Improving insulation with better windows and doors

The aim of all new homes and renovations should be to make every room more liveable. This includes meeting strict energy regulations that help future-proof our homes. An effective glazing system is a smart way to achieve this as it allows you to quickly upgrade a dwelling’s thermal performance.

Windows and doors can no longer be treated as just openings, rather as key components of a tight, well-insulated building envelope. The right type of glazing, frames, seals and installation techniques can help to boost a building’s energy efficiency for home dwellers.

But understanding how different windows and doors will interact with the design, orientation and climate zone of a home is a specialised science. And so is the job of convincing your client, or yourself as an owner-builder, that upfront costs will offer a significant return on investment over time. If trying to balance all this with the new energy star-rating rules makes your eyes glaze over, read on for some valuable insights.

Put glazing in the frame

Glazing enables the outside world to interact with a home’s interior. It’s a relationship that can be both good, and not so good. Large spans of glazing create stunning architectural features, framing scenery and connecting interiors with natural surroundings – that’s a good thing. And when you open windows to admit cool summer breezes, that’s also good thing. But when all that glass lets the soaring afternoon sun heat up the inside, or sucks the warmth out of a room on a cold winter’s night, that’s not so good.

According to the Australian Government Energy website, “Almost 90 per cent of a home’s heat is gained, and up to 40 per cent of heating energy is lost through its windows”. The takeaway? Choosing the right windows can make a home more comfortable naturally and has the knock-on effect of reducing energy bills and keeping clients happy. “Glazing plays an important role in insulating a building,” says Todd Hurst, owner of Hobart-based company MHM Property Development. “Insulation is the chink in a building’s armour – it should be one of the first considerations in a home upgrade.”

How to measure thermal performance

In the world of windows, U-values (used for glass) and R-values (usually used for opaque surfaces) measure resistance to conductive non-solar heat transfer – heat escaping or entering through the frame and glass of a window. A lower U-value (and higher R-value) results in better insulation and energy efficiency. During winter, a window with a higher U-value will lose more heat to the outside, whereas a window with a lower U-value will see less heat loss. In summer, a window with a high U-value will conduct more heat energy from outside to indoors, whereas a lower U-value will conduct less heat from the outside, keeping the room cooler and more comfortable. U-values usually fall between 8 (worst case) down to 1 (best case). In most cases, a low window U-value is better in all climates.

Another factor affecting thermal performance is the solar heat gain coefficient (SHGC). This measures the window’s ability to control heat transfer from solar radiation, and ranges from 0 to 1 with lower values indicating less solar heat gain. It’s intrinsically tied to a room’s orientation and the climate where the building is located.

Then there’s visible light transmission (VLT), which measures the amount of natural light that enters through the glass. You want to aim for a high VLT to maintain an abundance of natural light.

Lastly, you need to think about air infiltration, which measures the amount of leakage around the openings of windows and doors.

To maintain a consistent and comfortable room temperature, you should go for windows with a low U-value and air infiltration, but a high VLT to admit an abundance of natural light. The SHGC should be determined by a room’s orientation and the client’s personal preference. It’s a complex task that requires effective collaboration with experts. “The service at Bunnings Trade is second to none,” says Todd. “They make every complicated job easier for you.”

A quick guide to window shopping

Here’s a cheat sheet to help you pick the right product for different climates.

Feature: Low U-value (high R-value)
Function: Blocking conductive heat
Best for: Cold climates; reducing heat loss

Feature: Low SHGC
Function: Blocking direct sunlight
Best for: Hot climates, cooling-dominated homes

Feature: High SHGC
Function: Capturing free heat
Best for: Passive solar design in cold climates

Are double-glazed windows worth it?

It’s important to discuss this option with your client. Double-glazed windows not only affect a home’s comfort, noise levels and energy costs, but its resale value too. “They’re a sought-after feature by buyers who prioritise comfortable, cost-saving and quiet dwellings,” says Todd.

The amount of glazing on windows can slow down the conductive heat flows in both directions, making double-glazed windows superior to single-glazed ones for insulating a building. As double-glazed windows have a low U-value and reduce thermal loads, they’re also a practical way to help builders meet the new, higher energy efficiency requirements for new homes (see ‘Shoot for the stars’ below).

