Sydney’s mild reputation disguises how badly its housing performs. A typical unrenovated Sydney home built before 1990 has no wall insulation, single-glazed aluminium windows, uncontrolled air leakage, and a gas hot water system running at a fraction of the efficiency now available. These homes are cold in July and unbearable in a February heatwave, and their occupants pay for the difference every quarter.
Renovation is the only practical moment to fix this. Walls are open, floors are up, and the incremental cost of doing it properly is a fraction of retrofitting later. This guide covers what actually works in Sydney conditions, what it costs, what compliance requires, and what rebates are available in 2026.
A related guide to consider while planning this work is Do You Need Council Approval to Renovate in Sydney? The 2026 Rules Explained.
The Compliance Driver: BASIX
In NSW, BASIX applies to renovation and extension work with an estimated cost of $50,000 or more, and to all new dwellings and secondary dwellings. It applies whether you are going through a development application or a complying development certificate.
BASIX assesses three things:
- Energy — reduction in greenhouse gas emissions from fixed appliances and systems
- Water — reduction in potable water consumption, with targets up to 40 per cent
- Thermal comfort — benchmarked against a minimum 7-star NatHERS rating, mandatory since October 2023 and aligned with the National Construction Code
The thermal comfort component is where older Sydney homes struggle. Getting a 1930s bungalow with single glazing and uninsulated cavity walls to a 7-star equivalent outcome typically costs $8,000 to $25,000 in envelope upgrades. The certificate itself costs $400 to $1,500 including thermal modelling, and is valid for three months — so generate it once the design is settled, not before.
A practical note: BASIX assessment for a renovation is a whole-of-house exercise, not just the new work. This surprises many Sydney homeowners who expected only the extension to be assessed.
The Upgrades That Actually Work in Sydney
Sydney’s climate zone means cooling matters as much as heating. Interventions that work in Melbourne or Hobart are not automatically the right priorities here.
1. Ceiling insulation — the highest return available
Roof and ceiling heat gain is the dominant thermal load in a Sydney summer. Ceiling insulation is cheap, easy to retrofit, and delivers more comfort per dollar than anything else.
- Batts to R5.0 or higher, correctly installed with no gaps and no compression: $25 to $50 per square metre
- A typical Sydney house: $3,000 to $7,000
- Critical details: maintain clearance around downlights and flues, do not block eave ventilation, and ensure the insulation is continuous over the top plate at the wall junction
2. Roof and attic ventilation
A Sydney roof cavity can reach 60 degrees on a summer afternoon. Whirlybirds are largely ineffective; what works is adequate eave intake combined with ridge or high-level exhaust. Cost $800 to $3,000 and it reduces the load on both the insulation and the air conditioning.
3. Draught sealing — cheapest measure available
Uncontrolled air leakage in an older Sydney home can equal a permanently open window. Sealing costs very little and delivers immediately.
- Door and window seals, weather strips and door bottoms — $400 to $1,500
- Sealing gaps at floorboards, skirtings and service penetrations — $500 to $2,000
- Damper or seal to unused fireplaces — $150 to $600
- Sealed, insulated exhaust fans replacing open vents — $300 to $800 each
The caveat: sealing without ventilation creates condensation and mould in Sydney’s humidity. Pair draught sealing with controlled ventilation — good exhaust fans in wet areas and openable windows for cross ventilation.
4. External shading — better than any glass
On Sydney’s north and west elevations, external shading outperforms any glazing upgrade for summer comfort, because it stops the heat before it reaches the glass.
- Eave extensions and awnings — $600 to $2,500 per window
- External venetian or roller shutters — $1,200 to $3,500 per window
- Pergolas with deciduous planting — shade in summer, sun in winter, and cheap
- Correctly sized eaves on new work — designed for the sun angle, not the aesthetic
5. Glazing
Windows are typically the weakest element in a Sydney home’s envelope. Options in ascending order of cost and performance:
- Retrofit low-e film — $60 to $150 per square metre, modest improvement
- Secondary glazing — an internal glazed panel behind the existing window. $350 to $700 per square metre, excellent for heritage homes where the original sashes must stay
- Double glazing in aluminium — $700 to $1,200 per square metre
- Thermally broken double glazing — $900 to $1,800 per square metre, and the difference over standard aluminium is substantial
A whole-of-house window replacement on a typical Sydney home is $20,000 to $60,000. It is a large number, which is why glazing upgrades are best done as part of a broader renovation rather than standalone.
