Our series on whole-life emissions for different building types continues with three 60-year scenarios for a shopping mall

Whiteley_index

01 / Introduction

In our previous two articles on whole-life carbon, we examined prestige offices (18 May 2012) and new-build schools (14 September 2012). In these articles we looked at the European standard CEN TC 350 and its impact on the choice of materials, as well as the cost and benefits of taking the low-carbon route. In both cases we looked at conventionally constructed versions of each type and compared the whole-life carbon emissions of these against a low-carbon alternative.

This time we are looking at retail, specifically one of only two UK retail schemes opening this year. British Land and its joint venture partner USS kindly shared information on Whiteley Shopping Centre, a 320,000ft2 shopping centre in Hampshire which completes in May. What we are interested in in this article is what might happen over the next 60 years, and does this have any lessons for the present?

This redevelopment replaces an earlier, now demolished, nineties factory outlet. The new scheme consists of double-storey retail shells capable of extensive subdivision and includes landscaping and car parking. The new scheme is built to a high quality, and represents theforefront of a contemporary approach to sustainability.

The buildings consist of steel frames with in situ concrete slabs, insulated deck roof, and double and triple-height glazing with oak faced cladding. The subdivision walls are a stud wall system.

The developer has a detailed sustainability policy, including an environmental site management system to ISO 14001, procedures to minimise ground and surface water pollution (Environment Agency pollution prevention guidance 1, 5 and 6), and measures to manage water, waste, and energy use during the construction process. The completed scheme will be BREEAM “excellent” and includes rooftop photovoltaic arrays.
We have examined three possible future scenarios for the shopping centre in whole-life carbon terms. This is split into the construction phase to practical completion, and the “whole life” phase which covers the initial construction and the life of the centre over the 60-year period. We are covering the whole-life emissions from the landlord’s point of view - that is, excluding the tenant’s activities (see 03/Assumptions below). The commentary in the concluding section is generic to shopping centres of this type, and not specific to this scheme.

McL_Whiteley_Dec2012_019

Scenario A This is a baseline option, and assumes continual occupation over the 60-year period. Although this may not be typical for this type of development, it does represent a norm in that it replicates in terms of continuity the life of a typical high street. We have therefore assumed a refurbishment cycle as follows (see 04/Scenarios box for details): at year 10 there will be a partial refurbishment and at year 20 a major refurbishment; years 30 and 50 will be as per year 10; years 40 and 60 would be the same as year 20. The structural frame, floor and ground slabs and roof decking would always be retained.

Scenario B This represents the more likely life cycle of a typical shopping centre - that is, full redevelopment with all new materials every 20 years, at years 20, 40 and 60. There would be a partial refurbishment or “refresh” at the intermediate 10, 30 and 50 years.

Scenario C This is the same cycle as Scenario B; however, it assumes that the redevelopments at years 20, 40 and 60 include for a substantial proportion of on-site recycling of structural members, cladding and other materials. This would include demountable steel frame and assumes reusable concrete plank floor construction. This option also assumes off-site recycling of the unused material.

In addition to the above we have looked at the impact of changing the existing steel-concrete-deck superstructure with an all-timber alternative.
What is being referred to by the word “carbon” in this article is the whole basket of greenhouse gases that have the potential to cause damage in the atmosphere. These are measured in carbon dioxide equivalents, or KgCO2e for short.

02 / Whole-life carbon assessment: a brief recap

McL_Whiteley_Dec2012_012

The European standard CEN/TC 350 identifies four stages in the life of a building - product manufacture, construction, in-use and end-of-life - with more detailed sub-categories used to pinpoint specific sources of emissions.

The first stage encompasses the extraction of raw materials, their transport to a point of manufacture and the process of transforming them into construction products.

The second involves transporting construction products to site and the on-site processes involved in assembling them into a building.

The third, most complex, stage, covers the maintenance, repair, replacement and refurbishment cycles of the building, as well as the use of energy and water during its occupation.

In the final stage, the building is deconstructed and its redundant components transported off site, processed and disposed of.

At each stage, whole-life carbon analysis can identify solutions with lower carbon impacts, delivering considerable savings overall.

The first part of the standard, EN 15804, was published early in 2012 and establishes product category rules for environmental product declarations.

Last year, CEN TC 350 was incorporated into a British Standard BS EN 15978. Therefore, although not legally required, the framework for whole-life carbon now exists in the UK.

03 / Assumptions

McL_Whiteley_Dec2012_018

  • In practice the three scenarisos in this article would include many variables distinguishing one from another. We have chosen to limit these, partially for practical reasons given the scale of this article, and partially to try and isolate the key variables that make the biggest difference. For example, we have no data on the demolition of the previous scheme; however, as this would be the same for all three scenarios, it does not make a comparative impact.
  • For “Carbon at PC”, all three scenarios are shown as having the same embodied carbon at practical completion. In practice if you were designing for recycling this would be slightly different - for example, the carbon figures for precast concrete slabs are slightly higher than for in-situ slabs.
  • In each scenario we have assumed that the roof finishes, the renewables and the external works follow the same renewal cycles. They therefore become constants in the comparisons.
  • We have also assumed that tenant fit-out and churn and associated operational energy use by tenants is a constant between the scenarios.
  • The key comparisons are therefore the provision of the shells by the landlord and how the projected life of these shells under each scenario in carbon and build cost terms differ.

04 / Scenarios

All scenarios start from the same basis using the as-built information of the development. Carbon emission and cost data are divided into the following categories:

Demolition Emissions included over 60-year period. Not including demolition of the previous scheme

Substructure Below ground structure, including ground slabs

Superstructure Above ground structure, including roof structure

Internal fit-out Mezzanine floors and partitions between units

Roof Roof construction and rainwater fittings only

Lift/Escalator Not included as tenant item.

