By Mark R. Fowler
Published in the May 2006 issue of Today’s Facility Manager
No one type of ceiling is the answer to every set of facility management needs, especially when today’s ceiling products fall into one of three basic categories: suspended, furred, or direct contact. Each type has its own set of characteristic pros and cons, making it more difficult for facility professionals to decide what’s best for their interior spaces.
However, because of the significant access they offer, suspended ceilings are quite popular in the commercial market. They also feature large plenums which support HVAC ductwork and create flexibility for future remodels.
Suspended ceilings have a well established presence in commercial facilities, due to their excellent features and economic benefits. Because of these characteristics, they are the primary focus of this analysis.
Lath And Plaster
The oldest and most traditional type of suspended ceiling is lath and plaster. This construction provides a high level of abuse resistance along with a good life expectancy. Because plastering is no longer a common form of ceiling construction, it can prove to be one of the more expensive installation options. But along with the higher price point comes a greater degree of artistry; plaster suspended ceilings can be created in dome shapes or other unusual configurations.
The installation of a plaster suspended ceiling starts with hanger wires that are #8 gauge diameter galvanized, soft annealed steal wire; spacing is 4′ x 4′ for gypsum plaster and 3′ x 4′ for cement plaster. The hanger wires support main runners that are 11⁄2″ by 16 gauge cold rolled channels space 4′ on center; they should be galvanized or coated for exterior or humid conditions.
The main runners then support the furring channels that are wire tied and perpendicular to the main runners. Furring channels are 3⁄4″ by 16 gauge cold rolled channels; the type of lath will determine the spacing of the furring.
Generally, the spacing is 16″ on center for an expanded metal diamond lath weighing 3.4 pounds per square yard. Tie wire is 16 gauge or 18 gauge galvanized, soft annealed wire.
The plaster may be gypsum or Portland cement. Gypsum plaster offers good sound control, minimizes cracking, and provides enhanced fire ratings. Portland cement (often referred to as stucco) provides abuse resistance and is more appropriate for wet areas or those subject to high humidity.
This type of suspended ceiling is currently very popular. It provides good abuse resistance and produces a flat, seamless look at a reasonable cost. Access to the plenum area can be achieved through the installation of panels at various locations.
These systems can be generic or proprietary. Generic systems resemble lath and plaster suspension systems, with lighter gauge hanger wires and “hat” channels in lieu of furring channels. Hat channels have a flat face that allows for the gypsum panel to be screw applied to the suspension system.
Proprietary systems typically have a snap lock or snap in system that allows for faster installation. When proprietary systems are used, the installation instructions should be followed carefully. Customers are advised against mixing and matching systems which can, at best, make installation a challenge; at worst, it can mean a failed ceiling system.
There are several types of gypsum or cement board panel products that can be attached to either one of these kinds of suspension systems. Regular (or “type X” gypsum panels) are the most common for interior applications. Suitable for many locations, they accept paint well and easily provide joint treatment.
However, areas subject to severe weather conditions or high humidity may be better served by proprietary boards specifically designed for this kind of exposure. In a humid or damp environment, it would be wise to consider one of the following: Dens Glass Gold (GP Gypsum); GlasRoc (BPB Gypsum); or AquaTough (USG). The use of water resistant gypsum panels (Green Board) is not recommended for applications in areas subject to continuous moisture or high humidity.
Acoustical lay in ceilings provide the greatest degree of accessibility to the plenum area. They can also be easily retrofit as the needs of the building change. As the name implies, the panels lay in to the suspension systems.
Today, manufacturers in this product area produce a tremendous assortment of panels. Offerings may be wood, glacier snow drifts, or metal; some products even look like waves in the ocean. Suspension systems also come in a wide variety of styles, shapes, and sizes.
The three model codes of the U.S. have merged to become one: the International Building Code (IBC). First introduced in 2000 (and then again in 2003), the IBC has some significant changes for lay in acoustical ceilings in areas subject to seismic activity.
The previous codes relied on seismic zones, namely 0-2 and 3-4. The new IBC refers to Seismic Design Categories (SDC), which range from A-F. SDC is based on more than just location. Soil type and building occupancy are used to determine the SDC.
The installation and design of a suspended lay in ceiling can vary if the SDC is a D, E, or F. This may also affect remodel work to existing buildings.
One item in the IBC that may be surprising is the new requirement for seismic separation joints. These are now required and will break larger acoustical ceilings into 2,500 square foot sections with a seismic separation joint. The new code also requires large openings and escutcheon rings for fire sprinkler heads or a flexible head design.
Finally, when selecting the most suitable ceilings for their buildings, facility professionals should also evaluate the following: acoustics, life expectancy, climate/chemical exposure, abuse resistance, maintenance requirements, fire rating requirements, seismic needs, and aesthetics. Careful consideration of each one of these items will limit the choices for specific buildings or rooms and may provide the best possible ceiling to meet the facility’s overall needs.
Fowler is an architectural consultant with the Northwest Wall and Ceiling Bureau (NWCB). Based in Seattle, WA, the NWCB is an international construction association that routinely publishes industry standards and guidelines for the wall and ceiling industry. Any questions about this article can be directed to the author at [email protected].