The New Zealand Building Code
The Building Act 2004 is the legislation which governs the building industry in New Zealand, and amongst other duties it maintains, regulates and enforces The Building Code. The Building Code does not describe how a building must be constructed, but rather how the building will perform for its intended use. This allows for a wide range of materials and design solutions to be used, and covers off areas such as fire, insulation, structural strength, moisture control and durability.
The area of The Building Code which relates to thermal performance in new construction is called H1, and designers and contractors must prove compliance to local Councils that the new construction meets the minimum levels of H1.
When installing insulation into existing homes (retrofit), if you are insulating your external walls this is covered by the Building Code and the local Council will require you to obtain Building Consent in order to complete the work. Ceilings and under floors can be insulated without consent.
We recommend you regard H1 compliance as a minimum standard, not a target. Because H1 does not take into account the amount of timber within a wall, which reduces performance by the way of thermal bridging, it means the more timber, the less insulation, thereby reducing the overall thermal performance. A common method to drastically reduce thermal bridging in walls, is to add an additional interior cavity. This is normally 50mm thick, and can take a further R1.4 of insulation, essentially covering up most of the structural timber. This is similar to adding layers of clothing before going outside on a cold day, and also allows services such as plumbing and wiring to be run though the internal cavity – leaving the outside wall and insulation untouched. Another trend is to remove nogs (dwangs) which unless are needed for bracing panels, are not required under the Building Code, saving money on your frames and reducing thermal bridging.
Commonly used R-Values of insulation to meet minimum H1 Compliance
1 – Good insulation – commonly used R-Values to exceed H1 Compliance
2 – Better insulation – recommended upgrades based on timber framing construction, with a normal truss roof
3 – Best insulation – the best R-Values to achieve in order to exceed H1 Compliance and future-proof your home