Get what you paid for

Or why the Passive House certificate matters

By Rachel Rose, for Ethos Homes |  21 August 2021

Passive House is a standard for radically energy-efficient buildings: like homes that use up to 90% less energy for heating and cooling, while staying at a perfect temperature. Everywhere in the house, all the time.*

It’s also a system. Cherry-picking high-performance components (eg expensive European windows) without understanding how they interact with all the other factors can be a recipe for disaster. The biggest risk is creating a house that will massively overheat in summer. You don’t want to live in an oven or be forced to create a cave by keeping the curtains closed all the time.

Building scientist Jason Quinn wrote about this whole problem in a widely-read blog post on his website. It’s aimed at Passive House professionals but it’s seriously worth reading if you’re considering buying or building a high-performance home. Unfortunately, it’s even more relevant now than when he wrote it 18 months ago. 

Image of Passive House principles from PHI via Sustainable Engineering. But what you don’t see is the single most important feature of a high-performance home, according to Jason Quinn: energy modelling at design stage.

This is why we think reaching Passive House certification is so important. You can be sure you’re getting what you paid for. And by computer modelling the energy performance and then mechanically testing it during and after construction, the architect/designer and builder get precise feedback about how well they’ve done their job. Do that a few times and it really hones your skills as a building professional.

Beware those who say certification isn’t necessary or worth the money. Getting certified adds a tiny percentage of cost to your project but the certainty and confidence it provides are priceless. 

Here’s a blower door test in action. This happens at several key points during construction and measures how well the building envelope works. A certified Passive House needs a result less than 0.6ACH (It’s also a proxy for build quality: the lower the number, the better.) Photo by Passive House certifiers, Sustainable Engineering Limited.

Oh, and almost as a byproduct, the certified Passive House design and construction process creates very high quality buildings. Components will last longer, maintenance costs will be reduced and repairs are less likely. 

*This is hard to imagine for the generations of kiwis used to heating just one room (and who thus put off going to the toilet for an hour because it’s 10 degrees in the bathroom) or who routinely wear puffer jackets indoors.