OVERHEAD LIMITS—CEILINGS

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INTRODUCTION

The overhead limit, or ceiling plane, in any interior space represents one of the most significant elements of interior design. Not only does the ceiling occupy a large proportion of the total visible surface area, but it must also perform a wide variety of functions, such as providing sound control and supporting or containing lighting, HVAC equipment, sprinklers, smoke detectors, and other equipment. E.g., consider a room with dimensions of 20 ft by 30 ft with a 9-ft ceiling height (6.1 m by 9.1 m by 2.7 m). Of the total 2,100 ft^2 (195 m^2 ) of surface area on the floor, walls, and ceilings, the ceiling represents 600 ft^2 (55.7 m^2 ), or nearly 30% of the area and, unlike the walls and floor, the ceiling is entirely visible. Thinking of this construction element as an overhead limit helps the designer understand what is important in terms of both function and aesthetics.

Like vertical barriers, the ceiling plane is one of the major space-defining elements that interior designers can control. To the extent possible, given the fixed structure of the building and mechanical services, the ceiling plane can be created by the interior designer to define and give character to a space as well as provide all the functional requirements. Ceilings can be used to simply cover the structure and mechanical services of a building, to give scale to a space, to create a variety of spaces, and to help establish the design concept.

--- Ceiling concepts (a) exposed (b) direct attachment (c) suspended (d) combination

---- Closed-ceiling concepts (a) planar (b) modulated (c) coordinated with ground plane (d) emphasized volume (e) angled (f) curved (g) change of material (h) planar with drops

--- Open-ceiling concepts (a) roof as ceiling (b) plane defined by lighting (c) semiclosed with openings (d) floating planar elements (e) open grid (f) suspended point elements

ELEMENT CONCEPTS

As with partitions, the ceiling plane can be designed in thousands of different ways. It can be as simple as a flat gypsum wallboard ceiling in a house or suspended acoustical ceiling in a commercial structure to a combination of materials positioned at different heights and orientations with a mixture of lighting types. Ceilings can be a simple plane, curved, angled, a modulated series of heights, a mixture of open and closed areas, richly textured, single color, or a multiple of colors and finishes.

Because the basic architecture, structure, electrical, and mechanical services of a building are predetermined by the architect and engineers, the interior designer has four basic choices when designing the overhead limits of a space as it relates to the base building. These are shown diagrammatically.

Exposing services is the simplest approach. The underside of the floor or roof structure above is exposed, as are any mechanical and electrical services.

Although this approach has the advantages of minimizing cost and improving sustainability by not using any additional materials, sound control may be compromised and there is little opportunity to modulate space and create a finish that will enhance the design intent, unless the intent is a rough, industrial appearance.

Direct attachment, as shown in (b), can be as simple as screwing gypsum wallboard onto floor joists in a residence or spray-applied acoustical treatment on a concrete structure.

This method, however, limits any electrical or mechanical services to the space between structural members and generally results in a simple plane surface or all or some of the services being exposed. In most commercial buildings this approach is not even possible because most of the services are installed below the structure.

The most common method of creating a ceiling in commercial construction is by direct suspension of another material, typically acoustical tile in a grid, from the building's structure.

These types of ceilings are easy to construct, inexpensive, flexible, work with all building services, and offer a wide variety of finish and design possibilities.

Finally, the designer can use a combination of the previous three methods to tailor the type of ceiling with the functional and aesthetic needs of each space. This is a good way to control costs by placing more expensive ceiling construction in those areas of most importance and choosing less expensive options where it’s less important.

Within these four approaches to creating the ceiling plane, there are countless varieties.

They can be grouped into closed types and open types. Closed types completely separate the usable area from the plenum. Some of the possible concepts are shown.

The simplest, most common approach shown in is a planar, suspended acoustical ceiling, using either an exposed grid or a concealed grid. These are available in a wide variety of grid sizes, tile types, colors, and patterns. A suspended planar ceiling can also be constructed of gypsum wallboard. Other varieties of closed ceilings are discussed in more detail later in this section.

Open ceilings have all or a portion of the area above the suspended ceiling exposed to view. Some of the possible concepts for this approach are shown.

