How to build a sustainable house in 2025

When we were in the design phase of building our sustainable house 14 years ago I remember sitting across the table from the architect while he sketched the different arcs of the sun in the winter and summer and we did a lot of nodding and hmm-ing. We trusted that he could design us a sexy sustainable house (after stalking him for years!) but to be honest we had no idea back then just how damn good the house would turn out to be.

The penny didn’t drop until our first winter in the house and we could feel the warmth radiating under our feet and the sun (literally) on our shoulders.

This was straight after our first summer in the new house, and we’re talking a summer of no air-conditioning, cool floors underfoot and soft nor’east breezes wafting through most of the house.

If your dream house is sustainable, then this guide will show you (with pictures) how the elements of an eco house work together to give you a high-performing, energy efficient home like ours.

Let’s get started!

There are 7 keys to sustainable house design:

1. Choose the right site

If you haven’t bought your site yet this guide will help you work out which sites work best for a sustainable house.

The ideal site for a sustainable house is:

*south if you’re in the northern hemisphere.

If you can tick all of the above you’re doing well!

Most sites in urban areas have some kind of complication, especially if they face south or east making passive solar design very complex and sometimes impossible.

If you’ve bought or are interested in a south or east facing site, perhaps because the site has great views, good design by an experienced professional will be vital in order to capture as much solar gain as possible, perhaps using clerestory windows and/or skylights to get sun into areas that would otherwise get none.

Good design can solve a lot of problems.

Our house faced north, but was complicated by two ginormous Norfolk Island Pine trees that, without good design, would shade any potential extension.

We wanted to keep the trees (plus it was illegal to remove them).

Our architect was able to place the double garage and ‘outdoor room’ at the rear of the block where most of the shade was. For the main living areas he designed a skilion roof with high louvre windows so the living areas could be bathed in sun in winter when we needed it most.

2. Build only what you need

Australians build the biggest houses in the world, averaging a whopping 235sqm. The US isn’t far behind at 213sqm (2300sqf).

In the western world we’ve been lulled into believing ‘bigger is better’ and project or spec home builders have been eager to please – offering a lot of house for an affordable price.

But how affordable is it, really?

It’s not unusual for project homes to come standard with three or more living areas and at least that many bathrooms. They often take up the maximum building envelope, putting them in close proximity to neighbouring buildings and leaving them with little or no scope to orient the house in an energy-efficient way.

‘McMansions’ are bigger, sure, but they are really only better at using:

• More of the earths resources to build (than a smaller well-designed home);
• More fossil fuels for energy to run all the artificial heating and cooling that will be required
• More time and money for cleaning and maintenance; and
• More space that needs to be filled with “stuff” like furniture for the third living room.

That’s not to say you have to live in a tiny house to be sustainable. It’s more about thinking from a sustainable mindset and asking what space your family really needs and asking yourself how much time, money, and carbon footprint you’re willing to spend on an ongoing basis with the building or extension of your home.

When we built our house our kids were teenagers and we knew we would be empty-nesters sooner rather than later.

With this in mind, our architect designed a nice-sized master bedroom for us (as the long term tenants!), and rather than building bigger and giving the kids a large room each, he kept them in their small rooms and designed a multi-purpose room which could be shared and evolve over time to be used as a tv room/games room/library/study for the whole family to use.

3. Passive solar design

Passive solar design is at the heart of sustainable house design and means designing a house that can heat and cool itself with limited or no artificial heating.

Pretty cool, huh?

There are 6 basic elements to solar passive design:

The exact combination of these elements will be site-specific and work together to create what is known as a ‘thermal envelope’.

In the ‘warm temperate’ zone of Australia, where we live, there is quite a bit of fluctuation in the temperature between night and day, so the aim of passive solar design in this location is to absorb and retain as much solar heat into the house in the cooler months while also keeping out that heat in summer.

In climates where it is mostly hot, passive solar is about keeping the sun out and getting cool breezes through whereas in cold climates, passive solar is focused on keeping warm air in.

Designing with solar passive design can not only increase the comfort of your home but also save a significant amount on energy bills. New Zealand researchers performed computer modeling on 210 houses that complied with the building code but didn’t use passive solar design. Those houses were found to require two to three times the heating energy to maintain a comfortable temperature compared to a solar passive house costing a similar price.

Let’s look at each element of solar passive design in turn.

Orientation and building layout

When you’re optimising for northern sun, the best location for the building will usually be as close as possible to the southern boundary (vice versa in the northern hemisphere). This reduces the risk of shading from northern neighbours and also provides you with a sunny outdoor space to the north.

That said, there are other factors that could come into play when deciding the building location. If you’re in a hot climate and are more worried about cooling, then breezes might be prioritised over solar access.

Shading from buildings (including the likelihood of future buildings) and trees could also affect where the best location for the building is.

