I recently attended the 5th Passive House conference and trade show in Wellington. The weekend was a chance for Passive House designers, builders and home-owners to come together for talks and discussions on all things Passive House.
The conference left me feeling hopeful that the future is bright for increased building standards in New Zealand. The Passive House Standard is certainly one, already tried and tested, way in which this can be achieved. But what is this type of build all about, and how does this fit in the New Zealand context?
Certified Passive House in Christchurch, designed by THECA Architecture and built by Ethos Homes (image from “Passive House for New Zealand” by Jason Quinn, 2019.)
Why do we need increased building standards in New Zealand?
As Elrond Burrell of the Passive House Institute NZ says, there is a "quality deficit" in our housing in New Zealand, and that unfortunately has "dire health implications for our communities". In real terms this translates in to the highest rate of childhood asthma in the world, as well as excess winter mortality resulting in an estimated 1600 deaths a year.
This is primarily due to cold, damp and mould within our homes. Unfortunately, this relates to both older style homes and modern, new builds. The current building code is partly to blame with much lower standards compared with other developed countries.
While other countries, such as Germany, Sweden, the UK, and Canada are taking substantial measures to meet carbon emissions targets, New Zealand is far behind. Buildings built to the current NZ building code do not require a focus on energy efficiency and this in turn contributes to climate change.
The Passive House Standard has been offered as a solution to some of these issues.
Fundamental features of Passive House as found in the Dunedin Cohousing project, which is currently under construction (diagram from “Passive House for New Zealand” by Jason Quinn, 2019).
What is a Passive House?
The Passive House Standard was developed by the Passivhaus Institute in Darmstadt, Germany.
A home built to this standard is a high performance, energy efficient home. The focus when building a Passive House is on delivering a comfortable and well-ventilated home that requires very little energy, as well as being very quiet. As long as specific performance criteria are met, then a home built to the Passive House Standard can be of any size or style, and can use a range of different techniques and materials.
Why is the Passive House Standard different?
One of the big differences with this type of build is that the "as-built" performance of the home can be accurately predicted and verified prior to commencing construction. This is achieved using Passive House energy modelling software. This allows for any required changes to be made at the design stage rather than while the building is being constructed, saving on costly changes to the plans.
Image of a blower door test to assess for air tightness (image from “Passive House for New Zealand” by Jason Quinn, 2019).
How is the Passive House Standard achieved?
The high standard of energy efficiency and comfort is achieved primarily due to a focus on a high-performance building envelope (or building shell). The following elements are crucial to achieving this.
The interior of the building is encased in an airtightness layer. This layer prevents the loss of heat and draughts, as well as preventing moisture damage to the building structure. The level of air tightness can be assessed using the blower door test, as shown in the image above.
High quality insulation
To prevent heat loss and stabilise the internal temperature, floors, walls and ceilings are thoroughly insulated. The level of insulation is determined directly by the climate zone that the home is being built in.
High performance windows and doors
To ensure thermal performance and air tightness, windows and doors must meet strict criteria. Double glazing is a minimum standard in Passive homes, whereas triple glazing may be specified in certain parts of the country. The type of frame, and installation position is also an important consideration to meet the standard required. Passive House certified windows are available in a range of different frame materials.
Thermal bridge-free zone
In standard construction, thermal bridging occurs where the foundation meets the walls, the walls meet the ceiling, around window and door frames and where steel columns are used. This allows for heat to escape in colder months, or heat to penetrate in warmer months. Specific Passive House design details are used to prevent this effect.
A continuous mechanical ventilation system is used in Passive Homes. All incoming air is filtered of dust, pollen and pollution. A heat exchange system then recovers around 90% of the air before being removed from the home. Additional heating or cooling elements can also be added to maintain temperatures.
The New Zealand Experience
So far 24 Certified Passive Homes have been built in New Zealand. These homes are showcased in “Passive House for New Zealand” a concise summary of the Passive House experience in New Zealand written by Jason Quinn, one of NZ’s Passive Home gurus. You can get your free copy here.
If you want to find out more about building a better home for your family, get in touch with the Craft Homes team today.
Toby Tilsley, Director of Craft Homes