The most common open concept omits any type of suspended finish ceiling at all. This design concept is used to emphasize the architecture of the space or as a design concept in itself. For residential construction, the underside of the roof is often featured, showcasing, E.g., exposed beams, sloping roofs, or some other architectural feature. For commercial construction, exposing the roof or floor above often means exposing all the mechanical and electrical services as well. In both cases, the designer must decide how building services, such as lighting and ventilation, will be provided. Other varieties of open ceilings are discussed later in this section.

FUNCTION

As with partitions, the designer can make the best choice of materials and detailing methods by considering the various functions the ceiling needs to ful fill rather than just relying on standard suspended acoustical ceilings or gypsum wallboard.

Ceilings provide one or more of the following functions:

Covering structure, electrical, and mechanical services; Contributing to the overall design concept of the interior design De fining space; Controlling sound

Providing light r eflectance Holding luminaires Holding sprinkler heads Holding supply air registers and return-air grilles Holding speakers, smoke detectors, and other electrical equipment Supporting ceiling-suspended elements, such as signs or curtains If, e.g., a ceiling is to define a lower space within a high volume, that can be accomplished with a standard acoustical grid ceiling. However, it can also be achieved with an open grid of nearly any material, by lighting techniques that only emphasize the lower area of the volume, with a metal mesh, or any number of alternatives as long as the constraints of fire resistance and other requirements are met.

The ceiling can also contribute to the sustainability of a project. Refer to the sidebar for specific ways sustainability can be addressed through the design and detailing of the overhead plane.

Sustainability Issues Related to the Overhead Plane

Sustainability issues related to the overhead plane include the following:

_ Specify ceiling tile and other ceiling components with as much recycled content as possible. This includes mineral wool, recycled paper, recycled aluminum and steel, and corn and wheat starch binders instead of traditional binders. Most manufacturers now include recycled content in their product literature.

_ Specify ceiling tile that is zero or low-emitting for formaldehyde. The State of California Collaborative for High Performance Schools has a concentration limit of (33 µg/m3) 27 ppb (parts per billion) when tiles are in place and prior to occupancy with a suggested goal of (3 µg/m3) 2.5 ppb. For a product to be considered zero-emitting, the formaldehyde concentrations cannot exceed (2 µg/m3) 1.6 ppb.

_ For remodeling projects where existing tile is being replaced, try to recycle old tile. Several manufacturers have recycling programs for certain types and quantities of tile, if certain requirements are met.

_ Specify ceiling tile that has antimicrobial protection and conforms to ASTM D3273, Standard Test Method for Resistance to Mold on the Surface of Interior Coatings in an Environmental Chamber.

_ If appropriate for the occupancy, select tiles and other components with a high light r eflectance to improve daylighting and minimize the need for luminaires.

_When determining ceiling heights and ceiling transitions, consider view planes from the interior of the space to exterior windows to maximize views to the outside and to not obstruct available daylighting.

_Minimize the amount of material used by considering not using suspended ceilings where they may not be necessary. Coordinate with lighting and mechanical requirements because using a continuous suspended ceiling may reduce long-term energy use.

CONSTRAINTS

For ceilings, constraints most often include the existing slab-to-slab distance, requirements for acoustic control, seismic forces, budget, fire resistance, and flame spread. In commercial construction, most of the functional requirements described above can be satisfied without a separate finished ceiling. Even acoustical control can often be achieved with suspended acoustic panels.

For commercial construction, the common constraints today are acoustic needs, light r eflectance, the ability to inexpensively subdivide space with partitions extending to a suspended ceiling, and sustainability. Materials in Type I and Type II buildings must be non combustible and if the ceiling is part of a floor/ceiling fire-rated assembly in any construction type, the ceiling must be part of a fire-rated assembly. Generally, all the commercial ceiling products on the market meet these requirements. In most cases, lighting, sprinkler systems, HVAC systems, and other services can be installed independently of a finish ceiling, if desired.

--- Ceiling coordination items Align with major architectural elements?

