What the numbers actually mean.

A strip of plastic sits inside the aluminium frame so heat cannot travel straight through the metal.

Aluminium conducts heat fast. Without the break, your frame leaks warmth in winter and bakes in summer. With it, the frame stays closer to room temperature.

Look for: "Thermally broken". It either is or it is not.

Two panes of glass with a sealed air gap between them.

The trapped air is the insulator. One pane of glass is about as insulating as a bedsheet; two with a gap is closer to a jumper.

Look for: Numbers like 5+20A+5, meaning 5 mm glass, 20 mm air, 5 mm glass.

How fast heat escapes through the whole window. Lower is better.

This is the single number your energy assessor asks for. It decides whether your house passes its energy rating.

Look for: Under 4.0 is standard, under 3.0 is good, under 2.0 is high performance.

How much of the sun's heat comes through the glass. A number between 0 and 1.

Low SHGC keeps a west-facing room from cooking in February. High SHGC lets free winter sun warm a south-facing room. Neither is better; it depends which way the window faces.

An invisible metal coating that reflects heat back where it came from.

Keeps summer heat outside and winter heat inside, without tinting the view. Costs more than plain glass and usually pays for itself in running costs.

Two panes bonded around a clear plastic layer.

If it breaks it holds together instead of falling in shards. Required by law in some locations, and it cuts noise noticeably.

Heat-treated glass that is roughly four times stronger, and crumbles into blunt pieces instead of blades.

Required by law near doors, floors, baths and pools.

The air gap in a double-glazed unit is filled with argon gas instead of air.

Argon is denser than air, so heat moves through it more slowly. A small upgrade to the U-value for a small cost.

How many decibels the window cuts out. Higher is better.

The number people actually feel. Every 10 points is roughly half as loud to the human ear.

Look for: Rw 30 is standard, Rw 35+ for a main road, Rw 40+ for a flight path.

The wind-driven rain pressure the window was tested at before any water got through.

Measured in Pascals. Higher means it handles worse weather.

Look for: 150 Pa suits a sheltered suburban wall; exposed and coastal sites need 300 Pa or more.

How much air leaks through the window when it is shut.

This is where draughts come from, and where your heating bill goes. Lower is better.

How much wind the window is built to take.

Your house plans already state the rating your site needs: N-classes for most of the country, C-classes in cyclone regions. The window has to match or beat it.

Two wind pressures the window is tested at.

SLS (serviceability) is everyday strong wind, and the window must keep working normally. ULS (ultimate) is a once-in-decades storm, and the window must not fail or blow in.

How much bushfire exposure the window is built to survive, from BAL-LOW to BAL-FZ.

If you are in a designated bushfire area, your council sets the rating and the window must meet it. Non-negotiable.

The Australian Standard every external window and door must be tested against before it can legally go in a building.

It covers wind, water and structural performance. Not a marketing badge. The certifier will ask to see it.

The Australian Standard for where glass goes and what type it has to be.

It is what forces toughened or laminated glass near doors, floors, stairs, baths and pools.

An independent scheme that tests the whole window, frame and glass together, and gives it a star rating out of 10 for heating and for cooling.

Ratings for glass alone do not count. WERS rates the finished window.

The current national building code.

Since 2023 it requires new homes to hit a 7-star energy rating, and windows are usually the weakest point in the wall. This is why glazing choice now decides whether a house passes.

The software that gives a home its star rating out of 10.

It reads your window U-values and SHGC directly. Better windows, fewer stars needed elsewhere.

Hinged at the side, swings open like a door.

Seals tightly when shut and catches side breezes. Best all-round performer for weather sealing.

Hinged at the top, the bottom pushes outward.

Can stay open in light rain because the sash acts as a small awning.

One handle, two ways to open. Turn once and it swings inward like a door. Turn again and the top tilts in for ventilation.

The tilt position lets air in while staying secure and keeping rain out. The full swing lets you clean the outside of the glass from indoors.

Two sashes that slide up and down past each other.

The traditional look for heritage and period homes. Both sashes usually tilt in for cleaning.

Sashes glide sideways on a track.

Takes no space inside or outside the room, which suits walkways and tight sites.

Panels concertina and stack to one side, opening the whole width.

Used to join a kitchen to an alfresco area, or as a servery window over a bench.

Horizontal glass blades that pivot together like a venetian blind.

Gives the most airflow of any window type, and lets you dial ventilation and privacy up or down.

How much frame you see around the glass, in millimetres. Smaller means more view.

Slim sightlines look contemporary; chunkier frames carry more weight and bigger glass.

How deep the frame is, front to back.

Mostly matters to your builder: it has to suit the wall thickness and the reveal.

How thick the aluminium itself is.

A build-quality indicator. Thicker aluminium means a more rigid frame and bigger achievable panel sizes.

The specific aluminium alloy and heat treatment used for the frames.

It is the standard architectural grade worldwide: strong, corrosion-resistant, and takes a finish well.

A dry colour powder is applied electrostatically and baked on.

Much tougher than paint. It will not peel or brush off, and it carries its own warranty.

An electrical treatment that grows a hard protective layer out of the aluminium itself.

The finish is part of the metal, not a layer on top, so it cannot chip. Metallic tones only.

The vertical or horizontal bar where two sashes overlap.

It is the one line that sits in the middle of your view, so its width is worth knowing.

How many parallel rails the sliding sashes run on.

2-track: one panel slides past one fixed panel. 3-track: more panels stack, so a wider opening, but a deeper frame.

The insect screen and its own frame.

Integrated means it is built into the window system rather than clipped on afterwards, so it looks tidier and seals better.