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3 Sustainable building case studies

3.1 Introduction

Five detailed case studies in Section 3.4 cover the following types of buildings:

  • university
  • community library
  • high school
  • sub-district hospital
  • office.

While the case studies concentrate on individual buildings, their analysis has been supported by the additional review of up to four other projects for each building type, where possible. More than 20 non-residential buildings in New Zealand have now adopted sustainable strategies to a lesser or greater extent.

3.2 Specific findings

Costs

It is difficult to draw definitive conclusions about the costs of sustainable buildings, as their nature and extent varies widely. It can also be difficult to differentiate between sustainable design and architectural features. Table 1 shows the indicative cost/benefits for the case study buildings. Some of the case study buildings have proved cheaper, others cost-neutral, and some more expensive. In forming our view on the value case for sustainable building we have therefore supplemented the case study data with overseas experience, where the extent and market for sustainable buildings is more developed.

 

Table 1: Indicative cost/benefit summary for case study ecologically sustainable development (ESD) buildings

Building type

Benchmark building capital cost
$/m2

ESD building capital cost
$/m2

ESD building premium (saving)
$/m2

ESD building premium (saving)
%

Annual energy cost savings
$/m2

Annual water cost savings
$/m2

Total annual cost savings
$/m2

Simple payback
(years)

20-year NPV for ESD measures
$/m2

Tertiary education

2300

2000

-300

-15.0

6.3

0.0

6.3

N/A

-338

Hospital

2400

2435

35

1.5

9.5

1.0

10.5

3.33

-72

Secondary school

2430

2570

140

5.7

7.5

0.6

8.1

17.3

41

Library

2384

2494

110

4.9

7.5

0.0

7.5

14.67

32

Office - low/ medium ESD

2000

2130

120

6.0

11.0

0.3

11.3

10.65

-3

Office -medium/ high ESD

2000

2230

230

11.5

17.0

0.6

17.6

13.09

-23

Average

2252

2310

56

2.43

9.80

0.42

N/A

N/A

N/A

Median

2342

2333

115

5.30

8.50

0.45

N/A

N/A

N/A

Notes:

1. Discount rate of 8.5%

2. Energy and water costs assumed to increase at 3% above inflation.

3. Three-year pre-design and construction period, with 20-year consideration period.

4. Costs have been normalised to 2005.

5. The library case study includes a number of materials features which add significantly to the sustainability of the building but which do not have a direct payback to the building owner. These include certified timber, alternative to CCA and LOSP timber treatment, recycled wool acoustic insulation, ceiling tiles with 70% recycled content, plant systems endorsed under the environmental choice labelling scheme, modular carpets with 100% recycled face fibre, cement with 70% fly ash content, crushed demolition materials as hardcore, alternatives to PVC and on-site waste management. These measures were generally included within a 1% premium on top of the construction cost.

6. Alternative on-site stormwater management systems such as swales and rain gardens can generally be achieved for little or no cost premium provided the budget includes a reasonable allowance for landscaping. The hospital case study included a stormwater retention pond which attracted a relatively significant cost premium.

We conclude that the purely sustainable features of a building add around 2-6% to the cost, compared with a conventional building. As discussed elsewhere in this report, operating cost savings pay this back many times over during the life of the building. This compares to international data as follows:

  • Australia 2-4%
  • United Kingdom 10%
  • United States 0.7-6.5%

Building type affects the economics

The range of buildings illustrates that sustainable building strategies can be applied to any building type. The value case will, however, apply more to high intensity / long duration activities such as hospitals, than to low intensity / short duration activities such as schools. The nature of the building use may, however, make it harder to adopt certain sustainable strategies. Natural ventilation may have only limited application in hospitals, for instance, due to requirements for infection control, but can be widely adopted in other buildings such as schools. So although sustainable strategies can be applied to any building, their extent and value case differ significantly and require specific consideration.

Energy and water savings

The New Zealand case study buildings have all reduced energy and water usage (where conservation strategies have been implemented) compared to other buildings of the same type. However, predictions of energy used for the case study buildings have been generally optimistic compared to real data, generally because of extended hours of operation, inappropriate use of the building (particularly in the first year of operation), and factors that were not anticipated or interpreted correctly at the design stage.