--- 20 × 60 ceiling grid: sprinkler head 5' (1500) grid 5'-0" (1500) window mullions 5'-0" (1500) 20" x 48" (500 x 1200) luminaire 20" x 60" (500 x 1500) ceiling tile filler panel partition location centered on grid intermediate grid

--- Sprinkler spacing maximum 7'-6" (2286) minimum 3 times maximum dimension of obstruction vertical obstruction larger than 4" (100) up to a maximum of 24" (610) maximum 15' (4572) maximum 15' (4572) minimum 4" (102)

COORDINATION

When a suspended ceiling is used, the most common coordination efforts in overall planning are those required to locate the mechanical and electrical services to work with the design of the grid and to align exposed grid systems or other elements of the ceiling with the architectural elements of the building, such as window mullions, columns, and fixed partitions.

The designer may also want to coordinate the location of partitions with the ceiling grid or other main features of the ceiling design such as changes in ceiling material or changes in ceiling height.

In many cases, compromises must be made because one requirement may take precedence over another. E.g., in the short corridor section shown, the layout of the ceiling grid may require the designer to choose between centering the lights and sprinkler head midway between the partitions or in the center of the ceiling tile. Further, if cost is a consideration, sprinkler heads may need to be located at their maximum allowable spacing rather than aligned with other ceiling elements or centered in tiles.

For details, the method of joining the ceiling with vertical elements, such as partitions, columns, and exterior walls, also needs to be considered. This aspect of detailing is discussed here. Additional coordination of details must be made for material transitions, ceiling height transitions, and complex mechanical or electrical installations.

For office planning in which a demountable partition system is used, the size of the ceiling grid must be coordinated with required room sizes and lighting types to allow for the most flexibility in partition relocation. As shown, some demountable partition systems are designed to be located on the ceiling grid lines so that the top runner of the partition can be screwed into a slotted grid. Lighting, sprinkler heads, and HVAC registers and grilles are designed and specified to be movable within the main planning module, typically 5 ft by 5 ft (1500 mm by 1500 mm) or 4 ft by 4 ft (1200 mm by 1200 mm), allowing partitions to be placed as required.

If a hard ceiling, such as gypsum wallboard, is used, access panels need to be provided to allow access to electrical junction boxes, valves, mechanical equipment, and similar items.

If possible, the designer should coordinate with the mechanical and electrical engineers to position the items requiring access in such a way that the panels don’t create an unsightly view of the ceiling. In most cases, access panels mounted in a gypsum wallboard ceiling will get dirty with use and the joint compound around the panel will crack over time as the door is open and closed.

Sprinkler Spacing

Sprinklers in commercial construction must be positioned with maximum and minimum dimensions defined by NFPA 13, Installation of Sprinkler Systems and NFPA 13R, Installation of Sprinkler Systems in Residential Occupancies Up to and Including Four Stories in Height. NFPA 13D, Installation of Sprinkler Systems in One- and Two-family Dwellings and Manufactured Homes applies to residential design. The designer should know the basic requirements to make informed design decisions about coordinating sprinklers with the position of luminaires, HVAC air supply, and other ceiling mounted items. With knowledge of the essential spacing limitations, the interior designer can work with the mechanical engineer or fire protection engineer to locate sprinkler heads to work with the overall ceiling plan.

The NFPA 13 standard classifies the relative fire hazard of buildings into three groups: light, ordinary, and extra hazard. Each hazard classification is further divided into groups.

The hazard classification determines the required spacing of sprinklers and other regulations.

---- shows some of the basic requirements for light hazard occupancies. These include uses such as residential, offices, hospitals, schools, and restaurants. In these occupancies there must be one sprinkler for each 200 ft 2 (18.6 m^2 ), or 225 ft 2 (20.9 m^2 )if the design of the system is designed hydraulically, which most are. --- shows some of the requirement for hydraulically designed systems. There are other requirements for spacing near dropped beams and other obstructions. Refer to --- for typical clearances above the ceiling required for sprinkler heads and piping. For more detailed design requirements refer to NFPA 13.

---- Types of ceiling-mounted air diffusers (b) architectural (c) round (a) standard square (d) linear slot diffuser (e) nozzle (f) round, flush

HVAC Coordination

In most cases, coordinating the location of air supply registers, return-air grilles, and exhaust fan outlets is straightforward. The mechanical engineer determines the general location and capacity requirements of these items, but the interior designer can work with the engineer to

finalize the exact position in the ceiling. The designer may also request that the engineer use a particular type of air control device that is most appropriate for the design of the space. E.g., a linear slot diffuser may be preferable to a standard square air diffuser. --- shows some of the air diffuser types available, and ----1 lists some of the manufacturers of air terminal units.

