Overheating homes? The real problem is design, not too much insulation!

January 21, 2025
EXPOL News, Good design

As we experience the hottest summer in years, a critical debate is unfolding around New Zealand’s building standards, particularly around the H1 Energy Efficiency standards.
Construction Minister Chris Penk has suggested that stricter insulation requirements may be contributing to overheating in homes and driving up building costs. However, experts, including the Green Building Council, have firmly rejected these claims.

In a recent NZ Herald article, industry professionals highlighted that the real causes of overheating are more likely to be attributed to poor ventilation, large windows, lack of
shading, and inadequate building design, not insulation. Green Building Council representative, Cutler-Welsh, stressed that insulation is a key factor in preventing overheating, likening an insulated home to a chilly bin, where heat is kept out while the inside remains cool despite external temperatures rising.

The Building Research Association of New Zealand (Branz) corroborated the problem outlined by Cutler-Welsh, the way the house was built could cause it to overheat, “but the risk can be managed with good design”, Branz said. Branz also said it was a “misconception that insulation causes overheating in homes in summer, In reality, the opposite is usually true”

The concerns raised by Minister Penk about the potential impact of increased insulation standards on home affordability are also being questioned. While adding insulation to concrete slabs may increase costs slightly (around $21/m2), the added investment represents only 0.65% of a new build’s overall cost – a small price to pay for the long-term benefits of a cooler, more energy-efficient home.

Key points

Insulating a concrete slab with SLABX200 increases a new build’s cost by less than 1%.
The insulation helps achieve R-values between R1.9 and R3.1, improving overall energy efficiency.
Poorer-quality homes with inadequate insulation will only contribute to more severe overheating and higher energy consumption in the long run.

Cutler-Welsh also pointed out that once a house is built, it is difficult to mitigate overheating issues. The Building Code does not currently address overheating, leaving Kiwis vulnerable to stifling indoor temperatures. The Green Building Council is urging the government to rethink rolling back H1 standards, as doing so would undermine global best practices for energy efficiency and comfort.

In summary, reducing insulation standards could mean lower construction costs, but it will also lead to poorer-quality homes, with increased risk of overheating and higher long-term energy costs for homeowners.

We urge you to consider these facts and advocate for building practices that prioritise energy efficiency, comfort, and the well-being of New Zealand homeowners.

Have your say here:
Insulation requirements in housing and other buildings | Ministry of Business, Innovation & Employment