The Game Is Changing; Will You Be Ready? How Building Code Changes To H1/AS1 Affect Windows And Doors

Updated 18th July 2022. Immediately after MBIE has published their outcome of the consultation to delay the proposed changes to H1/AS1 Version 5. Read their document HERE

De-mystifying The Building Code Changes For Windows And Doors

A direct, informal summary, using colloquial and easy to understand language, for everybody out there. For architects, builders, fabricators, the public.

Before we start

MBIE have changed the building code requirements for the H1 Clause of the NZBC. This is the energy efficieny section and dictates how your walls, roofs, floor, skylights and windows and doors must perform with regards to energy efficiency. While this change covers many different areas of a building, this post will focus on windows and doors.

The changes happening are based around R-values, so it is important you know what these are! Simply put, R-values are the measure of how much heat a material resists. So the R-value of a window measures how much heat is stopped by your window and therefore doesn’t escape outside. The higher the R-value, the better the window at resisting heat transfer, meaning you house stays warmer for longer. 

For context, the best R-value you can get in a window is about R1.3 – this is with premium timber frames and triple glazing!

Two big myths to bust right away:

Firstly, is this really happening? Yes, it absolutely is really happening, and very soon it will be law.  
Secondly, isn’t MBIE looking at delaying this all? No, they have announced their decision, and the values for windows are proceeding more or less exactly as planned.


What do we know?

  1. New Zealand will be divided into 6 new climate zones
  2. Each zone (or group of zones) will need to meet separate minimum R-values
  3. There are three different ways of proving compliance

Each of these are explained below.

The six new climate zones

New Zealand is currently split into 3 zones, however with the new changes, this will double to 6 zones. These zones are based on the average climate of the areas in the zones and therefore must meet different R-values for insulation.

The new R-Values

Now you are familiar with what R-values are and which zone your house is in, we can get into the technical stuff – the numbers…

Currently, all the windows and doors in New Zealand houses must meet an R-value of R0.26. This is the value standard solid aluminium frames and clear double glazing meet. (When we say ‘solid’ aluminium frames we mean aluminium frames with no thermal break, not actual solid aluminium for the frame. These are sometimes also called ‘cold’ frames because they are so thermally inefficient!)

The graph below shows the new minimum R-values. Don’t worry about the timing yet – we will discuss this in more detail next. All you need to know at this stage is that the requirements are almost doubling! This increase is to bring NZ closer to international standards, but also to ensure that Kiwi’s houses are warmer and more efficient to heat – who doesn’t like that? Cozier and cheaper to warm. Say goodbye to cold bedrooms and living areas when you wake up on a winter’s morning!

These changes certainly are changing the way we specify and build houses. When the new requirements have been fully implemented, zones 1-4 will need to meet R0.46 and zones 5-6 will need to meet R0.50. There is also an interim step of R0.37 (more on this next). The table below shows some example frame and glass options that meet some of these new R-values. To find our more on R-values read What is a good R-value for windows in New Zealand?

R-ValueFrameGlass (Double Glazing)
0.37Solid aluminiumHigh Performance Low-E
0.37Thermally Broken AluminiumEntry Level Low-E
0.37uPVCStandard Clear
0.46Thermally Broken AluminiumMid-Range Low-E
0.46uPVCEntry Level Low-E
0.5Thermally Broken AluminiumHigh Performance Low-E
0.5uPVCEntry Level Low-E

When these changes are fully implemented, solid aluminium frames won’t comply – not even with high performing low-e glass!

So when do the R-values change?

Now we can discuss timing – as promised. MBIE have announced that there is a slight delay to their initial timeline, which softens the change and weans the industry into the new requirements. These dates refer to when you submit your building consent request, however there is no reason not to get higher performing windows now! Why continue building code minimum? Get in touch, we’d love to help Contact STÄRKE Windows & Doors

How do I prove compliance?

So now we know what R-values we need to hit, how do we prove that our windows and doors meet these new values? Easy:

There are three different ways of proving compliance:

  1. Schedule Method (low detail – based off pre-determined tables)
  2. Calculation Method (medium detail – based off your unique plans)
  3. Modelling method (high detail – based off special software)

Schedule Method:

The schedule method is what most of the fuss has been about. MBIE has released a table of minimum thermal performance standards, and the dates and the zones in which they come into play (discussed above).  This method is based off a table of average R values released by MBIE. By taking into account which frame and glass is used we can find the approx R-value of the window or door.