Tolerance Coordination

Tolerance coordination usually is not an issue because suspended ceilings can be installed very accurately (level, position, and alignment) independent of the building structure. Typical suspended ceilings are installed with laser levels and can generally be constructed level to within ±1/8 in. in 10 ft (3.2 mm in 3050 mm), often to within ±1/8 in. over the entire room area. Of course, if the ceiling does not touch other construction, minor variations in level, position, or size are not noticed. However, if a grid system is to be coordinated with the position of recessed downlights or sprinkler heads, additional effort may be needed to coordinate the work of electricians, mechanical contractors, sprinkler contractors, and finish system installers.

---- Air Diffuser Manufacturers

Manufacturer Web Site | Description

Acutherm www.acutherm.com Provides a variety of diffuser types AirConcepts, Inc. www.airconceptsinc.com Provides a variety of diffuser types Anemostat www.anemostat.com Provides a variety of diffuser types Carnes Company wwwlcarnes.com Provides a variety of diffuser types Krueger www.kruegar-hvac.com Provides round and square diffusers, linear slot diffusers, grilles, and registers Nailor Industries www.nailor.com Linear slot diffusers, square and round ceiling diffusers, and perforated diffusers Titus www.titus-hvac.com Provides a variety of diffuser types Trox USA www.troxusa.com Provides nozzle and swirl diffusers Tuttle and Bailey www.tuttleandbailey.com Provides a variety of diffuser types Sheiho International www.seiho.com Provides nozzle diffusers

---- Suspended Ceiling Manufacturers Manufacturer and Web site Description Alpro Acoustical Systems www.alproacoustics.com Supplies corrugated, perforated metal acoustical panels of aluminum or steel in flat panels, curves, and floating sections.

American Decorative Ceilings www.americandecoativeceilings.com Provides specialty ceilings including curved ceilings, tin ceiling replications, open grids, wood panels, corrugated, linear plank, linear metal ceilings, translucent panels for backlighting, metal panels, and floating "clouds." Armstrong www.armstrong.com One of the largest manufacturers of ceiling suspension systems, ceiling tiles, and specialty ceiling products including tiles, grids, specialty trim, curved ceilings. Provides drywall grid, wood panels, metal panels, open-grid ceilings, tin ceiling replications, coffers, floating "clouds," custom radial ceilings, and linear metal ceilings.

BPB America Inc. www.bpb-na.com Standard ceiling tiles and grids.

Ceilings Plus, Inc. www.ceilingsplus.com Offers a variety of specialty ceiling types including curved, serpentine, canted arc, corrugated, metal and wood open grid, linear metal, wood slat, wood panel, modular, and triangular grid shapes.

Chicago Metallic www.chicagometallic.com Supplies a wide variety of grids and panels as well as specialty items such as curved grids for floating "clouds" curved ceiling sections, perforated panels, tin ceiling replications, linear metal ceilings, open grids, coffers, and drywall grid (including curved).

Gordon Grid www.gordongrid.com Provides ceiling grid systems and aluminum, steel, or stainless steel panels in flat, curved, and custom con figurations, as well as luminous ceilings and perforated panels. Also provides linear metal ceilings.

Hunter Douglas www.hunterdouglascontract.com Techstyle suspended ceilings consisting of 1-1/8 in. (28.6 mm) thick honeycomb panels snapped to concealed grid to provide thin reveals between panels up to 48 in. by 72 in. (1220 mm by 1830 mm) in size.

illbruck acoustic, inc. www.illbruck-archprod.com Patterned, bevel-edged ceiling tiles with backer board for grid or adhesive installation. Also provides expanded metal ceiling panels.

Simplex Ceilings www.simplexceilings.com Metal pan ceilings for flat or curved installation in addition to concealed plank panels, curved ceilings, linear metal ceilings, open grids, and custom designs.

Tectum www.tectum.com Wood fiber ceiling panels, abuse resistant, paintable.

