Components

The primary parts of the chair are the back and the seat pan. The back may be molded plastic, metal, laminate, or wood—with or without padding and upholstery. The back may have a square, rounded, or more articulated silhouette. The upholstery can entirely wrap the back, or cover only the forward face, with or without reveals or tufting. The upholstery fabric can be a woven textile or leather.

The seat pan is molded plastic, metal, or wood—again, with or without padding and upholstery. The seat pan is hinged and self-rising, either by means of springs built into the hinge or by gravity acting on a counterweight built into the back of the seat pan. Gravity-action seats are both quieter and more reliable, but only available on higher end chairs.

In most cases, the back and seat pan mount to a pair of upright brackets called standards. Every two adjacent chairs share a standard, which is fastened either to the floor or to the seating riser. Variations are possible— each chair can have its own pedestal mount, which sometimes has a built-in air diffuser, or several chairs can be mounted to a horizontal beam supported by pedestals. Chairs designed to be removed, perhaps to clear space for patrons in wheelchairs, will have two standards and a sled base.

An armrest of wood, laminate, or molded plastic fastens to the top of the standard. Like the standard, the armrest is shared between adjacent chairs— creating a potential source of annoyance and disagreement. The standard at the end of the row is slightly different in construction, and end standards that are visible are usually dressed with a panel of wood, metal, or laminate. Or the end panel might be wrapped in the upholstery material, especially if the upholstery is leather. End panels often have integral aisle lights.

Chair Width

Chair backs and seats are manufactured in a range of widths used to create horizontal stagger between successive chair rows, as shown in Figure 12.7 in the last chapter. Width is measured as the centerline-to-centerline dimension between adjacent standards, so the actual width of the back or seat part is a few inches less than the nominal width. If the row is curved, the standards will be splayed, and chair width is measured along a theoretical arc called the “chair size line” or “setting out line.”

Chair widths grew gradually through most of the twentieth century: in 1900 the typical range was 18 to 20 inches, and by about 1990 it was 19 to 21. Since 1990, the rate of change has increased, and the current range is 20 to 24 inches.

Back Pitch

Back pitch is the angle of the chair back, which is set when the back is fastened to the standards.

Back pitch ranges from 12 degrees (which provides an upright posture for balcony seating with downward viewing angles) to 22 degrees (which provides a relaxed posture for orchestra seating where sightlines are closer to horizontal). Theater chairs almost always promote a more upright posture and have firmer padding than cinema chairs, which are heavily padded and sometimes recline. Unlike cinema, live performance depends on an alert and engaged audience.

Back pitch affects two critical dimensions—chair envelope and back over hang.

Figure 13.2 Fixed Auditorium Chairs on (a) Steep Slope and (b) Shallow Slope.

a = aisle accessway; b = chair envelope with seat up; b′ = chair envelope with seat down; s = row spacing; d = back overhang; a = back pitch

Source: Author

Chair Envelope

Chair envelope is simply the front-to-back dimension of the chair, measured “plumb line to plumb line.” Chair envelope may be measured with the seat down or with the seat up. If the seat is self-rising, the “seat up” dimension is used for code calculations. This dimension, labeled b in Figure 13.2, is usually between 18 and 22 inches. Because back pitch is set in the field, the same set of chair components can be assembled with different chair envelopes.

Back Overhang

The back overhang is the distance between the chair size line and a plumb line at the rear of the chair back. This is dimension d in Figure 13.2. Again, this dimension varies with back pitch—so it’s larger for chairs at the orchestra level and smaller for balcony seating. Because the chair back overhangs the riser face, up to 12 inches of extra depth must be allowed at the last row.

Number

The required number of wheelchair spaces varies, with proportionately more spaces required in smaller auditoriums. Table 13.1 indicates the minimum requirements according to the 2010 ADA Standards for Accessible Design.

Size

Individual wheelchair spaces must be at least 36 inches wide, while two side-by-side spaces must each be a minimum of 33 inches wide. It’s a good idea to provide both single and double spaces. The required depth is 48 inches for a space approached from the front or rear, and 60 inches for a space approached from the side. A single wheelchair space takes up almost the same footprint as four fixed auditorium chairs—two adjacent chairs in two successive rows. Wheelchair spaces must be level or sloped no more than 1:48. These requirements for size and floor slope make integrating wheelchair spaces within the seating rake a challenge.

