Recently, you may have noticed the phrases 'thermally-insulated', 'thermally-improved', or 'thermally-broken' cropping up and it’s more than just a buzzword. So, are thermally insulated windows worth it?
Yes. Thermally broken aluminium windows like UNO Thermal reach up to R0.52 in H1/AS1, against R0.39 for standard aluminium. That makes the R0.46 (zones 1–4) and R0.50 (zones 5–6) reference straightforward to meet without over-insulating walls and roofs, and gives warmer, drier homes with less condensation.
To understand the hype around thermally insulated windows, let’s explore how they perform and the benefits of installing them in your new project.
When installing aluminium windows, the frames are just as important as the glass itself. While double glazing and Low-E glass can reduce heat loss through the glass pane, there will still be a certain amount of heat transfer through the surrounding frame. This is especially the case with the commonly used, and conductive, aluminium frames. To overcome this, thermal breaks must be built into the frame to stop heat from escaping and cold from seeping in.
Thermal energy is transferred through materials that are touching, so by forming a physical, resistive barrier, this energy pathway can be blocked. To achieve this, thermally broken windows have a continuous polyamide bar that wraps around the entire frame. Being a low-conductive material, polyamide interrupts the heat transfer and helps to maintain a comfortable temperature in the house all year round.
Under H1, a window's R-value covers the glass and frame together. High-performance Low-E glass on its own only gets you halfway, which is why UNO Thermal combines a larger thermal strip with Low-E double or triple glazing. Think of the thermal break as double glazing for the frame: to make the investment in high-performance glass worthwhile, you need to invest in the frame too.
Placement matters as well. Installing the window in line with the wall insulation (a recessed window installation), and carefully detailing the junction between the window frame and the wall cladding, is critical to getting the full benefit of thermally improved windows.
To understand how a window’s thermal insulation stacks up against the required standards, you need to understand R-values and U-values. A U-value measures how much thermal energy is conducted through a particular material or item. This can range from low heat transfer (0.1) to high heat transfer (1.0).
On the other hand, an R-value represents how well a material resists thermal transfer based on its thickness and conductive properties. In other words, the higher the R-value is, the lower the U-value will be.
In the New Zealand Building Code, requirements for insulation are set according to R-values.
To understand the reasoning behind the new insulation standards, let's examine the key advantages of thermally broken frames.
To maintain a healthy and comfortable home, the temperature inside should be at least 18°C but without the correct insulation, that requires a lot of energy to maintain in both summer and winter. By preventing heat transfer in and out of the house, a thermally broken frame helps to keep internal temperatures steady.
The popularity of aluminium is for good reason — it is low maintenance, cost-effective, and recyclable. And in New Zealand’s changeable climate, the UV stability, corrosion resistance, and strength of aluminium are unmatched, even when compared with UPVC or timber windows.
Previously, the only downside with aluminium frames was the heat loss, but now, with thermal insulators, this is no longer a problem. This means aluminium windows with the thermal insulation strips will remain the number one choice.
As well as heat, sound can easily transfer through aluminium frames — which for urban residential homes, is a major drawback. By incorporating the thermal insulation strips, the sound transfer is also reduced, helping to keep external noises out and inside noises in.
In New Zealand, we’re no strangers to condensation and unfortunately, aluminium frames have been a contributor to this. As the warm moisture in the air hits the cold metal, it cools and forms droplets. Over time, this moisture can degrade the metal and produce mould.
However, with thermally broken windows, the chance of condensation forming on the frame is dramatically reduced. With condensation issues, it all comes back to how much moisture is inside your home and the amount of ventilation provided within your home.
The NZ Building Code H1 standard for all new build homes has been updated as we catch up to global insulation standards.
These higher standards bring many benefits, including:
The requirements vary based on the six climate zones outlined by the Ministry of Business, Innovation and Employment (MBIE).
On top of other insulation components, such as in the roof, floor, and walls, the standards for windows set a reference R-value for each climate zone. Under H1/AS1, the reference R-value for windows is R0.46 in climate zones 1–4 and R0.50 in zones 5–6.
If your new project is located in Northland, Auckland, Coromandel, Bay of Plenty, Hamilton, East Coast, or Taranaki, you must comply with the standards laid out for Zones 1 and 2.
If your new project is located in Manawatu, Horowhenua, Wellington, Nelson, Marlborough, Chatham Islands, Central Plateau, Wairarapa, or the West Coast, you must comply with the standards laid out for Zones 3 and 4.
If your new project is located in Canterbury, Coastal Otago, Inland Otago, Southland, or Stewart Island, you must comply with the standards laid out for Zones 5 and 6.
In UNO Hub, a typical UNO Thermal fixed window (1000 × 1200 mm) reaches R0.65* and a UNO Thermal sliding door (2100 × 2400 mm) reaches R0.60*, while standard aluminium double glazing sits around R0.24–R0.39. To see how your proposed windows will perform, enter your windows and doors into UNO Hub to generate project-specific construction R-values based on the actual sizes, configurations and products being specified.
*Typical construction R-values from UNO Hub for the stated sizes and configurations, with Low-E Lightbridge double glazing (Ug 1.1, SHGC 0.56) or the UNO door panel. R-values vary with size, configuration, glass and panel.
Thermally broken windows cost more upfront, so it helps to get your clients on the same page early. Three simple steps make the case:
If you are an architect, developer, or builder with a new project on the horizon, opting for thermally broken windows should be your first step. Not only will your clients be satisfied with the improved energy efficiency, but you will also be well-prepared for H1 compliance.
Eager to discuss your next new build or multi-residential housing project? Contact the team at UNO Windows & Doors. We will guide you through the H1 standards for your region and find a solution that works for you.
Please note that we do not supply windows for renovation projects or individual replacements.