Different Types of Glass for Timber Windows

Glass is the part of a timber window you look through every day and think about last. That's a shame, because the types of glass for timber windows in Sydney decide how warm a room stays in July, how loud the street sounds at 7am, and how the window reads from the kerb.

This guide covers the window glass types you'll actually be offered here, what each one does, and where each one belongs in the house.

Why Does Glass Choice Matter for Timber Windows?

Glass is the weakest thermal point in any window, and it's where most of your heating and cooling money escapes. Put a single 3mm pane in a timber frame and heat moves through the whole window at 5.5 watts per square metre for every degree of temperature difference between inside and out.

That number is a U-value, written W/m²K. It measures how quickly heat travels through the complete window, frame included, so lower is better. The gap between one glass type and another is bigger than most people expect.

Window Energy Rating Scheme figures, published in the Australian Government's Your Home guide, rate the options like this:

• Single glazed, timber frame: a score of 5.5. That's the rate heat escapes, so a lower number is better.
• Double glazed, same timber frame: 3.0. Same frame, same house, close to half the heat loss.
• Single glazed, aluminium frame: 6.9. Same glass as the first line, worse score, because metal frames leak heat too.
• How much of the sun's heat gets in: 0.69 single glazed against 0.61 double glazed, on a scale from 0 (none) to 1 (all of it).

Put simply, the right glass can nearly halve the heat a timber window loses, the wrong glass lets the afternoon sun cook a west room, and AS 1288 safety rules apply no matter how well a panel performs. Climate, orientation and safety decide which of the types of glass for timber windows belongs in each opening, which is exactly what the rest of this guide works through.

The Most Common Types of Glass for Timber Windows

Seven glass types cover almost every timber window we make, and most homes use two or three of them in the same build. Here's what each one is, in plain terms, and who it suits.

Clear Float Glass

Clear float is the standard annealed glass most windows have used for a century. It's floated on molten tin for a flat, distortion-free surface, and it comes in 3mm, 4mm, 5mm, 6mm, 8mm, 10mm and 12mm.

Annealed glass cools slowly, so it stays soft enough to cut, drill and shape. That's why it still suits restoration work, where a new pane has to match an old sight line. It's also the cheapest option per square metre and lets the most daylight through of anything on this list.

The trade-off is performance and safety. There's no impact protection, and insulation comes only from thickness. Weight is worth knowing too: at roughly 2.5kg per square metre for every millimetre, a 3mm pane is about 7.5kg. Use it where the sill is high, well clear of doors and stairs, and the budget is better spent on the frame.

Double Glazed Glass (Insulated Glass Units)

A double glazed unit, or IGU, is two panes sealed around a spacer with a 6mm to 18mm gap between them, and 12mm is often the best compromise between insulation and unit weight. The spacer holds desiccant to absorb any moisture inside, so the glass doesn't fog between the panes, and the cavity is filled with air or with argon, which conducts less heat.

Our own double glazed doors and windows use a 16mm unit: two skins of 5mm toughened clear glass, a pyrolytic Low-E coating on the inside face, desiccant spacers and an argon-filled centre void. One unit gives you safety glass, solar control and noise reduction together.

Double glazing also changes the window's engineering. Two 5mm panes weigh about 25kg per square metre before you add the spacer, so hinges, stays and the springs or cords in a double hung sash all need to be up to the load. We work that out at quoting stage, not on install day.

Toughened (Tempered) Safety Glass

Toughened glass is heated to about 620°C and then cooled fast with air jets, which locks the outer surfaces into compression and makes the pane roughly four to five times stronger than ordinary glass of the same thickness. When it breaks, it crumbles into small blunt granules instead of long shards, and that failure pattern earns it Grade A safety glass classification under AS 2208.

Every cut, hole and edge polish has to happen before toughening, because the glass can't be trimmed or drilled once it leaves the furnace. Large single panels can also be heat soaked to reduce the risk of a nickel sulphide inclusion causing a spontaneous break.

One honest point in a market full of sales claims: toughened glass gives you no extra thermal or acoustic benefit over ordinary glass of the same thickness and tint. You choose it for strength and for how it fails, not for comfort.

Laminated Safety Glass

Laminated glass bonds two or more panes to a plastic interlayer, usually PVB, under heat and pressure. The make-ups are named by total thickness: 6.38mm is 3mm glass, a 0.38mm interlayer and another 3mm of glass, then 8.38mm and 10.38mm follow the same pattern.