Building layout is an important part of good passive solar design to make sure particular rooms are positioned to get the advantage of the sun.

The main living spaces such as living, family and dining rooms should ideally be north facing (south facing in the northern hemisphere), giving them ample daylight and solar gain most of the year (with shading to prevent too much solar gain in summer).

West-facing living areas can also work well for households where the occupants are away during the day but home in the evenings. Not as good when you’re home on weekends though.

Bedrooms that face east will be cooler in the late afternoon and evening, making them more comfortable for summer sleeping.

South-facing rooms are best for rooms tha are used infrequently such as garages, laundry and bathrooms. They are not good for living areas as they receive low daylight and little or no heat gain.

Window design and placement

Windows are the weakest point in the thermal envelope of a building and can account for up to 40% of heat loss.

Windows that are designed with the right size, position, framing materials and glass can minimise heat loss and should be designed and positioned to:

Double-glazing is recommended if you want to build a sustainable house in a cold climates (or where the aim is to produce a fully passive house). Double glazed windows have two panes of glass that are separated by air or argon gas. While more expensive than single pane windows, double glazed windows are very effective at keeping heat inside a building in winter and reducing heat flow entering in summer.

Windows that are designed and placed in such a way to allow cross-ventilation through the house for passive cooling are an important feature of a sustainable house in a warm climate.

We used louvre windows extensively throughout our house and they work brilliantly to maximise and control cooling breezes through the house.

Shading

You’ve worked hard to get sunshine into the house in winter, but what about in summer when it’s the last thing you need?

The shading needs to do two things: keep summer sun out but still allow winter sun to get in.

Our architect designed the eaves and fixed awnings above all the north-facing glass which allows winter sun in but prevents summer sun from entering:

There are lots of options for shading but fixed awnings work well for us as they don’t need to be adjusted like some shutter and louvre systems.

Pergolas and verandahs can also be used so long as they are correctly sized and positioned according to the requirements of your house.

There are many useful resources online for calculating the path of the sun where you live with suggested shading types and sizes.

Thermal Mass

Thermal mass is a material which can absorb and store the sun’s heat, then release it later.

Examples include concrete, stone, rammed earth or bricks.

We have a polished concrete floor which absorbs the sun’s warmth in winter, then radiates it into the home throughout the day, continuing long after the sun has gone down and the outside temperature has dropped.

Check out some thermal mass in action…

Polished concrete floors for thermal mass

Airtightness & Ventilation

The final important component of passive solar design is airtight construction.

Draughts from gaps and cracks between building materials can cause up to 25% of heat loss from a home and also impact how cool your home is able to stay in summer. Any heat allowed to escape can carry a significant amount of moisture with it, which can cause its own problems.

Australian homes are estimated to leak 2-4 times as much air as North American or European buildings due to Australia having no minimum standards of airtightness unless you’re building a certified passive house.

In a sustainable house where passive temperature control is the ultimate aim, not sealing the building properly is like leaving your fridge door open and expecting the beer to stay cold!

New buildings should be wrapped with a continuous seal on the outside of the insulated frame before the cladding is installed. This is generally done by the builder and sometimes done by the insulation company. Air sealing should always be partnered with natural ventilation such as windows or vents.

4. Choose sustainable materials

One of the first things we had to decide when we bought our house was whether to keep it or knock it down. As we couldn’t afford to live anywhere else while we built the decision was remarkably easy!

Aside from financial constraints it would have been a shame to waste a perfectly good brick building no matter how ugly, poorly oriented and badly insulated it was. We could (sort of) fix the ugly part and we could definitely fix the insulation. The orientation ain’t ever gonna change (not until the next owners, anyhow).

While the most sustainable option is to reuse what you’ve got, it can come with its fair share of problems. I wish I had a dollar for every time our builder said he’d like to throw a match at the old house to avoid having to marry the old, uneven bits with the new structure.

Every choice you make for building materials and interior design will impact the environment to some extent, and as an eco-conscious consumer it will be a delicate balancing act between what you want, what you need and what’s best for the planet.

Some things to think about when deciding on materials:

Some materials have pro’s and cons that need to be weighed up.

Take concrete for example – excellent for thermal mass and durability but if it’s made in the traditional way with Portland cement, it’s terrible from an embodied carbon perspective. The good news is that these days some of the cement content can be replaced with planet-friendlier additives like fly ash and blast furnace slag, significantly reducing the carbon footprint.

5. Collect and conserve water

It’s mind-blowing to think that every single Aussie (on average) uses a whopping 100,000 litres of fresh water per year – that’s more per person than any other country 🙁

The main culprits are:

I know, I know, water-saving shower heads suck! But when you realise over a third of our household water is coming out of the shower heads, its cause for pause.

