This report considers the cost benefits of a variety of sustainable retrofits for the existing housing stock. The retrofit interventions costed are mainly energy and water related, and values are calculated for the four main centres and 11 house/ multiunit typologies. Health and comfort benefits are considered and the costs include initial costs of the measures and their replacements. Future operating costs are discounted and the results are expressed as net present values and benefit cost ratios. Typologies and locations are scaled up to derive national benefits. A spreadsheet model is provided on which users can change parameters and try various packages of measures.
Most of the measures were found to have net benefits in all four centres, i.e. Auckland, Wellington, Christchurch and Invercargill. All the measures in the Basic and Standard packages were cost-effective. In the Enhanced package, wall insulation retrofit was cost-effective but the other measures were either not cost-effective (rainwater tanks, hot water heat pump), or were cost-effective only in the cooler parts of the country (curtains, secondary glazing).