New Insulation Rules From 27 November: What They Mean for You

From 27 November 2026, the way new homes show they meet the insulation rules is changing. If your build is still being designed, or your consent hasn't gone in yet, this applies to you. The good news: the required level of warmth hasn't changed, and the new rules give designers more room to keep costs down.

What is changing?

Every new home has to meet clause H1 of the Building Code, which covers energy efficiency: how well the roof, walls, floor and windows keep the heat in. Until now there were three ways to show a home meets H1. The simplest, the "schedule method", set a minimum insulation level for each part of the house.

From 27 November 2026 the schedule method can no longer be used. Building consent applications must use the updated rules (H1/AS1 6th edition) and show compliance with either:

• the calculation method, which looks at the house as a whole, or

• the modelling method, a full computer model of the home's heat loss.

What stays the same

The overall standard hasn't changed. MBIE has said the level of energy efficiency and insulation required stays the same, so homes will still be built warm and dry. The difference is in how a designer gets there.

Why it can help keep your build cost down

The calculation method lets the designer trade one part of the house off against another. For example, a little more insulation in the ceiling can balance a larger window, instead of every element having to hit its own fixed minimum. MBIE expects this to lower upfront building costs.

There is a trade-off. Because the calculation method can sometimes meet the rules with less insulation, BRANZ analysis for MBIE estimated a sample house could use slightly more energy for heating, adding roughly $53 to $236 a year to the power bill. So it's worth talking about where a little extra insulation is good value for you.

What it means if you build with MH Builders

• We already have the H1 calculations done for our homes by BrightR, an energy specialist, as part of preparing your plans for consent.

• Your Fixed Price Proposal is priced off the consented design, so the insulation in your price is the insulation in your home.

• If you want a warmer home than the minimum, for example higher-rated insulation or better glazing, we price it as an option so you can see the cost before you decide.

• If your consent was lodged before 27 November, it can still be assessed under the previous rules.

The short version

The required warmth hasn't changed. How it's worked out has. For most people the change should be invisible, but it's a good moment to ask your builder how your home meets H1 and whether a small upgrade is worth it.

Want to know how this applies to your plans or section? Book a free chat with Clint or Eoin.