New Zealand’s energy efficiency rules (H1):
What’s changed for glazing, what to specify, and why timber joinery performs so well
By Aaron Dando – Owner, Dando Doors and Windows
If you’re building a new home, or doing a major renovation, you’ll hear the term “H1”. H1 is the New Zealand Building Code’s energy efficiency clause. It influences insulation, windows, and glazing performance.
MBIE updated the H1 documents in late 2025, with a transition period through to late 2026. The practical impact is that glazing is now more often treated as a performance input to compliance, rather than a simple note on the plans. This is not new news to most architects and energy assessors. However, it is very relevant for builders, developers and homeowners when it comes to quoting, procurement, and avoiding late changes.
We’re Dando Doors and Windows, a timber door and window manufacturer. This article explains how glazing is now typically handled, what flexibility remains, and what information we need to price and manufacture accurately.
1. Glazing isn’t just “double glazing” anymore
For many projects, the note “double glazing throughout” is now too vague at pricing stage.
That’s because there are multiple performance levels, and appearances, within double glazing. For example clear double glazing, Low E double glazing, Low E plus argon, warm edge spacers, different glass thicknesses, acoustic laminates, and safety glass requirements.
These choices can affect
• energy efficiency performance
• comfort and condensation behaviour
• the visual appearance of the glass
• cost and lead time, especially for large glazed doors
In short, glazing is often part of the energy efficiency compliance evidence, so it pays to confirm the intent early, before the job is priced and ordered.
2. Who decides the glazing performance
In practice, glazing performance is determined by the design team.
The architect or designer issues the drawings and specifications and controls the consent set. Sometimes an energy assessor or modeller is involved, particularly where modelling is used.
As the joiner, we don’t pick the H1 inputs. We manufacture to the specification and can offer options, but the project needs a clear glazing basis so the quote matches what will ultimately be approved and built.
3. Why plans and compliance documentation need to match, especially with modelling
Where modelling is used, the energy analysis is expected to align with what is shown in the consent documentation, as closely as reasonably practicable. The reason this matters is simple.
If the model assumes Low E plus argon, or a certain solar performance, but the drawings or specs only say “double glazing”, you can end up with late changes once someone locks in the compliance basis.
Late changes can mean repricing, variations, delays, and sometimes rechecking compliance.
Even when you’re not modelling, many teams now treat glazing as something that should be clearly specified early to keep procurement smooth.
4. A key shift from the old approach: less “minimum glazing R value”, more whole building performance
In earlier versions of the rules, it was common to see glazing discussed as a simple minimum “R value” requirement. For example R0.46 was a common benchmark for windows and doors in some zones in the previous framework.
Under the current framework, glazing is typically treated as an input into the overall calculation or modelling approach, rather than relying on one simple minimum note on the drawings.
For builders and homeowners, the takeaway is this
• you may see more projects using a window performance schedule
• you may see a clearer glass make up specification
• you may see less reliance on a single “minimum glazing R value” line
5. Timber joinery: warmer by design, and the numbers people care about
Timber is a naturally insulating material, and the frame is a real part of the overall window and door performance, not just the glass.
Using the current typical housing reference table commonly used for housing comparisons, timber framed windows and glazed doors sit at approximately
• R0.44 for a common clear double glazing performance band
• R0.56 for a common Low E double glazing performance band
In the same reference table, thermally broken aluminium sits lower for the equivalent glazing bands. In plain terms, on these common comparisons, timber framed windows and glazed doors deliver around 37.5 percent to 43.6 percent higher R value than thermally broken aluminium, noting that actual results vary by window size and design.
Why that matters is simple. Higher R value means less heat transfer through the window or door system. This typically improves comfort and helps reduce condensation risk, especially in bedrooms and living areas with large glazed openings.
6. Can a new build still use single glazing
In some special cases, single glazing can be explored, but only if the project’s designer or energy assessor can demonstrate compliance through the energy efficiency calculation or modelling approach.
Single glazing usually makes compliance harder unless other parts of the home are upgraded, for example roof, walls and floor, and or window areas are kept modest. In practice, most homeowners still choose double glazing, clear or Low E, for comfort, condensation control, and resale expectations.
The key point is that if a project team wants to explore alternatives, it needs to be done early and documented clearly so the quote, consent set, and compliance basis all line up.
7. Clear double glazing vs Low E: performance and appearance
This is one we discuss often with homeowners because it affects both feel and aesthetics.
In the past, when projects were commonly trying to meet a simple minimum glazing R value benchmark, Low E was often the default choice to help achieve the required performance. With the current approach being more flexible and more often supported by calculation or modelling, some projects can potentially meet the overall requirements using clear double glazing, depending on the design, glazing area, insulation levels, and other factors.
For many homeowners, the appeal of clear double glazing is simple
• it is usually the most neutral and crystal clear in appearance
• it can offer cost savings compared with higher performance glazing options
Low E double glazing can provide improved thermal performance, but it can sometimes show a slight tint, and in certain angles or lighting conditions it can show a subtle haze, sheen, or reflective film effect. This is often a normal visual characteristic of the coating interacting with daylight or strong internal LED lighting, not necessarily a defect.
If you’re sensitive to glass clarity, large feature glazing, strong downlights, or carefully curated interior finishes, it’s worth discussing early. We can help confirm glazing options and pricing so your final selection matches the look, comfort, and project requirements.
8. What we need to quote accurately, so you avoid late changes
To keep pricing clear and avoid variations, we ask for one of the following from the architect or designer.
Option 1, best, a performance requirement
A window and door schedule that states
• the required window and door performance, often shown as Uw or R value or Rwindow
• if modelling is used, any solar performance requirement, often called SHGC, and relevant shading assumptions
Option 2, a clear glazing specification
A schedule or spec clause that clearly states
• clear vs Low E, whether argon is used
• glass thickness and cavity, the insulated glass unit build up
• spacer type
• any safety or acoustic requirements
If the plans only say “double glazing”, we can still price, but we may need to provide options, because different double glazing make ups can perform, and look, quite differently.
9. Why early clarity saves time and money
When glazing is clearly specified early
• quotes are comparable, apples with apples
• lead times are more predictable
• there are fewer variations
• what gets installed matches the project’s energy efficiency compliance basis
Want help choosing the right glazing
Send us your plans and window schedule, even at concept stage. We’ll help you compare clear double glazing vs Low E vs Low E plus argon, explain the appearance differences, and make sure the quote reflects what’s intended for the build.
Need advice
If you are unsure about
• correct painting requirements
• warranty conditions
• maintenance obligations
• best practice for timber joinery
Please contact us early. We are always happy to help clarify what is required.
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