“With recent updates to the NCC regulations, double-glazed windows may be necessary for your build to meet the minimum 7-star rating standard,” says Todd.

Double-glazed windows feature two glass panes separated by an air gap filled with Argon gas. Argon, an inert gas, enhances insulation by trapping warm or cool air, helping to maintain a comfortable temperature year-round. According to Sustainability Victoria, double-glazed windows can prevent up to 30 per cent of heat loss or gain.

Overall, they can result in reduced condensation on cold nights, which helps prevent mould growth and moisture damage, and help to reduce external noise. “And when you pair double glazing with other technologies, including low-E coating to glass and thermal breaks to aluminium frames, you really boost the thermal insulation and positive effects,” Todd points out.

Remedy leaky home syndrome

While a well-insulated wall provides a superior thermal barrier, a leaky building envelope caused by poorly sealed openings acts like a ‘leaky ship’. A 3mm gap underneath an exterior door, for instance, can admit as much air as leaving a small window open. This allows conditioned air to escape and outside air to enter, degrading the thermal performance of a home.

“Households can save up to 25 per cent on power bills by preventing air infiltration using inexpensive, simple and effective air-sealing techniques”, says Todd. He suggests placing an inexpensive draught stopper along the bottom of the culprit door or attaching a door seal, and applying durable self-adhesive weather strips to sliding and double-hung window frames. For larger exterior gaps around windows, use a foam sealant.

Tip To find the air leak, hold tissue paper up to the seals and if the paper moves, that’s where the air is coming through.

Shoot for the stars

The National Construction Code (NCC) Volume Two 2022 in Australia has raised the bar for residential energy efficiency by introducing staged improvements in 2023. It mandates strict energy efficiency, sealing and glazing requirements for all new builds to improve thermal performance, increasing the minimum rating for homes from 6 stars to 7 under the Nationwide House Energy Rating Scheme (NatHERS). To ensure you comply with the current NCC code, Bunnings Trade offers compliant and professional-grade windows, doors and seals. “These product upgrades will make it easier to reach the 7-star NatHERS rating and energy-efficiency goals within budget,” notes Todd.

Keeping up standards

Windows and sliding doors made to Australian Standards AS 2047 and AS 1288 carry a certifying label. These standards cover safety, water resistance, air infiltration and other essential features. However, some Australian-made windows, including replacement windows for heritage homes, don’t need to comply with AS 2047.

Although fully imported windows may conform to overseas standards that doesn’t mean they comply to Australian testing requirements. If a window has no certification, don’t use it. Ask the experts at Bunnings Trade about certifications before purchasing windows or doors.

Windows and doors can be a significant source of heat during warmer months and heat loss during winter. Choosing the right window systems and placing them appropriately can impact long-term thermal performance and cost savings. By making informed choices you can create a comfortable and efficient dwelling, contributing to a greener future.

Need to upgrade a building’s thermal performance?

Contact your local Bunnings Trade team to find out more about our professional-grade window and door solutions. Our team can provide technical advice on product selection and installation techniques to help meet your insulation and energy efficiency goals.

Frequently asked questions

How do better windows and doors improve a home’s insulation?

High‑performing glazing, frames and seals help control conductive heat transfer and air infiltration, reducing energy loss and enhancing comfort year‑round.

What is a U‑value and why does it matter?

A U‑value measures how easily heat passes through a window. Lower U‑values mean better insulation, helping homes stay warmer in winter and cooler in summer.

Are double‑glazed windows worth the investment?

Yes – double glazing reduces heat loss or gain, cuts noise, lowers energy bills and can help meet updated NCC and NatHERS efficiency requirements.

How can I reduce air leaks around windows and doors?

Use draught stoppers, door seals, weather strips and foam sealants to block gaps. Even small openings can significantly affect a building’s thermal performance.

Do all windows meet Australian Standards?

Not necessarily. Always check for certification to AS 2047 and AS 1288 and consult Bunnings Trade experts to ensure products meet required regulations.