6. Underfloor insulation
A large share of Sydney housing has suspended timber floors over a ventilated subfloor. Retrofitting insulation between the joists is straightforward where there is crawl space, costs $30 to $60 per square metre, and noticeably improves winter comfort. Do not seal the subfloor ventilation — moisture must still escape.
7. Wall insulation
The hardest retrofit in Sydney. In a brick veneer home with a cavity, blown-in insulation is possible at $30 to $60 per square metre. In solid double-brick construction — very common in Sydney’s older stock — internal insulation must be approached carefully with a ventilated cavity and vapour-permeable build-up, or you create the damp problems described in our guide to renovating a Sydney terrace. Where walls are being re-lined anyway during a renovation, insulate then.
8. Hot water
Water heating is typically the largest single energy use in a Sydney home. A heat pump hot water system uses roughly a quarter of the energy of an electric resistance system.
- Heat pump hot water system installed — $3,500 to $6,500 before rebates, often $1,000 to $3,500 after
- Solar hot water with electric boost — $4,500 to $8,000 installed
- Payback period in Sydney, typically 3 to 6 years
9. Heating and cooling
A modern high-efficiency reverse-cycle split system is the most efficient way to heat and cool a Sydney home, delivering three to five units of heat per unit of electricity.
- Single split system installed — $1,800 to $3,500
- Multi-head system — $6,000 to $14,000
- Ducted reverse cycle — $12,000 to $25,000
Size the system to the improved envelope, not the existing one. Insulating first and then sizing the system correctly often saves more than the insulation cost.
10. Solar and batteries
- 6.6kW rooftop solar installed — $5,000 to $9,000 before STC discount, commonly $3,500 to $6,500 after
- 10kW system — $8,000 to $14,000 after incentives
- Home battery, 10kWh — $8,000 to $15,000 installed, before any applicable incentives
Do the electrical planning during the renovation even if the panels come later. Running conduit, upgrading the switchboard and providing space for an inverter and battery costs very little during construction and a great deal afterwards.
Rebates and Incentives in 2026
Programs change frequently and eligibility criteria are specific, so verify current details before relying on any figure. As a general map of what exists:
- Small-scale Renewable Energy Scheme (federal) — STCs that discount the upfront cost of solar PV, solar hot water and heat pump hot water systems. Applied at point of sale by the installer.
- NSW Energy Savings Scheme and Peak Demand Reduction Scheme — discounts delivered through accredited providers on hot water system upgrades, efficient appliances, lighting and, in some cases, air conditioning.
- NSW household energy upgrade programs — targeted support for insulation, efficient appliances and electrification, with eligibility often tied to concession card holders or specific household circumstances.
- Federal household energy support — battery and electrification incentives operating through installer discounts.
- Council programs — several Sydney councils run their own sustainability rebates for rainwater tanks, solar and insulation, generally modest but worth checking.
- Low-interest green loan products offered by major lenders for efficiency and electrification upgrades.
Two practical points. First, most rebates are claimed by the accredited installer and appear as a discount rather than a payment to you — so ask each quoting installer what incentives they will apply. Second, incentives frequently require the work to be done by an accredited provider, so confirm eligibility before engaging anyone.
Water Efficiency
BASIX includes water targets, and Sydney’s water restrictions history makes this more than a compliance exercise.
