The conversation about double glazing usually goes one way. How much does it cost? When will it pay back? Is it worth it for Perth?
The conversation rarely goes the other way. What does it cost to do nothing? What is the price of keeping the single glazed windows you have?
This article inverts the usual frame. Instead of asking what the upgrade costs, it asks what the status quo costs, drawn from Australian energy modelling, AGWA 7-star data, NCC 2022 energy efficiency provisions, and the building physics evidence on condensation damage. The total cost of single glazed windows in a Perth home is not zero. It is a slow drain spread across utility bills, frame and sill damage, sleep quality, and resale value.
How to Calculate the Annual Energy Cost Difference
A typical Perth home runs an air conditioner more hours than it runs a heater. The cooling load is the bigger number on most utility bills, and single glazed windows are the largest single component of that cooling load through the building envelope, particularly on west and unshaded north elevations.
Australian energy modelling published in December 2024, drawing on AGWA 7-star data, gives indicative annual savings from upgrading to double glazing. For a Brisbane single-storey home (the closest climate analogue to Perth in the model), the annual saving sits in the range of $530 to $726. Perth is not directly modelled, so the Brisbane figures are an extrapolation, but the cooling-dominant pattern is the same.
The number underestimates the Perth specific case in two ways. First, Perth has more 35-degree-plus days per year (26 on average per Bureau of Meteorology Perth climate data) than Brisbane. Second, Perth tariffs have risen faster than the eastern states over the past 5 years, so the energy cost per unit avoided is higher in Perth than the national model assumes. A conservative Perth estimate, extrapolated from the Brisbane modelling with Perth tariff and heat-day adjustments, sits in the range of $400 to $750.
Across a 10-year ownership period, that compounds. $400 to $750 a year, even ignoring tariff inflation, is $4,000 to $7,500 of avoidable energy cost. With realistic tariff inflation of 3 to 5 per cent annually, the 10-year cumulative number runs closer to $5,500 to $11,000.
For a Perth home with multiple west-facing rooms, the underestimate is larger because the cooling load on those rooms is disproportionate. Our guide to whether double glazing actually keeps Perth homes cooler in summer covers the thermal physics behind the difference.
What Ongoing Condensation Does to Window Frames, Sills and Walls
Perth winters are short and mild compared to most Australian capitals, but they include enough cool nights to push interior glass surface temperatures below the dew point on single glazed windows. The WHO 2009 Guidelines on Dampness and Mould describe the mechanism: when interior surfaces drop below the dew point of the room air, water condenses on those surfaces, which then sustains microbial growth and material damage.
A standard Perth living room at 21 degrees and 55 per cent relative humidity has a dew point of approximately 11 to 12 degrees. Single glazed window surfaces (U-value approximately 5.7 W/m²K) routinely sit at 8 to 12 degrees on a winter night, well within condensation territory. A standard IGU (U-value approximately 2.7 W/m²K) keeps the inner pane at approximately 16 to 18 degrees, above the dew point. No condensation forms.
What condensation does to the frame, the sill, and the surrounding plaster over years:
- Years 1 to 2: seasonal wetting starts. Architrave paint begins to bubble around the sill. Mould spots may appear on grout or sealant lines.
- Years 2 to 5: timber sills begin to soften where the wet line sits. Paint peels visibly. Plaster reveals can stain. Aluminium frames corrode less but their seal and gasket interfaces with the glass degrade faster.
- Years 5 to 10: if not addressed, timber sill replacement, plaster patching, and full repainting of the affected reveal becomes the only remediation path. Cost: $500 to $2,500 per affected window depending on extent and finishes.
- Beyond 10 years: structural framing behind the sill can be affected, particularly in older homes with timber framing and inadequate flashing.
For a Perth home with 15 windows of which 6 are on cool elevations susceptible to condensation, the cumulative remediation cost over 10 years runs $3,000 to $15,000 depending on whether the damage is caught early. Our guide to what single glazed windows are doing to your Perth home’s air quality covers the health side of the same problem.
How Noise from Single Glazed Windows Affects Sleep and Productivity
A standard 4 mm single glazed window has an Rw rating of approximately 29 dB (AU industry acoustic test data). A standard double glazed unit lifts this to approximately 32 Rw. An acoustic laminated double glazed unit can reach 37 to 42 Rw depending on configuration.
The difference between 29 and 37 Rw is not just 8 dB on a chart. The human ear perceives a 10 dB reduction as approximately halving the perceived loudness. For homes near Perth flight paths, busy roads, or freeway corridors, the acoustic impact of single glazed windows is the noise burden in the bedroom every night.
Long-running sleep research (cited by Asthma Australia and the WHO Environmental Noise Guidelines) ties chronic exposure to night-time noise above 40 dB to elevated rates of sleep fragmentation, reduced REM sleep, and daytime fatigue. Whether this translates to a measurable dollar cost depends on the household, but the cumulative effect on health, productivity and quality of life is not zero.
For homes in flight path or freeway-adjacent suburbs, the acoustic case for double glazing often outweighs the thermal case. Penot Double Glazing’s flight path noise reduction page covers the specifications that move the dial.
What Single Glazed Windows Do to a Perth Home’s Sale Price
This is the part of the cost-of-inaction conversation that no Perth-specific dataset cleanly answers. REIWA does not publish a single vs double glazing premium figure for Perth. Domain and realestate.com.au editorial cover energy efficiency in general terms but do not isolate glazing as a variable.