USG www.usg.com Wide variety of ceiling grids and panels, including specialty systems such as curved, angles, floating "clouds," linear metal ceilings, open grid, tin ceiling replications, translucent panels, coffers, and fiber-reinforced gypsum systems.

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METHODS

Manufacturers have provided hundreds of products for ceiling construction that the designer can use to develop project-specific solutions. The conceptual approaches shown are described in more detail in this section with listings of some of the manufacturers that provide useful products for developing details. Some of the ceiling designs shown can also be constructed with standard metal framing and gypsum wallboard or other materials, while some designs require a combination of proprietary products and generic construction materials. These are divided here into the two broad groups of closed- and open-ceiling systems.

Closed

PLANAR

A planar ceiling is often the simplest and least costly method of providing a finished ceiling and satisfying most of the functional needs of an overhead plane. In most cases, this is the standard 2 ft by 2 ft (600 mm by 600 mm) or 2 ft by 4 ft (600 mm by 1200 mm) lay-in acoustical ceiling.

These ceilings have the advantages of simple installation, acoustical control, light r eflectance, low cost, flexibility, accessibility to the plenum, and the ability to accommodate a wide variety of mechanical and electrical systems.

Since the development of suspended lay-in acoustical ceilings, designers have often objected to the finished appearance. Manufacturers have responded with a variety of grid types and panels to address the aesthetic objections as well as to provide specific system types of systems for specific building needs. Some of the varieties of grid profiles now available are shown. Panels also come in hundreds of different styles, patterns, colors, and edge treatments. Many of the ceiling manufacturers are listed. These include manufacturers of standard acoustical ceilings as well as specialty ceilings.

Planar ceilings may also be constructed with a concealed grid to eliminate the visible grid that many designers object to, while still maintaining acoustical control, accessibility to the plenum, and relatively low cost.

Flat gypsum wallboard ceilings can also easily be constructed, but they usually require access panels to allow for maintenance of mechanical and electrical equipment above the ceiling. Gypsum wallboard ceilings can be constructed on a framework of metal furring channels on cold-rolled steel channels or with proprietary T-bar grids. For small areas, such as corridors and restrooms, gypsum wallboard ceilings may also be installed on metal stud framing or wood framing if combustible materials are allowed by the local building code.

---- Gypsum wallboard ceiling framing (a) furring on steel channels (b) proprietary grid (c) steel studs framed to partitions 16" (400) o.c.

1-1/2" (38) steel channels 4'-0" (1220) o.c.

furring channels wire tied or clipped to steel channels intermediate tees 16" (400) o.c. on main runners 4'-0" (1220) o.c.

--- Ceiling height transitions available from 2" to 12" (50 to 300) acoustical or wallboard ceiling W-trim standard ceiling angle wallboard to wallboard transition acoustical ceiling to wallboard transition acoustical ceiling to wallboard transition aluminum trim (c) aluminum perimeter trim (a) wallboard transition with trim (b) standard bulkhead transition (d) transitions with aluminum trim clipped to ceiling grid metal framing gypsum wallboard

--- Lighting coves (a) standard metal framing (b) manufactured trim (c) floating ceiling with trim joint filled and sanded support bracket screwed to framing finish snapped to bracket anchor framing secure to avoid sagging available from 2" to 12" (50 to 300) acoustical or wallboard ceiling trim clipped to ceiling grid

---- Ceiling Trim Manufacturers Manufacturer Web Site Description

Alpro Acoustical Systems www.alproacoustics.com Edge trim for T-bar systems in straight and curved sections Armstrong www.armstrong.com Provides edge trim for floating ceilings, drapery pocket assemblies, panel transitions to drywall, and standard sized floating "clouds" Chicago Metallic www.chicagometallic.com Metal ceiling grids in a variety of con figurations as well as FRP grid sections Fry Reglet www.fryreglet.com Aluminum ceiling grid and trim pieces for ceiling-to-ceiling transitions Gordon Grid www.gordongrid.com Aluminum trim pieces for ceiling-to-ceiling transitions, as well as ceiling-to-wall transition moldings and perimeter pockets for drapery and cove lighting Trim-tex www.trim-tex.com Vinyl wallboard trim in a variety of con figurations for wallboard ceilings, vinyl crown molding, and some specialty ceiling trim

--

MODULATED

Modulated ceilings are those where the ceiling height varies. The ceiling may be continuous using the same material or may consist of one continuous closed portion with suspended "clouds." Some of the methods used to make the transition between ceiling heights are shown. These include using standard framing materials, as well as special manufactured accessories. Manufacturers of proprietary trim pieces are listed.