Wheelchairs and other mobility devices come in different sizes and configurations, and some will not fit within the minimum dimensions described above. Auditoriums for live performance depend upon high seating density to promote audience cohesion and responsiveness, and therefore minimum-sized spaces are usually provided. It’s good practice, however, to provide some locations that can accommodate larger mobility devices. Crossaisles and boxes can usually be designed to provide more room for a wheelchair user with little or no need for on-the-spot adjustments to adjacent seating.

Wheelchair spaces must not overlap circulation paths that are required by the building code or ADA. So, for example, a wheelchair space at the end of a row cannot block a required egress path for other patrons in that row. This requirement also means that access to a wheelchair space cannot be through another wheelchair space. But, if a circulation path is wider than required, a wheelchair space can overlap the excess width.

Integrality

The wheelchair spaces cannot be segregated from the other seating, and must enable patrons in wheelchairs to sit “shoulder to shoulder” with their companions. This means the wheelchair space must be on the same floor level as adjoining seats, and the size and position of the wheelchair space must allow the patron to sit next to patrons in adjoining seats.

Dispersion

Except in auditoriums seating 300 or fewer, the required number of wheelchair spaces must be dispersed both horizontally and vertically to allow choices of location, viewing angle, and sightlines. Once the required number of spaces has been dispersed, however, further dispersion is not required by the ADA. For example, if six wheelchair spaces are required, then patrons in wheelchairs need not be offered more than six distinct seating choices.

Horizontal dispersion means that spaces are distributed across the width of the auditorium or around the perimeter of a thrust or arena stage. Vertical dispersion requires wheelchair spaces at varying distances from the performance area. Spaces are required in at least 20 percent of all boxes and in each balcony or mezzanine that is located on an accessible route.

The dispersion requirements in the 2015 IBC are slightly different than the ADA requirements. The IBC requires wheelchair spaces on the main floor level and on one of every two additional levels, except that if the second level has fewer than 25 percent of all seats, or fewer than 300 seats, all wheelchair spaces can be at the main level.

Substantial Equivalency

The wheelchair spaces must provide sightlines and viewing angles that are comparable to or better than the sightlines and viewing angles provided to the general public. For example, wheelchair spaces cannot be provided only at the front of cinemas, where viewing angles to the screen are least desirable. Similarly, in spaces for live entertainment, it’s important to provide spaces on or near the centerline of the auditorium. If one divides the width of the auditorium into four equal segments, at least some wheel chair spaces should be within the center two segments.

The wheelchair spaces must provide sightlines over the heads of standing spectators if patrons are expected to stand during events. Satisfying the latter requirement while providing integrality and a feeling of intimacy is a significant design challenge. A few seating locations (for example, front rows and boxes) provide uninterrupted sightlines when other patrons stand, but a design that places all wheelchairs in these locations would not satisfy the requirements for dispersion.

Most case law concerning “standing sightlines” has involved sports stadiums or racing venues, where standing is common, and the application of this requirement to performing arts and live entertainment spaces is not clear. It is generally understood that the requirement does not apply to standing ovations, the only time spectators stand during traditional per forming arts events. However, standing may be acceptable at other times during popular music concerts and other types of live entertainment.

Exit Access

An exit access is a path from anywhere in a building that leads to an exit. In an auditorium, it’s the travel route from each chair or wheelchair space to one or more exits. It is a concept very relevant to the design of seating layouts, since the spaces between the rows of chairs, the aisles, and most open floor areas within the auditorium are all part of the exit access.

Exits

What constitutes an exit? Conceptually, the simplest exit is a door that leads directly to the exterior. Enclosed interior stairs, ramps, and corridors can also be exits, as can exterior stairs and ramps. Perhaps the most arcane of exits is the horizontal exit. This is a passage that brings you “horizontally” across a fire barrier into a “safe area.” “Horizontally” meaning without a significant change in level, and “safe” meaning protected from fire and smoke spreading from the area you just left!

Exit Discharge

You’ve probably guessed that exit discharge is the path from the terminus of an exit out to a public way or street. Since it is exterior to the building, the exit discharge does not affect the seating layout, and we won’t discuss it in detail.

