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On a hot Adelaide afternoon, sunlight through exposed glass can add heat to a room just when you most want to keep it out. Shading works: blocking that sun before it reaches the glass makes the room cooler and cuts the cooling load. No single percentage fits every South Australian household.
Adelaide is about 35°S. A west-facing living-room window and a north-facing window should not automatically get the same shade. A measured change at one window is not the same thing as a change in whole-home electricity use. Stan Bond has not run a local energy study of these products. The figures on this page come from the named sources, in the buildings and climates those sources actually used.
What the evidence says in one minute
Shading works: the evidence consistently shows that blocking sun before it reaches the glass makes homes cooler and cuts cooling load, and Australian Government guidance (YourHome) recommends it.
- External shading has the strongest summer effect because it stops sun before it reaches the glass. Australian Government guidance says effective shading can block up to 90% of the heat from direct sun. That's a solar-heat figure, not an energy saving.
- West and north-west glass deserve priority in Adelaide. North glass needs seasonal balance.
- Honeycomb blinds have the strongest Australian evidence among internal coverings.
- No single percentage fits every home. Results depend on orientation, glazing and use.
External shading and internal coverings do different jobs. Stopping the sun outside the glass is the stronger summer move. An internal blind or curtain can still change how the window behaves, and it can still matter for light, privacy and comfort. It should not be treated as the same thing as shade that never lets the sun reach the glass.
Key terms
- Solar heat gain
- Heat a room picks up when sunlight passes through glass and is absorbed by floors, walls and furnishings, which then warm the room.
- SHGC
- Solar heat gain coefficient. It describes how much of the sun's heat a window lets through. A lower SHGC means the glass itself admits less solar heat.
- U-value
- A measure of how readily heat conducts through a window assembly. A lower U-value means less conducted heat transfer. A change in U-value is not the same percentage change in a household energy bill.
- Cooling load
- The heat an air-conditioner has to remove to hold a set temperature. A lower cooling load is not, by itself, a lower electricity bill.
- Shade factor
- In NatHERS, an input that describes how an external covering reduces solar exposure inside the model. A default shade factor is a software input, not a measured saving.
- Measured and modelled
- Measured means sensors recorded a result in a real room, test house or window. Modelled means a simulation estimated a result from inputs and assumptions. Both can be useful. They are not the same kind of evidence.
Why sunlight through glass makes a room so hot
A window does more than conduct heat between indoors and outdoors. It also admits solar radiation. YourHome explains that solar radiation passing through glass is absorbed by internal surfaces, which then release heat into the room. That is why shade on the glass can change summer comfort even when the walls and roof are insulated.
Effective shading can block up to 90% of the heat from direct sun. That is heat from direct sun, not a 90% cut in cooling energy or in an electricity bill.
An external shade can intercept that sun before it reaches the glass. An internal blind or curtain sits inside the glazing line. It can reflect or absorb some of the radiation, and it can slow heat moving through the window, but the sunlight has already reached the glass.
That does not mean every window needs an external blind. A house with modest, already shaded glazing is a different problem from a large unprotected west-facing window. A north-facing window can also be useful in winter, so blocking it all year can work against the heating needs of a warm-temperate Adelaide home.
External shading stops the sun before it reaches the glass
External shading has the stronger summer case because the sun is stopped before it reaches the glass.
- YourHome's up to 90% figure is direct-sun heat, not a bill saving.
- US test houses measured lower cooling energy with exterior shades than with no shade, and lower again than with interior vinyl blinds.
- Shade geometry changes the result. A Darwin town-hall model is not an Adelaide house.
NSW household guidance describes the same mechanism: shutters and awnings outside a window can block solar energy before it passes through the glass, and it points to west-facing glass that takes intense afternoon sun. A bill figure on that NSW page is discussed under Numbers to treat carefully, because the page does not publish the method behind it.
Exterior shades delivered about 20% lower cooling energy than no shading, and about 10% lower cooling energy than interior vinyl blinds.
A conventional overhang reduced modelled cooling load by 9.2%. The best geometry tested reached 15.54%. Those are cooling-load results for a civic building in hot-humid Darwin, not a prediction for an Adelaide household bill.
