Changes To H1 AS1 Efficiency: What Does It Mean For The Renovator?

Leave a Comment / Choosing A Builder, Renovating / By Caleb Muntz / 4 minutes of reading

Important Vocab

R-value: “Insulation requirements are measured by R-value. R-value is a measure of resistance to heat flow. The higher the R-value, the better the insulation.” (Tenancy.gov, 2025)

Construction R-value: The value of an entire system. (E.g a R-value of a glass wool insulation may be R2.8, but because of timber framing, the insulation is interrupted and has a different R-value in practice). To calculate construction R-values, click here.

Introduction

Recently, we have had the announcement of the new H1 efficiency standard changes. With this, we have a 12-month transition period. The changes fully take place on the 26^th of November 2026. Consider working with roofing-palmerston-north/”>roofing experts for professional results. For professional help, contact experienced building contractors in your area.

But first, what is H1 efficiency? H1 is the thermal performance standard of the building code. H1 Acceptable solution 1 (H1 AS1) and Verification Method 1 refer to different methods to comply with the standard.

When does H1 apply to home renovations?

If you are doing minor renovations that don’t negatively affect the thermal performance of the building, you are not required to follow the new H1 standard. In the instance of windows, the performance of the new glazing can.

Additionally, if the spaces are non-habitable, e.g garages and sheds, or are a bathroom, there is no need to follow the H1 requirements (Provided they do not affect the performance of the main dwelling of the house). Another allowance is for buildings that are off the main power grid. As the building uses self-generated power, it does not need to abide by the efficiency standards.

Instances such as: adding an extension*, increasing the glazing percentage beyond 2%, the thermal performance of the new glazing less than 20% of the original, there is a requirement to adhere to the H1 standard (Builder Magazine, 2022). To calculate this, we can use the calculation method in the Excel spreadsheet available here.

*In this scenario, the whole extension is treated as a new build and must comply with the current building code.

From Restricted Building Work, 2023, By Licensed Building Practitioners. govt, https://www.lbp.govt.nz/for lbps/restricted-building-work/

What are the changes, and what do they mean to you?

With the addition of this version of H1/AS1, there is no longer a schedule method to show compliance. This is where there was a table of R-values for set areas as above. Previously, you were able to insulate these spaces up to the stated R-values and comply; this has since been removed.

During the transition period (From now until the 26^thof November 2026), this method is still valid.

Under H1 AS1 6^thedition, there is now only the calculation method and the modelling method to show that the building shows compliance. For simplicity, I would recommend sticking with the calculation method, as that only requires filling out an Excel spreadsheet with basic calculations or can be calculated by hand. Comparatively, the modelling method requires specialised software to do so.

The Calculation Method.

From H1 Energy Efficiency Acceptable Solution H1/AS1 Sixth Edition, 2025, Ministry of Business, Innovation and Employment. https://www.building.govt.nz/assets/Uploads/building-code-compliance/h1-energy efficiency/asvm/h1-energy-efficiency-as1-sixth-edition.pdf

The calculation method compares a reference house to the proposed building. As long as the thermal loss is equal to or less than the reference house, the building complies with H1.** The beauty of this method is that if you insulate one space less than required, you can substitute it with more insulation elsewhere.** The proposed house should have a heat loss less than or equal heat loss of the reference house. This is because the equation is for thermal loss. The lower the number, the better thermal retention the house has.

With this, there are still minimum requirements of:

r2.6 for roofs

r1.3 for floors

r1 for walls (H1/AS1, 2025)

As for windows, there is no set R-value in H1/AS1; however, all NZ window manufacturers make windows to an R-value of 0.46 or higher. This means all new windows produced should comply with the H1 Standard.

You can find the BRANZ Excel Calculation tool here.

Just Before you go…

There are a few important key points:

Putting insulation in exterior walls is restricted building work (RBW). This would require the input of a licensed building practitioner. To find out if your project is RBW, consult the table above or click here for more information.
Every project is different, although I have some general advice, it is always best to consult with a professional if you are unsure.
To get fully clued up, you can read the new solution here.

About The Author

Hi, I’m Caleb. I study architecture at EIT, due to graduate in 2027.

I am a young Kiwi who loves New Zealand and its vibrant innovation in the construction industry. During my studies at EIT, I have discovered my passion for Architectural writing. I really enjoy putting together and displaying my research to others.

As I continue my study into 2026, I hope I can continue this passion through my writing.