Straight Green: Green Building Rating Systems and Building Durability
It is an unwritten rule among green building enthusiasts that no building can truly be sustainable without also being durable. Most readily agree with this basic principle, intuitive and straightforward as it seems but defining building durability has proven to be very challenging for the drafters of green building rating systems. Is a durable building something that lasts for 10, 20, 50 or 100 years? Or is it something that simply doesn’t require an inordinate amount of repair and maintenance over its expected lifespan? Green building rating systems have made recent forays into defining and rewarding the design of durable buildings; the USGBC’s LEED for Homes and LEED Canada both have credits addressing building durability, as well as the recently released (for public comment) Green Building Initiative/ANSI Green Globes rating system. Unfortunately, they have all fallen short of the mark.
LEED Canada’s Materials and Resources Credit 8 – Durable Building requires building designers to develop a Building Durability Plan to ensure that the predicted service life of the building and its components exceeds the design service life. The credit draws from Canadian document CSA S478 – Guideline on Durability in Buildings to establish requirements and minimum benchmarks to achieve the single available point.
In satisfying the requirements for this credit, the designer is asked to establish a Design Service Life from Table 2 in the Guideline. Except for temporary buildings and parking structures, Table 2 requires that all buildings be designed for a service life in the range of 50 to 99 years. A project team is required to demonstrate that the building has been designed to achieve the established service life by “documenting effectiveness, modeling, or testing in accordance with Clauses 7.3, 7.4, and 7.5 of CSA S478” and by completing several tables within the Guideline.
The Guideline is vague about what one must do in satisfying the established requirements in the credit. The tables require a team to provide a wide range of information such as name and location of building, structural and “other” systems used, indoor and outdoor temperatures, wind speed, precipitation and soil type. The tables also require a team to establish the design service life of individual building components and assemblies such as footings, walls, roofing, windows, doors, walks, and decks. And finally, the team is required to establish a maintenance summary of every building component and assembly consisting of a failure categorization, remedial maintenance required (repair or replacement) and frequency of stated requirement and cost.
To get the point for this credit, the design professional is required to sign a LEED Letter Template declaring that: “a Building Durability Plan has been developed and implemented.” This has caused a great deal of consternation among building design professionals and insurance companies, for the simple reason that there is no way to ensure a building’s durability by developing and implementing a “durability plan” as outlined in the Guideline. In recognition of this problem, LEED Canada established a Durable Building Task Force that re-evaluated the credit and made several urgent recommendations, among them the following:
- Immediate clarification that the credit does not ensure building durability but that the building has been designed to be durable.
- CSA be asked to “update” the guideline and that more cladding systems be added.
- Requirement be added that building insurance policies contain no exclusionary language with regard to coverage for mold or building envelope (leaks) issues.
A similar building durability credit has been introduced in LEED for Homes, which, at the time of this writing, is in pilot stage. The credit language has undergone several revisions since first introduced. Under the current version, builders are required to complete a Durability Evaluation, implement a tiny handful of prescriptive moisture control strategies (non-paper faced tile backer board at tubs and showers, for example), and develop a “quality management program” during construction to ensure durability strategies were implemented. Points are available only upon the builder’s completion of a Durability Checklist and a third party Durability Inspection, which requires a third party provider to verify implementation of listed strategies.
The checklist in the LEED for Homes credit is very similar to the tables found in CSA S478. Once all the information is filled out, it is at the discretion of the builder or designer to establish strategies for “issues” that appear on the checklist. The builder is also required to sign a declaration affirming that the builder’s “quality management program” was enhanced to address issues identified as “moderate” or “high” risk. It is unclear what these risks are and how they are categorized.
The GBI’s Green Globes, at the time of this writing released for public comment, attempts to address building durability in the Materials and Resources assessment area, under 10.6.3 Building Service Life Plan. Achieving the five available points for this credit requires simply that a design team develop a plan that includes an estimate for the building’s overall service life, expected service life of building assemblies and materials that require periodic maintenance and “documentation.” The credit does not stipulate how to document or even what form documentation must assume but does list CSA’s S478 and ISO 15686 as “informational references.”
Getting it Right
So, as the USGBC and GBI see things, as long as I can fill out a bunch of tables and make my best guess as to how long a building and its assemblies might last, I have done enough and will be rewarded with points for designing a durable building. I am unconvinced.