Modulated ceilings are often used to create lighting coves for indirect lighting. Although such coves can be constructed with common metal framing and gypsum wallboard, premanufactured solutions are also available. Some of the methods of creating lighting coves are shown.

--- Types of ceiling grids (a) standard grid (b) narrow grid (c) tegular (d) bolt head (e) screw tegular (f) screw lay-in

Lighting coves are also commonly incorporated into ceiling and wall transitions, as discussed.

COORDINATED WITH GROUND PLANE

A variation of the modulated ceiling is one that is closely coordinated with a modulation of the ground plane as shown. The ceiling may either be raised or lowered relative to the surrounding ceiling, depending on the effect the designer wants. Raising the ceiling maintains a constant ceiling height above a raised platform, while lowering the ceiling changes the scale of the space and makes a much more intimate area. The ceiling transition can be made with a vertical plane, as shown or with angled, stepped, or curved sides.

EMPHASIZED VOLUME

Another variation of the modulated ceiling is one that is raised or lowered to emphasize a given area. Here, the floor plane remains unchanged, while the ceiling is used to change the scale and spatial emphasis. This design can be used where mechanical and electrical services above the ceiling preclude an overall high ceiling height but where one area is available for special treatment. The designer may need to coordinate with the mechanical engineer to locate ducts, sprinkler piping, and other services in such a way that the ceiling can be raised.

ANGLED

Where space is available, the ceiling plane can be varied, creating different ceiling heights and a more dynamic spatial volume. The variations can be made over small distances such as 4 ft to 6 ft (1200 mm to 1800 mm) or with large areas, possibly sized to correspond to a functional area below the ceiling. Where the exterior window height is high, angled ceilings sloping down from the head of the window are a useful way to r eflect natural light into a space, increasing daylighting efficiency.

CURVED

A curved ceiling plane creates a different dynamic than an angled ceiling, suggesting a smoother transition from one space to another. As with angled or modulated ceiling planes, curves can be used selectively over certain areas of the space to provide a design contrast with flat ceiling planes or to emphasize special areas, such as a corridor, dining area, or retail space.

Large, sweeping areas of curved ceilings are difficult to build, but smaller, premanufactured curved sections are available from some manufacturers.

CHANGE OF MATERIAL

Different materials can be used in ceiling construction for a variety of reasons. The designer may want to control costs by using a less expensive material, such as a suspended acoustical ceiling, in most areas and reserving more of the budget for constructing a more expensive material in just special areas. E.g., a gypsum wallboard modulated ceiling may be used in the reception area of an office space, while a standard suspended grid ceiling is used in the remainder of the area.

PLANAR WITH DROPS

A planar ceiling may be used to completely close the plenum for appearance or to minimize energy use, while still using separate elements below the plane of the ceiling.

The suspended elements can be used to emphasize space, to modulate the scale of the space, or to contain special lighting. While the dropped elements can be any material or con figuration, the limited heights in many interiors restrict the elements to flat, or nearly flat (angles or curved sections), suspended acoustical ceilings or pre-manufactured specialty ceilings, such as wood, metal, perforated metal, or glass. Several manufacturers offer floating "clouds" with edge trim that can easily be specified and installed.

Open

Open ceilings are those that expose all or a portion of the underside of the floor or roof above as well as mechanical and electrical services. Open ceilings are often used to save the cost of installing a separate suspended ceiling, to increase the size of space, or to use the esthetic of exposed structure and services as a design feature. However, eliminating a separate suspended ceiling to save costs should be carefully investigated with the assistance of the mechanical and electrical engineers. Although the first costs may be reduced, the life-cycle costs may higher.

This is due to increased energy use without a suspended ceiling because larger HVAC systems are required to heat or cool additional space and to create required air movement. In addition, open ceilings generally require more maintenance for cleaning and painting and are not as efficient at r eflecting both artificial and natural light.

