How we investigated creating a certified Passive House school building, how we failed, what we learnt and how it was still the right thing to do regardless.
Last year I completed my study to become a Certified Passive House Designer. Thanks to the amazing Kara Rosemeier, I learnt more about building physics and performance than in my previous 30 years of study and practice. This, even though my projects had received many awards for environment design!
The Passive House Standard is a proven way to create low energy comfortable, healthy buildings. Research has shown that they perform as the design predicted. I like that you can’t cheat. I have seen too many “environmentally designed buildings” that don’t perform as they are meant to. They use multiples more energy than designed and/or overheat.
With Passive House, you need to analyse all the details and junctions. The details make a big difference. Your modelling is rigorously independently reviewed by a certifier. Airtightness is tested checked during the build. Don’t fall for “designed to passive house principles”. This has no real meaning. The above critical activities have probably not happened.
Paying attention to Kara, I realised that the easy way to do a passive house wasn’t a house. It was a bigger commercial or institutional building. Small buildings are harder. A larger building, with its greater surface to volume ratio, will require lower insulation levels to meet the minimum heating demand. This larger volume also means they don’t need to be quite as airtight to meet the required 0.6 air changes/hour standard.
A new 1150m2 mass timber building we were designing at Sacred Heart College seemed a good candidate, so we got to work with the assistance of Elrond Burrell from VIA architecture. Elrond had worked on Passive House school projects in the UK. Collaboration is a great way to learn to develop passive house projects. We have also worked with Energy Architecture on a house. Similar to my Learning Environments Australasia work, with Passive House there is a great sense of community, with people readily prepared to help others.
We knew that glazing was going to be critical, so worked to a budget of 25% glazed area while Jono from Cosgrove’s showed that we could still achieve maximum daylighting points under Greenstar. The modelling that Elrond undertook, told us that to meet the Passive House Standard that we only needed a typical insulated 140mm timber frame wall, warm roof and insulated slab common to most new NZ school buildings. In fact, we were able to make sure we didn’t over insulated and fine-tune the insulation to where required.
This was because the modelling showed that adding more insulation in these elements wasn’t going to make the difference. The performance of the windows would make the difference. Windows are the weakest link in a building’s thermal envelope, and that’s where the focus had to be. Here we needed good thermally broken, triple glazed windows, installed in line with the insulation. We had hoped to make double glazing work. It is possible to achieve the passive house standard with only double glazing in some climate zones of New Zealand.
We found for a typical mid-size school building that all that was required, apart from careful modelling and design, was better-performing windows, a relatively inexpensive airtightness layer, and a fresh air mechanical ventilation system with heat recovery.
Adequate ventilation is a real issue in New Zealand’s schools. Studies have shown that “natural ventilation” doesn’t cut it most of the time and teachers have other jobs than window operators. Natural ventilation systems can be surprisingly complicated, expensive, and unreliable in large buildings. MVHR (mechanical ventilation with heat recovery) will not only help provide an energy-efficient building, but it will also provide dependable high levels of filtered fresh air needed to limit interior environments spreading disease. This is something we need to think about with Covid, let alone all the sick days we typically see in schools.
Unfortunately, our project was overtaken by increasing construction costs. Cost savings had to be found that meant we were unable to meet this standard. But we still believe it was the right process to take regardless. It allowed us at the earliest possible stage, with a relatively low cost, to optimise the building’s insulation levels, fenestration and potential thermal breaks. It told us what we needed to do if we were to have a higher-performing building, and what was unnecessary. Isn’t this something we would want on any project?
DesignPH and PHPP are fantastic tools to do this initial design work. They are widely used, regularly updated, with research showing the building’s real-life performance matches the modelled results, better than any other systems we have seen. It’s a great way to test your shading design and avoid overheating.
A key learning was around the workflow with other consultants on a commercial Passive House project. While PHPP is a great tool to design low energy, high performance, healthy buildings, it doesn’t provide the type of modelling a mechanical engineer will need. In a house, the bathroom and kitchen extract will go through heat recovery. Here, the mechanical engineer was not keen. Modelling showed for commercial this wasn’t too much of a heating energy penalty. Jason Quinn from Sustainable Engineering is working on a workflow for larger commercial buildings in New Zealand.
Overseas, there are many different types of buildings that meet the Passive House standard. There are many commercial and educational buildings. House is just a name for all buildings in Germany where the standard originated.
Our research has found that the standard is easily achievable in our temperate climate. With more and better windows, membrane and ventilation options now coming onto the market it is getting easier and easier. Wouldn’t it be great to see some commercial and education passive house buildings here in New Zealand? As COP26 in Glasgow tells us, we must act now!
Via architecture http://via-architecture.net/
Passive House Institute New Zealand https://passivehouse.nz/