An R-value measures how well a building element resists heat flow: the higher the R-value, the better it insulates. For windows and doors in New Zealand, what counts under H1 is the construction R-value of the whole unit, frame and glass together, and you can increase it with Low-E double glazing, thermally broken frames like UNO Thermal, and configurations with more glass and less frame.
Understanding R-values is key to designing energy-efficient buildings and selecting window and door solutions that support H1 compliance in New Zealand. This guide explains what R-values are, how they're calculated, what H1 currently asks for, and how to lift the R-value of your windows.
What is an R-value?
R-values describe how well insulation material resists heat flow. They can differ depending on thickness, the direction of the heat flow, and composition. The higher the rating, the more thermal insulation and the better the performance.
As with many insulation materials, 'thicker' doesn't necessarily mean better insulators, since some thinner materials might have better thermal resistance. For example, while 50mm polystyrene is considerably thinner than 80mm thick glass wool, both have an R-value of approximately 1.5.
What’s the difference between R-values and U-values?
While R-value measures thermal resistance, U-value measures thermal transmittance, or how easily heat passes through. If heat transfer through a material is minimal, its U-value will be low and its R-value will be high, making it a high-performing insulator.
A U-value is often quoted for insulated glass units (for example, Low-E Lightbridge has a Ug of 1.1), while the R-value is used for the performance of the whole window or building element. The R-value is the inverse of the U-value: R = 1/U, and U = 1/R.
How to calculate R-values
Calculating the R-value of a window is normally performed with thermal modelling software in accordance with New Zealand and European standards. This software takes into account the U-values and areas of each material comprising the window and calculates an overall U-value for the complete window as a combined whole. Our design team utilise this thermal modelling software to ensure compliance with the NZ Building Code H1 requirements.
Under the current H1 documents (H1/AS1 and H1/VM1 6th edition, and H1/AS2 and H1/VM2 2nd edition), the Schedule Method has been removed. Compliance is shown with the Calculation Method or the Modelling Method, and both use the construction R-values of your actual windows and doors. At UNO, we recommend using the Calculation Method as a minimum.
When using the Calculation Method, you can use the NZGBC H1 calculator to input all the square metre areas and construction R-values for each component. This will advise you of the heat loss from your building compared to the reference building, and if you are compliant with the code.
This also lets you play with the insulation numbers and gives you the ability to adjust insulation R-values in other areas, such as roof insulation or slab edge insulation, potentially saving you money.
Process for getting project-specific construction R-values easily and quickly:
- Enter your proposed windows and doors into UNO Hub.
- Adjust the sizes, configurations, glass and other project details as required.
- Generate project-specific construction R-values to use within your H1 Calculation Method assessment.
- Once your specification is finalised, download an R-value certificate from UNO Hub to support building consent.
New Zealand's current insulation standards
The current H1 documents were published on 27 November 2025, and the previous editions can no longer be used after 26 November 2026. Housing and buildings up to 300 m² follow H1/AS1 or H1/VM1, and buildings over 300 m² follow H1/AS2 or H1/VM2.
The H1 insulation changes aim to reduce the energy needed to heat new homes by around 40%, making them warmer, drier and cheaper to run, and contributing to New Zealand’s carbon-neutral goals.
R-value requirements for New Zealand
There are six climate zones in New Zealand. Zones 1–2 are the warmer northern areas, while zones 5–6 include colder areas such as Christchurch and Queenstown, where H1 asks for higher R-values.
What R-value do I need?
Under the H1/AS1 Calculation Method, your design isn't measured against a fixed R-value for each element. Instead, its heat loss must be no greater than that of a reference building of the same size and shape. That gives you flexibility: a better window can allow less insulation elsewhere, and the other way round.
There are still minimum R-values that each element must meet in H1/AS1, including:
- Roof: R2.6
- Wall: R1.0
- Floors other than slab-on-ground: R1.3
The Calculation Method can be used where glazing is 40% or less of the gross wall area. Check the full reference and minimum values for your building and climate zone in H1/AS1 6th edition.
Windows
There is no minimum R-value for windows under H1/AS1. Instead, the reference building uses windows and doors of R0.46 in climate zones 1–4 and R0.50 in zones 5–6. The closer your windows get to (or the further they exceed) those values, the easier the whole building is to get through H1.
To achieve strong thermal performance, both the joinery and glass specification need to be considered. Low-E glass improves insulation by reflecting heat back into the room. Combined with double glazing, argon gas and thermally broken aluminium frames, it creates a high-performance window system that significantly improves insulation and comfort year-round.
