Climate change housing costs

This Issue This is a part of the Climate change feature

By - , Build 156

BRANZ has been looking at the cost of building in measures to future-proof housing against climate change. The questions are, what do we need to do and what is the extra cost?

Slip in Wellington following heavy rain.
Slip in Wellington following heavy rain.

THE RESULTS of climate change on the New Zealand environment have been outlined by NIWA. In recent years, BRANZ has interpreted how these effects will impact on the built environment and, in particular, existing and new building stock.

Seven types of impact

Here, some of BRANZ’s work is updated using current building costs and forecasts of new housing (see Table 1) for impacts on buildings of:

  • driving rain
  • wind
  • hail
  • drought
  • bushfire
  • sea level rise
  • temperature.

The first four impacts relate to a more chaotic climate with storms and weather patterns becoming more intense. The last three impacts relate directly to global warming.

Table 1
Costs to mitigate for climate change in new housing
CHANGE IMPACTCHANGE TO 2080REGIONNO. NEW HOUSES/YR AFFECTEDCONSEQUENCEMITIGATION MEASURESCOST PER HOUSE ($)TOTAL COST ($M/YR)
Driving rain 10% increase Western NZ 9,000 Water penetration More frequent maintenance 285 236
Wind 8% loading increase All NZ 25,000 Damaged structure Strengthen framing, connectors and windows 700 17.5
Hail Severity increase Western NZ 9,000 Damaged roofing 0.55 mm roofing instead of 0.40 mm or tiles 1,326 11.9
Drought Return period down 50% Eastern NZ 5,000 Water shortages Rainwater tanks 4,700 23.5
Bush fire Fire days up 50% Eastern NZ 750 Fire damage Clear vegetation, use fire-resistant claddings 100 0.1
Sea level rise 0.2–0.5 m Coast/estuary 25 Damaged houses Move or lift house 25,000 0.6
Temperature Up 1.6–2.4°C Upper North Island 13,750 Unhealthy indoors Extra insulation, passive design 1,000 13.8
Total cost to adapt all new houses in affected regions for 2080 conditions       $69.9 million/year
Cost of mitigation measures as % of total cost       0.8%
Total cost to adapt all new houses for 2080 conditions       $8,750 million/year

Increasing intensity

The climate forecasts say these seven impacts will increase in magnitude over the next 50 years or so. The changes may not be immediately noticeable or smoothly increase from year to year. We expect, however, the impacts to increase each decade through to 2080 from the averages experienced in the past decade.

Driving rain, wind and hail

An increase in driving rain and strong wind affects buildings, increasing the risk of water penetration through the building envelope. This is turn may increase the need for and frequency of maintenance.

The intensity and frequency of wind storms are predicted to increase, increasing the load on the structure and its connectors, which may require strengthening.

There have been local and overseas examples of hail denting metal roofing and cracking concrete and clay roof tiles. These storms are expected to increase in size and frequency in western areas.

Droughts, bushfires and hotter

More drought periods are expected in wind shadow areas east of the main divide in both islands. This could affect municipal water supply, so the infrastructure may need expansion beyond what would be expected with population growth. Local authorities may mandate greater use of rainwater tanks. They may also promote the use of domestic greywater for toilets and outside uses.

We know from Australia and western North America that increased temperatures create a bushfire hazard, which can cause considerable damage every year.

Temperature rise offers some benefits in southern parts of New Zealand, such as reduced winter heating bills. However, summer cooling is already increasingly common in northern regions and will become more extensive to improve comfort levels and avoid adverse health effects.

Sea level rising faster than thought

Projections of sea level rise are significant and now expected to occur faster than previously thought. The best adaptation solution to this is not to build new housing in coastal areas or to design to increased floor levels.

It is likely these effects are not yet sufficiently understood and new housing will continue in areas at future risk. These houses will subsequently need lifting or other mitigation.

Cost under 1% to future-proof house

These impacts have been analysed and costed in Table 1. It indicates $70 million per year to meet 2080 conditions, a cost increase of less than 1% of total new housing costs.

Climate changes and the effects in Table 1 are expected to occur gradually. Houses typically have a life of at least 80 years, so houses built now could have another 20 to 30 years of life at full impact of climate change. In their early years of life, however, there will be little benefit.

The question is when

The question is when we should start upgrading our new houses for climate change impacts. To answer this properly the benefits of mitigation need to be calculated.

The original BRANZ report showed that by 2080, the benefits do outweigh the costs. However, it is not known when the break-even point is, and further work needs to be done on this.

For more

Download BRANZ Study Report 179 Assessment of the need to adapt buildings in New Zealand to the impacts of climate change from www.branz.co.nz/study_reports.

Download the PDF

More articles about these topics

Articles are correct at the time of publication but may have since become outdated.

Slip in Wellington following heavy rain.
Slip in Wellington following heavy rain.

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