Specifying drop-out ceilings beneath fire sprinklers
Fire protection engineers can specify ceilings beneath fire sprinklers, as identified in NFPA 13.
- Identify the various ways in which fire sprinklers can be suspended below a ceiling
- Learn about NFPA 13, the standard that identifies fire sprinkler installation
- Review the benefits, costs, and other issues associated with drop-out ceilings and fire sprinklers.
The very idea of suspending ceilings beneath automatic fire sprinklers sounds topsy-turvy. Sprinklers, the mind insists, must project into the space they protect so they can release their deluge without interference—even if it means cutting holes in ceiling panels and dropping pipes so sprinklers extend to the underside of the ceiling.
Yet at the same time, many designers yearn to unshackle sprinklers from ceilings. Surely, they intuit, there must be a way to:
- Simplify coordination of sprinkler and ceiling location
- Reduce sprinkler and ceiling installation costs
- Satisfy architectural concerns about the visual impact of sprinklers
- Get sprinklers out of occupied spaces where they can be damaged or difficult to clean.
One can, of course, simplify sprinkler and ceiling coordination by eliminating suspended ceilings and leaving the structure exposed. Ironically, this approach may not be the most economical if it adds the cost of painting overhead surfaces, exercising more care in locating the ducts, pipes, conduit, and other exposed-to-view services, and installing sound-absorbing materials to satisfy acoustical criteria. Plus, exposed services provide surfaces that collect dust and grime and may not be permitted in occupancies requiring hygienic conditions.
Another approach is to install sprinklers above a ceiling system with 70% minimum open area as permitted by NFPA 13: Standard for the Installation of Sprinkler Systems, 2016 edition, Paragraph 8.15.14. This still leaves the structure and services significantly exposed and presents many of the same drawbacks as having no ceiling. If the ceiling consists of egg crate, louver, or honeycomb panels, the ceiling can restrict the sideways travel of the sprinkler discharge. Lighting efficiency also is decreased because at least 70% of any light impinging on the ceiling from below is lost into the cavity above, and at least 30% of lumens from above-ceiling lamps are blocked if using a luminous ceiling scheme.
This article explores a third approach—drop-out ceilings. NFPA 13, Paragraph 3.3.9, defines a drop-out ceiling as:
A suspended ceiling system, which is installed below the sprinklers, with listed translucent or opaque panels that are heat-sensitive and fall from their setting when exposed to heat.
Drop-out ceiling systems have been in use since the development in the mid-20th century of modern suspended ceiling systems and suitable plastics. Most drop-out ceilings are made from either expanded polystyrene (EPS) foam or are thermoformed ceiling (TFC) panels. The thermal insulation properties of EPS make it useful in cold-storage facilities where they enable wet pipe fire sprinkler systems to be installed above rooms with freezing temperatures. EPS ceilings have many limitations, however, that have discouraged specifiers from considering drop-out ceilings in the past.
TFCs overcome these limitations, justifying a re-examination of drop-out ceilings. They are made from thermoformed vinyl just 0.013- or 0.030-in. thick. When exposed to sufficient heat, the vinyl panels soften, sag, and fall out of a standard metal ceiling grid. This exposes above-ceiling sprinklers to rising heat and allows sprinklers to activate without interference. The panels harden when they reach the relatively cooler floor and do not add meaningfully to the fuel load.
Cost and construction
Installing drop-out panels beneath sprinklers can be significantly less expensive than using mineral fiber panels with penetrating sprinklers. For example, drop-out ceilings eliminate the need to extend pipes from sprinkler mains to ceiling elevation. It becomes unnecessary to position sprinklers at panel centers; this means the layout of sprinklers can be optimized, shop drawings to coordinate sprinklers and ceiling installation can be eliminated, and less piping is required. Economical sprinklers styles can be used and decorative finishes, trim rings, and escutcheons can be eliminated. Ceiling installers do not have to cut holes for sprinklers. And sprinkler installers do not have to return to the project to adjust sprinkler locations after ceiling installation.
The affordability of any installation depends on the project conditions, products, and performance levels required. Thermoplastic panels, for example, are more affordable than high-performance and decorative mineral fiber panels and competitively priced with ordinary mineral fiber products.
While labor to install panels is similar regardless of material, cutting individual thermoformed panels for perimeter units may cost slightly more than scoring and breaking square-edged mineral fiber tiles and about the same as trimming tegular panels. However, waste will be reduced because thermoformed panels do not break easily during handling, as is common with mineral fiber panels. Thermoformed panels also nest compactly and several panels can be cut simultaneously with aviation snips.
As an example, an independent construction consultant prepared a detailed construction cost estimate comparing thermoformed and mineral-fiber ceiling panels for a 110,000-sq-ft office building in Oklahoma City. He investigated two scenarios and found that the drop-ceiling approach generated savings ranging from 72 cents to $3.29/sq ft, depending on the product selection. The estimate is based on open-shop wages, and savings are likely to be even greater in areas with prevailing wage rates.