Insulation for Houses in Aotearoa New Zealand
Insulation requirements changed significantly on 1 May 2023 for residential houses in Aotearoa NZ. The new requirements are all covered by H1 (Energy Efficiency) in the New Zealand Building Code (the Code).
New climate zones for New Zealand – Image sourced from Uno Windows & Doors
What is the Minimum R Rating for Insulation NZ?
A summary of the changes is provided within the Code in Table 2.1.2.2B – Minimum Construction R-values.
The country is now divided into 6 climate zones (also referred to as the Schedule Method).
Zone 1 (includes Auckland, Northland, Coromandel and much of Bay of Plenty) has the lowest requirements and the minimum acceptable solution is now R6.6 for roofs, R0.46 for windows, R2.0 for walls and R1.5 for concrete slabs on grade.
A good reference for the insulation requirements is found in the Comfortech© brochure, which shows how to lay out insulation in roofs to achieve the new required insulation R-values The H1Hub page on their website also provides good guidance on installation requirements.
A minimum of R0.46 for windows (as required for the Auckland region) means that you require a thermally broken aluminium frame together with a double layer of low-E glass installed with a thermal spacer. uPVC or timber frames are also acceptable.
Do I Need a Building Consent to Install Insulation?
You are permitted to add new or extra insulation to the ceiling, internal walls (where the internal wall is not a firewall separating an apartment or tenancy) and subfloor of a house or apartment without the requirement for a building consent.
However, you do require a building consent to add insulation to the exterior of your house. This requirement is because there may be weathertightness implications.
Insulation for a Rental Property in New Zealand
If you are a landlord, then you are required to provide insulation to an existing dwelling to the Healthy Home standards. These requirements form a part of the RTA (Residential Tenancies Act) and are available on the Tenancy Services website. Tenancy Services also provide excellent guidelines on the requirements for insulation in a tenanted dwelling. First of all, there are exemptions:
- Apartments where there is a habitable space above and below the apartment
- houses built on concrete slabs
- houses with skillion roofs where there is no ceiling space to install insulation
- You cannot practically access the ceiling or underfloor space without carrying out substantial building work (this exemption does not apply if you are working on your property and reroofing). The term “practically” means when the ceiling or underfloor space is either unsafe or impracticable to access. If there is a ceiling or boards around the perimeter of the subfloor then these must be opened up if it allows for safe access and there is sufficient room to install insulation.
Effective 1 July 2025, with the exception of the above, all private rentals must comply with the Healthy Home standards.
Thermal Bridging of Structural Elements
Dealing with thermal bridging structural elements has as yet not been adopted into the New Zealand Building Code, although it is currently under review and likely to be introduced in the not too far away future.
The issue here is that structural engineers often use 89x89x6 Square Hollow Section (SHS) posts inside wall cavities (to support upper-level steel beams), and the steel can act as a thermal transfer element: the increased heat outflow leads to low internal surface temperatures, which have a negative effect on thermal comfort and increases energy consumption.
To alleviate this potential thermal bridging issue, consideration is now being made to add insulation around steel structural members inside external walls.
If introduced, these new requirements may result in an increase in the stud dimensions in order to accommodate such structural elements with surrounding insulation, depending on the design requirements and the amount of load the posts are required to carry.
Risks Associated With Insulation
- Incorrect installation may mean that it does not get passed by a building inspector so ensure that you or your installer have complied with the installation requirements recommended by the manufacturer guidelines.
- Insulation cannot be run over downlights unless the downlights have been designed accordingly. There is a potential for fire due to heat build-up.
- You cannot use or repair foil insulation due to electrical safety concerns. The above are brief guidelines only, and it is the responsibility of the reader to obtain professional advice when considering insulation requirements for a dwelling.
The above are brief guidelines only, and it is the responsibility of the reader to obtain professional advice when considering insulation requirements for a dwelling.
Author: Stewart Hobbs - Principal Engineer at ProConsult
Stewart is the journal editor for SESOC (Structural Engineering Society New Zealand (Inc.)
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