2.17. Effects of the H1 insulation requirements on overheating and dampness risks in new housing

2.17.1. MBIE commissioned research in response to concerns

In early 2024, concerns were raised about the insulation changes from 2021. This included concerns that the increased insulation causes dampness issues and overheating in new housing.

In response to these concerns, and to inform this review of the H1 settings, MBIE commissioned BRANZ to undertake a comprehensive technical analysis. This included assessing the risks of overheating, internal moisture and mould as result of the changes made to insulation in 2021.

2.17.2. Overheating risk findings

Overheating risk is generally greatest during daytime. BRANZ’s analysis shows that the increased H1 insulation requirements from the 2021 changes help to reduce daytime overheating risks compared to the previous H1 settings. Increased insulation in the roof, wall, and windows typically reduce the risk of overheating during the daytime by reducing solar gain. However, the increased insulation also slows the cooling down of a building overnight. 

Many factors can contribute to overheating in buildings. This includes ventilation, building orientation and shading, window size and glazing. A poorly ventilated building with large windows may overheat where the design does not effectively allow for managing heating loads and cooling demands.

The Building Code sets the minimum performance a building must achieve; however it currently does not have a performance requirement to manage overheating in buildings, allowing some building designs to be at risk of overheating, irrespective of insulation levels. Potentially guidance, new H1 solutions, regulation, or some other approach could support designers with this potential risk.

2.17.3. Internal moisture risk findings

BRANZ’s analysis also found that the increased H1 insulation requirements are not increasing internal moisture risks in buildings. While higher insulation levels can influence the dynamic of internal moisture, key factors affecting internal moisture were found to be wall cladding colour, roof colour, the amount of moisture released inside a building and a building’s orientation.

Currently the Building Code sets minimum performance requirements for internal moisture under Clause E3.

2.17.4. Managing overheating and internal moisture in homes

SQ8. If you think MBIE should support building designers with designing homes that safeguard building occupants from high indoor temperatures in summer (overheating) and other potential moisture risks, what approach should MBIE take? 

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