Perspective from a Pupil of Passive Homes.
This is the first in a small series of passive house blogs where I outline how we may already have a solution to a problem we don’t know we will have.
What is the future of housing stock in Aotearoa? We can all attest to the ageing 4 bed, 1 bath, draughty and cold Villas and State homes that we have been raised in. These homes often sit on a quarter acre section of prime real estate, and even though these urban gems ooze charm and nostalgia. The cold ironic truth is that these places become neglected, and at some point need to be renovated or replaced. And it seems like the latter is the easiest and most profitable option.
But how does adding all this extra stock impact the already strained infrastructure systems that we rely on? Thats where a Passive House can come into play.
There are big challenges that the building industry faces in the coming years, as the threats of climate change continue to knock on the literal door. We are looking to make significant changes to the way we live our lives in order to mitigate the effects of a new environment.
The big target that has been set is for New Zealand to have 90% renewable energy by 2025, and with the changes to gas supply and a shift towards electric vehicles, how realistic is this goal?
With the average household of 2 adults and 2 children consuming more than 8000kWh of energy a year. Then add an extra 42,848 new housing consents being granted in the last year. We cannot rely on upgrades to infrastructure to power us through to our 2025 goal. We need to fix the problem from the ground up. And this is where Passive Homes can come into play.
A Passive house can be defined as;
a building, for which thermal comfort (ISO 7730) can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air.”
This housing type which is built with physics, far exceeds current New Zealand building standards. Full disclosure, I am new to the way of Passive house thinking. But I do believe in its principles.
- Building location and orientation
- Building layout
- Window design
- Thermal performance
All these attribute to a much more energy efficient house, so much so, that a fully certified Passive house needs to use as little as 15kWhs/m2 per year. To put that in perspective, there is often no need for any form of heating supply, with just the radiant heat of people and appliances being enough to create a sufficiently warm environment, and as more and more housing becomes higher density and we fill our houses with more and more electrical luxuries. The more and more sense it makes to harness the ambient energy.
- I’ll cover these in brief, a north facing building will allow for the most solar gains during the day. Design features such as soffits can play a role in the amount of solar gains and at what time of year, for example, a wider soffit can reduce gains in the summer when the sun is higher, but allow for more gains in the winter when the sun is lower.
- Building layout can restrict some aspects of design but mean that there is less heat loss, one of the keys are that the living and sleeping areas to face north, while the service areas such as the garage and bathrooms face south.
- Insulation is a no brainer; a higher quality and a higher R value insulation is a relatively low cost way to immediately make a house warmer. The code requirements for insulation are a lot less in the Far North than what they are in the Deep South. Regardless of where you live – higher quality insulation will keep the heat in on cold days just as well as keeping the heat out on hot days.
- Windows are important as even though they may only make up roughly 10% of a building envelope, that can count for up to 50% of heat losses. This is where the largest price difference in Passive house compared to conventional building. These extra features like E-glass, thermally broken frames and triple glazing can all save up to 60% of normal heat loss.
- As we build bigger and more complex housing, the amount of timber that we use during the construction process has also increased. Timber is not an efficient insulator and creates breaks in the insulation. As much as 34% of walls are made up of framing. This means that there is a large surface area for the cold outdoor air to bridge to the inside. By using a wider framing material, studs can spaced further apart, and thicker insulation can be used whilst still keeping the structural integrity of a building.
- Mechanical ventilation has a massive role to play, it allows for fresh air to be bought in and exchanged with the stale air that forms inside. The air inside a home is always comfortable and fresh without the need to open windows and doors. Often this process can include a heat exchange where the warmer air from your home heats the fresh air coming in (without mixing) retaining up tp 95% of the heat.
These changes all do come at a cost, anecdotally it is about 10-15% more expensive to build passive then conventionally.
Let’s break down some numbers; a conventional new build could cost around $3,000 per m2. So for a brand new 150m2 house $450,000, an additional 10% would bring it up to (for arguments sake) $500,000. Not a huge amount, but that could be a new vehicle sitting in the garage.
And using the theory that Passive housing can save around 80% energy of a conventional house. A typical Passive house can save upwards of $2000 a year. This equates to around about 25 years to pay off the initial upfront payment. Which seems to be a lot, but keep in mind the lifespan of the house and the inevitable price increases for power in the future. After or even sooner than 25 years, the investment in Passive will start to save money.
There are fears that the obvious accelerated rate of building, could lead us towards another building crisis “leaky building 2.0”. The urgent need for housing and rapid pace of the housing market means that new housing is built to the minimum code and little thought is put into how the house will perform over its lifetime. Continuing to build this way will just impede our efforts to reach our 2025 goal. The building industry must play its role in a greener and renewable energy world, we know that. and we could have the answer, and perhaps passive is the way.
For more information the Passive House Institute New Zealand website is worth a look https://passivehouse.nz/
Next up part 2.