Duplex Design & Approval Services in Sydney

How Much Does Duplex Design & Approval Cost in Sydney?

A duplex design-and-approval package with giantA typically costs $4,000–$11,000 ex GST in 2026, depending on slope, council, and whether your project fits the DA or CDC pathway. The table below shows a typical breakdown.

Component	DA pathway	CDC pathway
Concept + consent drawings	$2,500–$5,000	$2,250–$4,500
Statement of Environmental Effects (SEE)	$750–$1,500	n/a (SEPP comply)
BASIX + NatHERS certificate	$300–$600	$300–$600
Survey + geotechnical	$600–$1,250	$600–$1,250
Council / certifier lodgement fees	$500–$1,000	$750–$2,000
Total typical range	$4,500–$9,500	$4,000–$8,500

Excludes construction, structural/hydraulic engineering beyond standard scope, and authority contributions. Every giantA quote is fixed-fee and confirmed after a free site feasibility review.

Get a Fixed-Fee Quote

Is Your Site Suitable for a Duplex?

Lot size alone doesn't determine duplex viability. giantA assesses eight data sources before advising:

#	Check	Source	Cost to You
1	Zoning & planning permissibility	NSW Planning Portal	Free
2	Physical land data — dimensions, slope	NSW Spatial Portal	Free
3	Boundaries & easements	SIX Maps	Free
4	LEP & DCP controls (lot size, FSR, height)	Local council	Free
5	Hazards — flood, bushfire, heritage	Planning Certificate 10.7	$26.5–$80
6	Legal encumbrances — covenants, 88B	Title search	$6.5–$20
7	Exact dimensions	Registered survey plan	$600–$1,250
8	Professional feasibility review	giantA	Free

Get Your Free 8-Source Feasibility Report Turnaround: 2–3 business days.

Our Duplex Design & Approval Process

giantA delivers duplex approvals in 6 fixed stages, with a named designer and a fixed-fee proposal from the start.

1. Free Site Feasibility (Day 0–3). We pull your address through NSW Planning Portal, SIX Maps and your council's LEP / DCP. You receive a written go / no-go / go-with-conditions report.
2. Brief & Concept (Week 1–3). Site visit, brief workshop, 2–3 concept layouts, mirror-vs-detached massing options.
3. Design Development (Week 3–7). 3D model, materials selection, BASIX pre-assessment, geotechnical and survey coordination.
4. DA or CDC Documentation (Week 7–12). Full drawing set, Statement of Environmental Effects or CDC-compliant drawings, BASIX certificate, landscape and stormwater plans.
5. Lodgement & Assessment (Month 3–7). We lodge, respond to council RFIs and negotiate conditions. CDC path: 20-day determination.
6. Construction Certificate & Handover (Month 7–9). CC documentation ready to tender or take to our recommended builder panel.

Why Choose giantA for Your Duplex

• BDAA-accredited building designers — not drafters, not sales representatives.
• Registered Design Practitioner (NSW DBP Act) — required for Class 2 work; we exceed the baseline.
• In-house town-planning liaison — we speak council.
• Fixed-fee proposals after feasibility — no scope creep, no surprise variations at lodgement.
• End-to-end — design, BASIX, engineering coordination, certifier liaison, Construction Certificate.
• Recent duplex approvals across Sutherland Shire, Canterbury-Bankstown, Hills District, Northern Beaches, Georges River, Parramatta, Ryde and Hornsby.

See our recent duplex work: giantA duplex portfolio →

Sydney Areas We Service

Sutherland Shire · Canterbury-Bankstown · Georges River · Hills District (Baulkham Hills, Castle Hill, Kellyville) · Hornsby Shire · Northern Beaches · Parramatta · Ryde · Inner West · Cumberland · Blacktown · Penrith · Campbelltown · Liverpool · Fairfield · Ku-ring-gai · Willoughby · Wollongong · Central Coast.

Duplex Design & Approval — FAQs

What is the minimum block size for a duplex in Sydney?

Most NSW councils require a minimum of 400–500 m² for a duplex, with some councils requiring 550 m² or more. Frontage width and the council's specific LEP / DCP controls matter as much as area. giantA verifies your block against the exact controls in our free feasibility check.

How long does duplex DA approval take in NSW?

Typical DA timeframe is 3–6 months from lodgement to determination. Complying Development (CDC) is 20 days when your block complies with the Housing SEPP. End-to-end (design to consent) is normally 4–9 months.

Can I subdivide and sell each duplex separately?

Yes — via Torrens title subdivision if your council permits, or strata subdivision as the fallback. Subdivision potential is assessed in our feasibility stage.

Do I need an architect or a building designer for a duplex?

For duplexes (Class 1a) a Registered Design Practitioner or a registered architect can both prepare DA / CDC documentation. BDAA-accredited building designers like giantA typically charge less while delivering the same consent outcome.

What's the difference between a duplex and dual occupancy?

Legally the same in NSW planning terms — the planning term is dual occupancy. "Duplex" is the market term. Both can be attached or detached, Torrens or strata subdivided, subject to council.

How much does it cost to build a duplex after approval?

Construction typically runs $1,400–$2,100 per m² in 2026 — around $275,000–$1.1M for a 250 m² duplex. giantA works with your builder, or we can recommend from our panel.

Can I live in one side and rent out the other?

Yes — that's the most common duplex strategy. Each side needs independent services (water, electricity, drainage); we design that in from day one.

What if my block is sloping or irregular?

Sloping blocks often suit split-level duplex designs. We assess slope, drainage, retaining and sight-line impacts at the feasibility stage.