$30k-$40k Buys You an Extra Bedroom

1-bed granny flat (40-45 sqm internal): all-in $118,000-$167,000. 2-bed granny flat (55-60 sqm internal): all-in $150,000-$207,000.

Incremental spend: $32,000-$40,000 for an additional bedroom and slightly larger living area.

The per-sqm cost on the incremental 15-20 sqm is roughly $2,100-$2,400/sqm — bang in line with the overall granny flat build rate. You are not paying a 'premium' for the extra bedroom; you are paying the same per-sqm as the rest of the dwelling. Buildana (Lic. 487805C) has built both configurations across Fairfield, Liverpool, Cumberland and Canterbury-Bankstown.

Per-sqm Maths on the Incremental Spend

1-bed (45 sqm internal, medium brick veneer): • Construction: 45 × $2,370 = $106,650. • Site costs + connections + approvals + externals: $30k-$60k. • All-in: $136k-$167k.

2-bed (60 sqm internal, medium brick veneer): • Construction: 60 × $2,370 = $142,200. • Same site costs + connections + approvals + externals (these don't change much with size): $30k-$60k. • All-in: $172k-$202k.

Notice site costs, connection costs, approval costs are essentially identical for 1-bed vs 2-bed. The kitchen, the bathroom, the service connections, the sewer trench, the CDC fee — all the same. The ONLY thing that changes is the construction cost itself, which scales with floor area at roughly $2,300/sqm.

So for an extra $35k you get 15 sqm of extra dwelling. That 15 sqm is what becomes the second bedroom and a slightly bigger living area.

Rental Income Delta — Western Sydney 2026

Weekly rents (Buildana market data + REIA Q1 2026 rental snapshot):

Fairfield: 1-bed $310-$390 vs 2-bed $400-$480. Gap: $90/week. Liverpool: 1-bed $330-$400 vs 2-bed $420-$500. Gap: $90-$100/week. Canterbury-Bankstown: 1-bed $310-$390 vs 2-bed $400-$490. Gap: $90-$100/week. Cumberland: 1-bed $300-$380 vs 2-bed $390-$470. Gap: $90/week. Blacktown: 1-bed $290-$370 vs 2-bed $380-$460. Gap: $90/week.

The gap is remarkably consistent: $90-$100/week extra for a 2-bed across every LGA we work in. Annually that's $4,680-$5,200 in additional gross rent.

Not a single LGA in Western Sydney has 1-bed rents within $50/week of 2-bed rents. The market values that second bedroom strongly because the tenant pool for 2-beds is much bigger (couples, parents+child, two sharers all qualify) versus 1-beds (couples or singles only).

Lower vacancy is also significant — 2-bed granny flats in our portfolio lease 12-18 days faster on average.

ROI on the Extra $30k-$40k

Incremental spend: $35,000 average. Incremental annual rent: $4,940 average (gross, midpoint). Incremental net rent (after $400-$600 extra operating costs): ~$4,400/year.

ROI on the size upgrade: ~12.6% per year.

Payback on the extra spend: 7-8 years. After that, you have an extra bedroom generating $90-$100/week forever on top of the base 1-bed performance.

Capital valuation impact: 2-bed granny flats add $80k-$160k to property value at refinance. 1-bed granny flats add $50k-$110k. Capital gap: $30k-$50k — meaning the bank often recognises most or all of your incremental spend as additional property value, on top of the rental income.

Only skip the 2-bed if: • Budget is hard-capped under $150k all-in. • Block won't physically take 60 sqm + setbacks + outdoor area. • Dwelling is genuinely only for a single elderly parent with no intention to ever rent.

Contact Buildana for a free site assessment.

If the numbers stack up for your site, the next call is layout. Our 47 granny flat designs at /homes/granny-flats/designs are tagged by bedroom count and floor area so you can pick the plan that maximises rentable space without blowing the build cost.

May 2026 1-Bed vs 2-Bed Granny Flat — Cost and Yield Side-by-Side

Updated May 2026 numbers for the 1-bed vs 2-bed granny flat decision in Western Sydney:

1-bedroom granny flat (35–40sqm, medium spec brick veneer): • Construction: $148k–$192k • Site costs and connections: $14k–$28k • External works and approval: $12k–$24k • Total all-in: $174k–$244k • Typical rent (LGA midpoint): $360–$440/week • Annual rent: $18,720–$22,880 • Gross yield: 8.2–10.7%

2-bedroom granny flat (50–55sqm, medium spec brick veneer): • Construction: $185k–$235k • Site costs and connections: $14k–$28k • External works and approval: $12k–$24k • Total all-in: $211k–$287k • Typical rent: $420–$510/week • Annual rent: $21,840–$26,520 • Gross yield: 8.3–10.9%

2-bedroom granny flat (60sqm SEPP max, medium spec brick veneer): • Construction: $205k–$255k • Site costs and connections: $14k–$28k • External works and approval: $12k–$24k • Total all-in: $231k–$307k • Typical rent: $440–$540/week • Annual rent: $22,880–$28,080 • Gross yield: 8.1–10.6%

Reading the numbers: • Yield is broadly comparable across all three sizes — the extra rent per square metre flattens out. • The 2-bed at 50–55sqm consistently outperforms on yield in our data because the marginal $25k–$45k construction cost for the extra bedroom drives a $60–$100/week rent premium — that pays back in 12–18 months. • The 1-bed makes sense if you want a smaller footprint to preserve more rear yard for the principal dwelling, or if your site doesn't have room for a 60sqm second dwelling. • The 2-bed at 60sqm (SEPP max) is the highest-rent option but doesn't materially outperform the 50–55sqm version on yield. Choose 60sqm if you want a more comfortable second bedroom or a small study nook, not for the rent uplift alone.

For LGA-specific rent ranges and yields: /insights/granny-flat-cost-sydney.