Get Ready for Winter Weather

Nov. 2, 2006
These winter-weather problems won’t affect your facility if you take appropriate action

The weather outside might be frightful, but you and your team don’t have to be afraid. Winter conditions can cause serious damage to the exterior and interior of any commercial building (see the examples below of buildings in Denver and Minneapolis if you’re in doubt); however, if you prepare your facilities for freezing temperatures, snow, and ice, you can face November, December, January, and February with confidence ...

“There is a notorious building in Denver (the Wells Fargo Center) - it has two quarter-circles on top with a straight piece in between. Right after it was built, snow started to build up on the lower quarter-circle (there was a 3-foot-wide gutter at the bottom). As snow started sliding down, it missed the gutter; there was a huge mass of ice and snow falling to ground level and hitting a glass atrium below,” says Tim Reinhold, Tampa, FL-based Institute for Business & Home Safety’s director of engineering and vice president. The building was refitted with glass using heating elements similar to a rear-window defroster on a car; there haven’t been any problems since then.

Minneapolis’ IDS Tower is another example. The building has a mechanical area set in about 40 stories high. During the first few winters of occupancy, building management noticed a problem: Ice was building up in the mechanical area and then dropping 40 stories down onto a U.S. highway. Adding heating elements and drains to the exterior of the building solved the problem.

Although these situations sound like reasons to panic (and they are), there were straightforward solutions applied to address both problems. And, while circumstances of this magnitude are atypical, year after year, winter conditions affect your facility, too - whether you realize it or not.

Who’s in Charge - You or the Weather?
Moisture is the No. 1 concern regarding snow/ice and how they affect commercial facilities. According to the Washington, D.C.-based U.S. Environmental Protection Agency (EPA), there are four primary methods for preventing snow from causing moisture problems in buildings: 1) sloped roofs (which are less likely to cause major moisture damage from snow as compared to flat roofs); 2) ground slope (surface water should quickly move away from the building instead of ponding next to it); 3) covered entries (exterior entries should prevent snow from being blown into the building); and 4) air intakes (a section of sloped intake plenum can be added to cause moisture to flow to the outside or to a drain). See the images below for more information about these methods. In addition to the EPA’s suggestions, there are other methods for addressing winter-related problems as well.

Problem: Ice dams (ridges of ice that form at the eaves of sloped roofs, trapping draining water and causing inward leakage water that can result in the formation of dangerous icicles) occur when the upper part of a roof is below 32 degrees F. and the warmth of the eave is above 32 degrees F. “[Ice dams] occur most often on roofs that aren’t vented or have minimal venting, have large eave overhangs, etc.,” says Greg Doelp, principal, Waltham, MA-based Simpson Gumpertz & Heger Inc. “[They] can contribute to leakage, cause physical damage due to weight or from falling ice, interfere with building egress, or cause other problems, depending on the environment and how severe the ice-damming problem is.”

Solution: Doelp emphasizes that proper roof design (venting the roof system so that the underside of the roof deck is at a uniform temperature, and eliminating or reducing the use of overhangs, for example) minimizes the formation of ice dams; so does keeping eaves free of leaves and debris, and keeping the roof free of snow (when possible). Roof design can reduce the effects of ice dams, too, by incorporating adequate membrane underlayment underneath sloped roofing systems, etc. Experts also recommend that facilities professionals check to make sure drains are not blocked (and that ice isn’t sealing them shut). “If you’ve got an isolated drain and you don’t have a way of keeping the ice melted in the area around it, the ice will bridge over the top. You won’t know that it stopped functioning, but it’s officially out of commission,” says Reinhold. Doelp agrees: “Building owners should inspect their drains, gutters, and downspouts to make sure they’re clear and free-flowing before the snow and ice hits. If you’ve got leaking gutters and they’re dripping onto a sidewalk below, an unnoticeable ice patch will form on the sidewalk after it refreezes at night.”

