Building a well designed, passive solar house can mean comfort in both summer and winter, with minimal energy inputs.
On the hottest day of summer, it’s comfortable and cool inside. On the coldest night of the year, passively collected solar heat warms your bones.
Enjoying a simple passive house does require participation from its residents, however. Even well designed passive houses need active people.
More and more, we’re understanding that good health, whether it be for ourselves, our homes, the things we use everyday and also for our ecosystems, requires us to actively participate.
The pressed-apon-us dream of ‘just flick this switch and everything is taken care of’ has done our planet, our communities and our bodies few favours.
For a supposed benefit of not having to do anything as a result of flicking that switch, we’re sacrificing the long-term health of… everything.
Health of our atmosphere and ecosystems as we cool + heat our houses with coal-fired energy. Health of our family as we opt for processed food from far away over a simple meal prepared at home with basic, local ingredients and our own labour.
The health of our tropical forests as we choose cheap new building materials, over taking a bit of extra time to source plentiful second-hand or locally sourced ones. Yep, we all know the list is long – much longer than the above. It’s big and it’s scary.
So, activate. By becoming more active wherever you can (turn off the aircon and design for better shade, take the train, make it yourself, fix it when it breaks) we actually arm ourselves, and our kids, friends and communities, for becoming more self-reliant in the face of future change.
Which can only be a good thing, really. Activity breeds resilience. Which breeds confidence. Which breeds the ability to thrive with less just-switch-it-on stuff. All good traits that we all can use.
Ok, so back to passive solar building design + living.
By designing your house well for your climate’s context, it’s possible to build (or retrofit) a comfortable home that uses very little energy – yet are still a lovely place to live, in all four seasons.
And these design elements can be usually be implemented very cheaply, especially when you consider the long-term savings.
Just as long as we’re prepared to actively participate with our house on an ongoing basis. A little bit each day.
How you achieve this goal of passive heating and cooling depends on your climate.
Strategies for passive heating + cooling (temperate climate)
In temperate climates, the summer days are hot but most nights are cool. And the winter nights are cold, while the winter days often bring some sun.
All these factors can be utilized to create a comfortable home all year round.
Primary to temperate passive house design is three big factors: good insulation, good thermal mass, and good solar gain.
Good insulation: placed on the outer layer of the house walls and also in the roof cavity, to stop heat entering or leaving the house. This might be in the form of strawbale walls, light earth, or some other insulative materials.
Good thermal mass: this goes on the inside of the house, to store heat – thick earth render on the inside of walls, internal mudbrick walls, earth, mudbrick or stone floors, and so on.
Solar gain: the side of the house that faces the equator (north, here in Australia) is the warm side in winter and should have the majority of the windows. This will allow lots of solar energy to enter the building in the winter, and this basic premise can be used to greatly lower winter energy costs.
In a temperate environment, you can simplify the passive solar design, and how you run the house, into two basic modes – winter and summer.
Winter – the blanket effect
In winter, the nights are properly cold, with slightly warmer days that are sometimes sunny. This is the season of creating the blanket effect.
In short, the aim in winter is to collect and store heat energy in the house, and let it out as little as possible. With small habitual behaviours performed every day over a six month period, this can be an incredibly effective way to create a comfortable and consistent inside temperature.
Catching heat: the most passive way to catch heat energy is to utilize the sun, with good house design. Big equitorial facing windows allow the low winter sun to shine into the house and onto the floor and interior walls.
Well-designed eave angles support this by letting the lower sun into the equitorial side of the house in winter, but not in summer when the sun is high.
A glasshouse on the equitorial side of a building, which opens into the main space, will further enhance this effect. Solar energy is caught and the warmed air escapes into the main house, warming it considerably.
Wood stoves are another effective aspect for winter heating, especially if they’re also cooking your food and heating your water, as well as warming the house. If fuelled by sustainably harvested firewood, they’re another form of regenerative + effective energy.
This is where the internal thermal mass of the house comes in – day after day, the thermal mass of the internal walls and floor slowly but surely absorb all that heat. Over time, this builds up to be a considerable heat bank that ‘gives back’ on a 24 hour basis, little by little. Completely passive heating.
The insulation’s job is to prevent that heat escaping – the outside walls and the roofspace must surround and store this internal pocket of heat, like a blanket.
