How to Make an Old Home Energy Efficient: The Right Order of Upgrades

Get a baseline rating

Before any upgrade, get a NatHERS Existing Homes Assessment or, in Victoria, a Residential Efficiency Scorecard. For $300–$600, an accredited assessor models your home in CSIRO's NatHERS engine and tells you exactly which upgrades add the most stars per dollar for your specific house.

A Melbourne weatherboard home and a Brisbane brick veneer need very different first moves. Generic advice ("insulate the ceiling first") is usually right, but generic advice can't tell you whether your double-brick walls are worth blown-in insulation, or whether your west-facing windows need film, awnings or full replacement.

Cost: $300–$600. Saves: Typically $5,000–$15,000 of wasted retrofit spend by ranking what actually moves your rating. Find an assessor in our assessor directory.

Air-seal the building shell

Pre-2000 Australian homes leak air equivalent to leaving a medium-sized window open year-round. Sealing draughts is the single highest-return action you can take: it costs $50–$500 DIY (or $1,500–$3,000 for a professional whole-home seal) and cuts heating/cooling loads by 15–25% immediately.

What to seal, in priority order:

• • Exhaust fans in bathrooms, laundries and kitchens — fit self-closing backdraft dampers ($15–$25 each).
• • Unused chimneys and flues — chimney balloon or sheet ($30–$50).
• • Door undercuts and frames — door sweeps + weatherstripping ($30–$80 per door).
• • Window frames — silicone caulk gaps where frame meets wall.
• • Wall penetrations — gaps around pipes under sinks, behind toilets, around aircon conduits.
• • Skirting boards and floor edges in homes with timber floors over a ventilated subfloor.

Why it must come first: insulation only works in still air. Insulating a draughty cavity is like wearing a jumper with the zip down. See our guide to DIY draught sealing.

Top up the ceiling insulation

Ceiling/roof heat loss accounts for 25–35% of an uninsulated home's total. Many homes built before 1990 have R1.5 or no insulation at all; today's NCC minimum is R5.0–R6.0 depending on climate zone. Topping up is fast, non-disruptive and tax-rebate eligible in most states.

What it costs:

• • Top-up batts (R3.0 over existing R1.5–R2.0): $1,500–$2,500 for a 3-bedroom home.
• • Full removal + new install (if existing insulation is compressed, mouldy, or contains old foil): $3,000–$5,000.
• • Blown-in cellulose (for cathedral or restricted-access ceilings): $2,500–$4,500.

Watch out for: downlights and exhaust fans need IC-4 rated covers before insulation goes over them, or they're a fire risk. A good installer includes these in the quote.

Why second: ceiling insulation pays back in 3–5 years through reduced heating and cooling. Find insulation installers in your area.

Insulate walls and floors

External walls account for 15–25% of heat loss in an uninsulated home; suspended timber floors over a subfloor add another 5–10%. The right approach depends on construction type:

• • Brick veneer: blown-in insulation through cavity ($2,500–$5,000) — best ROI of all wall options.
• • Weatherboard: remove boards, fit R2.5 batts, replace — usually combined with re-cladding ($8,000–$25,000).
• • Double brick: hardest. Internal insulated plasterboard is the realistic option ($150–$250/m² of wall area).
• • Suspended floors: R2.5 batts fitted from underneath if subfloor clearance allows ($2,500–$5,000 for a 3-bedroom home).
• • Concrete slab: can't be insulated retrospectively. Use rugs and reverse-cycle floor consoles instead.

Skip-it test: if your walls are double brick on a concrete slab in a mild climate (Brisbane, Perth coast), the payback can be 15+ years. Spend the money on glazing instead. Your NatHERS report will tell you.

Upgrade glazing — in stages

A single-glazed aluminium window has an R-value of about 0.15 — effectively an outdoor surface inside your wall. Windows are usually the largest weak point in an older home, but full replacement is expensive ($800–$1,500 per window installed). Stage it:

• • Stage A — under $500 total: heavy curtains with pelmets on every window, low-E window film on west-facing glass.
• • Stage B — $3,000–$8,000: secondary glazing (acrylic panels magnetically fitted inside existing frames) on living and bedroom windows. Performs almost as well as double glazing at a third the cost.
• • Stage C — $15,000–$40,000: full uPVC or thermally-broken aluminium double glazing. Only worth it if you're already replacing rotten frames or doing a major renovation.

Find window and glazing specialists for stages B and C.

Replace gas with efficient electric

With the shell now tight and insulated, your heating and hot water loads have dropped 30–50%. That's the right time to electrify — because you can now buy a smaller heat pump and a smaller solar system to run it. See why the switch off gas is coming.

The three priority replacements (in order):

• • Hot water → heat pump: $3,500–$5,000 installed (after rebates often $1,500–$3,000). Cuts hot water energy use by 60–70%. Highest ROI gas replacement.
• • Space heating → reverse-cycle aircon: $2,500–$6,000 per zone installed. A modern unit delivers 4–5 kWh of heat per 1 kWh of electricity — three times more efficient than gas ducted heating.
• • Cooktop → induction: $1,500–$4,000. Last on the electrification list — gas cooking is only 5–10% of household energy.

Find HVAC installers and heat pump hot water specialists in your area.

Add solar PV, then a battery

Solar is last for a reason: a sealed, insulated, fully-electric home needs roughly half the kW of solar that a leaky, gas-heated home does. Buy solar first and you'll oversize the system, pay $5,000–$8,000 more than needed, and feed cheap energy back to the grid for 5c/kWh.

• • Solar PV (6.6–10 kW typical): $5,000–$10,000 installed after STC rebate. Payback 4–7 years.
• • Battery (10–13 kWh): $8,000–$15,000. Federal Cheaper Home Batteries Program (from 1 July 2025) cuts cost ~30%. Payback 7–10 years.
• • EV charger pre-wire: $500–$1,500 if you're getting the electrician on-site anyway.

Find a solar installer who sizes the system to your post-retrofit load — not your current bill.

The retrofit sequence at a glance

1. 0NatHERS assessment — baseline rating + ranked upgrade list ($300–$600).
2. 1Air-seal draughts, exhausts, chimneys ($50–$3,000).
3. 2Top up ceiling insulation to R5–R6 ($1,500–$3,000).
4. 3Wall + floor insulation where construction allows ($2,000–$8,000).
5. 4Glazing upgrades — curtains → secondary glazing → double glazing.
6. 5Electrify — heat pump hot water, reverse-cycle aircon, induction.
7. 6Solar + battery sized for your post-retrofit load.

Done in this order, a $25,000 budget can move a typical 1.5-star Australian home to a comfortable 5-star with bills 50–65% lower. Done in the wrong order, you'll spend the same and stay cold.