The interlayer is the whole point. When the glass cracks, the fragments stay stuck to the plastic, so the panel holds its shape and the opening stays covered. Nothing lands on the floor, or on whoever is standing under it.

It also filters most of the sun's UV, which protects timber floors and furniture, and acoustic interlayers take a noticeable bite out of traffic noise. That combination makes it the pick for overhead glazing, exposed elevations, security, and homes close to a main road or rail line.

Like toughened glass, it can't be cut once it's laminated. Order the size you need.

Low-E (Low Emissivity) Glass

Low-E glass carries an invisible metallic coating, far thinner than a human hair, that changes how the surface handles radiant heat. It lets daylight through while slowing the long-wave infrared heat that tries to leak back out through the glass.

There are two families. Pyrolytic coatings are applied while the glass is still hot on the float line, so they're hard, durable and can be used in a single pane. Vacuum-deposited soft coatings perform slightly better but are delicate, so they only ever go inside a sealed unit where they're protected.

Coating position matters as much as the coating. In our units the Low-E face sits on the inside of the outer pane, facing the cavity, where handling and cleaning can't reach it.

You also get a choice of emphasis. High solar gain Low-E suits a north window you want to collect winter sun through. Low solar gain Low-E suits a west window you want to defend from summer heat. Same product family, opposite jobs.

Frosted and Obscure Privacy Glass

Obscure glass hides the view without blocking the light. The effect comes from acid etching, sandblasting, rolling a pattern into the glass, or a mix of all three, and each method gives a different texture and a different level of privacy.

We hold patterns such as Satinlite, Acid Etched, Glue Chip, Soft White, Narrow Reeded and Broad Reeded. Reeded patterns give you vertical lines and a softer, more directed light. Satin and acid etched finishes give an even, milky diffusion that suits contemporary bathrooms.

Privacy is not the same as safety. Some patterns are only made for window glazing and aren't available as safety glass, so if the panel is in a door, in a bathroom or near the floor, the pattern has to be one that's made as toughened or laminated. Our full glazing range separates the two lists clearly.

Expect to clean textured glass a little more often than clear. Patterned faces hold dust and soap film in the texture.

Leadlight and Decorative Glass

Leadlight is coloured or textured glass held together by lead cames, and in Sydney it's mostly found in Federation, Interwar and heritage homes. It's part of the architecture, not just the glazing.

The good news is that leadlight no longer has to mean a cold, draughty window. A leadlight panel can be encapsulated behind clear glass, or built into a double or triple glazed unit, so you keep the original glass and get modern performance around it. Our Federation archtop doors, for instance, come with triple glazed leadlights.

Restoration is the other path. Old lead can sag and the putty can fail, and re-leading a panel is often cheaper than replacing it, especially on a fanlight or fixed light where the shape can't be matched off the shelf.

Watch the heat. Dark coloured glass absorbs sun and gets hot, so it needs to be toughened or laminated wherever there's a thermal risk.

Here's how the seven window glass types compare on the things that usually decide a purchase.

Uw and SHGCw figures from Window Energy Rating Scheme data published by Your Home (Australian Government). Uw is the whole window, glass and frame together.

Which Glass Type Works Best for Each Room?

Start with orientation and safety, then choose the glass. Those two factors narrow the field faster than any style guide.

• North-facing living areas: you want the winter sun, so pick a higher solar gain glass and let the eave do the summer shading. A deep eave plus clear or high gain Low-E double glazing is hard to beat in a Sydney climate zone 5 home.
• West-facing rooms: the afternoon sun is the enemy here. Go for low solar gain Low-E, or a toned glass in an IGU, and don't leave a large west panel unshaded.
• Bedrooms: comfort is about noise more than heat. A laminated pane, or an IGU with a laminated inner pane, cuts traffic and gives you a security benefit at the same time.
• Bathrooms: AS 1288 requires safety glass, so specify a pattern that's made as toughened or laminated. Satinlite or Acid Etched gives privacy without losing daylight.
• Kitchens: clear glass, easy to clean, and check for splashback proximity. Grease film on textured glass is a losing battle.
• Hallways and stairwells: stairway glazing sits inside the AS 1288 human impact rules, so toughened or laminated is the starting point, not an upgrade.
• Heritage front rooms: keep the leadlight and encapsulate it, or build it into a new unit. Replacing original decorative glass can cost more in character than it saves in performance.

