Wasting Energy or Catching Fire
Builders nationwide are installing more and more home fire sprinkler systems. Often the motivation for installation is the requirement in the 2009 International Residential Code (IRC) for automatic fire sprinkler systems in townhomes and one- and two-family dwellings. According to this code, the sprinkler system must be installed in accordance with IRC Section P2904 or the National Fire Protection Association (NFPA) Standard 13D, "Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes." While the value of sprinklers remains a contentious issue, the reality is that sprinklers are currently being installed and will continue to play some role in construction. Therefore, builders and contractors need to be aware of the implications that sprinklers have for the thermal building envelope. And they need to know how to install sprinklers to maximize occupant safety and building performance.
In the Field
As a green-building verifier who inspects single-family detached and attached, multifamily, and light commercial buildings, I often find sprinkler systems installed in my projects. In the southeastern United States, residential sprinkler systems tend to be limited to multifamily projects. Recently I was performing an Energy Star predrywall inspection on a multifamily building that raised some concerns regarding ceiling-mounted sprinklers and the building envelope. An effective building envelope requires a complete and continuous thermal barrier (insulation) and air barrier (drywall, oriented strand board, plywood, or another air-impervious material). Whenever the thermal and air barrier diverge, or one is missing altogether, a thermal bypass occurs. For an insulated ceiling to perform adequately, the insulation must be in contact with the air barrier—in this case, the drywall.
During my inspections, I've found that wherever there were ceiling-mounted sprinklers, there was also a thermal bypass where the sprinkler pipe prevented the insulation from meeting the drywall air barrier. Often when I ask builders about this, they simply say, "This is what the code official wants." After pondering the situation for a while, I decided to dig deeper.
IRC Section P2904 makes no mention of insulation, although chapter 26 does reference general plumbing requirements. In chapter 26, it states that plumbing pipes are not allowed in any locations of the home that are subjected to freezing temperatures unless "adequate provision is made to protect [them] from freezing by insulation or heat or both" (P2603.6). In addition, Section P2904 contains requirements for the temperature rating of sprinklers, but it provides no guidance on how to maintain acceptable temperature ranges around the system.
Common practice is to run the sprinkler pipes above the ceiling joists and cover the pipes with kraft-faced batts. In some municipalities, including much of Georgia, where I live, polyethylene is installed across the tops of the ceiling joists and the insulation is installed above the poly (see photo to left). This is commonly referred to as tenting. Insulation is installed above the pipes, creating an air space the depth of the ceiling joists. The goal is for the air space to remain close to the house temperature, which prevents the sprinkler from freezing. As heat moves through the drywall, it warms the uninsulated air cavity below the insulation.
Since the poly is not installed to act as an effective air barrier, I suspect that much of the heat in the air space is lost to the attic. Luckily for the sprinkler pipe, the heat transfer through the drywall offsets that loss to the attic. I have yet to see field data showing how warm the air cavity space is relative to the attic, though it's obvious that the design works, and it is used frequently around the country. From a building science standpoint, there is a risk of condensation forming on the underside of the polyethylene when moist air moves through drywall penetrations, such as the sprinkler heads, during the heating season. Condensation may also form on the topside of the poly in the cooling season if the poly is brought below the dew point of the attic air.
What Does the Code Say?
Sprinklers may be independent, stand-alone systems, or the sprinkler pipes may be combined with the potable-water distribution system. Antifreeze solutions are commonly used for stand-alone systems, but they cannot be used in combined systems, which must therefore be insulated. As noted above, the 2009 IRC provides little guidance on insulating sprinkler systems. For details on insulating pipes, you must look to NFPA Standard 13D. Section A.8.3.1 states that "in areas subject to freezing, care should be taken in unheated attic spaces to cover sprinkler piping completely with insulation." Sprinkler pipes may be run above, run through, or notched below ceiling joists (see Figures 1 and 2). One option is for the sprinkler insulation to fill the cavity and completely surround the pipe. Another alternative is to install the sprinkler pipe below the joists and fully cover the pipe with insulation. NFPA does specify that insulation should be installed following the manufacturer's guidelines and notes that compression reduces the R-value of insulation.
What Do Installers Think?
Now we see that insulating above and below the sprinkler pipe is acceptable by NFPA and IRC, but what do the installers think? I decided to ask Mark Coad, director at Residential Design, LLC. Mark installed sprinkler systems for over 20 years, and his company now designs systems for buildings nationwide. Mark explained that "tenting of sprinkler pipes in attics became more popular in the last two years after the flammability of improperly mixed antifreeze solutions became an issue." Tenting is also recommended by PEX manufacturers "so that the sprinkler system and domestic drinking water systems can be combined," which helps to reduce the overall system costs. NFPA has yet to adopt the new process, though it will probably do so in the future.
Although the code shows sprinkler pipes fully encapsulated with insulation as an acceptable means of freeze protection, Mark is not convinced. Since the water in the sprinkler pipes is not moving, unlike other plumbing runs in a home, surrounding the pipe in insulation is not typically enough to keep it from freezing, except in the most temperate climates. Yes, there is an energy penalty associated with tenting, but it gets the job done and prevents home damage from pipes bursting. So what are the other options?
Mark explained that occasionally builders use furr-downs or soffits to bring the sprinkler pipes within the building envelope. This is commonly specified as a method of bringing HVAC ductwork inside the building envelope—the drawbacks being cost and aesthetics. Another option is to use sidewall sprinklers on the upper floors; these sprinklers are run in interior walls. Ceiling pendant sprinklers can then be used on the lower floors. Here the primary concern is aesthetics. Concealed flat-plate sprinklers are common for ceilings and have recently become available for sidewall applications. And finally, dedicated sprinkler systems with an antifreezing agent may be used, but these tend to be more expensive, and there have been reports of faulty installation in the past.
Read about NFPA Standard 13D.
Recommendations for Delivering Safety and Energy Efficiency
I first looked at this issue through the lens of energy conservation, believing that there must be a way to install sprinklers without compromising building performance. After talking to Mark, I now see that sprinklers and ductwork are actually quite similar. In both cases, you want to bring the equipment within the building envelope. Ideally sprinklers should be installed in dropped soffits or interior walls and floors. Ductwork is run in unconditioned attics and crawl spaces because this method is cheap and contractors are familiar with it. The primary drivers for tenting are contractor familiarity, affordability, and aesthetics. Clearly there are numerous benefits to sprinkler systems, but let's make sure they don't diminish energy performance.
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