Accessible Routes and Egress

Not all means of egress components are usable by persons with impaired mobility. As defined by the ADA and the building code, the term “accessible route” refers to a circulation path usable to persons with impaired mobility, including persons in wheelchairs. The building code goes on to define requirements for accessible means of egress. We’ll look at both accessible routes and accessible egress later in this chapter.

We concern ourselves with these definitions because the ADA and the building code are full of special names and specific requirements for every part of the means of egress system, and the exit access requirements (especially) determine the basics of theater seating layouts. What follows is a general overview. The reader is cautioned to research the specific requirements in his or her code jurisdiction.

Hypothetical Range

By adding the minimum 12-inch aisle accessway to a tight 18-inch chair envelope, we arrive at a hypothetical minimum row spacing of 30 inches— much too tight for comfort! In this case, the building code specifies egress width, not patron comfort. If we add the widest required accessway of 22 inches with a generous chair envelope of 22 inches, we arrive at a “maximum” row spacing of 44 inches. We’ve described a hypothetical range of 30 to 44 inches.

Practical Range

In actual practice, row spacing falls within a smaller range, say 34 to 42 inches. At the low end, 34 inches provides an acceptable level of comfort on a shallow slope, but 36 inches is preferred, and larger spacing is sometimes provided. On a shallow slope, the space below the chair in front is available as leg space, allowing a tighter row spacing. To maintain the same level of comfort, row spacing must increase as the slope increases, because the back of the chair in front limits leg room. As noted in the last chapter, balconies often have longer rows, and this requires wider accessways. Between the requirements for leg room and egress width, row spacing in balconies usually ranges between 38 and 42 inches.

Comfort Versus Density

In all cases, the tradeoff between comfort and seating density must be considered. Wider chairs and generous row spacing provide increased creature comfort and more “personal space.” Increased row spacing makes it easier for patrons to travel along the accessway, especially past patrons who are already seated. But increasing the average chair width and row spacing also reduces the density of the seating and the cohesiveness of the audience. An auditorium of a given footprint built today will hold just half the number of seats as the same size auditorium built in 1900. The difference in capacity is largely due to increases in seat width and row spacing, and has a significant and detrimental effect on the responsiveness of the audience and the liveliness of the performance.

Capacity

Aisle capacity varies with slope: aisles may be level, ramped, or stepped. A stepped aisle is also called an aisle stair. (We covered the details of aisle slopes in the last chapter.) An aisle that is level or has a slope less than 1:12 has a capacity of one person for every 0.2 inches of width. A ramped aisle steeper than 1:12 has a capacity of one person for every 0.22 inches of width. And an aisle stair has a capacity of one person for every 0.3 inches of width. (The code also contains adjustment factors for certain dimensions and for smoke-protected seating, but the capacities listed above apply to most circumstances.)

Catchment Areas

The required capacity of an aisle depends on the number of seats it serves. To determine this, each level of the auditorium is divided into catchment areas that assume proportionate use of the means of egress capacity. Figure 13.3 shows a simple example—a single level auditorium with 500 seats is served by four doors of equal width. We assume one quarter of the audience will exit through each of the four doors, so the portion of aisle leading to each door must have a capacity of 125 people. If the aisles have a slope greater than 1:12, the width required is 125 times 0.22 or 27.5 inches.

Figure 13.3 Catchment Area Example (after NFPA)

Source: Author

Note that in making this calculation we don’t assume that audience members will tend to exit through the main entrance, nor do we assume that audience members will exit through the door closest to their seat.

Minimum Width

The actual width of aisles is often determined not by the capacity calculation, but by a separate code requirement for minimum width. Table 13.2 lists minimum aisle widths according to the 2015 edition of the IBC.

The aisles in our example from Figure 13.3 are sloped aisles with seats on only one side, serving more than five rows. According to Table 13.2, their minimum required width is 36 inches. The minimum required width is significantly larger than the width required by the capacity calculation, which is quite common in smaller auditoriums.

Uniform Width

If egress is possible in either direction, as in our example in Figure 13.3, then the aisle must be uniform in width.

