This is the final report of the exploratory phase of a study of durability and service life issues related to green building. The overall objective of the project is to determine how service life considerations can be appropriately included in green building rating systems such as LEED and Green Globes. The intent at this exploratory stage is to widen our understanding of, and bring together, the factors that influence a building envelope’s service life.
The immediate Phase I objectives were to:
- examine and make recommendations regarding terminology and the basic elements that should be considered when considering service life from a whole building perspective;
- determine the international state of the art regarding building-related service life research, standards/guidelines and rating system approaches;
- document factors typically affecting material service life and building lifespans from a building science perspective; and
- develop a recommended work plan for subsequent phases of the study.
This report covers the first three objectives.
There appears to be widespread support within the green building community for taking building service life explicitly into account in rating systems. One approach would be to credit buildings designed for a long service life, 100 years for example. However, the limited empirical evidence is that many buildings have relatively short lives for a variety of reasons, some of which have nothing to do with the building design or components — factors such as changing land values and urban re-development, construction practices and quality, and the quality of maintenance.
Although the length of time a building remains standing should certainly be on the sustainable building agenda, this does not necessarily translate into always designing and building for a very long service life. It is equally important to design for deconstruction when the building is not likely to stand for a long time for one reason or another. Similarly, the flexibility or adaptability of a building can be a critical determinant of its ultimate life span. We address sustainability best when we design for a service life that matches the service life that can be expected or predicted, without losing sight of the end-of-life environmental effects.
There is often confusion about related concepts of building longevity, service life, maintenance requirements, and material or component durability. Establishing a common understanding of the terminology is therefore a key step. The problem is that many of the words have connotations in day-to-day conversation that often conflict with the strict, more technical definitions. Yet it is essential that we hold to the more precise technical usage if we are to have clarity when we address the concept of service life. The most detailed technical definitions have been developed in the following two publications, which are described in Appendices A and B, respectively:
- ISO 15686-1 Building & Construction Assets Service Life Planning: General Principles; Building Service Life and Green Building Rating Systems ii and
- Canadian Standard Association (CSA) 478-95 Guideline on Durability in Buildings.
Following a review of the various terms as defined in the two publications, we recommend the following definitions:
Service Life: The actual period of time during which the building or any of its components performs without unforeseen costs or disruption for maintenance and repair.
Design Service Life: The service life specified by the designer in accordance with the expectations (or requirements) of the owners of the building.
Predicted Service Life: The service life forecast from recorded performance, previous experience, tests, or modeling.
Durability: The ability of a building or any of its components to perform its required functions in its service environment over a period of time without unforeseen cost for maintenance or repair.
Differential service life: The concept that there are service life differences between the components of a building system such that the service life of one component can affect the service life of another.
Life cycle costing (LCC): A technique that can be brought to bear in making decisions about relative initial and long-term maintenance or operating costs.
It is especially important to maintain the distinction between the terms ‘service life’ and ‘durability’. In a given situation, we can ask whether the actual service life is likely to meet or exceed the design service life. The answer should reflect a prediction of service life based on component and whole building durability factors under specified service conditions. None of the service life definitions deal with how long a building may actually stand, only with how long it will, or should, stand without unforeseen costs or disruption. Decisions to rehabilitate or fully renovate a building envelope and extend its life span beyond the original design service life criteria will certainly depend on the condition of the materials that remain, but it will also depend on such factors as adaptability and location, as well as the aesthetic and cultural values that may underpin the decision to retain parts or all of an envelope. In short, even the precise definitions of service life do not, in fact cannot, deal with the ultimate lifespan of any given building. The uncertainties are too great and we can only really focus on those aspects that can be interpreted, measured, estimated or predicted with some degree of certainty.
Building Envelope Performance
The focus of this exploratory study is on the building envelope, including the various agents that comprise the service environment in which the envelope must function. Building science can be defined as the body of knowledge regarding heat, air and moisture flow in buildings resulting from these agents, and their effect on building materials and occupants. All definitions of service life and durability include references to the service environment, underscoring the key concept that durability is a function of both a material and its environment, a point too often misunderstood by designers.
The majority of building envelope failures can be attributed to water in one of its many forms (gas, liquid and solid). Water degradation can take the form of biological degradation, freeze/thaw cycling or frost heave, condensation, high relative humidity (RH) levels, water ingress and absorption. Other environmental effects that are harmful to buildings are air, and its components (oxygen, nitrogen, carbon dioxide, sulphur dioxide), wind, biological and ecological agents, temperature and solar radiation.
