Unit Development in the Southwest: What You Need to Know Before You Develop

R-Code density coding tells you how many dwellings could theoretically fit on a block. Site constraints, council requirements, and design standards tell you how many can be approved and built. The gap between those two numbers is where many development feasibilities fall over.

Developing a residential lot into two or more dwellings, a duplex, grouped housing, or small unit project, is one of the most common investment strategies in the Southwest property market. It's also one of the most process-intensive, and the constraints are more specific than many developers starting out realise.

The planning framework

In WA, multi-residential development is governed by the Residential Design Codes (R-Codes). Volume 1 covers single houses and grouped dwellings; Volume 2 (the Medium Density Housing Code) applies to certain medium-density types. Before any design work starts:

•      Confirm your lot's R-Code density — this sets the minimum lot size per dwelling and the theoretical development ceiling.

•      Check local planning policy overlays — many Southwest councils have Local Planning Policies (LPPs) that impose design quality requirements above the state R-Code minimum — requirements around materials, landscaping, and building character that affect cost and design approach.

•      Understand the approval pathway — depending on the project type and council, a development application (DA) may be required. Some grouped dwellings can be assessed under deemed-to-comply provisions; others require a full DA.

What drives development viability

•      Outdoor living areas — each dwelling must provide a minimum primary outdoor living area (typically 24m² for a two-bedroom dwelling) that receives adequate sun and has privacy. On compact lots, fitting compliant outdoor areas for each dwelling is often the binding constraint on yield.

•      Parking — one bay per dwelling (for up to two bedrooms) or two bays (three bedrooms or more). The arrangement and access for parking must work independently for each dwelling.

•      Site coverage and open space — R-Code open space requirements apply to the Lot as a whole. Driveways and paved areas count against open space, which limits how intensively the site can be developed.

•      Privacy and overlooking — upper-floor habitable room windows have minimum setback requirements from boundaries. In multi-dwelling developments, privacy between dwellings must also be managed.

A realistic feasibility example

A 700m² lot at R30 in Bunbury theoretically supports two dwellings at 350m² each (R30 minimum lot size). In practice: after accounting for the front and rear setbacks, two independent outdoor living areas (24m² each), two double-width driveways, and the common boundary setback, the buildable area for each dwelling may be significantly less than you'd expect from the lot size alone.

Running a real feasibility assessment, not just a density calculation, is the only reliable way to determine what's achievable. We do this as the first step in every unit development project.

Frequently Asked Questions

What is the difference between grouped housing and multiple dwellings under the R-Codes?

Grouped housing consists of two or more dwellings on the same lot with separate outdoor living areas at ground level, typically what most people think of as a duplex or villa development. Multiple dwellings are defined differently and assessed under a separate part of the R-Codes. The distinction affects setback calculations and open space requirements.

How long does a development application take in the Southwest?

For grouped housing DAs, allow 3–5 months from lodgement to approval in most Southwest councils, assuming no significant issues. Sites with BAL requirements, vegetation overlays, or heritage considerations can take longer. Allow a further 2–3 months for building permit after DA approval.

Do I need a planning consultant or just a building designer?

For straightforward grouped housing in a standard zone without complex overlays, a building designer with planning experience can manage the full process. For complex sites, rezonings, or projects requiring strategic planning input, a dedicated planning consultant adds value. We're transparent about when a specialist planner would be beneficial.

Thinking about developing your lot? Let's start with a feasibility conversation before you go any further at fastlane.drafting@gmail.com