3.4 How to proceed with the service life assessment in building and product LCA studies

This section introduces the main concepts of service life planning. These are useful for practitioners who intend to carry out an LCA study for product and building

One characteristic of LCA studies in the construction sector is the assessment of technical systems that often have very long service lives. Estimations of service lifespans of one or more decades are typically more difficult to oversee than the service lifespans of consumer products, for example. As a consequence, and depending on other parameters, estimations of the service life of buildings and products may have a major influence on the LCA results. In this context, the concept of service life planning, which is closely related to [ISO 15686], and which is frequently cited in EN 15804 and EN 15978, is a relevant and very general aspect of LCA in the construction sector. An introduction to service life planning is therefore given in this section.

There is a considerable momentum behind initiatives to provide the construction sector with methodologies, tools and standards for service life planning and sustainable construction. This EeBGuide can be regarded as a further example of this movement. The following gives a brief introduction to service life planning, as an area derived from scientific research on service life prediction for materials and products. Service life planning of construction works aims to support an approach to engineering of technical systems that meets the requirements of a life cycle perspective on the overall system.

What is service life planning about?

Buildings are normally expected to be long-lived engineered works. As for any other technical system, they are designed to meet expected requirements over a foreseen lifetime. How, then, should these requirements be expressed, and how can the essential properties of the engineered system be optimized to ensure that the requirements are met? Buildings offer an extra complication, as the long service life will often include a shift or change in performance requirements with time.

Service life planning offers a systematic approach to this process, and over the past two decades standards as well as other tools for life cycle engineering have been developed. A service life planning assessment of a building may be performed for limited technical and economic reasons, but since the end of the 1980s environmental concerns and sustainability in construction have typically been the main driving forces.

A European perspective

The Construction Products Directive (CPD) was created with the aim of removing barriers to trade, and in this specific area it has little direct reference to sustainability. However, it has a clear bearing on the performance of buildings (construction works) over time, and provides important direction for international, European and national work on standards and codes. The CPD fixes the essential requirements for construction works (both buildings and civil engineering works).

These requirements must, subject to normal maintenance, be satisfied for an economically reasonable working life. This horizontal requirement of the CPD presupposes a service life planning assessment of the construction works. The works should be designed for an anticipated design life (working life), and the service life planned by being composed of service life declared products.

The CPD has an aim of connecting the building and the building products put on the European market and used in these works. It therefore specifies the level of performance of these products: they “have such characteristics that the works in which they are to be incorporated, assembled, applied or installed, can, if properly designed and built, satisfy the essential requirements.” This is the notion of ‘fitness for the intended use’ of a building product. The link between the essential requirements of the works and the product characteristics to be assessed is fixed in Interpretative Documents (IDs) [Guidance Paper F 2004].

Figure 9: The working life of construction works as illustrated in the CPD Guidance Paper on Durability [Guidance Paper F 2004].

The CPD further specifies that a building product is fit for its intended use if it conforms to: (i) a harmonized European standard (drafted by CEN/CENELEC), (ii) a European Technical Approval (issued by an EOTA [CEC 1988] member), or (iii) a non-harmonized technical specification (e.g. a national technical specification) recognized at Community level; the three are denoted as technical specifications. According to the CPD: “The products must be suitable for construction works that (as a whole and in their separate parts) are fit for their intended use, account being taken of economy, and in this connection satisfy the following essential requirements where the works are subject to regulations containing such requirements. Such requirements must, subject to normal maintenance, be satisfied for an economically reasonable working life.” Furthermore, the Interpretative Documents provide that product standards and Guidelines for European Technical Approval (ETAGs) “should include indications concerning the working life of the products in relation to the intended uses and the methods for its assessment.”

The CPD is being revised and elevated to the level of a regulation, Construction Products Regulation (CPR), which is expected to be implemented by July 2013. With CPR’s sustainable use of resources added as the seventh basic requirement (renamed ‘essential requirements’) for construction works, service life planning is likely to gain even more significance in the European construction context.

Standards for service life planning

ISO standardization (ISO TC59/SC14) to support service life planning started in 1993, when a working group was established through a significant European initiative. Guiding concepts were needed regarding the service life of building products to help implement the Construction Products Directive. As the subject area was rightly seen to have international relevance, ISO work became based on cooperation with CEN.

The scope of ISO TC59/SC14 is to document the steps to be taken at various stages of the building life cycle, to ensure that the resulting building (or other constructed facility) will last for its intended life without incurring large unexpected expenditures.

The concept

A building (construction work) is designed for a certain design life (working life). Building parts not accessible from a technical and economical point of view should be designed for the same service life as the building. Other building parts and products may have a shorter, but declared, service life (see Figure 10).

Figure 10: the service life planning concept

 

Service life planning standards

The ISO 15686 standards (see Table 6) give guidance on all aspects of service life planning (SLP). Part 1 gives the general design principles and procedures of SLP, whereas Part 8 describes the requirements for reference service lives (RSL) of products and components.

The RSL should be used and adjusted in the design process to establish the service life of a product/component in a particular use or design situation. The Part 8 standard also provides guidance on methods to be used in the design process for this adaptation of an RSL. These methods and models are described under the generic name the factor method, but comprise a set of approaches, from simple checklist adjustments, through multiplication methods, to more advanced (but not necessarily more complicated) functional models.

Who provides reference service lives?

This has been an essential question and point of discussion all through the standardization work. The conclusion – and solution – is that the responsibility for providing RSLs for products lies mainly with the producers of the products in question. Research should be undertaken to support these RSLs with methodologies, i.e. how to test and declare a reference service life, and the ISO 15686 standards provide examples. Publicly initiated and funded databases have appeared, and may be significant drivers of progress, but will most likely have less influence than market-driven and developed initiatives.

Table 6: The ISO 15686 standards, with the general title Building and constructed assets – Service life planning, includes the following parts

Standard

Subject

ISO 15686-1 General principles Provides general design principles and procedures for planning the service life of buildings and construction works
ISO 15686-2 Service life prediction procedures Describes a procedure that facilitates service life predictions for building products and components
ISO 15686-3 Performance audits and reviews Describes the approach and procedures to be applied to pre-briefing, briefing, design, construction, life care management, and disposal of buildings and construction works
ISO/AWI 15686-4 Data requirements Technical specification describing the data requirements needed to carry out service life planning, considering various service environments and other in-use conditions. In cooperation with the International Alliance for Interoperability (IAI), the aim is also to describe IFC compliance for the ISO 15686 series
ISO 15686-5 Life cycle costing Provides guidance on developing a model of capital and running costs of a project, so that the overall costs can be assessed, and how this data can be used for financial appraisal
ISO 15686-6 Procedure for considering environmental impacts

Standard providing guidance on assessing the relative environmental impacts of alternate service life designs, and identifying the interface between environmental LCA and service life planning
ISO 15686-7 Performance evaluation for feedback of service life data from practice A generic basis for performance evaluation and feedback of service life data from existing buildings and construction works
ISO 15686-8 Reference service life and service life estimation

Describes how to provide, format and extract reference service lives of components, etc., to establish their service life in a particular application. It also provides the factor method to carry out such estimations.
ISO/TS 15686-9 Guidance on provision of reference service life data

Guides building products manufacturers and standard writers on addressing durability and service life declarations in product standards. The work was performed in cooperation with CEN TG on durability, supporting European product standards.
ISO/CD 15686-10 Functional performance Provides process guidance for managing the capability of a constructed asset through the service life of that asset to meet the stated levels of requirements.

 


3     How to use this guidance document


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