House size to be 18-20 'builders' squares (or 162- 180 square meters), three bedrooms, home office, two living areas, master bedroom with ensuite, family bathroom with separate toilet, detached garage (for Devins work materials and tools) and a detached car port.
As this is Devin's first construction of a Passive House, to make sure we achieve certification, he wanted to keep the exterior wall layout as simple as possible. Therefore the house is a simple rectangular shape, this is to help minimise thermal bridges (but more on that later).
As you can see the main living areas are on the north side of the house, including the home office as we will use this space more than the Master Bedroom. The bathroom, ensuite and laundry are towards the south/west side.
In regards to the size, 18-20 squares for a house is considered on the smaller side in Australia. There were a few reason for this. Firstly, Australia is known to have large homes, 27 squares (243 square meters) which is the average house size. A typical new home these days will boast spare bedrooms for guests or multiple living rooms and formal dining rooms. Personally, Devin and I do not wish to conform to the general mentality that bigger equals better. We don't want to work for the next 30 years to be paying off spare rooms.
The second reason for building a smaller house is because we honestly don't know how much extra it is going to cost to build a certified Passive House. We have heard at seminars and from others in the industry that you can expect to pay anywhere from 10-20% more than what any other new '6 star energy' home would cost. In Europe the cited price difference for a Passive House is only a 5% increase in cost. Since Passive House is so new in Australia, there is no demand on Australian manufacturers for products that will comply with the Passive House standard, therefore naturally the products are going to cost more. So ultimately we wanted to make sure we could afford to build it.
After Anthony our draftsman had completed the initial drawing concepts, it was over to Clare our Passive House consultant to literally run the numbers. This is done in the Passive House Planning Package (PPHP), which I will not attempt to explain as there is no way I could do it justice. Other than to say that every single detail is calculated and used, from Melbournes climate data, the altitude, what materials are to be used internally and externally on the house right down to how many people will be living in the house and much more.
To achieve a certified Passive House there are very strict performance criteria that must be met. At this stage what we are most interested in, is how much the house needs heating and cooling. After all the ultimate goal for a Passive House is to eliminate the need for conventional heating and cooling. Therefore, specifically to be certified as a Passive House, the heating and cooling demand must be equal or less than 15KWh/m2 per year. So what does that mean? The way I like to think about it is that if a Passive House was a person it would need one apple (say 50 calories) a day to run. In comparison a '6 star energy' rating is based off 120KWh/m2, and would consume a burger (around 400 calories) every day.
To achieve this heating/cooling demand, Clare's report tells us what level of insulation and glazing requirements are needed. From this information we were able to start speaking to suppliers, primarily window manufacturers to assess what was both available and financially viable.
These rendered images Anthony made really started to give us a feel for the size of the spaces and what it would look like finished.