Home Extension Builder St Marys — Approved in 60 Days
St Marys 2760 extensions with tight approval timelines. CDC where eligible (~15 days), DA via Penrith City Council in 40–60 days. Construction 12–24 weeks depending on scope.
HIA Member
MBA NSW0476 300 300Quick Answer
A home extension in St Marys costs $150,000–$600,000+. Rear extension from $150K, second-storey addition from $300K. Buildana manages design, Penrith City Council approvals, and construction under one fixed-price contract.
St Marys Home Extensions — Fixed Price
St Marys homeowners with 1950s–1980s + 2010s+ R4 apartments-era properties are increasingly turning to home extensions to gain space without the disruption of a full move. With typical lots of 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release), most St Marys properties can accommodate ground-floor or second-storey extensions under Penrith City Council's planning controls. Buildana manages feasibility, design, approvals, and construction for St Marys extension projects under one fixed-price contract.
On the ground in St Marys (2760), the practical numbers shape every home extension. Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts soil — extremely reactive clay — pushes engineered foundation work into the $45,000–$80,000 bracket on most 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release) blocks. R2 / R3 / R4 mixed (St Marys CBD) zoning under Penrith City Council sets the building envelope, with R3 Medium Density pockets that open up dual occupancy options on qualifying lots. Median sale price across St Marys sits at $850K–$1.3M typical; $1.0M–$1.6M Glenmore Park/Jordan Springs premium master-planned; $1.6M–$3.0M+ Mulgoa/Wallacia/Castlereagh acreage, which frames the build-versus-buy decision from the start. Local services anchor around St Marys Village + Queen Street + Western Sydney Airport rail (under construction), and that proximity affects everything from rental demand to construction site access.
Buildana manages the complete home extension process in St Marys — from design consultation and structural engineering through to DA or CDC approval, and fixed-price construction to handover. Extend your home without the stress.
Read our Home Extension Cost Guide 2026 or explore extension approval pathways in NSW.
- Home extensions in St Marys from $150K
- Penrith City Council DA and CDC approvals managed
- Ground floor, rear and second-storey additions
- Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts soil — structural engineering included
- 1950s–1980s + 2010s+ R4 apartments-era homes assessed for extension suitability
- Connect new to existing — clean, matched finish
- 6-year structural warranty
- Free design consultation — near St Marys station
Reviewed by Oliver Alameri
Licensed Builder (NSW 487805C) · Master of Property Development · PhD Student · Building across Western Sydney since 2010
Why Extend Your Home in St Marys?
St Marys is the LGA's secondary CBD with its own station and shopping precinct — Queen Street the spine, R3/R4 redevelopment ramping around the station with the upcoming Western Sydney Airport rail link. Older fibro/brick stock on side streets ripe for KDR. Industrial-legacy contamination overlays on the eastern edge.
St Marys sits in the City of Penrith local government area with 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release) residential blocks and R2 / R3 / R4 mixed (St Marys CBD) zoning. Building costs are around the Sydney metro average, balancing construction value with lifestyle and growth. St Marys station gives St Marys direct rail access — a strong draw for residents and tenants. 1950s–1980s + 2010s+ R4 apartments-era homes in St Marys often have good structural foundations worth building on. Extensions add living space at a fraction of the full rebuild cost. Ground conditions (Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts) across St Marys are well understood by local builders — Buildana's engineering accounts for extremely reactive soil movement.
