across Sydney’s infill and greenfield areas, including as a housing type under the Low Rise Housing Diversity Code in the State Environmental Planning Policy (Exempt and Complying Development Codes) 2008. From a stormwater perspective, terraces are the hardest small-residential typology to drain well: walls sit on the boundary, side setbacks vanish, roofs interlock along party walls, and every lot is narrow. Here is what builders need to know before lodging.

Zero-Lot Drainage: Where Does the Water Physically Go?

On a conventional house, roof water drops down external walls and runs in pipes through the side setback. On a terrace there may be no side setback at all, which forces three design decisions:

• Downpipe placement. With party walls on both sides, downpipes can generally only sit on the front and rear elevations, or internally – and internal downpipes carry strict requirements under AS/NZS 3500.3:2021 because a failure discharges inside the building.
• Pipe routes. Ground-level drainage usually has to run front-to-back within each narrow lot, threading between footings, services and landscaping. Congested rear courtyards with sewer, stormwater and tank overflow in a two-metre strip are normal – coordinate early.
• Surface water. Courtyards and paved rear yards on zero-lot blocks cannot shed water sideways onto the neighbour. Falls, strip drains and pits must keep each lot’s surface water inside its own boundaries until it reaches the legal discharge system.

Party Walls and Shared Roof Junctions

Terrace roofs commonly meet above party walls, creating either a parapet with a box gutter behind it or abutting roof planes draining in opposite directions. Key considerations:

• Box gutters along party walls must be designed to AS/NZS 3500.3:2021 with proper sumps, rainheads or overflow devices, because an overflowing box gutter above a party wall leaks into two homes and creates an instant neighbour dispute. Document size, fall, sump and overflow on the drawings.
• Keep catchments separated by lot wherever possible. Each terrace’s roof should ideally drain entirely to its own downpipes. Once one lot’s roof drains across another’s, you have shared infrastructure needing legal protection.
• Fire-rated penetrations. Where any drainage element passes through or sits within party wall construction, it must not compromise the wall’s fire resistance under the NCC – a coordination item between hydraulic and structural documentation.

Inter-Allotment Easements: The Make-or-Break Item

Terrace rows are often long and flat, or fall away from the street. Lots that cannot drain by gravity to the street need an inter-allotment drainage easement – a registered easement allowing piped discharge through downstream lots to the street or council system. For terrace projects:

• In greenfield estates, easements are usually created at the subdivision stage – verify they exist and are adequate for your connection before assuming.
• In infill projects, creating a new easement over a neighbour’s land requires their agreement (or a costly court process), so identify the need at feasibility, not at CC stage.
• Shared private drainage lines serving multiple terraces should sit within easements or common property, with clear maintenance responsibility – councils and certifiers will ask.

Detention, Tanks and the Usual Approvals Layer

On top of the geometry problems, terrace projects still carry the standard requirements: on-site detention where the council’s DCP requires it (sometimes provided as a shared system for the row, which then needs a positive covenant), BASIX rainwater tanks for each dwelling squeezed into small courtyards – slimline and underdeck tanks are common – and roof drainage sized to AS/NZS 3500.3:2021. Because every council treats detention and discharge differently, confirm the current DCP requirements for the specific site early in design.

Practical Tips for Builders

• Get the stormwater concept done alongside the architectural layout – on terraces, drainage feasibility can dictate dwelling levels and courtyard falls.
• Resolve easements before contracts are signed, not after.
• Insist on a documented box gutter design for every party-wall junction.
• Keep each lot hydraulically independent wherever the layout allows.

Terrace Project on the Drawing Board?

Contrive Consultants prepares council-ready stormwater and roof drainage plans for terrace and infill housing across Sydney and NSW, including zero-lot drainage layouts, box gutter design and easement strategy. Browse our services or contact us on +61 497 848 111 or info@contriveconsultants.com.au.