Buildings enjoyed by users

The individual New Zealand case study buildings are almost all well liked by their users, as confirmed by both formal post-occupancy evaluations and anecdotal response. The sample is small and relates more to the better buildings, but New Zealand sustainable buildings generally have positive user satisfaction and potential benefits in terms of productivity, and are within the upper 5% of buildings surveyed by the Probe Study methodology (Leaman and Bordass, 2001). This may be largely due to the nature of the projects, with motivated clients and users, the relative simplicity / clarity of design intent of the sustainable strategies, and the interest, follow up and fine tuning of performance post-occupancy.

Time and budget constraints lead to lost opportunities

A number of the case study buildings faced an initial scepticism to adopting sustainable building strategies due to unfamiliarity, concerns about cost and performance and a lack of completed projects in the New Zealand context. In many instances, sustainable features were regarded as optional and were compromised - particularly when budgets were under pressure - even if they were not the cause of the situation. Sustainable features can be seen as soft targets for cost cutting - particularly for quantity surveyors and project managers.

Sustainable buildings prove to be reliable

The design and technologies employed in the case study buildings have generally proved reliable and fit for purpose. Any issues have been resolved during the first year of operation, as is normally the case for a conventional building. Some issues of summertime overheating in naturally ventilated buildings in the hotter and more humid Auckland environment could have been better addressed at the design stage - normally by a reduction in glass area or by better shading.

Award winning

Most of the case study buildings are of a high architectural quality, as shown by the architectural awards they have received. This has undoubtedly added to the experience for all involved - client, design team and users. It has also added to the general user satisfaction of some of the case study buildings subject to post-occupancy evaluation. Combining sustainability and architectural excellence requires a much more involved, and therefore expensive, design process. Some of the perceived extra costs of sustainable buildings may be due to this combination.

Generally, the completed case study buildings may be considered state-of-the-art rather than leading edge, at least in an international context, and are therefore not highly innovative. The challenge has been to reinterpret some international approaches in terms of availability of materials and equipment within the constraints of the New Zealand construction market and cost envelope. Clients and design teams have been challenged to think harder and leaner to change the normal construction process and, in doing so, have unintentionally added to the sustainability of the overall solution in comparison to overseas buildings.

Commitment from clients

In all the case study buildings, clients have accepted the sustainable path. In hindsight, some would have gone further. The increased capital cost premium paid by some has quickly looked like a sound, far-sighted investment as energy costs have increased beyond expectation over the past 10 years. The statement is often made - "I wish we had done more".

3.3 Conclusions

Some general conclusions can be drawn from the case study buildings:

  • The difference in the initial capital cost of the case study buildings compared to conventional good quality buildings varies quite widely (from 15% less to 11.5% more), with sustainable features initially costing an average of 2-6% more.
  • Energy costs for the case study buildings are 35-50% of those for similar conventional buildings.
  • The sample is small and relates to perhaps the better quality buildings, but it can be concluded that New Zealand's sustainable buildings generally have positive user satisfaction and potential benefits in terms of productivity. They are within the upper 5% of buildings surveyed by the Probe Study methodology.
  • The range of case study buildings illustrates that sustainable building strategies can be applied to any building type.
  • The range of sustainable strategies being adopted is growing and has moved from conscious attempts to save energy to increasingly holistic approaches, which address not just energy but a wider range of environmental issues including water use, materials selection and waste management.
  • The design and technologies employed in the case study buildings have proved generally reliable and fit for purpose.
  • Many of the sustainable buildings are award winning and are of a high architectural standard. However, this has sometimes led to the costs of the sustainable aspects of the building appearing higher than they actually were.
  • Sustainable design is most successful when experienced consultants are brought in at an early stage in the initial design brief and the procurement process.

Sustainable buildings represent a viable and increasingly attractive alternative to conventional buildings with benefits in terms of operating costs, user satisfaction, future proofing and environmental protection.

3.4 The case studies

University - Mathematics, Statistics and Computer Science Building

Community library - South Christchurch Library and Service Centre

High school - Albany Junior High School

Sub-district hospital - Waitakere Hospital

Office - CentrePort / Statistics New Zealand Building, Wellington