Home extension builder in St Marys — key facts
- Suburb
- St Marys, NSW 2760
- Council / LGA
- Penrith City Council (City of Penrith)
- Primary zoning
- R2 / R3 / R4 mixed (St Marys CBD)
- Typical lot size
- 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release)
- Soil class
- Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts
- Median house price
- $850K–$1.3M typical; $1.0M–$1.6M Glenmore Park/Jordan Springs premium master-planned; $1.6M–$3.0M+ Mulgoa/Wallacia/Castlereagh acreage
- Home era
- 1950s–1980s + 2010s+ R4 apartments
- Typical price range
- $150,000 – $600,000+
- Typical timeline
- 6–12 months design to handover
- Approval pathway
- CDC for most rear extensions, DA for second-storey
Building in St Marys — Local Context
St Marys Block Realities
Typical St Marys blocks are 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release) on Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts ground (extremely reactive clay). For a extension, the structural envelope is more constrained than the headline lot size suggests — once you subtract setbacks, easements, landscaped area requirements, and any tree preservation, the actual buildable area is usually 35-45% of the block. We map that early in the feasibility stage so you're designing to what's actually allowed, not what looks possible from the title plan. Foundation cost band on most St Marys blocks: $45,000–$80,000.
Planning Controls in St Marys
St Marys is zoned R2 / R3 / R4 mixed (St Marys CBD) with R3 Medium Density pockets. Penrith City Council controls FSR, height limits (typically 8.5–9m), site coverage, landscaped area minimums, and setbacks. For a extension, the binding constraints on most 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release) blocks here are: front setback (around 4.5–6m), side setbacks (1.0–1.5m articulated), rear (3–6m depending on lot depth), and landscaped area (usually 35–40%). Buildana's design team works to those numbers from the first sketch — no late re-design when council comes back with comments.
Where the Money Goes on a St Marys Extension
Cost breakdown for a typical extension in St Marys: structure and frame around 30%, slab and foundations 8–14% (driven by Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts soil), roofing and external 10–12%, services (plumbing, electrical, HVAC) 12–18%, fit-out (kitchen, bathrooms, joinery) 18–25%, and finishes (paint, tiles, flooring) 8–12%. The remaining 4–6% covers approvals, certifications, and site establishment. Buildana itemises every line so you see what you're paying for — no lump sums hiding margin.
Designing for the St Marys Streetscape
St Marys's housing stock is predominantly from the 1950s–1980s + 2010s+ R4 apartments.. The local anchor is St Marys Village + Queen Street + Western Sydney Airport rail (under construction). For a home extension, the streetscape question matters more than most builders admit — a brand-new double-storey on a street of single-storey 1950s–1980s + 2010s+ R4 apartments weatherboards will draw council attention on bulk and scale, even if technically compliant. Buildana designs the front elevation to read appropriately for the street while modernising the floor plan and structure behind it. Materials palette, roof pitch, fenestration rhythm — all chosen to settle into the existing rhythm rather than fight it.
What Recent Approvals Show
Penrith City Council's recent decisions for Extensions in St Marys reveal a clear pattern — applications with proper structural engineering tied to the existing footings on Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts soil and clean shadow analysis to neighbours' POS are progressing without RFIs. Sloppy lodgement adds 4-8 weeks of round-trip; clean lodgement doesn't.
Builder's Take on St Marys
Matching brick on a St Marys extension: 1950s–1980s + 2010s+ R4 apartments brick is often discontinued. We specify a close-match or deliberately contrast with render or cladding so the extension reads as intentional, not as a failed match. Done well, an intentional contrast looks better than a forced match.
Extension or move? In St Marys, the maths usually favours extension once you factor in stamp duty ($40K–$60K), agent fees ($25K–$40K), and moving costs. An extension of $200K–$350K often delivers the space without the 12-week disruption of moving.
St Marys vs Nearby Suburbs
St Marys vs nearby suburbs — key metrics for extending.
