To apply the knowledge gained by the misfortune of others and past test results, a consultant with significant experience contributing to the design team is a good beginning. He or she typically provides an evaluation of historical meteorological records to establish the exterior microclimate. These results would then be combined with an experience-based measure of ice and snow accumulations on all exterior surfaces, in the context of the overall façade. Once an estimation of potential is created, this result is expressed in terms of a relative frequency of occurrence and severity of potential hazard.
To place judgment on the result, a project-specific criterion is developed to assess if the predicted results are acceptable. This last point brings light to a significant issue with which designers struggle in the absence of prescribed building code regulations. What is an acceptable result with respect to falling, sliding, or windblown ice and snow from a building? Should a design be evaluated by the size of ice pieces that could fall? Or should the criterion be focused on snow depth and density similar to snow load criteria? Could a light snowfall create a significant hazard on a particular building geometry? (The answer is, invariably, “Yes.”) Or should the criterion focus on other buildings in the region to set the standard? Currently, there is no defined decision or guidance from building codes to answer this question.
Choosing a path
To address concerns or predicted potential hazards from ice and snow, the mediation options are generally expressed in one of three categories.
Design modifications
This category is relatively self-explanatory—recommendations to modify specific details of a building design are made. This is the most cost-effective means to reduce risk and can often mitigate issues with small-scale modifications not having a significant impact on esthetics.
Examples can include:
- shape of parapet caps or roof edges;
- form of solar shading devices;
- mullions; and
- other curtain wall details.
Another example is in reference to larger building forms that, with slight modifications of shape, size, or location (e.g. mechanical penthouses) can reduce problematic ice or snow formations.
Mitigation measures
This category comprises various measures of which some are off-the-shelf products, and others are project-specific strategies created to match the individual building design. The most common of these are snow guards or cleats that can reduce falling snow, or the use of heat trace to remove melt water and reduce ice and icicle formations.
However, it has been shown time and time again if items such as snow guards or heat trace are incorrectly used or installed, they can actually create more severe conditions—therefore, expert advice is prudent. Regarding esthetics, the integration of mitigation measures directly into the design is often desirable. This type of solution requires the implementation of ice and snow strategies early in the design stages.
Operational protocol
This last category has two aspects to it. First, it is important to understand the potential for hazardous ice and snow can be reduced, but not eliminated. Therefore, the need to monitor and inspect a building during the winter season is always recommended. This process is best conveyed via the development of ‘winter operational protocols’ that can be provided to building operators upon completion of a building.
A comprehensive protocol can be both proactive as well as reactive, prescribing:
- aspects of potentially problematic weather forecasts;
- locations on the building for observation; and
- building specific interactions with weather conditions for early identification of problematic snow or ice formations.
This becomes an excellent way for the design team to convey to the owner how the building is expected to perform in the winter season.
Photo © Gregory Johnston/Dreamstime.com
Second, the extent of mitigation or design modifications incorporated into the design can neither eliminate all potential hazards nor anticipate all extreme, severe, or unusual weather events. Additionally, the mitigation of falling ice and snow hazards is designed for more typical winter weather conditions and not tailored to these extreme weather events. Therefore, developing a winter operational protocol can further convey to the owner what actions to take before, during, and after these events to maintain a safe operating condition for the completed building.
Moving forward
Once a mitigation strategy has been developed and accepted by a design team, and the respective drawing details have been sketched up, typically one of two avenues toward a final design becomes evident. Either:
- the design team is satisfied with the anticipated performance of the design modifications and mitigation measures; or
- further validation and optimization is required.
Validating and optimizing modifications or mitigation measures typically occurs in a cold-room laboratory using full-scale, thermally correct mockups of the façade that can be manipulated for fine-tuning. A cold room is a controlled environment where a test assembly can be put through warm and cold cycles, and bombarded with ice, snow, sleet, and wind in various combinations to learn key performance aspects of the assembly.
It is the authors’ hope this article has created awareness over the potential issue of falling ice and snow from buildings, along with the significant influence the industry trends of technology and energy reduction are having on façade performance. It is also our hope design professionals become more aware of the experts available with direct experience who can review proposed building designs and identify early in the process possible concerns, and then bring a best practice approach to reduce risk. The application and documentation of industry best practices, during design or immediately after an incident, is an excellent way to demonstrate due diligence with respect to falling ice and snow.
Mike Carter, CET, is a director and the lead technical consultant of Northern Microclimate, an architectural consulting firm that focuses on the prediction, evaluation, and mitigation of falling ice and snow. A member of the Council on Tall Buildings and Urban Habitat (CTBUH), he has 16 years of experience assessing the performance of the built environment with respect to the exterior microclimate, specifically in relation to cold climates. Carter gained this experience by conducting a significant number of scale model wind tunnel studies, water flume snow simulations, and full-scale laboratory and in-the-field research projects over his career. He has consulted on projects throughout the world, ranging from hospitals, sport stadiums, and museums, to super-tall buildings and structures. Carter can be contacted at mike.carter@northernmicroclimate.com
Roman Stangl, CET, is a director and the lead project manager of Northern Microclimate. A CTBUH member with international experience, he has spent more than six years assessing issues that exist in the built environment and surrounding local microclimate, specifically in relation to cold climates. Stangl can be reached via e-mail at roman.stangl@northernmicroclimate.com.