What is observable in the WA market:
- NCC 2022 7-star NatHERS energy efficiency requirements applied to all new Class 1 buildings in WA from 1 May 2025. Every new home built in Perth from that date forward is, by law, more energy efficient than a typical 1980s or 1990s brick veneer with single glazed windows.
- Buyer expectations on energy performance rise with each year of the new standard.
- Acoustic performance is increasingly listed in real estate marketing copy for homes in flight path and main road suburbs.
The honest framing: there is no published Perth dataset on the resale premium for double glazing, but the gap between an upgraded home and an unupgraded home is widening as the standard for new builds rises. For homeowners planning to sell within 5 to 10 years, this is worth weighing in the decision.
Cost of Inaction Summary Table
Indicative cumulative cost of keeping single glazed windows in a typical Perth home (10 windows, mixed orientations, 1990s build):
| Period | Energy bill difference | Condensation remediation | Noise impact | Total avoidable cost |
|---|---|---|---|---|
| 3 years | $1,500 to $2,800 | $0 to $1,500 | Hard to quantify, household-specific | $1,500 to $4,300 |
| 5 years | $2,800 to $4,800 | $1,000 to $4,000 | As above | $3,800 to $8,800 |
| 10 years | $5,500 to $11,000 | $3,000 to $15,000 | As above | $8,500 to $26,000 |
The energy figures use Australian energy modelling published in December 2024 with conservative tariff inflation applied for Perth. The condensation figures use building industry remediation ranges for affected windows. The noise impact is genuine but not quantifiable in dollars without household-specific data.
Indicative remediation ranges based on building industry repair data; no Perth-specific published study quantifies these costs.
For context, a typical Perth double glazing upgrade for 10 windows plus 2 doors with thermally broken aluminium runs $24,000 to $36,000 supply and install per the Penot Double Glazing cost guide for Perth. The 10-year cost of inaction ($8,500 to $26,000) is in the same order of magnitude as the upgrade itself.
When Staying Put Genuinely Makes Financial Sense
Single glazed windows are not always the wrong call. Four cases where keeping them is the right financial decision:
- Planned ownership period is under 3 years and the home is on the market soon
- Windows are in good condition (no condensation issues, no frame damage) and the home’s elevations are favourable (south-facing main living, shaded north windows, good eaves)
- Major renovation or demolition is planned within 5 years
- Financial constraint genuinely makes the upgrade impossible right now, in which case secondary glazing on the worst rooms can be a stepped approach
Outside these cases, the cumulative 10-year cost of inaction usually exceeds the upgrade cost, particularly for homes with west-facing exposure or flight path noise. The how to finance double glazing Perth guide covers humm90 interest-free options for spreading the cost.
How to Use This Information When Getting a Quote
The cost-of-inaction framing changes the conversation with a supplier. Instead of asking “is this worth it”, the question becomes “what is the break-even period given my actual energy bills, my actual climate exposure, and my actual ownership horizon”.
Three things worth doing before a quote:
- Pull the last 12 months of energy bills. Note the kWh used for cooling specifically if your retailer breaks it out.
- Walk the windows. Note which ones get morning sun, afternoon sun, or none. West-facing and unshaded north windows are where the upgrade pays back fastest.
- Note which rooms are coldest in winter and warmest in summer. These rooms are usually where the glass spec is doing the least.
With this information in hand, the quote conversation can be specific rather than generic. A good supplier will spec the glass and frame differently by orientation, prioritising the rooms where the avoidable cost is highest.
Where Penot Double Glazing Fits
Penot Double Glazing is a full AGWA member based at 92 Beechboro Rd S, Bayswater WA 6053. The standard double glazed window and door range is specified per opening rather than as a one-size-fits-all spec, so the rooms where the cost of inaction is highest get the highest-impact glass and frame upgrade.
For a quote that maps the upgrade against your actual energy bills, orientation and ownership horizon, book a free in-home assessment. Compare options across the double glazed windows Perth range, call 1300 121 603, or visit the Bayswater showroom at 92 Beechboro Rd S.
How Much Extra Do Single Glazed Windows Cost a Perth Homeowner Each Year?
Indicative annual energy bill difference between a comparable single and double glazed Perth home sits in the range of $400 to $750, drawn from Australian energy modelling published December 2024 using AGWA 7-star data. Perth is not directly modelled, so the Brisbane figures are the closest proxy. The figure varies with house size, orientation, AC use, tariff and the spec of the comparison. Comfort, condensation, acoustic and resale benefits are not counted in this number.
Does Single Glazing Damage Perth Window Frames Over Time?
Yes, indirectly. Persistent condensation on single glazed surfaces in winter wets the frame, sill and adjacent architrave. Over 2 to 5 years of seasonal condensation, timber sills can develop rot, paint can bubble and peel, and plaster reveals can stain. Aluminium frames corrode less but the seal and gasket interfaces around the glass degrade faster when wet.
Do Single Glazed Windows Affect a Perth Home’s Sale Price?
Anecdotally yes, but no public Perth-specific dataset quantifies the impact. REIWA, Domain and realestate.com.au editorial does not publish a measured single vs double glazing resale figure for the Perth market. What is observable: 7-star NatHERS performance is now the legal minimum for new builds in WA from 1 May 2025, which raises buyer expectations on energy performance over time.
When Does It Make Financial Sense to Keep Single Glazed Windows in Perth?
When the planned ownership period is under 3 years and the home is on the market soon. When the windows are in good condition and the rooms are not on west or north-facing elevations exposed to summer heat. When the home is being substantially renovated or demolished within the next 5 years. Outside these cases, the cumulative cost of inaction usually exceeds the cost of the upgrade over a 10-year horizon.
