Curbing Sprinkler System Water Damage

By Scott A. Futrell

Weather-related water damage due to automatic sprinkler systems may be preventable. Sprinkler systems may be our best choice in the struggle between fire, life safety and property protection, but water damage, happening on, or shortly after, a cold winter day, can be very expensive for property owners and occupants and need not involve a fire.

A number of factors can contribute to a large, weather-related water damage loss. These include the building enclosure, some of the building's mechanical systems, the homeowner or occupant, the sprinkler system design and installation and the choices made by the design team (architect, fire protection engineer, mechanical engineer, design/build general contractor). Any one of these variables, alone or in combination, may lead to a large water damage loss.

This article does not discuss manufacturing or fabrication problems or the installation mistakes that are possible with sprinkler systems and their components. Those can also contribute to or facilitate a loss, especially if some of the other factors are present.

Weather

Any time temperatures are below 40 F (4 C) and water is present, the weather can become a factor, because the possibility of freezing exists. The length of exposure to these temperatures, the chemical content or makeup of the water and whether the water is moving or not are some factors that affect the potential for freezing. As air temperature goes down and wind speed picks up, the potential for freezing increases significantly. Temperatures below -20 F (-29 C) are not uncommon between November and February in many parts of the northern United States and Canada. Actual air temperature extremes - not to be confused with wind-chill temperatures - can go below -40 F (-40 C). If the design of a building and its sprinkler system are not based on these minimum temperatures, and if the designers and installers of the sprinkler system, the building enclosure and the insulation are not appropriately protecting water-filled pipes (steel or plastic), then there is a high probability that a water loss will occur sometime during the life of that building.

Building enclosure

The integrity of the building enclosure is another factor. Air filtration due to the wind or a negative mechanical air flow design, the use of permeable building materials or cold penetration through unsealed exterior openings are some of the possible avenues for cold air to reach water-filled piping. Some exterior materials (stucco, for example) provide a better seal to air infiltration than bricks or concrete blocks. Caulking all exterior penetrations seals the penetrations from air infiltration as long as the caulk remains viable. Using a foam spray-on insulation on rim joists may produce a much better seal against air infiltration than do batt-type fiberglass or blown-in insulation.

Mechanical equipment

The design and installation of mechanical systems and equipment such as those for heating and ventilating can be a factor. These systems are often designed so that buildings are operating with a neutral or slightly negative airflow, meaning that a small amount of outside air is being drawn into the area or building. This negative airflow includes the air intake for the furnace or other heating equipment, and it can increase as kitchen and bathroom exhaust fans are used. The furnace intake air pipe alone can bring cold air into the building envelope every time the furnace operates. If water-filled pipes are located in close proximity to these air intakes, the possibility of water freezing increases.

Improperly sealed openings, cracks in the exterior enclosure or porous building materials can not only allow wind driven cold air into the building but can also increase the flow of cold air drawn in by the negative mechanical system design. In large buildings, the balancing or incorrect balancing of mechanical systems can also contribute to the negative airflow. Cold air being blown by the wind or drawn in by negative system design or exhaust fans, or by a combination of these factors, will seek the area of least resistance. If a water-filled pipe is in its path (even in a ceiling or floor space that has been blown full of insulation but not sealed from the exterior exposure) that cold air will eventually freeze the water.

Homeowner or occupant

The homeowner or occupant must be sure to perform necessary inspections, testing and maintenance on systems. For water-filled sprinkler systems, the required inspection, testing and maintenance is minimal (as compared to dry sprinkler systems or antifreeze solution-filled sprinkler systems). If water-filled pipes are near exterior walls or in an attic, the integrity of the barrier (insulation, caulking, vapor barrier) necessary to protect the piping, which is subject to freezing temperatures and to the warmth of the occupied spaces, must be maintained for the life of the building. The integrity of enclosures built around sprinkler piping must be maintained over the life of the building, as must any plastic, foam or caulk that is included in the enclosure.

The minimum air temperature that the building was designed for must be maintained throughout every nook and cranny where a sprinkler system or domestic water pipe might be installed. An occupant who chooses to set the thermostat back (to 55 F (12 C), for example) for a period of time needs to realize that this will be the air temperature at or near the thermostat, not throughout the building. Exterior locations or concealed locations may be significantly colder; if the air temperature is low and any of the previously indicated air infiltration events occur, if insulation isn't the proper depth, and if it's windy, water within the sprinkler system components may freeze.

Sprinkler system

Water-filled sprinkler piping installed in the insulation in unheated spaces, either between floors or in the attic, is insulated from the heat of the building. If these pipes are combined with dry type sprinklers in the insulation that protrude through building walls to the exterior, the pipe and components are insulated from the heat, but are potentially exposed to cold temperatures and wind. Any combination that allows the rate of the heat loss to exceed the rate of replenishment of the heat, the transfer of cold temperatures through the pipe or the infiltration of cold if the enclosure is not tight, can lead to freezing and water damage. Sprinkler piping designed or installed in close proximity to exterior walls, in any combination of these factors may increase the possibility of water-filled piping freezing during extreme weather conditions.

Design team

The choices made by the design team during the building design can reduce or increase the probability of water-filled pipes freezing. For example, eliminating sprinklers in combustible concealed spaces by filling those spaces with non-combustible insulation in accordance with the National Fire Protection Association Standard 13, <I>Standard for the Installation of Sprinkler Systems<I>, may reduce sprinkler system costs. However, this choice may not ensure that adequate heat will be available for any water-filled piping installed in those insulated spaces and may increase the possibility of freezing the piping. Additional choices include the design of the mechanical systems and the location of thermostats, heat vents and return air grilles.

In buildings of combustible construction, where the ceiling space of tuck-under garages (that is actually the floor space for the occupied floor above the garage) is used for sprinkler or domestic piping, the garage must be heated to avoid or minimize the possibility of the water freezing. Other design team choices relative to sprinkler piping include the location of dryer vents and intake air ducts for fireplaces and furnaces and the location and size of soffits near exterior walls. All of these have the potential for combining with water-filled pipes and contributing to the freezing of the water.

Ice plugs

The freezing of water does not always lead to a failure of the sprinklers, pipe or fittings. The probabilities are fairly good that, when the water freezes, it will cause a component failure; the chance of failure increases as temperatures decrease and the time that the component is exposed to freezing conditions increases. Another type of failure is the formation of ice plugs. Ice plugs form in wet and dry sprinkler systems when water or moisture freezes, but the freezing does not break the pipe or fittings. Ice has been found, documented and removed from pipes with no apparent physical damage to components. An ice plug in a sprinkler pipe during a fire is not a desirable situation; the ice itself becomes a detriment to the operation of the sprinkler system.

Conclusion

Many factors can lead to water damage from the failure of a sprinkler or domestic water system caused by the cold weather. To minimize the potential, close coordination and significantly better communication is necessary from building design concept through construction and beyond. This coordination and communication is not one way. It has to include the design team, the general contractor, the insulation contractor, the mechanical contractor and the sprinkler contractor. Ultimately, owners and occupants need to be brought into this too. The design team should supply them with information regarding minimum temperature settings and the relation of those settings to actual temperatures throughout the interior of the building.

Scott A. Futrell, PE, SET is a fire protection consultant with Futrell Fire Consult & Design Inc., in Osseo, Minnesota. He has more than 30 years experience designing, specifying and investigating fire protection systems. He is a co-author of "Designers Guide to Automatic Sprinkler Systems," available from the Society of Fire Protection Engineers and can be reached by e-mail at scottf@ffcdi.com or by visiting www.ffdci.com.