But doesn’t it cost more? This is the inevitable question about building a sustainable house, and with good reason. The most expensive investment most people will make in their life is their house, and the financial cost and constraints of mortgages and deposits is onerous. Logic says that if a house has to be “sustainable” as something additional to simply providing shelter there must also be additional cost.

There have been lots of attempts to quantify the cost implications but it is not a simple equation and there is no definitive answer. Some estimate an extra cost of just a few percent, others say as much as 10-15%, but these estimates fail to take account of some practical issues.

Prioritise Sustainable Outcomes

If sustainable design principles are prioritised from the outset, then the eco-friendly features will not be “additional” but will be integral to the design. Budget allocation will be directed towards these features, and savings will be made in other areas. This is the nature of any building project, we just have to change where we focus our efforts. We might need to consider simplifying other aspects of the design, and in a free market that is a choice consumers can make.

Economies of Scale

The reason houses sold by the major housebuilders cost what they do is because they build them by the hundreds, sometimes by the thousands, and they achieve economies of scale. This affects every part of the supply chain, from the purchase of the land, the designers, the contractors and the suppliers (and yes, the lawyers too). If we build ecohouses at that same scale, they will also benefit from these economies of scale.

Renewables as an Investment

A significant proportion of the eco-specific costs are renewable energy systems – solar panels, heat pumps etc. – but it should be recognised these are an investment and will pay a return on investment (ROI) through reduced energy bills. So even if renewables are paid for as part of a mortgage, it makes sense to identify their installation cost (and their energy cost savings) separately from the house construction cost.

Value for Money

There is an old mantra in the building industry that you can have a “good, quick build but it won’t be cheap” where any of those three outcomes can be interchanged. The point is that if you want quality it does come at cost, and a lot of sustainable construction issues do come down to quality. For example, making a building more airtight, which is a key part of energy efficiency, is fundamentally a quality assurance issue by the joiners on site. This greater attention to detail ensures a higher quality outcome for the house as a whole, and that means better value for money.

Higher Valuation

The fact that sustainable houses provide better value for money is starting to be recognised in their valuation for mortgages and resale. Research lead by the UK Green Building Council, supported by industry organisations including the Nationwide Building Society, indicated that the monthly savings from energy bills in homes with EPC ratings of A or B “could equate to around £4,000 in additional mortgage finance” for a typical family home. Barclays Bank offers a Green Mortgage with a lower interest rate. There are also lenders that specialise in sustainability, such as the Triodos Bank or Ecological Building Society.

One of the most intersting practical demonstrations of the enhanced value is Village Homes in Davis, California, where the resale value of houses is significantly higher than for surrounding suburban developments which are otherwise comparable.

At the moment there is no sustainable house “product” on the market to point to for a cost comparison, but if these practical issues are addressed there is every reason why a sustainable house should be cost competitive in the mass market.