Ensuring your carefully captured heat doesn’t escape out the windows is essential too – double glazed windows are great if you can include them, but keeping windows closed, as well as good thick blinds and curtains can also make a huge difference to storing heat – actively opened and closed at different times of the day as the sun crosses the sky.
Summer – the esky effect
In the summer, the sun is high in the sky and the days are hot, with the nights somewhat cooler. These factors can all be used to keep a well-designed house as cool as possible.
(An esky is an Australian term for chilly-bin or cooler box, just by the way)
Catching cool: well what you’re actually doing is actively avoiding catching heat energy inside your house, but lets call that catching cool. The opposite of the winter design, in summer the aim is to actively avoid solar energy falling on the house’s walls, or entering the main house – minimising heat in the house in every way.
This can be done partly with good eave design, which prevents any direct sunlight entering the house, especially on the equitorial side which will be hottest throughout the day.
If the house has an equitorial-side glasshouse, summer indoor plantings can further shade the equitorial side of the house, or the glasshouse roof can be covered.
Again, active use of curtains and blinds can make a big difference to the amount of solar energy that enters the house each day.
Storing cool: the great thing about thermal mass is that just as it can act as a heat bank in winter, it can also act as a cool bank in summer.
What little heat does enter the house in summer is absorbed by the thermal mass of floor and walls, which stabilises the inside temperature.
The insulation of the outer walls and roofspace acts like an eski to store that cool air inside the house, and not let it out.
At night time, when the temperature drops to below the temperature inside the house, the entire house is opened – every window and door.
This allows the thermal mass to release what little heat it has collected over the day back out into the night air, and the internal temperature of the house is cooled down as low as possible, ready for the next hot day.
Sailing the house:
On some summer days, particularly after a long run of hot days with warm nights, the internal temperature of the house can build up to the point where you need to start working with airflow to stay cool inside.
Having air run over your skin enhances your body’s evaporative cooling and, while it doesn’t actually lower the temperature of the air in your house, it can feel great on a very hot day!
Good design and placement of vents and windows helps in this situation a lot. Like tweaking the sails on a sailing ship, you are tweaking what vents and windows are opened and what is closed, to make the most use of the wind or airflow within the house for the passive cooling of the people inside it.
A vent, window or door on the coolest side of the house can be opened – the lower to the ground the opening is, the better. This might be the south side, or the eastern side of your house.
Then the top-most window or vent in the house is opened – just one. When designed (or re-jigged) well, this can lead to a flow of the coolest-possible air circulating through the house, from bottom to top, until the temperature outside cools down again in the night.
Active people, passive house. Happy, comfortable living with low or no energy inputs.
No, it won’t be as cold or as warm as a airconditioned shopping mall. But then, when it comes to self reliance and building permanently sustainable systems for living, our families don’t really need shopping malls.
What we do need is good, simple and achievable design strategies that we can use to create comfortable spaces for ourselves and our communities, long term.
Other climates need different strategies to heat and cool a home, of course. In colder climates, the thermal mass is enhanced, as is the insulation, as is the energy needed to heat winter spaces.
In warmer climates, NOT storing any heat in the form of thermal mass becomes paramount, as does airflow and evaporative cooling. And so on. There’s plenty of great resources on appropriate natural building for your climate, no matter where you are.
No flicking of switches or outsourcing of impacts required. Just good and thoughtful design for passive houses and active people, and simple, comfortable living as a result.
- Making a DIY Earthen Floor: two methods
- Natural Building: Deciding which Method to use for Walls
- Building a Portable Reciprocal Roundhouse Frame
- Roundhouse build: making a Living Roof
- All our resources on Natural Building
- Viva Living Homes – who teach our Natural Building courses. Legends.
- Your Home – website with lots of resources.
- Earth Render – James Henderson
- Roundwood Timber Framing – Ben Law
- Melliodora: A case study in cool climate permaculture – David Holmgren
- Owner Builder Magazine – lots of great resources
- Tiny homes, simple shelter – Lloyd Khan
- The New Strawbale Home – Gibbs Smith
And a special shoutout to Sarah Anderson who, many years ago, described the process of wwoofing in New Mexico and ‘sailing the house’ on a daily basis – its such a lovely term! Thanks lady.