Table 13.2 Minimum Aisle Widths per IBC 2015 in Inches

Longitudinal and Radial Aisles

The most common aisles are longitudinal (also called parallel) and radial. Longitudinal aisles are parallel to the centerline of the auditorium, and radial aisles are perpendicular to curved or faceted seating rows. As Figure 13.3 indicates, the same aisle can transition from radial to longitudinal. Smaller auditoriums will have two or four aisles. Larger auditoriums may have multiple seating banks separated by multiple longitudinal or radial aisles.

As discussed in the last chapter, center aisles are rarely used. They are feasible only if the seating slope provides first row vision, and they take up space that would otherwise provide prime viewing positions.

Crossaisles

Crossaisles connect longitudinal or radial aisles to each other or to doors leading out of the auditorium. If egress paths converge at a crossaisle, then the capacity of the crossaisle must be not less than the combined capacity of the converging aisles. Requirements for minimum width also apply.

It’s possible to have a crossaisle, or portion of a crossaisle, that is not part of the exit access. Figure 13.4 shows a single-level auditorium divided into four equal catchment areas, each served by an exit door. Unlike our previous example, this auditorium also has a crossaisle. The patrons in catchment area C follow either aisle C or C’ to the crossaisle at E, which leads to exit C. The capacity of the crossaisle at E must equal the capacity of the converging aisles C and C’. Since the auditorium is symmetrical, the same analysis applies to catchment area D and the crossaisle at G. But note that the crossaisle at F doesn’t serve any of the four catchment areas and is not part of the egress system. (Because the auditorium in this example is so small, all of the aisle widths are actually determined by the requirements for minimum widths found in Table 13.2.)

Figure 13.4 Catchment Area Example with Crossaisle

Source: Author

Dead-End Aisles

Normally, both ends of an aisle must lead to a crossaisle, door, or other means of egress. Aisles C and D in Figure 13.4 are examples of dead-end aisles. One end of the aisle leads to the crossaisle and exit, but the other end terminates at the front of the stage. Dead-end aisles like this are allowed if they are no more than 20 feet in length.

But if you examine Figure 13.4, you’ll see that aisles C and D are longer than 20 feet. (The aisles serve nine rows. Even if the row spacing were 30 inches, the aisle length would be 270 inches or 22.5 feet. If row spacing is a more reasonable 36 inches, then the aisle length is 27 feet.) Dead-end aisles longer than 20 feet are allowed under an exception in the code that acknowledges that exiting patrons often cross the auditorium by walking along the aisle accessways. Dead-end aisles longer than 20 feet are allowed if the seats at the “dead end” (that is, the seats past 20 feet) are no more than 24 seats from another aisle along an aisle accessway that has a clear width of 12 inches plus 0.6 inch for every chair above seven.

Accessible Routes

The concept of an accessible route is defined by the ADA and the building code, and may include walking surfaces with a slope not steeper than 1:20, doorways of certain dimensions, ramps with a slope not steeper than 1:12, elevators, and wheelchair platform lifts. As much as possible, the accessible route provided for patrons in wheelchairs must be coincident with the main circulation path. However, circulation components that do not serve accessible areas do not have to be accessible. This is important because much of the circulation within the auditorium is not accessible. Making the entire auditorium accessible would fundamentally alter the nature of the space and the performances taking place there, and the ADA does not require this.

The ADA and the building code include many detailed requirements for the components of accessible routes. Generally, routes must have at least 36 inches of clear width, and if a person in a wheelchair must turn around, a 60-inch-clear circle is required. There are additional requirements for passing space and clear areas around doors and fixtures. Walking surfaces with slopes between 1:20 and 1:12 are considered ramps, and must meet requirements for landings and handrails. Slopes greater than 1:12 are not allowed. Note that auditorium aisles with slopes less than 1:12 are not usually accessible routes, because they do not comply with the requirements for ramps and railings.

Platform lifts are allowed only to provide access to certain areas, including performing areas and wheelchair spaces within the auditorium. (They may also be used to provide wheelchair access to non-public spaces serving five or fewer occupants, which covers most control rooms.) Whenever possible, accessible routes should provide universal and equal (not segregated) access. Platform lifts are obviously separate accommodation for persons in wheelchairs, and their use should be kept to a minimum. Also, to be accessible and usable, platform lifts must be maintained in working order, and too often they are not.