A thoroughly more convincing set of recommendations and guidelines for increasing the durability of buildings can be found in Building Science Digest 144, “Increasing the Durability of Building Constructions,” written by renowned building scientist Joseph Lstiburek. In this paper, the author describes building failure mechanisms, what we already have in codes and federal requirements to minimize failures, what we cannot control and design for, and the four remaining things that we can design and plan for: water, heat, ultraviolet radiation and insects. These four “damage functions” are the main focus of the document and arguably address more than 90 percent of current industry durability issues.
Lstiburek’s paper is a must read for anyone interested in understanding why buildings fail prematurely and what we can do to prevent it. It should also be the cornerstone of any durable building credits within green building rating systems.
Building Durability: Theory Meets Reality
A 2004 paper “Keeping Walls Dry,” by Dale Kerr P. Eng begins: “Water is the most significant factor in the deterioration of buildings.” His paper draws on several Canadian studies commissioned by Canada Mortgage and Housing Corp. over the past decade that examine common causes of building failures. Contributing factors to moisture problems in buildings are reported as being lack of sufficient detailing, lack of inspection during construction, and lack of understanding of basic building science. The paper states that 90 percent of the problems investigated in the largest of the studies were related to interface details between wall components and penetrations, and only 10 percent were related to the basic wall assembly. The paper includes a table that itemizes in more detail the exact causes of these failures, which can be distilled down to three things: the complete absence of sealant joints, poor flashing, and poor installation. Unfortunately, there is no statistic offered showing what the percentage is of buildings without significant leakage problems vs. otherwise.
Unlike the vague, unpersuasive durability guidelines in LEED and Green Globes, Lstiburek provides clear, actionable items that design teams can implement to increase a building’s durability and service life. In the tables provided, the guesswork is removed, service life estimates for building elements is provided based on building science and historical data. The author even suggests how green building rating systems can incorporate the contents of the paper in developing a scientifically sound, simple to use credit for building durability.
How long must a building exist before it can be labeled “durable?” According to “Survey on Actual Service Lives for North American Buildings,” a paper by Jennifer O’Connor, research scientist for Forintek Canada Corp., service lives of most buildings are probably far shorter than their theoretical maximum lives. The paper surveyed 227 buildings demolished from 2002-2003 in the city of Minneapolis/St Paul. Of these, 105 were non-residential with structural systems of wood, steel and concrete, and a wide variety of cladding and fenestration systems. The vast majority of buildings in the survey fell into just three categories of reasons for demolition: area redevelopment (34 percent), lack of maintenance (24 percent), and building no longer suitable for intended use (22 percent). Of the non-residential buildings, more than half were demolished within 50 years.
Wood buildings in the study had the longest life spans, the majority having survived for more than 75 years. More than half of all the demolished concrete buildings fell into the 26 to 50 year category. The paper concludes that the assumption that designing for durability is an environmental imperative is unsupported in the absence of life cycle assessment and accurate lifespan predictions. It suggests that: “Rather than attempt to predict the future and design permanent structures with an infinite lifespan, we are probably better off in acknowledging our inability to make such predictions and instead design for easy adaptation and material recovery.”
It is obvious that strict adherence to current green building durability requirements will do very little to ensure a building’s durability and increased service life. Giving points away for describing the project’s micro climate, “enhancing” a quality management program, and arbitrarily establishing “quality control” strategies are not likely to have any real impact on a building’s durability. The information presented in O’Conner’s paper begs the question “how long is long enough?” It is clear from her research that efforts in designing 100-year-old buildings are wasted if useful lives of common buildings are actually limited to something much less. Lstiburek and Kerr bring much needed building science and historical building failure evidence into the picture, providing proper focus in developing appropriate durability measures.
Current green building rating system credits have the beginnings of what could, with a little tweaking, evolve into a meaningful, easily understood and implemented set of requirements. In addition to adopting Lstiburek’s recommendations and guidelines for water, heat, ultraviolet radiation and insects, consensus-based testing, and inspection standards and guidelines should also be incorporated. Designing metal flashings in accordance with the SMACNA Architectural Sheet Metal Manual, installing vapor retarders under slabs on grade in accordance with ASTM E1745, and requiring inspection in accordance with NIBS Guideline 3-2006 Annex M.2 for Joint Sealants Checklist are examples of the things that these credits must include to be meaningful and effective. W&C