- WELS-rated tapware, showerheads and toilets — minimal additional cost, meaningful reduction
- Rainwater tank plumbed to toilets and laundry — $3,000 to $8,000 installed
- Drought-tolerant landscaping and efficient irrigation
- Greywater diversion systems — $2,500 to $8,000, with approval requirements
Sequencing: What to Do First
If the budget is limited, this order delivers the most comfort per dollar in Sydney:
- Draught sealing — under $2,000, immediate effect
- Ceiling insulation — $3,000 to $7,000, largest single improvement
- External shading on north and west glazing — targets Sydney’s dominant summer load
- Heat pump hot water — largest energy bill reduction, strong rebates
- Underfloor insulation where a subfloor exists
- Efficient split systems sized to the improved envelope
- Solar PV
- Glazing upgrades — highest cost, best done during a broader renovation
- Wall insulation — only when walls are open
- Battery storage — once the rest is done
The Case for Doing It During the Renovation
Every one of these measures is dramatically cheaper when the house is already open. Insulating a wall during a renovation costs the price of the batts. Insulating it afterwards costs the price of removing and replacing the lining. Running conduit for future solar during a rewire costs almost nothing; retrofitting it means chasing walls again.
A related guide to consider while planning this work is Ceiling Insulation Upgrades: Top Up Existing Batts or Replace Them?.
Sydney homeowners routinely spend $200,000 on a renovation and leave the house performing as badly as it did before, because the energy work was seen as an optional extra rather than part of the scope. The envelope upgrades that make a real difference typically represent five to ten per cent of a renovation budget — and they are the only part of the project that pays you back every quarter for the next thirty years.
For the broader cost picture see our Sydney renovation cost guide, and for the approval implications of crossing the $50,000 threshold, our guide to council approval in Sydney.
Understanding Your Home’s Current Performance
Before spending on upgrades, it is worth knowing where the losses actually are. Two low-cost assessments are available in Sydney:
- A thermal imaging survey — $400 to $900 — shows missing insulation, thermal bridges and air leakage paths visually. Best performed on a cold morning or a hot afternoon when the temperature differential is greatest.
- A blower door test — $600 to $1,500 — measures the home’s air leakage rate. Older Sydney homes commonly test at 15 to 25 air changes per hour at 50 pascals; a well-sealed modern home is under 5.
Both frequently redirect spending. Owners who assumed they needed double glazing often discover that their losses are dominated by an uninsulated ceiling and a gap under every door — problems that cost a tenth as much to solve.
Electrification: Removing Gas
Most Sydney homes still have gas for cooking, hot water and sometimes heating. The economics of retaining it have shifted, because gas supply charges are fixed regardless of consumption. A household using gas only for cooking pays a daily supply charge that frequently exceeds the value of the gas consumed.
The full electrification path:
- Induction cooktop replacing gas — $1,200 to $4,000 including the electrical circuit. Induction is faster than gas, easier to clean, and does not release combustion products into the kitchen.
- Heat pump hot water replacing instantaneous gas — $3,500 to $6,500 before rebates
- Reverse-cycle split systems replacing gas heating — $1,800 to $3,500 per unit
- Gas disconnection and meter removal — often free or a small fee, and it eliminates the daily supply charge permanently
Do the electrical planning during the renovation. An induction cooktop needs a dedicated circuit, a heat pump needs an outdoor location with clearances and drainage, and the switchboard often needs capacity for both. All of this is straightforward while walls are open and expensive afterwards.
Indoor Air Quality and Condensation Risk
The most common unintended consequence of energy upgrades in Sydney is condensation. A home that leaked air freely and was heated intermittently rarely had a moisture problem; the same home sealed, insulated and heated consistently can develop mould within a season.
The principles that prevent it:
- Ventilate deliberately. Exhaust fans in wet areas and kitchens, ducted outside and sized to the room, running with a timer.
- Do not seal a subfloor. Ventilated subfloors in Sydney’s raised timber-floor housing must keep their airflow.
- Maintain roof space ventilation when insulating a ceiling.
- Understand vapour permeability. Insulating a solid brick wall internally without a ventilated cavity moves the dew point inside the wall, which is how well-insulated old houses develop hidden decay.
- Consider heat recovery ventilation on comprehensively sealed renovations — it supplies fresh air continuously while recovering most of the heat.