Facade Glazing and composite cladding panels.

Sanitary fittings Not included as tenant item.

Renewables PV panels on roof

External works Service yard, landscape and car park.

Plant/Building service Base provision, perimeter and security lighting system only. Main M&E by tenants

Operational energy Indicative base load from perimeter and security lighting, and so on

Scenario A: Continuous occupation with refurbishment cycle

Year 10 A partial refurbishment to replace: timber cladding, render rainscreen, entrance and service doors, cladding seals, rainwater gutters on roof, all mezzanine floors and partitions between shop units. Reuse and recycle rate for demolished materials is assumed to be market average.
Year 20 A major refurbishment to cover scope listed in year 10 with additional replacement of: all composite cladding panels, all roof panels, 50% glazing units (including roof lights), all service yard, landscape, car park and PV panels. Reuse and recycle rate for demolished materials is assumed to be market average.
Year 30 Same as year 10
Year 40 Same as year 20
Year 50 Same as year 10
Year 60 Same as year 20

Scenario B: All-new redevelopment every 20 years

Year 10 Same partial refurbishment as year 10 of scenario A
Year 20 Existing buildings demolished, full retail redevelopment with all new material including new service yard, landscape, car park and PV panels. No reuse of material on site and reuse and recycle rate for demolished materials is assumed to be market average.
Year 30 Same as year 10
Year 40 Same as year 20
Year 50 Same as year 10
Year 60 Same as year 20

Scenario C: Redevelopment every 20 years recycling existing structure

Year 10 Same partial refurbishment as year 10 of scenario A
Year 20 Existing buildings demolished, full retail redevelopment with substantial proportion of on-site recycling and reuse of existing materials. Existing materials reused to provide 70% of superstructure, 50% of glazing units and 50% of substructure. New material for rest of building including new service yards, landscape, car park and PV panels. Unused materials will be recycled off site.
Year 30 Same as year 10
Year 40 Same as year 20
Year 50 Same as year 10
Year 60 Same as year 20

CO2 emissions comparison

whole life costs scenario a

whole life costs scenario b

whole life costs scenario c

whole life costs table

05 / Findings

The overall cheapest in carbon terms is not surprisingly scenario A. However, the difference between scenario A and the full demolition and rebuild scenario B is 59%, whereas the difference between A and recycle and rebuild is only 23%. This clearly shows up the carbon benefits of designing for and undertaking whole-scale recycling.
Demolition and removal for B is significantly greater than for A, by a factor of nearly 2.5, whereas reuse reduces additional carbon to a factor of 1.3. In carbon terms, omitting a large element of removal and waste creation is
clearly beneficial.

  • The biggest variables are in the substructure, with 121 KgCO2e for A, 483 for B and 302 for C. The carbon impacts of rebuilding the substructure every 20 years are huge.
  • Superstructure is similar to the above: the whole-life carbon quadruples from full retention to continual new-build, but only doubles for the recycled option.
  • Plant and building services are only slightly greater with the continual new-build option, scenario B, in comparison to the other two scenarios.
  • The use of an all-timber superstructure represents nearly a 10% improvement on the carbon position at practical completion for all options. This benefit is maintained in absolute terms for the whole-life picture. but reduces proportionately as carbon expenditure rises in other areas.
  • The use of precast concrete slabs is very marginally worse in carbon terms than in-situ slabs at practical completion; however, carbon benefits of precast concrete are apparent in all scenarios over the 60-year period. This is partially due to recycling benefits, as you would anticipate, and partially due to reduced demolition carbon impacts.
  • In cost terms over the 60-year period, scenario B is unsurprisingly 54% more expensive than A, whereas the recycling option C is 20% cheaper than full replacement B.

06 / Conclusions

  • The most carbon-efficient approach is to build a durable building and to keep it, carrying out refurbishment as necessary. This suggests that in carbon terms not only should individual buildings be designed for a long life, but also the layout - that is, the “town planning” of shopping centres should be designed for the longer term. This implies that the buildings need to be inherently flexible and therefore less prone to commercial redundancy.
  • All three scenarios give the same level of “newness” of visible finishes. The scope for wholesale change is restricted by the lower carbon/cost alternatives.
  • Designing for recycling has clear carbon benefits, implying future flexibility. It may be too much to expect that a shopping centre will remain unchanged for 60 years, but if local adjustments can be achieved easily - that is, through flexible construction - then the carbon impacts of such alterations will be less serious. Even if you do not propose to recycle structure on site, designing for easy deconstruction has carbon benefits. We would also suggest that designing for flexible deconstruction aids maintenance and refurbishment.
  • Using timber superstructure does have carbon benefits in initial construction, and if recycled this benefit can be extended. There are several key issues with timber construction that affect its environmental performance - for example, the glues used in laminating (natural polymers rather than synthetic), and what happens to timber at the “end of life”. If timber is sent to landfill, it will have very negative effects on the environment.
  • Wholesale replacement of buildings on a 20-year (or less) cycle is very expensive in both carbon and financial terms and very inefficient in terms of resources. Designing for durability and a longer life at both the “town planning” and building scales should help reduce the occurrence of commercial redundancy in this type of shopping centre. In addition, flexible, elemental construction will help mitigate, in carbon terms, the changes that are likely to occur during a scheme’s life.

Acknowledgments:

The Whole Life Cost modelling has been produced by Sturgis Carbon Profiling. Our thanks to Sarah Cary of British Land for information, advice and help, Aaron Edlington of RLB for providing cost advice, and Christina Stuart of Sturgis Carbon Profiling for her diagrams.