Improving building performance

Renovation provides an opportunity to improve insulation, energy efficiency, and other aspects of building performance.

There are a number of renovation options that owners may not be aware of that should be raised with them early in the design process because of the potential benefits they can bring. Many of these building performance improvements can not only improve occupants’ health and comfort but also pay for themselves over time through lower running costs.

Insulation

Insulation may help to reduce power costs, but the pay-off enjoyed by some homeowners is warmer homes rather than reduced power bills. Comfort can be vastly improved by insulation retrofits when done properly. 

For example, in one Wanaka house, the average temperature in the living room rose from 12.3°C to 17.5°C after insulation was added, and the bedroom temperature rose from a chilly 9.1°C to 14.0°C.

As part of a renovation, wall linings can be replaced so that insulation can be added. If the renovation includes replacement of a skillion roof or another roof type with limited roof space, this provides an opportunity to install roof insulation.

Costs and benefits

BRANZ research in 2010 considered the costs and benefits of various energy- and water-efficiency measures in homes in Auckland, Wellington, Christchurch and Invercargill. It found that, in all four centres, adding a minimum R4 insulation to an uninsulated ceiling had a cost-benefit ratio of greater than 1 over a 10-year period (in other words, the improvement paid for itself within 10 years).

Typically, the benefits are greatest in colder parts of the country. For example, adding polystyrene or fill insulation under a suspended timber floor is definitely worth considering in Invercargill, but has a much lower benefit-cost ratio in Auckland.

Replacing existing single-glazed windows with double-glazed windows did not give a cost-benefit ratio greater than 1 in any of the four centres, but may be worth considering if the windows are to be replaced anyway.

These calculations ignore any improvements in the value of the home that result from insulation and double-glazing retrofits.

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Other improvements to energy performance

In the same BRANZ research, several other energy efficiency measures had cost-benefit ratios of greater than 1 in all four cities. These included: 

  • draught-proofing doors and/or windows
  • installing energy-efficient light bulbs
  • adding insulation wrap to hot water cylinders or replacing the cylinder, and 
  • installing low-flow shower heads (which reduce hot water use).

As with insulation, the benefits are typically greatest in colder parts of the country.

Replacing an existing hot water system with a solar water heating system did not give a cost-benefit ratio greater than 1 in any of the four centres, but solar water heating systems may be considered if you are planning to replace a hot water cylinder and old piping anyway. Also worth considering if the existing hot water system is being replaced are heat pump and wetback systems.

These calculations ignore any possible increases in value or sale price of a renovated house arising from energy efficiency measures.

Research consortium Beacon Pathway Ltd conducted research about potential retrofit technologies for housing. It considered more than 100 technologies, scoring them for affordability, community desirability, future-proofing, investment potential, landscape, performance, health and resource use.

The most favoured energy efficiency technologies were bulk insulation, air–air heat exchangers, passive cooling, wood-pellet burners, efficient appliances, solar water heating, energy efficient lights, and double glazing. In general, proven technologies scored the highest. 

Another option worth considering is replacing existing wood burners with efficient wood or pellet burners.

Improving water efficiency

Water efficiency improvements can reduce water charges and help to ease pressure on costly local authority infrastructure.

In the BRANZ research referred to above, two low-cost water efficiency technologies had cost-benefit ratios of 1 or above in all four cities. They were: replacing on older toilet cistern with a modern dual-flush cistern; and installing low-flow showerheads.

In the Beacon Pathway Ltd research, rainwater harvesting, permeable pavers and efficient appliances were among the most favoured technologies.

Where major plumbing work is being undertaken, therefore, consider installing rainwater collection tanks and even a greywater system. BRANZ research has found that mains water use can be reduced by 60% if rainwater is used for laundry taps and rainwater or greywater is used for toilets and outdoor taps.

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Essential repairs and deferred maintenance

Renovation provides an opportunity to carry out essential repairs or deferred maintenance. See budget and feasibility for more.