| Suburb | Median Price | Typical Lot | Soil Class | Era | Station |
|---|---|---|---|---|---|
| St Marys2760this suburb | $850K–$1.3M typical; $1.0M–$1.6M Glenmore Park/Jordan Springs premium master-planned; $1.6M–$3.0M+ Mulgoa/Wallacia/Castlereagh acreage | 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release) | Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts | 1950s–1980s + 2010s+ R4 apartments | St Marys |
| Werrington2747 | $850K–$1.3M typical; $1.0M–$1.6M Glenmore Park/Jordan Springs premium master-planned; $1.6M–$3.0M+ Mulgoa/Wallacia/Castlereagh acreage | 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release) | Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts | 1960s–1980s fibro/brick veneer (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys) + 1990s–2010s brick (Glenmore Park/Cambridge Gardens) + 2010s+ master-planned (Jordan Springs/Caddens/Claremont Meadows) | Werrington |
| Cambridge Park2747 | $850K–$1.3M typical; $1.0M–$1.6M Glenmore Park/Jordan Springs premium master-planned; $1.6M–$3.0M+ Mulgoa/Wallacia/Castlereagh acreage | 450–750m² typical (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys); 250–450m² master-planned (Jordan Springs/Caddens/Glenmore Park new release) | Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts | 1960s–1980s fibro/brick veneer (Cranebrook/Werrington/Cambridge Park/Kingswood/St Marys) + 1990s–2010s brick (Glenmore Park/Cambridge Gardens) + 2010s+ master-planned (Jordan Springs/Caddens/Claremont Meadows) | Werrington (1 km) |
| Jordan Springs2747 | $1.0M–$1.4M | 300–500m² | Class M (Wianamatta Shale predominant) / Class P/E (Hawkesbury–Nepean alluvial corridor on Cranebrook/Castlereagh/Emu Plains/Penrith Lakes; flood planning controls under Penrith DCP 2014) / industrial-legacy contamination overlays on Werrington/St Marys legacy precincts | 2010s–present master-planned | St Marys (5 km) + future Western Sydney Airport rail |
Median price, soil class, and lot size shape build feasibility and final cost. Buildana assesses every site against these and other constraints during the free feasibility stage.
Have a question about your project?
Talk to our team — free site assessment and fixed-price quote.
Cost Guide
| Item | Estimated Range |
|---|---|
| Simple rear extension (single wall removal, no roof change) | $90,000 – $200,000 |
| Moderate extension (multiple openings, roof extended) | $200,000 – $380,000 |
| Complex extension (structural steel portals, re-roofing) | $380,000 – $600,000 |
| Second-storey tie-in (existing house re-engineered) | $350,000 – $650,000 |
Prices are indicative for Western Sydney (2025). Actual costs depend on site, specifications, and approvals.
How It Works
From First Call to Final Key
The first job on an extension is finding out what you're extending onto. St Marys homes from the 1950s–1980s + 2010s+ R4 apartments were built to different standards — we open walls, check footings, verify load paths. The existing house has to carry the new work.
⏱Design follows the existing roof. A bad extension looks like a bolt-on; a good one reads as original. Matched brickwork or contrasting render (whichever the architecture calls for), tied-in roofline, continuous flooring where it should be continuous.
⏱Construction happens while you live in the house. That means weatherproofing every night, staging the works so kitchens and bathrooms don't disappear on the same week, and keeping the site clean of debris that doesn't belong in a family home.
⏱Finish is seamless. Paint match, floor match, roofline match, brick match where possible. The only way to tell the extension is new is the date on the plans.
⏱Our Team
Oliver Alameri
Founder / Director / Builder · MPropDev · PhD Student
Ahmad Alameri
Accounts Manager
Claire Wendell
Project Manager
Estimate Your Build Cost
Use our free calculator to get an instant cost estimate for your project
Ready to take the next step?
Free consultation — no obligation, no pressure.
Frequently Asked Questions
“Buildana built our granny flat in just 12 weeks. Fast approvals, great communication, and a beautiful final product. Highly recommend.”
Fatima Al-Rashid
Liverpool, NSW
We Build Across Sydney
Headquartered in Western Sydney's Fairfield. Active across all 28 metropolitan Sydney LGAs — from Penrith to the Eastern Suburbs, the Hills to the Sutherland Shire.
Last updated: 1 April 2026
Extend Your Home in St Marys
Free design consultation for St Marys 2760. We'll assess your home, design the extension, and provide a fixed-price quote.
Start Your Project