Different types of timber windows in Sydney also take glass differently. A double hung sash has to carry its own weight on springs or cords, a casement loads its hinges, and a fixed light only has to satisfy wind load and safety. Our double hung timber windows at Sydney Woodworkers are built with the glazing weight in mind from the start.

Can You Double Glaze Timber Windows?

Usually you can, if the frame is sound and the rebate is deep enough. It's a sash-by-sash question, not a house-wide yes or no.

The rebate is the groove in the sash that the glass beds into, and a 16mm unit needs one deep enough to hold the unit and a glazing bead over it. Plenty of older sashes were cut for 3mm or 4mm glass, so that sash either gets re-bated in the workshop or replaced. Weight matters next, because an extra 25kg per square metre will make tired springs, cords and hinges sag or stick.

Sealing and consent finish the job. Old felt and worn parting beads undo most of the gain, and in a heritage conservation area changing the glazing or the profile may need council consent before you order. Where a frame genuinely can't take a unit, secondary glazing on the inside face is the fallback: Your Home notes it controls noise well but won't match a sealed unit thermally, because the perimeter can't be fully sealed.

Glass and Timber: What to Consider Before You Choose

Glass and timber move differently, and the joint between them is where windows fail. Get that interface right and both will last decades.

• Orientation and climate zone: Sydney isn't one climate on paper. Eastern Sydney sits in NCC climate zone 5, warm temperate, while western Sydney is zone 6, mild temperate with hotter summer peaks and colder winter mornings. The same design can need different glass on either side of the city.
• Rebate and beading: the bead holds the unit in. It also has to drain and vent, or water sits against the timber and starts the rot that kills sashes.
• Species and coating: we stock Surian cedar and build to any size, and the coating is what keeps water out of the end grain. Glass choice can't rescue a frame that isn't sealed.
• Condensation: single glazing gives you a cold inside surface, so moisture in the air lands on the glass. A sealed unit with argon keeps the inner pane warmer and stays clear. NSW also expects condensation management to be considered, which is another reason ventilation and frame performance go with glazing decisions.
• Noise: it's mass and a gap that stop sound. Laminated glass adds mass, an IGU adds the gap, and the sealing decides how much of either you actually get.
• Bushfire: if the site is in a designated bushfire prone area, AS 3959 applies and the glass and any screens have to suit the BAL rating. Our Stealshield screens are made to meet bushfire code requirements.
• Maintenance access: a sash that tilts or lifts for cleaning saves a ladder every season, and glass you can't reach is glass you won't clean.

Get those seven points right at the design stage and the window will do its job quietly for the next few decades.

Australian Standards for Window Glass (What You Need to Know)

Four standards do most of the work on a Sydney timber window, and your certifier will want to see all of them satisfied.

1. AS 1288:2021, Glass in buildings: selection and installation. The current edition, which replaced the 2006 version, and a primary reference document for the NCC. It sets out where safety glass is required for human impact: glass in doors, glazing within 300mm of a door opening, glazing whose lowest sight line is under 500mm above the floor, bathroom glazing, and stairway glazing.
2. AS 2208, Safety glazing materials in buildings. Defines Grade A and Grade B safety glazing. Safety glass has to be permanently marked so a surveyor can read the grade on site, which is also why a hidden or unreadable stamp causes problems at final inspection.
3. AS 2047:2014, Windows and external glazed doors in buildings. Covers materials, construction, installation and glazing, plus the performance testing for wind and water. It's referenced in both volumes of the NCC for all building classes.
4. NCC 2022 energy efficiency, applied in NSW through BASIX. New homes need the equivalent of a 7-star thermal rating, and NSW lifted its BASIX standards to match from 1 October 2023 under the Sustainable Buildings SEPP. Glass is one of the biggest levers on that rating.

That's the plain-English version, not the standards themselves, and it doesn't replace your certifier or building surveyor. If you want the detail, Standards Australia's overview of AS 1288:2021 and the ABCB climate map are both good starting points.

Conclusion

Three things decide which of the types of glass for timber windows you should buy: where the window faces, what job it has to do, and where the panel sits in the wall. Get the orientation right and the room feels comfortable all year. Get the safety positions right and the build passes inspection. Everything after that comes down to taste and budget.

So start with safety glass wherever a panel sits in or near a door, below 500mm, in a bathroom or beside a stair. Then let the energy ratings and your orientation choose between clear, Low-E and double glazed. The leadlight, the reeded pattern or the plain clear view is the part you actually get to enjoy.

Frequently Asked Questions