Calculation Method:

The calculation method provides much more flexibility than the schedule method, and would generally result in a better building outcome… and more importantly, can save you lots of money on unnecessary insulation! The New Zealand Green Building Council (NZGBC) has released a very helpful calculator, which can be found here, If, for example, you put in windows with a value of R0.5, or even the easy to achieve R0.67, you will find on most plans the ceiling insulation can be significantly reduced. With this method, yes, your windows and doors may cost more, however they will perform better meaning you can save in other areas on insulation.

Modelling Method:

The modelling method is the most advanced, but also gives the best overall building outcomes. It takes into account the orientation and location of the building, how all the components work together, and ensures that negative outcomes (like overheating) are picked up in the design process. Modelling your building will cost a few thousand dollars, however will likely save you this much and more on building material efficiencies, and certainly will save you more in heating and cooling over the lifespan of the building.

We’ve done a more comprehensive blog on this particular topic… we recommend having a read here – H1 Compliance Genius: R0.74 windows offer design freedom back!

How are the R-Values of joinery calculated? (the boring bit)

Bear with us on this one… it is technical but it is helpful to understand.

The thermal performance of windows is generally calculated in R-values (in NZ) or U values (overseas). There are plenty of articles on the internet explaining these in more detail, which we recommend looking up. Basically, R value = how much heat the window resists and U value = how much heat the window lets through.

So, what we need to know here is this: U values are loosely the inverse of R values.
Dividing the value by 1 gives you the value of the other; for example, 1/R = U, and 1/U = R.

The way to calculate the R-value of a window is roughly as follows:

The result of this formula will give you the U-value. Now, to find the R-value, all you need to do is get the inverse of it as mentioned above, and voila, you now have the R-value for the window.

What this means is that there are six variables to play which affect the R-value:

  1. U value of glass (normally somewhere between 0.6 and 3)
  2. Area of glass (dependent on the size of the window)
  3. U value of frame (normally varies from 8 for standard aluminium, to 3.5 for thermally broken aluminium, and down from there for UPVC and timber.
  4. Area of the frame (depending on frame design and size of the window, number of mullions, sashes, etc)
  5. PSI value of the glass edge spacer.
  6. Length of glass edge spacer (dependent on window layout and size)

(you can get the U values of the glass, frame, and the PSI value of the spacer from suppliers)

Currently, we aren’t required to consider the performance of the install detail, so these are the only six variables – simple right! Of the six variables, three of them are tied to the actual size of windows, not the design of the suite, so will be a consideration for architects and designers when planning the size, location, and shape of the windows.

The other three variables relate to the thermal performance of the frame, glazing, and glass spacer. The easiest two to change are the glazing and glass spacer; there are “warm edge” spacers available, and glazing can be specified with increasing levels of Low-E coating, thicker spacers, and gas infill, all of which improve performance incrementally, but also increase cost.

The last variable is the selection of the joinery suite, which goes from standard aluminium frames to thermally broken frames, with timber and UPVC being at the highest performing end of the market; once again increasing cost with performance increases.

What else do I need to do worry about?

This covers most of it for windows…! However, the changes don’t just affect windows, they also affect quite several other areas of the building, from walls, roof, and underfloor details. If you are involved in these areas of building, there’s lots more learning to do!

It should be mentioned that the acceptable R values for commercial buildings will also be increasing – from the current status quo of zero. It will likely mean that double glazing is required for all exterior joinery in these situations, which shouldn’t cause much of an upset to the market – lots of this is already being done.

Where does STÄRKE sit with all of this?

We here are Stärke are very excited; it’s a long overdue revision of the standards, and it brings significant change to a market which is somewhat stagnant… proof of this is that the current standards, as admitted by MBIE, are less than half the performance of internationally accepted standards!

Stärke currently has multiple broad suites, from our Ambiance Inline uPVC system and aluminium systems for residential, industrial and façades . We are extremely confident in the performance of the suites and are already providing many houselots of joinery which exceed the new standards. We also are passionate about the install detail, which currently isn’t mentioned, but we went right ahead and designed a new one anyway… which you can read about here – Window installation in NZ; the one big mistake commonly made in New Zealand