Problem: Stephen Condren, senior project manager at Waltham, MA-based Simpson Gumpertz & Heger Inc., points out that, in older buildings with protruding architectural features made out of stone or cast concrete, freeze-thaw conditions can weaken those features. These types of conditions also affect buildings with exterior shelves or protrusions, especially if the external pieces allow ice to form following a period of partial thaw.

Solution: “It’s a good idea for the building owner to inspect the building and make sure that those pieces aren’t loose and ready to fall off. Freeze-thaw in stone and concrete will deteriorate it and break it apart,” says Condren. Ice and snow melts and drips off the building during the day as temperatures rise; the dripping continues at night when things freeze again. “If you have a building entry point with this potential hazard, you may want to look into providing something to protect [tenants and occupants] so that they’re not likely to be struck by something falling from the building.” If there are parts of your building that don’t have good drainage and flashing, those systems will be exposed to freeze-thaw damage as well.

Problem: Correctly built roofs are designed to endure snow and ice loads in terms of pounds per square foot (based upon the expected frequency and severity of snowstorms in the area, the type of the structure, safety risks, etc.). But, when that load is exceeded by the presence of heavy/wet snow and ice, intense vertical loads are placed on the roofing system, causing permanent sagging or drooping and allowing for water leakage. Vertical loading can affect horizontal forces as well, making exterior walls shift slightly outward. According to Reinhold, glass skylights (particularly sawtooth skylights) can also contribute, allowing for the possibility of additional snow build-up. “Eventually, that snow and ice will slide off and leave a huge lump of ice and snow sitting on your roof that will add to the chances of water leakage,” says Reinhold. Many commercial roofs are also topped with HVAC equipment, vent pipes, and other elements, combining to make the roof especially vulnerable to water intrusion as a result of snow and ice.

Solution: To aid in the maintenance of your roof in the wintertime, repeat these four words: “Know your snow load.” When roof loads are below their actual load capacity, any sagging or deflection that occurs will disappear after the load is removed and probably won’t be visible. When the loading exceeds the design loads, however, the sagging and deflections become permanent. In severe cases, the roof collapses under the excess weight. To prevent this, do some research to find out what your roofing system’s snow load is and then find out if it’s up to code (if it’s not, it needs to be). Reinhold explains that heat tracing is also a viable option to control snow and ice on commercial buildings with flat surfaces (particularly at higher levels). Heat tracing looks like electrical wire, but the filaments inside are a certain distance apart with a material around them that heats up as energy is applied to them.

Problem: High winds can cause icicles, snow, and pieces of ice collecting in windowsills and other crevices to be blown off (especially on taller buildings). At high elevations, it can also cause snow and ice accumulation on a flat roof to be lifted off and thrown downward.

Solution: Install a flashing system with an angle to it; that way, the snow and ice will drain off instead of building up and blowing off. In future new construction and renovation projects, look for curtainwall systems that create more of a “flush” façade to rule out this situation.

Problem: To compensate for colder, drier air, facilities professionals often increase humidity levels for comfort. “If the building envelope hasn’t been designed to handle increased humidity - when you get a temperature gradient across your envelope - whether it be at your roof, your window, or your wall, you will also have a moisture gradient. You’ve got moisture in gaseous form trying to diffuse from the inside to the outside; if it gets into the building envelope and starts to condense, you can accumulate water, which will further reduce insulating properties of the wall and cause potential mold issues and concealed corrosion of wall components. If enough of it accumulates, you start to actually freeze and damage some of your wall and window components,” says Condren.

Solution: Make sure that your building envelope can handle the increased humidity levels. Condren emphasizes that this problem occurs primarily when new tenants take over a building, or when a building is renovated for a new purpose (and the building envelope’s capabilities weren’t taken into consideration). According to the U.S. EPA, water vapor in the indoor air can condense onto cold surfaces (windows, walls, and the underside of roof decks) during the winter season. The organization recommends that windows and doors with frames and spacers around edges (that also have thermal breaks) be used when possible.

