July 30, 2019
Desiging a Zero Carbon (zero bill) home

In 2012, I was lucky enough to work on a fantastic project - then called "The Cape Paterson Ecovillage", and now just "The Cape". It was ahead of its time, and perhaps still is, and was being planned just as the big drop in solar power costs were happening. 

Are you dreaming of power bills cheaper than a cup of coffee? Here is a short blog about what I learned on that project, and how you can apply that to your own, zero emission home project (without the need for eco bling).

Sociable Weaver 10 star home

A zero emission home. What is that?

I think the accepted definition is a home that produces as much clean energy as it uses, year to year, usually solar panels on the roof at a minimum, and perhaps some battery storage to help ride through black-outs or just maximise self-consumption.

The idea goes much further though. You may consider what energy you use for "back up" when the sun isn't shining, for example it makes sense to buy renewable energy from the grid at a minimum. 

You can also consider the "embodied carbon" in the house itself, for example, are you using concrete, steel or other energy intensive materials? Would you better off using sustainable timber, or hempcrete instead? 

Probably the biggest questions that come up when doing a zero emission, and hopefully a (near) zero bill home are:

  • how much to spend on "passive" design features, like double glazed windows, as well as just how to get those passive features "right";
  • and of course, how to heat and cool the home actively (if its needed) as well as hot water choices - all of those things can become way more complicated than they need to be.

At Cape Paterson, we helped recruit a team of architects to design ten zero emission homes amazingly these eco home designs are still all here and available for free - hat tip to The Cape Team!) and here is what we learned:

zero emission home

Designing a Zero Emission Home: Step 1

Ok, step 1 is basically taking a deep breath, relaxing, and realising that if you do this right, it is not going to cost the earth. What?! Sustainability, green, eco-friendly, all comes at a premium right? Wrong!

It's only going to cost a bomb if you are doing it wrong, typically.

At The Cape, and on many other projects we've worked on informally and otherwise, designing sustainable is rarely "expensive" and only ever costs slightly more, with the benefits you get far outweighing the cost. 

If at any point of your project you feel like costs are blowing out and its all too hard, you may not be working with someone who knows the ropes and has done this before.

Designing a Zero Emission Home: Step 2

Understand why you are designing your home, not just what you are trying to design.

Is this a forever home? Or something to grow old in with a loved one?

Is it to raise a family in? Or is it going to be home for a growing family for years to come?

Is it just for you, and something to share with friends and family and loved one as they come and go?

The reason it is so important to think in this way, is it will help you focus on the things you really need in the home, rather than the things you may want, or the things you think you want.

Sure, we all like a treat here and there, and a home design with features that will make you happy for years to come, despite serving no practical use in your day, can be well worth it - its just not the place to start. So take a moment to think, what does your future look like?

future planning

Designing a Zero Emission Home: Step 3

Organising space.

Ok, time to think about things like floor plans, orientations and how on earth you will make sure that winter sun will heat your home as it rises in the north-east and sets in the north-west (the winter sun trajectory is quite narrow), while the summer sun, with its broader arc that extends even to the south-east and south-west in southern zones of Australia, doesn't make its way inside...

The trick to organising space to ensure effective passive design is to start with your main living/kitchen/lounge areas. These are the spaces you will occupy first thing in the morning when you get up (when it may be cold), and last thing at night before turning in (when it could be hot). 

These spaces are going to become like a central energy bank for the rest of your house - they are going to be a source of warmth in winter and cool in summer, and rooms like the bedrooms, studies, a laundry or media room will simply hang off this space and benefit from it's "energy".

Check the floor plan below - simple but effective if you have a long north facing edge to work with. You can imagine how on a more square footprint, rooms 2 and 3 could wing around to the south, but would still be comfortable as they would benefit for the natural warmth and cool or the main living space (I like the garage as a buffer to the western and south western sun too). 

sustainable home floor plan

Think about it. Your bedrooms are typically small, contained spaces that will be (relatively) easy to heat and cool. Most people enjoy getting under the covers on a cool night in a cool room - so don't waste spaces like this by having them soak up the prime north facing light.

Your main living/kitchen/lounge areas should have a nice north facing aspect, with eaves wide enough to block direct summer sun, but let winter sun in. Precise design requirements will vary around Australia, but roughly 1m of width to your eve, for every 2m of ceiling height, should do the trick. External summer shading that retracts or can be removed in winter, or even deciduous vines and trees to the north are a great complement to internal design features too.

