Taking Passive House to everybody New tools for improving standard plans

17 May 2021 by Sara Wareing

For Oliver and Alex, the path to building their ‘forever home’ had been long. There were lots of competing demands for their budget. They’d read enough to know they wanted a better than Code-minimum house. A bespoke, architecturally-designed house wasn’t an option. Instead they had poured through the catalogues of group home builders.

Source: Schematic design example report. © Sustainable Engineering Ltd

They wanted a dry, warm, well-built home that didn’t cost a lot to keep comfortable and healthy. Was it impossible on their budget? They were overwhelmed by trying to sort through the promises about sustainable, green, eco-houses, high-performance…

When people like Oliver and Alex have contacted us in the past, we’ve had to tell them to call us back once they have a set of plans, sections and elevations drawn up. Only then could we assess the performance and advise whether it could meet a Passive House Institute standard and what it would take. 

Unfortunately, by the time plans have been drawn up, the money for design has often been spent and there’s probably emotional investment in the floor plan and appearance of the home. However, the site, materials, orientation or form factor of that plan (or a combination of those) may make higher-performance difficult or very expensive. 

Like the rest of the team at Sustainable Engineering, I passionately want to see a wider range of Passive House buildings in New Zealand, especially affordable first homes. (It’s not just professional, it’s personal: I’m designing my own first home on a section in Wellington.) We know the physics: the most cost-efficient way to build a Passive House building is to take performance into account from the very beginning of the design.

So we’ve created a new service to do just that. We call it the ‘shoebox model’ because we can give home builders vital feedback just on the basis of a sketch or a floor plan, the site and an estimate of the glazing (either as an area or a percentage). It’s quick, easy and cheap, purposely created to provide just enough feedback at just the right time in the design process. 

You’ll find out if you’re on the right track, early enough to adapt. You can see what constructions you would require to meet various levels of performance: the full Passive House standard, the PHI Low Energy Building standard or anywhere else better than the Building Code minimum.   Just as important, we’ll talk through the project with you and/or your designer, going over what you want to achieve, the Passive House principles to keep foremost in mind and any opportunities we see in your plans for either easy wins or large risks.

While not a full predictive model—that comes later—it will tell you what R-values are required for any given-level of performance. If you know what construction system you want to use (eg SIP, timber frame, brick cladding) the report will include very clear and helpful graphs, as shown below. 

A typical group home wall assembly will have a timber fraction of around 27.5%. The y-axis charts increasing amounts of wall insulation. Either the timber fraction or the insulation value (or both) need to change to reach higher-levels of performance. 

A typical group home wall assembly will have a timber fraction of around 27.5%. The y-axis charts increasing amounts of wall insulation. Either the timber fraction or the insulation value (or both) need to change to reach higher-levels of performance.

Graph: Sustainable Engineering Ltd

This initial model can be easily edited if you entirely change your concept. (Or if you have two widely different concepts or are considering different sites, we could evaluate both. Having an indication of their relative performance might make the decision between them much easier.)

A shoebox model is useful for major renovations and refits as well as brand new builds. So far, most of New Zealand’s Passive Houses have been pretty big-budget affairs, designed and built by people with specialist Passive House qualifications. With the shoebox model, we want to reach a different part of the homebuilding market: empowering home owners to make evidence-based decisions and providing mass-market designers and builders the information they need to create their first higher-performing homes.

The shoebox model (technically, “Schematic Design”) is a fixed price, $950 +GST and the turnaround is fast. The results are available in a matter of days. It will save you money, it will give you enough certainty to move onto the next stage of design and most importantly, it could save you from years of regret and wondering ‘what if ..?’

Believe me, I know how stressful the design and build process is. I don’t think anybody should have the stress of spending so much money without knowing what they’ll get at the end. Or, living with the disappointment of a brand-new house that is still cold, damp and hard to heat, which is what I fear Oliver and Alex have ended up with.

See an anonymised shoebox model report here.

PS Yes we are Passive House nerds here at Sustainable Engineering. But we’ll back you no matter where on the continuum of ‘better-than-Code’ you’re aiming to build. This service isn’t about persuading you to build to a particular standard. It’s all about giving you the right information at the right time so you can make the right decision for you and your circumstances.