Granny Flat in Mernda, Northern Melbourne
A granny flat is a self-contained secondary dwelling on the same block as an existing house. Melbourne granny flats are hugely popular for teenager retreats, aged parents, home offices and rental income, but the rules on what you can and cannot rent out separately vary by council.
What to know about Mernda
Northern rail-corridor suburb now largely established, with remaining lots and some rebuild activity.
A mixed suburb where you will find both new-estate blocks and infill sites with older homes. The right build strategy depends heavily on which side of the suburb you land in.
Cost snapshot
Granny Flat build costs in Mernda
Base-build rate (mid-range)
$2,700 - $3,600/m²
RLB Q4 2025 — Melbourne, custom (excl. GST)
Typical size
50–90 m²
Habitable area, indicative
Indicative build cost
$135,000 – $325,000
Base build only; excludes land, site works, fees & GST
Build timeframe
6–10 months
Design to handover
Approval pathway
6–12 weeks (often building consent only under 60m²)
Victoria planning scheme
Victoria average (ABS)
$485,292 · $1,914/m²
ABS Building Activity 2024–25, completed detached house
Indicative planning figures only — a builder's fixed-price contract is always final. Sourced from RLB Rider Digest (Q4 2025), ABS Building Activity 2024–25, Cotality Cordell CCCI.
Council rules and overlays for granny flat in this area
In Victoria, a new build generally needs a planning permit (where the local planning scheme requires one) and a building permit issued by a registered building surveyor. Overlays such as Bushfire Management, Heritage, Significant Landscape and Development Contributions can apply, and growth-area blocks may attract the Growth Areas Infrastructure Contribution (GAIC). Confirm current requirements with your local council and the Victorian Building Authority before finalising a design.
The 3 decisions that shape your granny flat in Mernda
Attached or detached
Detached granny flats give privacy and are easier to lease separately. Attached extensions cost less because they share a wall and services.
Can you legally rent it out?
Some councils allow separate leases, others treat granny flats as ancillary to the main dwelling. Get this in writing before you build.
Site drainage
A second roof on the same block doubles stormwater load. Councils will ask how you plan to handle it.
Granny Flat FAQs for Mernda
How big can my granny flat be?▾
Under 60m² of habitable floor area is usually the cutoff for streamlined planning consent, though the exact rule varies by council. Larger granny flats need full development approval.
Can I rent my granny flat separately?▾
It depends on your council. Some allow separate tenancies, others only allow it to house family. Confirm with council in writing before you build.
Does it need its own driveway?▾
Not required in most cases but recommended if the granny flat is intended for a separate tenant. Off-street parking allocation matters at planning consent stage.
Will building a granny flat add to my rates?▾
Yes, adding habitable floor area typically increases your capital improved value and therefore your council rates. The uplift is usually modest.
Do I need a separate meter?▾
You can either sub-meter the granny flat under the main house account or install a separate connection. Separate is cleaner if you plan to rent it out.