Accessible Means of Egress

The building code requires that all accessible spaces have one or more accessible means of egress. An accessible route can serve as part of an accessible means of egress. In addition, elevators, platform lifts, horizontal exits, ramps, and stairways may be part of an accessible means of egress—if they meet certain detailed requirements. Areas of refuge (spaces protected from smoke and fire where a person unable to use the stairs can await instruction or assistance) were once a common feature of accessible means of egress, but now they are required in just a few circumstances.

Number

Two exits are required for seating levels designed for 50 to 500 people. This increases to three for levels with 501 to 1,000 people, and above 1,000 the requirement is four. Note that the same exit (say, an enclosed stair) can serve multiple seating levels, as long as it has sufficient capacity.

Location and Capacity

If an auditorium seats more than 300 and has an identifiable main entrance, then that entrance is considered the main exit, and it must have a capacity sufficient for at least half of the auditorium occupants. This requirement is based on the observation that most patrons attempt to leave the auditorium by the way they entered. All other exits combined must also have a capacity for at least half of the occupants.

Exit Remoteness and Common Paths

Exits must be remote from each other, to offer a choice of egress paths. In an auditorium with two exits, the distance between the exits must be greater than one-half of the diagonal measurement of the auditorium. If the building is sprinklered, the requirement is one-third of the diagonal.

“Common path of travel” is a related concept. It’s the travel distance from any seat or wheelchair space to a point where the person exiting has a choice of two paths of travel to two exits. In most cases this distance must be no more than 30 feet, but it can be 75 feet in areas that seat fewer than 50 people.

Travel Path

The total length of the exit access may not exceed 200 feet in a non-sprinklered building and 250 in a sprinklered building. This distance is measured from each seat, along the rows of seats, and down the center of each aisle to the nearest exit. In most cases travel distance is not a limiting factor when laying out the seating. By way of comparison, the footprint of the auditorium at the Dolby Theatre (the largest venue illustrated in Chapter 1) is 140 feet deep and 120 feet wide.

Note, however, that the actual exit can be well outside of the auditorium. A door at the perimeter of the auditorium isn’t an exit unless it leads directly to the exterior or to an exit corridor or stair. If instead the door leads to an exit access corridor or to the lobby, then the patron will not reach the actual exit until he or she has traversed this space and exited to the exterior or into an exit stair or corridor.

Handrails

Handrails are required on ramps and stairs for the safety and convenience of building occupants, including on ramped aisles and aisle stairs. However, handrails are not required on ramped aisles when there are seats on both sides of the aisle. Where there are seats on both sides of an aisle stair, a series of “hairpin” handrails can be provided at each side of the aisle. The gaps between these handrails must, of course, allow ingress and egress from each row. The alternative is a handrail along the center of the aisle. This type of handrail must also have gaps to allow patrons to cross from one side of the aisle to the other. Gaps of at least 22 inches and not more than 36 inches must be provided at least every five rows.

Guards

Guards provide protection from openings in walls and floors and from changes in floor elevation exceeding 30 inches. Guards in auditoriums must be 42 inches high, unless they interfere with sightlines, in which case they must be at least 26 inches high. Minimum 26-inch high guards are typically required in front of seating in balconies, galleries, boxes, and parterres. This is also the minimum required height at orchestra pits, voms, and along crossaisles. Guards required to be at least 26 inches high will typically be designed to be as high as sightlines allow, and the height of railings in front of boxes and parterres and at the orchestra pit is usually about 30 inches.

If a balcony aisle terminates at the balcony front, the guard at the end of the aisle must be at least 36 inches high and the diagonal dimension between the top of the rail and the nosing of the nearest tread must be at least 42 inches.

Theaters are one of the few building types where the public encounters guards that are less than 42 inches high, and the height of guards in theaters, especially in upper balconies, is often raised as a concern. A guard less than 42 inches high is perceived as unusual, and it makes some patrons feel uncomfortable or unsafe. We can sympathize and acknowledge that they feel unsafe, without concluding that the environment itself is unsafe. In a review of this issue for the American Society of Theatre Consultants, Paul Sanow concludes that “falls from theatre balconies are simply not common” and the issue is one of “perception of risk.”