ROOF AS CEILING

The first type of open ceiling is simply no ceiling at all. All the structure and building services are exposed. This approach generally only work in cases where no, or very little, partitioning is required, such as open plan offices, retail stores, manufacturing plants, and the like. The height of the floor above and the irregularity of lighting, pips, and ductwork, make it difficult to extend partitions to the structure above.

In most cases, the pipes and ducts must be painted and the designer may want these element laid out in a particular way for aesthetic reasons, both of which increase the cost of using this approach. Usually, the designer specifies a light paint color to make the service visible and improve r eflectance.

From a visual standpoint, the effect of this type of overhead plane is that of an irregular space, high and low points being defined by the size and position of the lights and mechanical services.

PLANE DEFINED BY LIGHTING

A variation of the totally open ceiling is to create a perceived ceiling plane with lighting.

One hundred percent down-lighting is used at a uniform elevation and all walls, structure, mechanical, and electrical services above the lights are painted black. The effect is a ceiling plane at the level of the luminaires. Although the services can be seen the eye adjusts to the higher light level and anything above the lights is not noticed. The main disadvantage to this ceiling design is the lack of light r eflectance, for either improved daylighting or higher efficiency artificial lighting. Generally, more luminaires are needed with this technique than with a continuous, high-r eflectance ceiling.

SEMICLOSED WITH OPENINGS

A semi-closed ceiling with openings has the majority of the ceiling closed, with only portions open to the area above the ceiling. The closed portion can be a simple planar ceiling or it can be formed with angles or curves. Although this type of ceiling creates a strong overhead plane, there is still some sense of spatial modulation.

The openings may allow visibility to the structure and mechanical services above or vision may be blocked with a separate ceiling system above the surface of the lower ceiling.

Return air is drawn into the plenum through the openings, eliminating the need for return air grilles.

FLOATING PLANAR ELEMENTS

A variation of the semi-closed ceiling design is one with separate planar elements that seem to float below the structure and mechanical services. With this type of overhead plane, more of the ceiling is open than with the semi-closed type and the suspended elements may be at various elevations and consist of varying shapes and sizes of construction. The sense of spatial modulation is greater with this type of ceiling than with the semi-closed one. Refer to ---- for manufacturers that supply specialty ceilings and trim that can be used to create this ceiling type.

OPEN GRID

An open grid ceiling uses a suspended assembly of elements, usually of uniform size and spacing to create a strong visual plane, while allowing air to freely circulate between the occupied space and the volume above the ceiling. Most commonly, open grids consist of small, square grids or linear elements. A linear metal ceiling is a variety of this ceiling type. Refer to ----- for manufactures of open-grid ceilings.

Open-grid ceilings create an effect similar to a plane defined by lighting. The grid r eflects ambient light, while the area above the grid is dark; the effect is that only the grid is visible, even when a person looks directly up.

SUSPENDED POINT ELEMENTS

A ceiling may be completely open, as with the roof as ceiling type illustrated, but with visually prominent element suspended in the space. These elements may be luminaires, acoustic panels, banners, signs, air diffusers, or any combination to create a field of elements. The overhead plane is largely defined by the floor or roof structure above but modulated by the size, position, shape, color, and density of the suspended elements.

With fewer elements, the structure and mechanical and electrical services are emphasized; with more elements the ceiling takes on the effect of floating planar elements or an open-grid ceiling.

---- Open Grid Ceiling Manufacturers Manufacturer Web Site Description Alpro Acoustical Systems www.alproacoustics.com Acoustical baffles Armstrong www.armstrong.com Metalworks aluminum system Ceilings Plus www.ceilingsplus.com Beamz retangular or square system in a variety of baffle sizes and grid sizes Chicago Metallic www.chicagometallic.com Magna T-Cell , Intaline, CubeGrid, BeamGrid, and GraphGrid systems Gordon Grid www.gordongrid.com Beam Mate wide open grid system and Fin Mate suspended fins in flat or curved con figurations Simplex Ceilings www.simplexceilings.com Aluminum grids from 1 in. to 6 in. (25 mm to 152 mm) square or custom sizes. USG www.usg.com GridWare, WireWorks, and WireWorks Forms

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