Durability: Can We Afford it in a Carbon Constrained World?

David Baggs CEO & Technical Director

The latest UN IPCC climate change report explains how climate change will affect human society. Current atmospheric CO2 levels are at approximately 350ppm, while historically, the pre-industrial levels were 280ppm. It is believed that in only approximately 10 years (2020) of Business-As-Usual (BAU) Greenhouse Gas Emissions (GGEs), that CO2 levels will likely be greater than 400 ppm and it is already unlikely that we will avoid a 1-1.5oC or more warming in average global temperatures.1

With 35 or so more years of BAU emissions, levels of 550ppm are expected by around 2050, to result in a 2-3 degree rise in temperatures above pre-industrial levels. It is believed this will cause widespread damage to ecosystems (up to 30% of plant and animal species becoming extinct worldwide) and hazards to human health (from heat stress and greater spread of tropical diseases).2 At this level of temperature increase, sea level increases of between  0.33m-1.25 m are also expected depending on the modelling assumptions.3

If we are to limit climate change to only 0.5o where climate impacts will not be severe, it is believed a 60% reduction from the projected 2050 levels is required. This brings the CO2 level target to 330pmm. It is believed by many scientists that these key temperature thresholds are likely 'tipping points' from which the ecosystem may not be able to pull back, as  runaway 'negative feedback loops' are created within the ecosystem.1

The Role of Buildings

Buildings account for one sixth of the world's fresh water withdrawals, one quarter of its wood harvest, and two fifths of its material and energy flows… Building and construction activities worldwide consume three billion tons of raw materials each year or 40 per cent of total global use...4

Furthermore, the growth in this sector has been astronomical over the last 50 or so years and growth continues aggressively across the globe.

A significant amount of energy and embodied GGEs is 'hidden' and largely ignored within the materials used in the fabric of cities, buildings and their infrastructure. The energy & emissions embodied within materials, products and technologies is a key factor in the carbon footprint of cities as a result of their raw materials procurement, manufacturing, packaging, maintenance and replacement/disposal is being overlooked in the macro studies of potential CO2e savings.

When we look at the relevant proportions of operational vs. embodied energy (with its attendant climate impacting emissions) in the residential and commercial sectors, the majority of energy is consumed in operational energy. However, we also see a significant proportion of overall energy resulting from the energy embodied in both structure and fitout. This becomes even more significant as operational energy efficiency increases.

Embodied Energy (EE) is measure that has been traditionally used to assess the energy expended in all aspects of a product's manufacture including raw materials and transport. It is also a proxy measure for resource depletion and reduced environmental quality as a result of fossil fuel combustion emissions from energy generation.

Furthermore, in recent times we are using less and less renewable sources of materials in favour of non-renewable materials. While non-renewable materials tend to be more durable, renewable materials not only tend be lower in embodied energy, but they contain carbon and in some circumstances can lock it up for relatively long period - i.e. 20-100 years or more.

Embodied Energy vs Embodied Carbon and GGE Factors

One of the major characteristics of EE is that is measures the energy inputs into materials in MJ. As a measure, it does not however look at the energy potential of a product, nor does it consider the source of the energy or the climate change impacts of the energy source. A product could appear quite high in embodied energy and yet have been manufactured with 100% green energy such as solar or even recovered landfill methane which could have near neutral or even beneficial GGE impacts. Likewise, if the material absorbs C02 in its growing or manufacture, e.g. timber, bamboo, reeds, natural latex etc, or in its mineralization e.g. TecEco Magnesia cement, it could be a net C02 sink, providing a net GGE benefit (beneficial) from a climate change perspective yet show a positive EE figure.

What is more, C02 is not the only greenhouse gas. Many other gases such as carbon monoxide (3), methane (21), nitrogen oxide (40), nitrous oxide (310) and carbon tetrachloride (1400) have significantly higher climate change impacts. GGEs are measured in kgC02 equivalents/kg material (kgCO2e/kg).5

When these gases are generated during raw material processing or product manufacture, the EE data can be quite different to the GGE data as can be seen in Table 1 below showing a GGE comparison of a set of structurally equivalent sheet metal alternatives. When EE data only is considered, aluminium performs worse than both other materials, yet when the GGE factor is applied, both stainless steel and aluminium are virtually the same and only approximately 3 times worse than the galvanized steel sheet rather than the approximately 3-5 times EE.

Table 1. Greenhouse gas emissions of structurally comparative metal sheet- (*GGE Factors for Australia derived from 6)7

Metals

 

Thick-ness

(mm)

Mass

(kg/m2)

 

EE

(MJ/m2)

GGE

(kgCO2e/

kg)

GGE

(kgCO2e)

Aluminium sheet

1.6

4.3

772

4.35*

18.7

Stainless steel sheet

0.45

3.6

455

5.18*

18.6

Galvabond™ Steel Sheet

0.55

4.3

164

1.32* (incl gal.)

