You may have heard about the highly anticipated updates to H1, the section of the New Zealand Building Code that governs energy efficiency. These updates address insulation, windows, and other thermal performance details. For decades, H1 has lagged behind international standards, leaving New Zealanders in housing that has been proven to contribute to respiratory illness, mould, and poor thermal comfort.
The minimum requirements have been insufficient for generations. Architects and designers have been working around them, but the building code itself has been a barrier to common-sense detailing — especially when it comes to windows.
Section E2 of the Building Code governs weathertightness and external moisture. For good reason — the leaky building crisis of the 1990s and 2000s is still fresh in New Zealand's collective memory. E2's response was to mandate that windows be installed outside the building envelope, effectively pushing them to the outer face of the wall.
The problem? This placement puts windows in the worst possible position for thermal performance. Instead of sitting within the insulation layer, they bridge across it. A window that could be performing at R1.8 or higher is instead compromised by having its frame exposed on the cold side of the wall, creating a direct thermal bridge to the outside.
The mechanism that caused the leaky building crisis was poor drainage, inadequate flashings, and untreated timber framing rotting behind rendered claddings — not recessed windows per se. But the regulatory response was broad, and it had unintended consequences for thermal performance that took over a decade to begin correcting.
Over the years, we've developed specific flashing details that allow windows to be brought inward, closer to or within the insulation layer, while still maintaining weathertightness. These work — we've built them, they perform, they don't leak.
But each project requires its own detailing. Each council may interpret the Acceptable Solutions differently. Each builder needs to understand and commit to a slightly non-standard approach. The result is that recessed windows are still the exception, not the norm.
This approach has limits. It relies on designers, councils, and builders all being on the same page. In an industry already stretched thin, asking every project to invent custom weathertightness details for windows is not scalable.
For the better part of a decade, I've argued that this problem needs to be solved by window manufacturers themselves. A window should be a certified, tested assembly that can be installed anywhere the designer specifies — including recessed into the insulation layer — with a manufacturer-approved flashing solution that councils can accept without additional engineering.
The responsibility should not sit entirely on the building code, nor on designers, nor on territorial authorities. The product and its manufacturer should provide the dependable solution. When you buy a European window system, you get a tested installation kit for various wall constructions. That's the standard we should expect in New Zealand.
Recent changes to H1 are forcing the industry to address this. With higher required R-values for windows, it's no longer possible to meet code with a standard double-glazed unit slapped on the outside of a timber frame. Insulated frames, thermal breaks, and careful installation are now requirements, not optional upgrades.
We're starting to see a shift. A few window manufacturers have acknowledged the issue and are bringing products that perform and recess properly. Thermally broken aluminium and uPVC systems are increasingly common. But we're still limited to a handful of specific products that genuinely solve the problem.
If you're planning a new home and performance matters to you, here's what to ask your designer and window supplier:
1. Where will the window sit relative to the insulation layer?
The answer should be: "Within it, or aligned with it." Anything else means your best thermal element is compromised.
2. What is the manufacturer's recessed installation detail?
If they don't have one, they're not the right supplier for a high-performance build.
3. Has the council consented this detail before?
Proven details are better than novel ones. Modern councils are becoming more familiar with recessed installations, but it still varies by region.
4. Is the frame thermally broken?
Not all "thermally broken" frames are equal. Check the actual frame R-value, not just the marketing.
The H1 changes are long overdue, and they're finally forcing the kind of thinking that should have been standard practice years ago. But the real work happens at the detail level — and that's where experienced design makes the difference.
Thinking about a high-performance home with properly detailed windows? We've designed and consented recessed window details across Christchurch and Canterbury.
Discuss Your ProjectPreviously published on sips.network (2022). Updated for VILA.nz.