Passive solar heating and cooling can look quite technical, but the rules of thumb are simple:

  • Dedicate say 60-70% (maximum) of your north facing wall to glazing. Note: floor to ceiling glazing is often wasteful purely from an energy perspective - the top 1m or so of glass is unlikely to let any light in (because the eaves will shadow it, even in winter), but it will let a lot of heat out, even if it is double glazed; 
  • Subject to other design goals, consider glazing that starts at the say 50cm up from the floor, and stops 1m before the ceiling - this gives you the bench chance at winter sun coming in, while summer sun stays out, while limited "wasted" glazing (see first point above);
  • Consider a decent smattering of eastern, or north eastern glazing - morning sun is typically underrated, but is great for taking the chill off mornings when you need it most;
  • Minimise glazing to the west and south, or eliminate it altogether - sometimes just one or two nice "picture frame" style of windows can work well, allowing soft natural light and a view line, without a bit heat loss or gain.
  • Use thermal mass wisely ! Things like concrete and brick inside your home are great in climate zones with a large difference between night time and day time temperatures, and winter and summer temperatures to some extent. They can act as a temperature buffer, storing day time heat or day time "coolth" to be released into the night. But get it wrong at your peril! As your temperature buffer will become a temperature amplifier, making a hotter day hotter and harder to cool your home, and vice versa.

Ok, thats a lot about glazing right...and a bit about thermal mass... why all the glazing talk? Can't you just double glaze and be done with it?

No Way !

Double glazing has, at best, about the same level of insulation as an uninsulated, light-weight, leaky wall. As in, its a really terrible insulater. I hear this from people all the time:

"Why is my house so cold in winter? I have all this double glazing ?!"

I'm sorry, but an architect, or builder, sold you up the river on that. 

Floor to ceiling glazing is the common killer of an otherwise perfectly performing home and that's before even thinking about the budget!

Designing a Zero Emission Home: Step 4

Ok, perhaps last but not least, Step4 - the fit out details.

Trust me, if you have done the above steps, you have 80% of the hard work done when designing a zero emission (zero bill home). The balance of decisions are usually pretty straightforward, and go like:

  • Insulate sub floor, walls and ceilings. A minimum of R2.5-R3 under the floor, R3-4 in the walls and R4-6 in the ceilings (R-values are used to qualify how good insulation is at...well.... insulating) (pick the upper end of those R-values in more extreme climates, like alpine or semi-desert climate zones, or the lower end in mild coastal climates); 
  • If you are doing concrete floors than 1) think again 2) check your contractor knows their stuff 3) make sure the edges are going to be properly insulated 4) think again... seriously, an insulated floating floor is going to work just fine in a new build - you typically don't "need" all that thermal mass in the floor. It is such a common thing to "go wrong" on a new build, you need to be 110% sure your contractor can get it right;
  • Go for an efficient, electric heat pump for all your hot water needs. When I first worked on the Cape, the plan was to do solar hot water AND a heat pump. Best to cut out the middle-man, save the roof space for solar panels, and just run your heat pump during the day (say 11am-1pm) when your solar panels are cranking;
  • Go all electric for heating and cooling with efficient heat pumps - you can even do electric hydronic these days - not only does this make sense financially, it means you get most value out of your solar panels, improve air quality in the home (no gas), and its much better for the environment (so long as you are solar powered). Small split system air-conditioners are now super efficient and cheap to run, and in a well designed, insulated home, it doesn't take much grunt to heat or cool inside.

And last not but least - choosing a solar system size to suit your needs and goals. More or less, I would suggest:

  • 3kW system is pretty much the minimum when it comes to solar "these days", and will be enough for an efficient new home to be carbon neutral most of the time. It really is a cheap source of energy, particularly as you increase the system size, because each additional kW tends to be cheaper than the last (up to about 100kW). Anything less than 3kW, and you are pretty much selling yourself short.
  • 5kW-7kW is probably the go for most family homes - this should easily be enough for your all-electric needs (producing 20-28kWh/day on average), and even gives you energy to spare if you want to plug in and charge an electric vehicle at home - for a bit of fun, check out our blog on sizing solar for your electric ute.
  • Go for up to 10kW if you are a serious, stay at home energy user. Perhaps you are running a workshop from home, or maybe even thinking to go off grid in the future. Put it this way, not many people are going to "need" more than 10kW. Sure, go there if you want to make a statement, or make an oversized contribution to a clean electricity grid, but bear in mind you may have issues connecting to the grid, or at least an expensive 3-phase connection if you go much bigger than 10kW.

Designing a Zero Emission Home: Step 5

Is there a step 5? 

Are you designing a zero emission home and think we missed something? 

Drop us a line and we will improve the advice above, we are always keen to hear from people and looking to improve our advice where we can.

Or if you just need more guidance on going solar in general? Check out our guide to going solar here.