5.7

Table 2. Equivalent solar efficiency sun shade materials options ranked by embodied carbon dioxide equivalents (kgCO2e/m2). 7

Sun Shade Material

Mass

kg/m2 (approx)

EE

MJ/m2

GGE

(kgCO2e/

kg)

GGE

(kgCO2e/

m2)

Aluminium fixed louvres - 150mm (extruded elliptical) virgin source

20.4

4000

9.205

189

Stainless Steel - batten style - 28mm slat - 8.5kg/m2 incl. frame

8.5

 

3825

5.457

46

Colorbond steel batten style - 55mm slat

16-22

 

3410-4690

1.3 approx.

21-29

Lattice - Colorbond Steel - 28mm slat

14.4

3070

1.3

19

Concrete - precast, 75mm

118

350

0.114

16

Aluminium elliptical blade louvres- 150mm 50% recycled

20.4

 

1000

0.71

14

Natural Hardwood -120x140mm louvres 10 blades/m

28

10

-2.8

-78

Likewise the rankings for different sunscreen materials differ between EE and GGE notably recycled aluminium, and colorbond compared to both stainless steel and virgin aluminium. In this instance the aluminium performs worse than stainless steel, due purely to the mass of aluminium used in the specific system measured.

Hence, while using EE is still useful when fuel sources are known to calculate health and resource depletion impacts, if we are to accurately gauge climate change impacts of buildings and materials, we need to focus specifically on GGE factors.

Sustainability and durability

One of the key strategies promoted in sustainability to date has been increased durability. It has been assumed that designing and specifying for longevity will mean less resource demand and lower overall life-cycle energy consumption and GGEs. While in the long term there is no doubt this is true, many building materials, technologies, infrastructure, etc., being installed now will last well beyond 2050 and their durability may well embody significant GGE emissions that will only be amortised over these time periods. However, if we commit to a long-lived material with a high GGE impacts now, in the short term it will add dramatically to GGE emissions and have the potential to bring us to the tipping point/s faster. This begs the questions - 'Can we afford durability at all costs?'.

Can We Afford Durability At All Costs?

In this author's opinion, the simple answer is no, we can no longer afford durability at all costs. We need to consider embodied C02e in relation to the longevity of the material and based on maintenance and replacement regimes, determine whether from a climate change impact perspective it might not be better to use a less durable, but replaceable, very low impact material. In other words, we need to do an Embodied GGE payback analysis for each material and context before making a decision to specify any particular materials because of its durability - particularly if it is high in GGEs.

In Table 2, concrete and 50% recycled aluminium can be seen to be both robust and durable relatively low GGE equivalents, but a timber screen selected in Durability Grade 1 timber and left unfinished to grey, might need replacing in 10-30 years and during this period will not generate CO2 but reduce it (note the minus GGE Factor of -78 for timber). If detailed for easy replacement and reasonable sized sections are used, the timber might either last even longer or be suitable for re-milling and re-use thereafter. This approach has traditionally been used for shakes, shingles, fencing and fence posts and weatherboards etc.

Obviously, we would not want this approach to put extra pressure on remnant native forests, but sourced from Forest Stewardship Council (FSC) certified regrowth or plantation forests. Even if painting and repainting were to be considered, in most low rise situations, the GGEs associated with painting are very low at (excluding labour approximately 1.0kgCO2e/m2- derived from8).

Conclusion: Durability Must Pay its Way

Durability is an important factor in minimising ecological and health impacts providing whole-of-life cycle impacts do not generate significant short term GGEs or health impacts from coal fired or other power generation.

From a global warming and climate change perspective, avoiding GGEs in the short term is likely to be essential to reduce the rapid progress toward major tipping point CO2 concentration levels expected to be reached at BAU emission rates by 2020 and 2050.

To avoid making the progress towards these tipping points more rapid, durability should be analysed on a whole-of life-basis to provide CO2e 'pay back' preferably within approx 10 years (2020) but absolutely prior to approx 35 years (2050) calculated and updated in line with current thinking on climate change tipping points.

 

References:

  1. Accessed 14/6/12 at http://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return
  2. Intergovernmental Panel on Climate Change, Working Group II Contribution to the Fourth Assessment Report into Climate Change 2007: Climate Change Impacts, Adaptation and Vulnerability, World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), Geneva Switzerland.
  3. Accessed 11th Nov 2007 at http://www.nhcgov.com/AgnAndDpt/PLNG/Pages/Env.aspx (no longer accessible)
  4. Roodman, DM & Lenssen, N (1995), A Building Revolution: How Ecology and Health Concerns are Transforming Construction, Worldwatch Institute, Washington, DC: Worldwatch Institute.
  5. Accessed 11th Nov 2007 at http://www.ici.com/ICIPLC/ici-she/2003/pages/current/she_challenge_2005/data_tables.htm (no longer accessible)
  6. Alcorn, A., (2003), Embodied Energy and CO2 Coefficients for NZ Building Materials, Centre for Building Performance Research
  7. Baggs, D., (2007), Life Cycle Analysis and Embodied Energy, Ecospecifier Seminar Series, Ecospecifier, Brisbane.
  8. Hammond, G. and Jones, C., (2006), Inventory of Carbon and Energy, University of Bath, UK.