Differential service life is a particularly important subject because it relates to the premature removal of building components simply because they are part of a system comprised of components with varying service lives: the component with the shortest life dictates the life span of the system as a whole. It is therefore important to harmonize the service life of system components and ensure the accessibility of components for periodic maintenance, repair and replacement.
Tools and Methods
Contrary to one of the starting premises for this study, we have found that there are tools to help take service life into account in the design process; particularly those embedded in the CSA 478- 95 guideline and the ISO 15686 standard. The question is why these tools are not more frequently applied. One reason may be their complexity, and the consequent requirement for appropriate expertise within the design team. Unfortunately, design teams are often limited in terms of both expertise and budget from properly considering all of the agents that can affect envelope performance, yet this is what the tools are asking of the team. As well, there is insufficient empirical evidence from outside of the testing laboratory about the full spectrum of reasons for building envelope failure, and the ways in which different agents may synergistically react. It may be that the tools can be greatly simplified by concentrating on a more narrow range of factors.
Life cycle costing (LCC) is one of the methods recommended by both ISO and CSA, to help with explicit decisions involving trade-offs between initial and ongoing costs. For example, an LCC may show that a long expected service life product with a high initial cost and low maintenance costs makes sense. But an LCC may also lead to decisions to use a lower first cost product that requires more long-term maintenance and even periodic replacement. There is nothing inherently wrong with that kind of decision from a building service life perspective, provided one does not run afoul of the differential service life issue. The fact that the LCC results lead to a conscious choice means that the later costs for maintenance or replacement of a component will not be unforeseen.
Financial and Other Systemic Considerations
A critical aspect of the service life issue that is touched on in this report, but not yet explored in depth, is the role of contract terms and financial arrangements under which buildings are designed, constructed, and operated. The contracts under which design teams operate may not sufficiently compensate them for the work required to properly take service life into account beyond the strict code requirements. Those contracts, in turn, often reflect an emphasis on first costs at the expense of long-term planning. Even in the face of policies dictating a full life cycle costing approach to decisions, we too often see first costs and schedules as the controlling factors.
In addition, developer financial planning horizons are typically much shorter than even a modest building life span of 40 - 60 years, and decisions are therefore driven more by shorter term financial imperatives than by longer term service life considerations. These kinds of problems are exaggerated under the various kinds of leasing arrangements that are becoming more common. But one would not expect such factors to be overriding in the case of buildings such as courthouses and schools that have, or should have, long-term cultural or social importance. The anecdotal evidence so far is that formal service life considerations are seldom brought to bear in those design processes, and we need to better understand the impediments.
We also have to take account of the potential for area redevelopment or other changes in the urban
fabric that are likely to affect a building’s life span. It may often be the case that we are better to
set a relatively short design service life and therefore design for disassembly or deconstruction. Similarly, designing for maximum flexibility or adaptability can be a critical determinant in the ultimate life span of a building. The fact is that any method or tool for taking service life into account in building design has to recognize and incorporate the realities of the market place as well as the desirable outcomes from a ‘green building’ perspective.
Rating System Approaches
Defining or judging service life has been problematic for the developers of green building rating or assessment systems, and few tackle the subject from a holistic perspective. Indeed, while much information exists worldwide on building and material service life, building construction, and green building systems, there is little discussion of all three subjects as an interrelated whole. LEED Canada is the only rating system reviewed with a service life credit that accounts for whole building aspects, instead of just building components and assemblies, awarding one point for the development and implementation of a Building Durability Plan in accordance with the principles of CSA S478-95. This credit is achieved when the predicted service life of a building meets or exceeds its design life. Where the design life of individual building components and assemblies is less than that of the building, it must be designed so that the relevant components or assemblies can be replaced easily, thus accounting for differential service life concerns. Designers who opt for this credit must develop a durability plan in accordance with CSA S478-95 and must also utilize a qualified building science specialist in the building design.
There has been resistance to this particular credit due to potential liability arising from seeming to
“guarantee” a durable building. There are also concerns about the cost of documenting a credit of
this nature in sufficient detail to clearly demonstrate achievement. The Canadian Green Building Council has established a Durable Building Task Force to examine the issues related to this credit,
including the need to simplify documentation.
None of the other rating systems reviewed has service life credit requirements that approach the detail of the CSA 478-95 Guideline on which the LEED Canada credit is based, or of the comparable ISO 15686-1 standard. While some rating systems encourage service life prediction and planning, the crucial process of consciously deciding on a design service life and comparing to a predicted service life is not taken into account in other rating systems. The approach of specifying a required or recommended building or component service life, such as 50 years, seems arbitrary and even counter-productive because it does not take account of the building type, function or location, all factors that should have a bearing on the design service life.