Water-saving toilets can also be problematic with, ahem, certain bodily functions. But there’s a strong case for going “mellow yellow” and if you have to press twice the rest of the time then that’s a great compromise in my book!

Water-efficient appliances like dishwashers and washing machines are a different story – they work really well with a fraction of the water used by lower star-rated appliances. It’s also worth checking water used by clothes dryers – I was shocked to discover recently how much water they use.

Water-efficient taps aerate water to reduce water use and are a no-brainer for an eco-house or any house, really.

Before buying any appliances that use water, be sure to check the star rating of appliances, taps, toilets and shower heads in Australia, New Zealand, USA and the UK/Europe.

Rainwater Harvesting

Collecting your own water has lots of obvious benefits:

• Reduces the need for new dams or desalination plants
• Protects remaining environmental flows in rivers
• Decreases stormwater runoff and local flooding
• Saves money on water bills

Not to mention that warm, fuzzy feeling you’ll get 😉

Rainwater harvesting is a mandatory for new homes and major renovations in Australia however the minimum requirements are disappointingly conservative:

• 
  Minimum rainfall catchment area of 50m2 (roof, gutters)
  
• 
  Minimum capacity of 2,000 litres rainwater storage
  
• 
  Must connect to all flushing toilets in the building.
  

We decided to install 2 x 4,500 litre tanks. They feed off our roof and supply our garden watering system, toilets and washing machine.

Aussies can use this handy tool to work out what size tanks you need.

6. Run on the sun: solar power and hot water

Solar power

Solar power is clean, renewable, sustainable, and a heck of a lot cheaper and better for the planet than buying it off the grid.

Solar has a high upfront cost but prices are coming down all the time. It’s worth researching government incentives or rebates available in your area that are in place to drive the uptake of solar power systems.

Solar panels can be installed on any surface that gets sunlight: roofs, walls, or even mounted on the ground if space allows.

A solar expert can help you determine how many panels you need based on:

1. 
   How much power you want to generate,
   
2. 
   How efficient and effective individual panels are,
   
3. 
   How much sunlight and roof space is available, and
   
4. 
   What you can afford.
   

Solar panels are rated in watts (W), so the first step is assessing how many kilowatt (kWh) hours per day you want to generate, which can be done by looking at your power bills for the last 12 months and calculating your daily average across the year.

Solar panels exposed to 6 hours or more of sunlight when the sun is at its peak are ideal as they generate the most power.

With the right size and “sun-hours” solar panels are more than capable of providing you with your entire household’s electricity needs.

A solar expert can work out the best location, tilting and panel types to optimise sun-hours and power generation.

If there’s not a lot of optimal roof space, higher wattage panels may be suggested.

Solar isn’t feasible for all homes as some have site limitations like roof direction and shading. For homes where solar is feasible, you can’t beat free electricity, insulating yourself from ever-increasing electricity prices and lowering greenhouse gas emissions.

If you want to live completely off the grid then you will need to look at back up battery options as well.

Solar hot water

In homes, water heating is the largest contributor to greenhouse gas emissions and second biggest user of household energy use after space heating and cooling.

Energy efficient water heating will therefore make a big difference to energy use, costs and emissions.

As solar energy is variable, an electric or gas booster is required to cover cloudy days.

As a solar system relies on flat plate or evacuated tube panels on the roof, the same considerations discussed above in solar power apply in terms of optimum roof angle.

In our home, getting sun through the windows was the priority, leaving us with skillion roof facing away from the sun and no good for solar panels but we were able to use tilt frames to accomodate evacuated tubes for our solar hot water system.

An expert can help you decide whether solar or another type of energy efficient water heating is best option for your home.

7. Energy-efficient lighting and appliances

Lighting

The most sustainable light is daylight so sustainable interior design should always aim to orientate and position rooms to take best advantage of this natural resource, particularly living areas.

Daylight can also be maximised with:

• Skylights and light tubes can let in light without adding heat in summer or losing warmth in winter if they are the right size and position.
• Light interior colours for walls and surfaces reflect more light and reduce the level of artificial lighting required.

Some ways to increase the efficiency of artificial lighting:

With lighting consuming 6% of the average household’s energy use, efficient and well-designed lighting saves not only emissions but also your back pocket.

Appliances

Appliances such as ovens, cooktops, white goods and TV’s can account for a third of a household’s energy use, so reducing the energy they use can significantly impact your carbon footprint and cost.

Energy can be saved by:

Many countries have an energy rating system in place to help you choose the most energy efficient appliances – some of them are Energy Star in the USA, Energy Rating in Australia, Energy Rating Labels in New Zealand and the EU energy rating system.

Conclusion

I hope this guide has gone some way to explaining the variety of factors that come into play when you’re looking to achieve a high performing, energy efficient home, whether it be a new build or the renovation of an existing house.

Let us know if this guide was helpful and where you’re planning to build in the comments 🙂

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