Durable Building Technologies
Balancing Cost, Design Factors and Service Life of Components
Dec 23, 2008
Long life for a building implies a 50 to 99 year time frame. Design of building assemblies can technically accommodate this, but there is a problem: individual components may not be up to the task, and poor construction can undermine the best design intentions by resulting in moisture accumulation and degradation of building stock.
Building science engineers who are advocates of durable and energy efficient building design acknowledge designers face a dilemma with every building: do they design for the long term with quality building systems and flexible designs, or do they meet client demands to save money by building for the short to mid term?
Design Service Life
Most building designers consciously plan for a design service life, in response to a client’s specifications and cheque book. This service life, or period of time during which the building or any of its components performs without requiring repair and maintenance, varies depending on the quality of the design, components and construction.
A building designed with a longer service life is generally more costly than one designed with the least expensive components. Adhering to minimal building standards reduces not only the building’s cost but the longevity of the building envelope, which in turn may contribute to building failures.
Designers have to balance cost and service life design while meeting client expectations. Halsall Associates, a firm of engineers and consultants with expertise in Canadian building design, recommends designers work with Canadian building standard CSA-S478 to achieve this balance.
Improving Thermal Performance in Buildings
In North America, thermal storage continues to be inadequately addressed, with a consequent increase in the heating and cooling requirements of buildings. Given increasing concerns about climate change, many building scientists question an architectural preference for fully-glazed buildings. Even on a cold day, these buildings may require cooling.
Calculations of energy use in commercial buildings have demonstrated that air conditioning produces the largest amount of CO2, and is a major cost from an operational perspective. Heating is the second largest energy user, and hence green house gas generator, in a building. Exterior shading for windows helps improve thermal performance, but as studies of building failures demonstrate, components like external shutters do not always live up to the design service life specified for the building.
Here is the designer’s dilemma magnified: to compensate for the amount of glazing on a façade—the glazing usually being introduced as a design feature because of the sense of transparency glass conveys—external shutters are added. The shutters reduce overheating and glare, and may be fixed or operated manually. Over time, these shutters no longer function effectively, or users may leave them in the same position all the time, failing to capitalize on passive solar heat gain for heating purposes on a cold day.
Building Durability Plan
Adhering to CSA-S478 and developing a building durability plan are two methods for realizing sustainable buildings. A building durability plan calculates the predicted service life of the building assembly and the likelihood of failure. Shortcuts such as cheaper components or single layer moisture barriers are reflected in the plan by a shorter service life.
Engineers involved in architectural projects confront one final dilemma: designing for longer life and lower energy may not produce the kind of design architects and clients want. On the other hand, poorly designed and cheaper components that wear badly fail to retain their beauty; they can also lead to unhealthy and unsafe buildings. Multi-disciplinary collaboration between architects and engineers is required if today’s building stock is still going to be attractive and inhabitable for future generations.
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