After painstakingly researching, consulting on and citing improvements to thermal performance in the NZ Building Code for years, MBIE was directed by its incoming minister to investigate rolling back changes. Chris Penk cited anecdotes from a couple of Tauranga group home builders that more insulation was causing overheating as his rationale, all while banging on the housing shortage drum.
In response, MBIE has just released a consultation document, which I’ve read carefully. It’s a clever and frankly gutsy move on the whole that takes the opportunity to improve the building science underpinning the regulations. That will be cold comfort though for those component suppliers who have invested in new products to meet the higher performance requirements rolled out from 2021.
Getting aligned with reality
This document suggests MBIE is seeking to hold a course all while skillfully tacking under some strong headwinds. Two different governments want to be seen to be achieving different things. Labour wanted to be seen to improve housing quality and take action on climate change. National wants to be seen to be making it cheaper and easier to build new homes. So MBIE has offered up reduced wall insulation requirements; R1.6 compared to R2. But Labour’s R2 walls weren’t, because the timber fraction was grossly underestimated and that impacted real world insulation performance. I went into all the technical detail of this here following the Beacon Pathway report.
MBIE is proposing to introduce a timber percentage fraction that aligns with reality, 38%, unless a designer can demonstrate that a lower framing fraction is justified. Just so we’re all crystal clear: a R1.6 wall with a 38% timber fraction under National is in reality the same wall with the same performance as a R2 wall with a nominal 16% timber fraction under Labour.
There are two benefits to this fix. Innovative and better-performing wall assemblies with no or minimised timber framing—think SIP or prefabricated wall panels—are no longer disadvantaged by being compared to a fictitious timber wall construction in the reference building. Second, it’s always preferable that building regulations correspond to reality. The first step to fixing a problem is acknowledging that you have one.
From the Beacon Pathway report, Measuring the extent of thermal bridging in external timber-framed walls.
The change that will generate more reaction though is deleting the schedule method of compliance. This is audacious. It’s a change those of us who care about better buildings all support. It would make all building designers look at the energy balance at design stage because with the easy option off the table, they’ll need to use either the calculation or modelling method. It will mean a small increase in the cost of design but used for good, would produce much more comfortable, efficient buildings at minimal additional cost.
But it would also be possible to use either of these compliance pathways to wring out savings on capital costs by building a worse home for a bit less upfront cost. This is what is making suppliers nervous. This strategy of course increases operational costs—money spent on heating and cooling for the lifetime of the building. Or in communities where there’s no money available for larger power bills, what increases is the sum of human unhappiness and ill health.
MBIE has also taken the opportunity to introduce a lot of small fixes or clarifications. I welcome the removal of some common ‘cheats’ used to make poor buildings pass H1. For instance, the proposal defines the reference building SHGC for glazing and reduces internal loads by nearly 50% to better match the reality of much more efficient modern appliances and widespread uptake of LED lighting.
It’s not all good
I was disappointed that no requirements were included to address overheating (even as the document noted that more research confirms more insulation does not drive overheating). We have the knowledge and means to prevent buildings overheating and it’s crucially important we do so for the sake of people’s health, keeping our electricity grid running and reducing New Zealand’s carbon emissions.
The other disappointment was the decision to use overall internal dimensions to measure areas for H1. There are three possible ways to measure according to the relevant ISO standard. The proposal is better than internal dimensions, which produces some deeply unfortunate unintended consequences in multi-story construction. But external dimensions would make calculation of thermal bridges much simpler at the point in the future when New Zealand finally requires predictive thermal models for Code compliance.
Using internal dimensions means almost every single junction in a timber frame building has an energy loss that matters and every one of them will need accounting for. For the record, I understand why MBIE has made this choice; the wall area becomes larger when using external dimensions and designers who don’t know better could use that to increase window glazing percentages even further.
Penalising innovation
I’ve been taking a lot of calls from suppliers and manufacturers concerned that these changes will chill demand for the products they introduced to meet the improved insulation requirements that started rolling out in 2021. A number of firms invested in sourcing or developing superior components, like slab insulation methods or better quality windows. It used to be that politicians loved to celebrate that kind of home-grown innovation, ingenuity and commitment to improvement.
(Concrete slabs are the default foundation for New Zealand homes. Not insulating them? That’s the dumbest thing imaginable, in almost every climate zone. You literally cannot fix an uninsulated slab. Even though retrofitting insulation above the slab is theoretically possible, the cost and the list of consequences is so massive it is practically impossible.)
We need policy settings that are rational and stable, not subject to whiplash due to political forces. MBIE is to be commended for its efforts to find a middle path for the long term good.