UNO recommends Low-E Lightbridge or Low-E Xcel double glazing across all climate zones, and Low-E Xtreme or Performatech can lift the R-value further where needed.
Discover energy-efficient glass
Current R-value Requirements for Windows
For windows and doors, the reference values used in H1 are:
| Building | Zones 1–2 | Zones 3–4 | Zone 5 | Zone 6 |
|---|---|---|---|---|
| Housing and buildings up to 300 m² (H1/AS1, H1/VM1) | R0.46 | R0.46 | R0.50 | R0.50 |
| Buildings over 300 m² (H1/AS2, H1/VM2) | R0.33 | R0.37 | R0.40 | R0.42 |
These values apply to the entire window unit, including both glazing and joinery. Read more about the H1 building code changes and H1 requirements for commercial buildings.
Want to compare materials? We’ve broken down the performance of aluminium vs uPVC window systems to help you make the best call for your multi-residential project.
Read more: Aluminium vs uPVC – What’s Best for Multi-Residential?
Increasing the R-value of windows
To get the most from your windows, it helps to understand the options. Here are the pros and cons of each.
Timber window frames
Many homes in New Zealand have timber window frames and since wood is a naturally effective insulant and is relatively sustainable, it’s easy to see why. However, the high cost and constant maintenance required with timber frames have meant they’ve become a far less common option in new build houses.
uPVC window frames
Window frames made of uPVC are reasonably durable and easy to maintain, however they will need replacing sooner than aluminium. uPVC is a type of plastic that’s weather resistant, soundproof, and highly insulating. It is an effective choice, but as it is largely imported from Europe this can lead to hidden costs or delays, which is why it isn’t widely used in New Zealand.
Compare aluminium vs uPVC window systems
Thermally broken aluminium windows
Standard aluminium framing is known for its higher conductivity, but thermally broken windows are a different story altogether. Thermally broken frames are reinforced with insulating polyamide bars which separate the inside frame from the outside frame, reducing the heat transfer between the exterior and interior. This makes them an energy-efficient, extremely durable and low-maintenance option with a streamlined design.
The fastest way to lift a window's R-value is the frame and the glass together. UNO Thermal aluminium windows combine a larger thermal break with Low-E double glazing to reach R0.65 for a typical 1000 × 1200 mm fixed window and R0.60 for a 2100 × 2400 mm sliding door*. UNO Hub generates the construction R-value for every window in your project.
For comparison, the generic H1/AS1 values for double-glazed windows are R0.24–R0.39 for standard aluminium and R0.30–R0.52 for thermally broken aluminium.
*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). R-values vary with size, configuration and glass. Sign up to UNO Hub to generate the construction R-values for your project.
How to achieve higher R-values for aluminium windows
Since each project is unique, there is no one-size-fits-all maximum R-value. However, let’s consider an example where the total area for windows and doors is approximately 35 square metres, with configurations as shown in the below images. Using the UNO Thermal window suite and a double-glazed Low-E product with a Ug-value of 1.1, we can achieve a construction R-value of R0.61.
Taking it a step further, we can explore other double-glazed Low-E options, such as a product with a Ug value of 1.0. The same project could achieve an R-value of R0.65.
Furthermore, if we consider a triple-glazed option with a Ug-value of 0.6, we could achieve an R-value of R0.83.
Frequently asked questions
What R-value do windows need in New Zealand?
There's no minimum window R-value under H1/AS1. Your design is compared with a reference building that uses R0.46 windows and doors in climate zones 1–4 and R0.50 in zones 5–6 (R0.33–R0.42 for buildings over 300 m²).
Is the R-value of the glass the same as the window R-value?
No. The window's construction R-value includes the glass, the frame and the edge of the glazing unit. The glass is usually described by its Ug value, and the frame can pull the overall figure down, which is why a thermally broken frame like UNO Thermal matters.
How do I increase the R-value of my windows?
Use Low-E double glazing, a thermally broken frame, and configurations with more glass and less frame, such as fixed panes where you don't need an opening. You can test each change in UNO Hub.
Can I still use the Schedule Method?
No. The Schedule Method has been removed from the current H1 documents. Use the Calculation Method or the Modelling Method, both of which use construction R-values for your windows and doors.
How do I get R-values for my project?
Sign up to UNO Hub, enter your windows and doors, and UNO Hub generates the construction R-value report for your exact sizes, configurations and glass.
Get accurate R-values with UNO Hub
Because every project is different, enter your proposed windows and doors into UNO Hub to calculate construction R-values based on the actual sizes, configurations and products being specified.
Want to understand how window R-values influence cost and compliance strategies? Explore our breakdown: Ideal R-Value vs. Window Costs