The honest reading of the Darwin work is that external geometry can change cooling performance. It is not a reason to expect 9.2% or 15.54% off an Adelaide electricity bill.
| Question | External shading | Internal covering |
|---|---|---|
| Where it acts | Before the glass | Inside the glazing line |
| Summer job | Stops direct sun reaching the glass | Can reflect or absorb some heat after the sun has reached the glass, and can slow heat transfer |
| What it is not | A single Adelaide bill saving | The same job as stopping the sun outside |
Awnings
External awnings for window shading can keep direct sun off the glass when the awning covers the opening and is in place while the sun is on it. Coverage, sun angle and how the awning is used still decide the result. This page does not treat any Stan Bond awning as the product those laboratories tested.
Awnings kept closed through the cooling season cut modelled annual heating and cooling energy by 15% compared with no shades. The model was calibrated with field data. It is a US residential result, not an Adelaide bill.
The Phoenix cases reported 14–20% lower cooling energy from residential awnings, depending on the window and awning. The work was produced by a university centre and commissioned in connection with an awning manufacturers' association. It is supporting evidence, not an Adelaide figure.
Outdoor and zip-track outdoor blinds
Research on exterior fabric shades supports shading outside the glass. The same PNNL test houses, with cooling switched off on a sunny comparison, stayed about 5°C cooler with exterior shades than an identical house with interior vinyl blinds. That is a comfort measurement in US test houses, not a bill.
No Australian study has yet tested zip-track outdoor blinds specifically, and none has tested Ziptrak outdoor blinds specifically. Side-retained exterior fabric is a plausible way to shade outside the glass. The studies above did not test those products, and there is a real evidence gap until an Australian residential trial does.
Where internal blinds and curtains still help
Internal coverings are not thermally irrelevant. They can change heat transfer at the window, cut glare, and control light and privacy. They sit behind the glass, so they are the second line for summer sun, not a substitute for shade outside a badly exposed window.
NatHERS recognises internal coverings, including roller blinds, honeycomb blinds, plantation shutters and curtains. The method distinguishes fit, how much light the covering lets through, and insulation. It does not publish one cooling percentage for every internal product in every Adelaide house.
Honeycomb blinds: what QUT measured and what it modelled
QUT measured the window, then modelled one Queensland building. Those are two different results.
- Measured: window thermal transmittance down about 56% on average, across a range of about 50–62%.
- Modelled, blinds closed throughout: 12.5% less cooling electricity, 57.7% less solar heat gain through the windows, and 4.6% less total energy.
- The building was an aged-care facility in Caboolture, not a detached Adelaide house.
Honeycomb cellular blinds are the internal product with the strongest Australian evidence in this set. The QUT Fernhill project should be read once. Later write-ups of the same experiment are not a second trial, so the percentages are not stacked.
Window thermal transmittance fell by about 56% on average, in a range of about 50–62%, depending on the cellular construction tested. That is a window measurement, not a whole-home energy saving.
With the measured blind properties in the building model, and the blinds closed throughout, cooling electricity was 12.5% lower, solar heat gain through the exterior windows was 57.7% lower, and total energy was 4.6% lower. That is a model of that facility, not a prediction for your home.
Roller shutters
Ozroll Rollashield roller shutters are an external covering. Closed, they stop sun before it reaches the glass. NatHERS models roller shutters that way, alongside awnings and canvas blinds. When an assessor cannot determine the exact external shade factor, the method uses a 70% default, described as equivalent to selecting a canvas blind or roller shutter in the software.
The 70% figure is a shade-factor input in the software. It does not mean a roller shutter blocks 70% of heat, and it is not a 70% energy saving. No percentage on this page is attributed to Ozroll Rollashield.
Ozroll publishes a thermal insulation bulletin, updated in 2015, reporting NatHERS modelling for homes and residential units in Sydney, Melbourne and Perth. It supports the benefit of reducing winter heat loss and summer heat gain. The supplier summary describes assumptions about insulation and shutter operation; the underlying assessor report was not recovered. Its modelled percentages are not a prediction for an Adelaide home. See Numbers to treat carefully for the figures and their limits.
