For many Perth property owners, the ideal subdivision is not to demolish the home they already have. It is to keep the existing residence and create a new lot in the backyard or beside it.
This can be an excellent development strategy, but the answer is not determined by backyard size alone. The existing house has to work with the proposed new boundaries, access, parking, outdoor areas and services.
Why retain the existing house?
Keeping a suitable existing dwelling can offer several advantages:
- avoiding the cost and waste associated with demolition;
- retaining an existing rental or owner-occupied home;
- maintaining established streetscape character;
- reducing the amount of new construction required;
- creating a new rear or side lot that can be sold or developed; and
- allowing development to be staged rather than undertaken all at once.
The R-Codes explanatory guidance specifically recognises that retaining existing dwellings can support housing diversity, reduce embodied energy and demolition waste, and help maintain established streetscape character where appropriate.
Where is the existing house positioned?
The position of the home is often the single biggest factor.
A residence located toward the front of a deep block with usable side access can be a strong candidate for a backyard subdivision. A home positioned through the centre of the lot, or very close to the only possible access side, can make the exercise much more difficult.
Sometimes a small intervention changes the result completely - for example removing an old carport, garage, patio or side addition to create the access width needed for the rear lot.
The new boundaries change how the existing house is assessed
One of the most important points is that the retained dwelling is assessed against the proposed new lot boundaries, not only against today's external property boundaries.
That means a wall, window, patio, garage or eave that is perfectly acceptable on the current property can become an issue once a new boundary is drawn closer to it.
The R-Codes explanatory guidance states that lot-boundary setbacks for a retained dwelling are calculated to the new proposed site or lot boundaries.
This is why the subdivision design and the existing-house drawings need to be considered together.
Access to the new rear lot
If the new lot sits behind the existing home, vehicle access is usually provided through a battleaxe leg or, in some survey-strata layouts, a common-property driveway.
Current WAPC Operational Policy 2.2 says a residential battleaxe leg should generally be at least 4.0m wide for R2-R40 land and 3.6m wide for R50 and above. This accommodates a 3.0m constructed driveway, landscaping space and necessary utility services.
Where an existing dwelling is retained beside a communal street or battleaxe leg, the WAPC generally expects no eaves or other protrusions into the driveway and sufficient space for required car parking and safe vehicle manoeuvring.
In practice, this is often where older side carports, eaves, meter boxes and additions need close attention.
Does the front house still have enough parking?
Creating a driveway to the rear lot can remove or change the existing home's parking.
The retained residence still needs an appropriate parking solution after subdivision. Depending on the R-Code, dwelling type and local framework, this may require redesigning a carport, driveway or manoeuvring area.
The WAPC's policy expressly identifies adequate car parking and safe manoeuvring as considerations where an existing dwelling is retained beside a battleaxe leg or communal street.
What happens to the backyard and outdoor living area?
A common mistake is to draw the new rear boundary as close to the existing house as possible to maximise the new lot.
That can leave the retained dwelling with a poor or non-compliant outdoor area and an awkward relationship between living rooms, fencing and the new driveway.
The R-Codes guidance says private open space for the retained dwelling should be prioritised where a design is being considered on merit.
A slightly smaller new lot can sometimes create a much more valuable overall development if the front home still feels like a proper residence rather than a house that has had its backyard cut away.
Will the existing house need upgrading?
Possibly.
Depending on the subdivision type, local planning framework and condition of the dwelling, works may be required before subdivision conditions can be cleared.
Potential items include:
- new or relocated car parking;
- removal or modification of patios, sheds, garages or eaves;
- new fencing and gates;
- changes to outdoor living areas;
- separation or reconfiguration of sewer and plumbing;
- electrical meter or switchboard changes;
- new landscaping or tree provision;
- upgrades to the appearance of the retained dwelling where required by an applicable approval or policy; and
- building or development approvals for alterations where necessary.
The R-Codes explanatory guidance notes that upgrading the appearance of an existing dwelling may be required as a condition of subdivision or development approval in some circumstances.
Green title or survey-strata?
Both can be used in retain-and-subdivide projects depending on the site.
| Freehold / green title | Survey-strata |
|---|---|
| Creates separate freehold lots shown on a deposited plan. It is often attractive where each lot can operate independently and access/services can be resolved without common property. | Creates lots defined by surveyed land boundaries. A survey-strata scheme may include common property, which can be useful for a shared driveway or other shared areas. |
| Often suits side-by-side or some battleaxe arrangements where the access leg forms part of the rear lot. | Can be flexible where access or servicing is best handled through common property. |
| The best option depends on the actual geometry and service strategy rather than a simple preference for one title type. | Scheme arrangements and future ownership considerations should be understood before selecting this structure. |
When does retaining the house stop making sense?
Keeping the existing home is not automatically the most profitable option.
Demolition may become the stronger strategy where:
- the house sits in the centre of the block and prevents an efficient subdivision;
- access to the rear cannot be achieved without major alterations;
- the retained dwelling requires extensive upgrades;
- the existing house is in poor structural or marketable condition;
- retaining it dramatically reduces the number or quality of new lots; or
- a coordinated new duplex, triplex or grouped dwelling development would use the land much more effectively.
The right answer comes from comparing both scenarios rather than assuming that demolition is bad or retention is always cheaper.
Should I design the future rear house before subdividing?
You do not necessarily need full building documentation before subdivision, but it is often very useful to test a concept design.
A lot that meets the minimum planning area can still be difficult to build on because of orientation, shape, access, retaining, outdoor living, parking or servicing.
Testing a future dwelling during feasibility helps make sure the subdivision is creating a genuinely useful property rather than simply an approved parcel of land.
A practical retain-and-subdivide feasibility check
Before committing to an application, we would generally want to establish:
- the R-Code and subdivision potential;
- the likely new boundary location;
- clear access to the rear or side lot;
- the effect on the existing home's parking and outdoor living;
- setbacks from the retained building to new boundaries;
- existing and proposed services;
- structures that need removal or modification;
- likely subdivision conditions and site works;
- a concept for the future new dwelling or saleable lot; and
- whether the financial outcome still stacks up.
How Shoreline Design can help
Retain-and-subdivide projects are where combining residential design and subdivision thinking is particularly valuable.
Shoreline Design can review the existing house, test subdivision options, consider the future dwelling and then assist with approvals, consultant coordination and the subdivision process if the project proceeds.
The objective is not just to create another title. It is to leave the owner with two properties that both work.
This article is general information for Perth property owners. Planning rules, fees and costs change, and every property is different, so check the requirements for your own property before you act on it.