There’s been a lot of chatter in social forums about Low Energy Buildings recently so it’s timely to consider exactly what they are and why they matter. Back in 2018 when I was working on my first book about Passive House (available here), I wrote:
A PHI Low Energy Building (LEB) is the next-best-thing to a Certified Passive House. It was intended to recognise near-miss buildings which targeted Certified Passive House but just missed meeting the standard or are particularly challenging. These buildings are required to be equally as healthy and durable but are able to use slightly more energy than a Certified Passive House. To be certified [as] a PHI LEB, the building must use no more than 30 kW/m2/year for heating, and cooling; and achieve an <1 ACHn50.
In three years, much has changed. Among the Passive House community worldwide, people are far more focused on carbon emissions now given the urgency of the climate crisis is ever clearer. For that reason alone, I no longer think it is fair (if it ever was) to characterise LEB as a badge for trying.
Low Energy Buildings are a crucial stepping stone that indicate how we get from here to there (ie from 99% of new buildings* constructed to the historically tragically low Building Code minimum to zero carbon building).
I refer you again to the carbon roadmap Kāinga Ora has been circulating. Look closely: in the step changes required to meet our 2050 carbon neutral commitment, by 2027 all new buildings will need to hit the LEB standard of using less than 30kWh/m2/a. That’s in advance of the 2030-2035 final cap which is the same as the thermal performance of a certified Passive House.
Getting from Code-minimum to the performance of a certified LEB is a big step and the hardest one. In all but the warmest New Zealand climates, a LEB will boast all the building components and methodologies present in a certified Passive House: better performing windows and doors, extra insulation, minimised thermal bridges, mechanical ventilation and an airtight building layer. The moisture protection criteria for a LEB is also the same as for a Certified Passive House. Crucially, that LEB will have been energy modelled at design stage, just like a Passive House. Its energy performance was predicted and then independently verified once built.
My 2020 rant about cargo-cult architecture hit a nerve and was very widely read. If anyone needs an explanation why it is a very bad idea to skip energy modelling while sprinkling in higher-performing components, please go read it. Also, every new build should have continuous mechanical ventilation. I’ve written plenty about that too.
A certified LEB is likely to be by far the best house the owners have ever lived in. There are very few of them currently built in New Zealand: only seven have been certified at time of writing. However some homes built above Code standards under various brands or slogans may perform to this standard: as always, if it’s not energy modelled and verified by an independent expert post construction, how would anyone know?
We need to celebrate every LEB that is built in the place of a Code-minimum house or office etc. So you’re going to be seeing and hearing a lot more about LEBs; or at least buildings that hit the same level of energy efficiency.
*This is not a statistic anyone collects; I made the number up but if it’s wrong it’s not out by much.