WEB EXCLUSIVE: Assessing the Potential Effects of Climate Change on High-Rise Residential Buildings
Traditionally, building design has relied to a considerable extent on historic climate data accumulated over time to provide design criteria for everything in buildings including structural systems, cladding and windows, site drainage and HVAC systems. There are indications, however, that our climate is beginning to change. Putting aside for a moment what may be the cause, if our climate is actually changing as many experts believe, this historic data may no longer best represent future environmental conditions over the service life of buildings.
Over the next 40 years, if buildings do experience increases in environmental loads (temperature, relative humidity, rainfall, snowfall, wind pressures, and UV radiation), in addition to changing the design criteria, these changes could have a significant impact on our building stock. Obviously these issues are of interest to design professionals.
Engineers Canada and the Public Infrastructure Engineering Vulnerability Committee (PIEVC) have been overseeing the execution of climate change (CC) vulnerability assessments on four key public asset categories. (In addition to public buildings PIEVC is also accessing transportation assets, storm/waste water treatment/collection systems, and water resource systems.) Using a case study on a sample building as a model, this article discusses the five-step protocol used to assess the effects of CC on buildings highlighting some of the components that may be prone to CC risk.
The CC assessment protocol established by PIEVC includes rigorous review of the climatic parameters that are expected to change in the next 40 years, along with assessments of the impact changes may have on buildings.
Protocols include determining the most important building components, identifying the CC parameters and values, probability of occurrence, and a risk assessment (RA). In most cases recommendations on specific building systems as well as on their operations and maintenance can then be derived.
Step 1 – Project Definition: This step develops a description of the building including location, infrastructure detail, historical climate loads, age, and other relevant factors. The project definitions stage includes developing a component inventory, a time horizon (40 to 50 years), relevant climate parameters, climate baseline and determination of the cumulative effects of CC.
Step 2 – Data Collection: Includes identification of building components to be assessed and climate factors to be considered. The CC projection information is derived from a variety of sources, including the Canadian CC scenarios web site and peer-reviewed studies with results applicable to Ontario cities. www.cccsn.ca
Components are typically sorted by major building systems and then into sub-systems generally grouped under the following headings: Site, Structure, Building Envelope, Mechanical HVAC, Plumbing and Drainage, Electrical, Elevator, Life Safety, and Finishes.
Step 3 – Risk Assessment (RA): This step involves identifying those components that may be vulnerable to CC. If insufficient data exists on the level of risk or expected performance, recommendations for research or other action may to be given.
The RA involves identifying how vulnerable building components may be to CC and the consequence on a particular building component based on specific aspects of CC. Independent assessment of the likelihood of occurrence of climate event(s) enables determination of an overall risk rating.
Step 4 – Engineering Analysis: Some RA’s may require analysis of various CC impact scenarios to determine the level of vulnerability.
Step 5 – Recommendations and Conclusions: Based on the results of Steps 1 to 4, recommendations may be required, including: action to upgrade the infrastructure; management action to accommodate changes to building capacity; performance monitoring and/or recommendations for additional research and analysis. In some cases no action may be required.
After completion of steps 1 to 4, a preliminary analysis suggested that the notable building components determined to be at “Medium Risk” to the impact of CC included:
- Building Envelope, particularly with respect to moisture management and heat/cooling losses;
- Mechanical drainage systems at risk of inducing flooding;
- Emergency electrical supply systems associated with capacity to deal with power outages;
- Note that the grounds and site were deemed to be at risk however they are addressed by other studies commissioned by PIEVC.
Overview of Case Study Building
The building that was the focus of this CC assessment was one of approximately 2,000 high-rise residential towers, many of which were constructed during Canada’s remarkable building boom that corresponded to rapid urbanization of the early ‘60s and ‘70s.
The skill and effort that was involved was nothing short of remarkable and with various improvements in construction techniques and technologies, construction workers were able to put an average of 40,000 apartment units on the market ever year. These buildings were the subject of a well-known project that developed what is known as the Tower Renewal Guidelines (http://www.daniels.utoronto.ca/trg).
The rigid exterior masonry walls of these structures offer an excellent substrate for the support of “overcladding” systems, and combined with other energy saving measures can cut the total energy requirements by one half and substantially reduce carbon emissions. However when they were designed and built 50 years ago, southern Ontario was an entirely different design and construction environment from what we see today.
Energy consumption was not a priority and speed of construction was considered an important factor. It’s also important to consider that the construction materials and building systems were quite different from what we see today. There have been incredible advances and innovations in just about every aspect of building design, construction and maintenance.
Our expectations of the built environment have also evolved. For example, the majority of these buildings were constructed without central air-conditioning and most had minimal insulation. However the basic framework of most of these structures are so incredibly well-built it and robust in nature that it has been suggested that the “armature”, or concrete structural elements have the service life of over 300 years – if properly protected by renewable façades*.
The solid exterior masonry walls of these structures offer an excellent substrate for the support of renewable façades systems and combined with other energy saving measures can cut the total energy requirements by one half.
The term “overcladding” refers to the installation of a new thermally effective “skin” over the existing façade of a building. Typically a full-scale overcladding project involves replacing the windows, and because of the energy demand reduction the buildings HVAC systems can be replaced and downsized.
Advantages of overcladding include:
- Overcladding is more financially and ecologically reasonable than demolition and reconstruction;
- Work can be carried out while the building is still in use with minimal impact on occupancy and with limited disruption to the fabric of the building;
- Improves energy efficiency, thermal performance & air tightness;
- Optimizes use of thermal mass & enables transfer of the dew point outside the structural wall element;
- Increases the life expectancy of the building;
news aging facades and improves appearance of structures;
- Lowers maintenance costs and allows upgrading of building services;
- Improves air quality, sound insulation and general comfort levels;
- Helps eliminate internal problems such as condensation and mould.
The application of thermal overcladding has been accomplished in over 15 countries in Europe with documented success. It is estimated that it would cost five or six times as much money in today’s economy to replace these buildings. It would also cost twice as much to demolish them and dispose of the materials as it did to construct them in the first place.
The successful models in Europe for projects of this nature also involved educating and interacting with both the tenants and property management with regard to health and safety issues and maintenance of what amounts to a “new built” construction.
Additional Research and Analysis
Canadian building codes do not currently incorporate values arising from CC prediction models. As predictive models are enhanced and reliability becomes more aligned with the empirical data, prediction data on environmental loads should be included in the climatological data available to designers. In addition, research is needed to develop the effects of combination loading involving environmental conditions.
At present, the success or failure of moisture control methods relies on competent design, quality of materials, resistance to deterioration, and installation practices. “Loads” for design for moisture control and applicable “resistance” factors similar to that routinely employed by structural designers may be a paradigm worth pursuing.
A properly executed overcladding project, which includes window replacement and downsizing of HVAC systems not only enables buildings to resist the impact of climate change but can also to extend the structures effective service life. In addition, projects of this nature can also modernize building services, improved indoor comfort and meet the expectations of the occupants.
Gerald R. Genge, a well-known building scientist, has directed over 3,000 investigations of building performance problems and completed over 2,000 design and construction review assignments. He also served as President of the Ontario Building Envelope Council and is a designated “Consulting Engineer” and “Building Design Specialist”. www.grgbuilding.com
Brian Burton has published a number of articles on overcladding technologies and climate change and he is now involved with the new start-up company that specializes in technical business writing and assists companies interested in selling goods and services to government: Award Bid Management Services. http://award-bid-management-services.com