Roller and blockout blinds
NatHERS treats indoor roller blinds as an internal covering. The effect depends on fit, fabric and how much light the cloth lets through. Blockout blinds use an opaque cloth. Blockout describes light, not heat. A cloth that stops light passing through it can still leave gaps at the edges, and it does not automatically become an external shade.
Modelled cooling-energy savings were 30–68% in Melbourne and 6–19% in Darwin. The only reason to show that range here is that climate changed the result. These are office models, not Adelaide homes, and they are not a roller-blind saving.
Outside shading does more for west-facing summer sun than an internal roller blind alone. This page does not put one cooling percentage on a roller blind or a blockout blind.
Curtains and plantation shutters
Curtains as an internal window layer can slow heat moving through a window. How well they fit, and how much air can move around the edges, changes that result. The clearest measurement in this set is a winter test, not a summer cooling trial.
Drawing the curtains reduced heat flux through the window by about 10–20 W/m². That is winter heat loss, not a summer cooling-energy percentage.
In rooms without air-conditioning, closing the existing curtains produced about a 1°C difference at the hottest part of one comparison day. The comparison was short, and later observations were less clean, including a sign that closed curtains can hold heat that has already built up. It is a comfort note, not a cooling percentage.
Indoor plantation shutters are an internal covering that NatHERS recognises. Fit and the air path around the panels still matter. This search did not find independent Australian research that puts a cooling-energy percentage on plantation shutters, so this page does not quote one. For strong summer sun, external shading does the heavy lifting.
What this means for an Adelaide home
Adelaide is about 35° south. Summer shade and useful winter sun both matter, and orientation should come before the product name.
| Orientation | Solar-control issue | Evidence-led response |
|---|---|---|
| West | Low-angle afternoon sun is hard to stop with a shallow horizontal projection and can drive overheating. | Look at external shading first, where it can be fitted. Adjustable systems leave a choice about when the glass is covered. An internal layer can still help with light, privacy and a second thermal effect. It is not doing the same job. |
| North | High summer sun and lower winter sun. A fixed shade that is too deep can cut useful winter sun as well as summer sun. | Horizontal shade, sized for the high summer sun, can leave a path for lower winter sun. Adjustable shade is useful on a retrofit because it can be opened when winter sun is wanted. |
| North-west | A mix of higher-angle and lower-angle sun through the day. | YourHome specifically recommends adjustable shading on north-west elevations. A single fixed depth is a weaker match than shade you can move. |
How you use shading matters
An adjustable shade only controls solar gain when it is in the position that intercepts the sun. On a hot day, shade a strongly exposed window before direct sun reaches the glass, rather than after the room is already hot. Give west and north-west glass particular attention as the afternoon sun arrives.
In winter, think about whether north-facing sun is useful before leaving adjustable external shade closed. Operate outdoor products within the instructions for that system, including wind and weather limits. NSW guidance, for example, advises bringing the relevant awnings in during storms or high wind.
Motorised outdoor blinds and timers can make it easier to put the shade in place before the sun hits the glass. That is an operation point. It is not a measured energy saving, and this page does not quote a motorisation percentage. For a hot-day routine, see how to use blinds and awnings in a heatwave.
Heatwaves and comfort
Some of the measurements are about how hot a room feels when the cooling is off. They are comfort results, not bill results, and they are not health outcomes.
On a sunny comparison with the cooling switched off, the house with exterior shades stayed about 5°C cooler than the house with interior vinyl blinds.
Numbers you'll see online and what they really measure
Large percentages online often measure something other than an Adelaide household's cooling bill. This is the only place this page quotes the NSW bill figure and the unrecovered roller-shutter industry range.
