Passivhaus meets Architecture

When Passivhaus meets Architecture, compromises need to be made to achieve a certain outcome.

Initially we looked at having glass blocks between the garage and the entry of the home we were building in Whalley Street. The glass blocks may have made it, with an increased insulation specification to the rest of the building, a second layer of them, and a likely reduction in area. However, it was eventually agreed not to use them, even though the aesthetic was architecturally delightful. Passivhaus won that compromise.

Having an eternally optimistic mindset, I assumed that any building could be made into a Passivhaus. The experience from this situation and others has led me to think that the one and only rule of thumb when dealing with a Passivhaus project is:
There is no rule of thumb when working with Passivhaus.

You are likely to under- or over-estimate the ramifications of different aspects of the building envelope when you use a rule of thumb to reach certification. Instead, it is a lot easier to step back into architecture school (as we did) and use solar passive principles to determine the large brush strokes of architectural design. These are largely estimates based on previous experience and include things like ‘adequate window area to floor area’, ‘detrimental effect of window orientation and ‘thermal performance of floors, walls and roof’.

When you apply one rule of thumb to a Passivhaus project, you must also apply the rest for it to be anywhere near an adequate representation of the model used for the said ‘rule of thumb’. For example, if you allow enough insulation for a building with a certain window to floor area ratio, it is going to underperform when the window area is doubled, as was the case at Whalley Street. An increase in ceiling insulation has proven helpful to offset the wall insulation requirements. The Whalley Street residence has delightful views and makes the best use of its position adjacent to All Nations Park, so it is quite understandable that a greater number of windows were used in the design to draw attention to the myriad views from the upstairs living area.

What does Passivhaus mean to this project?

The Passivhaus standard requires that you meet thermal performance, airtightness and fresh air restraints. Sure, a biproduct of this stringent standard is a reduction in energy used in heating and cooling throughout the year, but it is the comfort level achieved that encourages the standard in all parts of the world. In Australia, there is a direct link between a poor performing building envelopes and cold-related deaths during a subjectively milder Winter when compared with Winter in other parts of the world. There is a chance to overcome this when employing the Passivhaus standard to dwellings.

The Whalley Street residence went down the Passivhaus path as a mature aged project, meaning we started looking at the feasibility of Passivhaus at a late stage and had to ramp up the involvement at lightning speed to ensure its viability. With the expertise of the professional collaborative teams we had, we were in a position to accept the challenge.
Of the Passivhaus requirements, airtightness is the one the builder is responsible for. During site meetings at Whalley Street, we have been fortunate to work with Nick and Ben from Appetite for Construction on detailing that works in both a practical and scientific sense. Each detail is carefully considered and we wait in anticipation for the blower door test to determine the compliance of the dwelling to the standard later this month.

The other two requirements, thermal performance and fresh air, are determined respectively by the Passivhaus Designer and the Mechanical Engineer. In principle it is possible to interpret the three requirements as indoor, outdoor and transfer zones. (Please note that I have combined the Passivhaus principles ‘thermal insulation’, ‘thermal bridges’ and ‘windows’ into one requirement for pragmatic understanding.) Thermal performance is outdoor, airtightness is indoor and fresh air is transfer. Occupants have the choice to close off the building or leave the windows open to connect to nature: sounds, smells and sights!

Had the modelling of Passivhaus occurred earlier, it may have affected the outcome of the home. It was important that the design take some semblance of precedence over designing an efficient building purely from a scientific point of view. In hindsight, it was the belated commencement that encouraged an earnest adherence to most of the architectural development of the dwelling. To get across the line, and based on advice from modelling in the Passivhaus Planning Package, a lot of insulation was added to the ceiling, upper floor walls and some of the lower floor walls; glass blocks were removed from the entry way; window glass was upgraded; and a north-facing window was removed to prevent excessive heat gains. Additional temporary shading was also proposed on the eastern windows to prevent excessive morning heat gains.

My only tip in retrospect would be to start a little earlier to ensure that design integrity and building physics can marry at an earlier stage and avoid repeated documentation amendments (thank goodness for builders with patience). Being able to act quickly with the teams at DiMase Architects and Appetite for Construction has been a major contributor to the success of the implementation of the Passivhaus standard in this dwelling.

Further, careful performance modelling demonstrated that the house could work without an air conditioner, and this is a huge bonus. Also, through Passivhaus modelling it was determined that removing the proposed solar PV alleviated the costs of the insulation upgrades by a substantial amount and, instead, the home is likely to be supplied with GreenPower.

Every house can be made into a Passivhaus; that is the principle by which the Passivhaus Planning Package works. Cost and practicality ultimately determine the decision to proceed with the Passivhaus standard or not.In the case of the Whalley Street project, we are excited and fortunate to have the right people on board to proceed towards certification.

Stay tuned.

Alex Slater