Australian Passive Solar Home

Here are four simple questions that you’d think would be easy for Passivhaus proponents in Australia to address – but they simply refuse to do so.

1. If Passivhaus is purportedly for everyone, why are all Passivhaus homes so expensive?

2. If working with nature is a design goal of energy efficient housing, why do the five Passivhaus principles completely ignore working with the climate and in fact simply attempt to create a barrier to it?

3. If Passivhaus is effective in Australian summers, (a) why do the non-air-conditioned Passivhaus criteria allow so much overheating? (b) why do all Australian Passivhaus homes that I am aware of need air conditioning? and (c) why do Passivhaus homes get hot inside when air conditioning is not being used?

4. Given (3) above, and the need for power to run a mechanical ventilator, how can Passivhaus be justified in a warming climate subject to power failures?

As I say, you’ll never get answers to any of these questions, so I’ve done it for them.

If Passivhaus is purportedly for everyone, why are all Passivhaus homes so expensive?

Passivhaus is for rich people. A Passivhaus costs 50-100 per cent more than a normal Australian house. There are no Passivhaus homes in Australia that I have been able to find that, on a per square metre basis, cost anything like the amount of a normal home (e.g. $3000 per square metre).

The extra cost is because of:

– special insulation
– special windows and external doors
– special mechanical ventilator
– special trades
– special design services
– special testing
– special certification

Passivhaus is an expensive approach to energy efficient housing, one that simply isn’t needed in mild southern Australian climates. If you’re interested in social justice, you should be strongly arguing against Passivhaus.

If working with nature is a design goal of energy efficient housing, why do the five Passivhaus principles completely ignore working with the climate and in fact simply attempt to create a barrier to it?

The five Passivhaus principles do not vary with climate. This is because each principle attempts to exclude the climate as much as possible, rather than working with it. The five principles are:

– high-quality insulation
– thermal bridge-free construction
– airtightness
– high-performance windows and external doors
– heat recovery ventilation

Missing in these five are the energy efficient principles of approaches that work with the climate, e.g.:

– orientation
– shading
– using sunshine to warm the house in winter
– natural ventilation
– thermal mass

People who want energy efficient housing to work with the climate should be arguing strongly against the Passivhaus approach.

If Passivhaus is effective in Australian summers, (a) why do the non-air-conditioned Passivhaus criteria allow so much overheating? (b) why do all Australian Passivhaus homes I am aware of need air conditioning? (c) why do Passivhaus homes get so hot inside when air conditioning is not being used?

The short answer is that Passivhaus is quite ineffective in hot conditions.

(a) The non-air-conditioned Passivhaus standard allows no less than 10 per cent of the hours in a year to have an interior temp over 25 deg C – and with no upper limit! That’s 9.7 hours every single day of an Australian summer where inside the house it can be over 25 deg C e.g.+ it can be 28, or 30 – or whatever.

(b) As you’d then expect from (a), all Australian Passivhaus homes that I am aware of have air conditioning. Just like any normal priced home, they need it!

(c) If you see logging for a Passivhaus home in Australia where the air conditioning has been left switched off, you’ll see interior temperatures of 27-29 deg C on hot days – and they weren’t even in long, hot spells (heatwaves)! The reason this occurs is simple: the standard was never designed for hot weather and so it lacks fundamental design foci needed for good hot weather performance.

If you’re interested in energy efficient house designs that perform well in hot weather, you should be arguing against Passivhaus.

Given the requirement for air conditioning in hot weather, and the need for power to run a mechanical ventilator, how can Passivhaus be justified in a warming climate subject to power failures?

It can’t – it’s a poor approach.

Without power for air conditioning, on a hot day a Passivhaus will get hotter and hotter – it cannot fail to do otherwise as it doesn’t have internal thermal mass to absorb the heat. Without power, the air quality in a Passivhaus will get worse and worse – it cannot fail to do otherwise as it depends on power to gain fresh air. Opening a window or door will give fresh air but the house will get even hotter.

If you’re interested in house resilience during summer power failures, you should be arguing strongly against Passivhaus.

Conclusion

Except in very unusual circumstances, Passivhaus is poorly suited to southern Australian climates. If you’re interested in taking the approach, ask a lot of questions and be highly sceptical of much of the promotion that you’ll see.