| Figure you may see | What it actually measures | Why it is not your bill |
|---|---|---|
| Up to 90% (YourHome) | Heat from direct sun, where shading is effective | A solar-heat figure, not cooling energy and not an electricity bill |
| 57.7% (QUT, 2021) | Modelled solar heat gain through the windows of one Queensland aged-care facility, blinds closed throughout | Window solar gain in that model, not a household electricity bill. The same model put cooling electricity at 12.5% and total energy at 4.6% |
| 70% (NatHERS) | Default shade-factor input when the exact external covering is unknown, equivalent in the software to a canvas blind or roller shutter | A modelling input, not a measured saving |
| Up to 40% (NSW, 2025) | A heating-and-cooling bill figure on a NSW guidance page | The page does not publish the study, the dwelling or the method behind that maximum, so it is not used as a typical result |
| 27–34% (industry pages) | Heating-and-cooling energy figures circulated for roller shutters in Sydney, Melbourne and Perth | The primary assessor report was not recovered, so this is an industry claim, not independent proof of a product |
| Up to 68% (Abu Dhabi, 2022) | Simulated cooling energy for shutter configurations in a hot-arid case study | Not transferable to an Australian aluminium roller shutter as a product claim |
| 30–68% and 6–19% (Begert, 2011) | Modelled office cooling energy, Melbourne compared with Darwin | An office model. The spread is the point: climate changed the result |
| About 24% (Bunning, 2016) | Modelled life-cycle energy over 25 years for an external Venetian system in Melbourne and Brisbane offices, compared with that study's base shading | Life-cycle energy, not a cooling-electricity saving |
So how much will shading save in an Adelaide home?
The evidence does not justify one universal Adelaide percentage.
- A large unshaded west window is a different opportunity from a small north window under a correctly sized eave.
- A household that cools all afternoon has a different energy response from one that rarely uses air-conditioning.
- An internal cellular blind changes window heat transfer differently from an external awning that intercepts direct sun.
- There is no Stan Bond or other local energy study to convert these results into a South Australian household figure.
QUT measured window-level thermal performance and separately modelled building energy in subtropical aged care. Mohammed and colleagues modelled external shade geometry on a Darwin town hall. Begert and Hertzsch modelled office blinds under Melbourne and Darwin conditions. YourHome is the clearest guide for applying the principle in Adelaide: shade unwanted summer sun according to orientation, and keep useful winter sun in a warm-temperate climate.
For a homeowner, that is a more useful way to decide than shopping from the largest percentage quoted online.
Choosing external or internal shading
Start with the window, not the product name. If it faces west or north-west and takes strong afternoon sun, ask whether more of that sun can be stopped outside the glass. If it faces north, think about summer shade and winter sun together. If an external solution is impractical, or you also need privacy, darkness or another internal layer, compare internal options on those needs.
External options include external awnings for window shading and outdoor blinds for external shading. Zip-track outdoor blinds, Ziptrak outdoor blinds and Ozroll Rollashield roller shutters are linked from the sections above, where the evidence limit for each one is stated. Internal options are the same: honeycomb cellular blinds, indoor roller blinds, blockout blinds, curtains and indoor plantation shutters are linked where their evidence is set out.
For many homes the practical answer is layered. External shade for the most exposed glass, and an internal covering chosen for privacy, light and a further effect at the window. That is a design principle. It is not a claim that every home needs two products, and it is not a claim that either product was energy-tested as a Stan Bond installation.
How we assessed the evidence
We looked first for Australian Government guidance, Australian measurements and published building-energy studies. For each result we asked five questions.
- Was it measured or modelled? A sensor reading and a simulation are useful in different ways.
- What was measured? Window heat transfer, cooling load, heating and cooling energy, and an electricity bill are different outcomes.
- What building was used? An office, an aged-care facility or a town hall does not automatically stand in for a detached Adelaide home.
- What climate and orientation applied? Adelaide needs both summer shade and useful winter sun.
- How were the shades operated? A covering left open during the strongest sun cannot match one that is closed for that sun. The QUT and Begert work both show that operating assumptions change the result.
Grades in the source table follow that reading. A is strong primary guidance, national-laboratory work or published research with a clear method. B is credible work with a transfer limit, such as a model, a non-residential building, a different climate, or an interim result. C is weak for a performance claim, because the method behind the percentage is missing or the primary analysis cannot be inspected. D is not used as proof. Nothing on this page is graded D, and a grade is not a product score.
Study results stay in the context they came from. A cooling-load percentage, a window U-value change, or an overseas result is not converted into an expected Stan Bond customer saving.
Sources
Commercial disclosure
Stan Bond supplies window furnishings and shading products discussed in this article. The independent studies cited above did not test Stan Bond products unless expressly stated. Their results apply to the products, buildings, climates and operating assumptions used by the original researchers.