“If you’ve got a systematic problem that’s occurring over and over again, look for a design solution to get rid of the problem so that you’re not having to do something every day or every month to try to keep on top of it,” recommends Reinhold. “For example, when we found that ice and snow were building up in the windowsills of a high-rise building, the solution was pretty simple - a different kind of flashing system with an angle to it was installed so that snow and ice would drain off and not build up.” He emphasizes that there are usually fairly simple solutions if a recurring problem exists; the other part of the solution is maintenance (taking the necessary steps to minimize the effects of snow and ice before, during, and after each snowfall).

Your INDOOR To-Do List
Ensuring that heating equipment functions properly can reduce heating costs by 5 percent (and by much more if major problems are found and addressed as a result of a pre-winter-weather inspection). Use this list to begin winterizing your building’s interior:

  • Inspect heating ducts and seal any leaks (direct leaks in duct systems can result in large heat losses).
  • Check air filters throughout the building (dirty or clogged air filters reduce air flow, increasing the energy use required for heating).
  • Calibrate thermostats to ensure that they are functioning properly. Otherwise, the heating system receives the wrong signals regarding when to start and stop.
  • Educate occupants about electric space heaters and provide an alternative to address comfort and work-environment complaints. Discomfort is often an indication of broader heating-system failure; addressing these larger problems is more efficient than having individual space heaters.
  • Encourage occupants near windows to open shades or blinds on sunny days to take advantage of natural heat and reduce the burden on the heating system.
  • Fully insulate all cold-water pipes and fittings, and condensate drain pipes, with appropriate insulation. Fully insulate all cold refrigerant lines similar to cold-water pipes.
  • Fully insulate cold-air supply ducts.

Your OUTDOOR To-Do List
One of the primary causes of indoor moisture is poor control of snow and ice. Use this list to begin winterizing your building’s exterior:

  • Check all rooftop penetrations regularly from inside and out.
  • Confirm the condition of the flashings around skylights, stack vents, and other rooftop elements.
  • Ensure that operable windows shut and lock tightly.
  • Inspect weather-stripping elements.
  • Look for “fogged” windows, indicating a seal failure.
  • Inspect window joints and flashings on the exterior for continuous seal integrity. If the windows are part of a drainable wall system, check to ensure that flashing opening and weep holes are not clogged.
  • Make sure that drains are not blocked (and that ice isn't sealing them shut). If ice does tend to bridge over drains, look for a design solution (installing heat tracing to keep the area free of ice, for example). Infrared lights can also be useful

Precipitation Control
There are four primary methods to prevent snow from causing moisture problems in buildings: 1) sloped roofs, 2) ground slope, 3) covered entries, and 4) air intakes. Problems in these areas generally allow moisture to leak or be blown into the building.

1. Sloped Roofs. Over the life of a building, sloped roofs are less likely to cause major moisture damage from snow as compared to flat roofs. The resulting space under a sloped roof can be used for HVAC equipment and ductwork, and other mechanical and electrical equipment. Catwalks will allow year-round access to the equipment for easier and more-timely maintenance.

2. Ground Slope. Ensure that the ground next to the building slopes away from the foundation. This is a well-understood design practice, yet sometimes a newly finished building has surface water ponding next to the building instead of quickly moving away from it.

3. Covered Entries. Ensure that exterior entries have sufficient overhang to prevent snow from being blown into the building or large amounts of moisture collecting directly in front of the entry where it can be tracked into the building.

4. Air Intakes. Consider adding a section of sloped intake plenum that causes moisture to flow to the outside or to a drain if intake grilles are not designed to completely eliminate snow intake.

Leah B. Garris ([email protected]) is senior associate editor at Buildings magazine.

Precipitation Control
There are four primary methods to prevent snow from causing moisture problems in buildings: 1) sloped roofs, 2) ground slope, 3) covered entries, and 4) air intakes. Problems in these areas generally allow moisture to leak or be blown into the building.

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