Throughout the project we've kept a detailed record of costs so we can give an accurate figure of what it costs to build a Zero Energy House.
Every line item from every invoice has been recorded, with the spreadsheet stretching to over 1,100 rows.
Every line item from every invoice has been recorded, and the spreadsheet now stretches to over 1,100 rows. We still have some finishing touches to apply to the house so it will probably end up even bigger.
There's a lot of analysis to do on that data before we can comfortably say what a Zero Energy House would cost to build. Simply communicating the total cost of our house is misleading as there are things we've done that both increase and decrease the cost to the next person:
- We've negotiated supplier discounts on some products in return for association with the project. Those costs need to be adjusted back to what a normal homeowner would pay.
- There are some areas of the house where we've spent money on goals other than Zero Energy, e.g., water efficiency, materials quality. These are equally important and we want to be very clear about which costs contribute to Zero Energy and which contribute to these other goals.
As we consolidate the costs we're also comparing them with what it would cost to build to New Zealand's current building code - and taking into account the long-term running costs of a home in each scenario.
Costs will be communicated in stages within the three performance content phases.
At this stage we are presenting high-level costs for each of the three performance phases:
- In the comfort phase we'll communicate what it cost to avoid the need for heating (extra framing, insulation, and glazing) compared with building a house to code and installing, running, and maintaining a heating system.
- In the water phase we'll present the cost of all the water efficiency measures (rainwater tank, low-flow fittings, greywater system) and compare it to a home built (and run) without them.
- In the energy phase we'll show the costs of the solar system and compare it to paying for energy over the lifetime of the system.
Following those three phases we'll present a final wrap-up of all costs.
Following those three phases we'll present a final wrap-up of all costs to show what it could cost the next person to build their own. At that point we'll also allow for long-term factors such as inflation, mortgage rates, and electricity price forecasts.
For the time being, the chart below shows the proportional split of costs across various aspects of the project. This will be updated as we consolidate those 1,100 line items...