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    Buildings more than 300m2 - Walls

    New construction R-values & how to achieve them

    Insulation is a barrier. It helps keep the heat in during the winter and can help keep the heat out during summer. This means that insulation is beneficial even in the warmest part of the country.

    To be effective, the barrier has to be continuous in the building. That’s why the changes to Building Code clause H1 Energy Efficiency look at insulating all parts of a building – including ceilings, walls, floors, windows, doors and skylights. Below is an overview of the changes to construction R-value requirements in different parts of a building, and how they can be achieved.

    Minimum R-values for Floors for housing in H1/AS1 and H1/VM1

    Options Climate Zone
    1 2 3 4 5 6
    Current minimum requirements R1.3
    Slab-on-ground floors 1 May 2023 R1.5 R1.5 R1.5 R1.5 R1.6 R1.7

    New construction R-values for floors

    From 1 May 2023, the minimum R-values for floors will increase in all climate zones. The table above shows the construction R-value required. The previous R-value for the entire country was R1.3.

    Increases to floor insulation are two-fold, differing over climate zone – as with all building elements – but also depending on whether you have a concrete slab-on-ground floor, or another type (most commonly suspended floors).

    The new minimum construction R-values are lower – R1.5 to R1.7 – for concrete slab-on-ground floors than for other floor types – R2.5 to R3.0. According to MBIE, this is because it’s much more challenging for slab-on-ground floors to achieve significantly higher R-values than with other types, such as suspended timber floors.

    However, even the small increase required for unheated slab-on-ground floors in the warmest four climate zones – a move from R1.3 to R1.5 – is greater than it appears. That’s because the background calculation method used for the 5th edition has changed. According to BRANZ, the increase is the equivalent of going to R2.0 under the previous approach. R1.5 means most slabs in buildings under 300m2 will be specified with some combination of perimeter and under-slab insulation.

    In the future, MBIE expects that this differentiation between the floor types to be removed and slab-on-ground floors will need to achieve even higher levels of insulation.

    It’s unlikely that there will be a big shift in the types of products that can be used, but a change in the installation methods will be needed. For example, insulation added to non-slab-on-ground floors will no longer be able to be held in place with staples due to their increased thickness.

    The new R-value requirements are also different for heated slab-on-ground floors. See table below.

    Schedule method minimum construction R-value requirements (m3K/W) for concrete slab-on-ground floors

    Climate Zone
    1 2 3 4 5 6
    Current Minimum Requirements
    Unheated slab floors R1.3
    Heated slab floors R1.9
    Minimum from 1 May 20203 (for Housing)
    Unheated slab floors R1.5 R1.6 R1.7
    Heated slab floors R2.5 R2.8 R3.0

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