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Everything You Need To Know - 4 Part Series: Sight Lines

In the beginning of this 4 part series on Educational Seating, I listed out all the common terms used in the educational seating industry.  Week 2, covered Seating Code Considerations and all the codes and restrictions you need to consider when planning your space. In Week 3, I went in-depth on types of Seating Configurations, placement, and mixing configuration designs. This post I’m going over a very important piece of the seating configuration puzzle: sight lines.

Sight lines refer to the chair occupant’s unobstructed view of a focal point on the stage or screen. The focal points vary and are most often determined by the facility's main use. Examples include:

  • Dance performances dictate the need for a clear view of the dancers’ feet

  • Worship services require a clear view of the speaker’s head and shoulders

  • An unobstructed view of the entire screen is required in a movie theatre

There are two methods for improving sight lines: changes in elevation and chair stagger.

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Elevated sight line study:

Sight lines can be improved by elevating the focal point and creating elevation change between rows. The use of a radius layout also helps to improve sight lines. Irwin Seating Company can provide a study showing sight line clearances. Of course, this data is only relevant in the preliminary stages of design. Once concrete is poured, the mold is cast and sight lines cannot be improved easily.

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Above is an example of a sight line study that shows clearances for each of the rows, or selected rows, in the auditorium. The angular differences from row-to-row provide excellent sight line clearance near the front of the auditorium. In the rear of the auditorium, it is necessary to increase elevation at a greater rate than in the front of the room.

Chair Stagger Methods:

Irwin Seating Company can help optimize sight lines, but a building’s design is the most important factor. There are four distinct arrangements of staggered seating layouts typically used:

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Alternating Chair Sizes: By alternating chair sizes within rows, a stagger is created that allows patrons to see between those seated in front of them.

Odd – Even Parallel: This method alternates the size and quantity of chairs in a row in order to improve sight lines. In the example shown above, alternating rows of 11, 20" chairs and 10, 22" chairs improves sight lines. Rows of nine or fewer chairs are very difficult to accommodate using this method.

Odd – Even Tapered: Pick a chair size, and increase the chair count by one in successive rows. Obviously, this offers limitations on chair counts.

Sawtooth Stagger: Simply shift alternate rows by a half chair total, or shift successive rows one-quarter chair each way.

The alternating chair sizes and the parallel odd – even methods are the most common methods used to create chair stagger. The saw-tooth stagger is not used often, because it creates uneven row ends.

Rear Wall Accommodation:

Accommodation of rear walls is always an important consideration but is critical when treads and risers are being used. Here's a simple example:

A commonly specified row spacing is 36", and a common misconception is that all rows need to be designed and constructed to that dimension. Designing rear rows that bump up against an obstruction at the same depth as others fails to account for the necessary back pitch overhang, and this has ripple effect throughout the space.

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In the illustration above, the rear row is installed tight against the wall, but in order to provide the required clear passage, the row in front needs to be installed forward of where it should be. This is repeated right on down the line. Doing this creates hazardous gaps along the row where a patron can slip a foot between the riser face and the chair back. To alleviate the safety issue, backs in the rear row are often installed at an uncomfortably erect pitch, perhaps with a different model that has a smaller envelope or, in some instances, not installed at all.

The preferred method to accommodate a rear obstruction is to design the last row with a longer tread as shown below.

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This design allows proper placement of the chairs to act as a gap filler while providing the required clear passage.

The photo below illustrates this issue. In this auditorium, room for the rear wall was taken into consideration, and the rear tread is 44" deep with the tread depth in the rows before at 38". However, the acoustical panels were not considered, and the backs had to be installed at a very erect pitch to keep clear passage at an acceptable space. As this shows, if the rear wall and top tread is not taken into consideration, all rows of seating get pushed forward, creating hazardous gaps down the row between the chair backs and riser face.

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Intermediate Steps:

Intermediate step design and construction is another subject that needs to be considered carefully to insure patron safety. When we draw a layout, we try to fill the row from side-to-side to eliminate hazardous gaps so it's critical to design intermediate steps that provide enough space to fit the required chair sizes and quantity in the row. For straight layouts, we can often provide different chair sizes to fill the space between steps as shown here.

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This issue of hazardous gaps with intermediate steps is most often seen when treads and risers are constructed on a radius. A common mistake occurs when the intermediate steps are constructed parallel to a wall or some other architectural element. Chair standards need to be installed perpendicular to the riser face and dangerous gaps are created when steps do not match the angle of the chair standards. Here is a simple example:

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Riser Mounting Chairs:

Irwin Seating Company can mount chair standards to the face of a riser. Most models can be mounted on risers between 4-1/2" to 21" in height. Part of my job is to verify the chair model and riser height compatibility.

Requirements for mounting chairs to concrete risers are illustrated here:

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Irwin Seating Company can (and has) mounted chairs to other substrates like wood, steel and aluminum. Should you wish to use an alternative material, we will verify and discuss with you the feasibility of the requested material.

Floor Mounting:

Floor mounting chairs is the most common method of securing them to the building. Even chairs on risers are often mounted to the treads and not the riser face. Inclined floors are accommodated with the chair's mounting feet angled to match the incline of the floor.

Requirements for mounting to concrete floors are shown here:

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Radius design issues:

To begin the discussion on radius design, we need to point out that different models have different rules in regards to the radius they can be installed on. Early in your project, this would be discussed.

The use of a radius layout can help improve sight lines. One common mistake is designing all rows with a constant radius. Doing this pinches the aisle ends together, which can compromise back to back spacing and clear passage. Using concentric radii keeps the row spacing consistent through the entire row.

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When adding an incline to a radius layout, it is important to note that the concrete breaks must follow the radii. It is important that incline breaks be set in an increment of the row spacing for two important reasons:

  1. For comfort, the chair should be installed on the same incline that the patrons foot will rest on

  2. To insure anchor integrity, anchors need to be set 2" from a break

In addition, an inclined radius must have a bowled floor in order to keep chair standards from "toeing" in and to keep the chair level.

Aisle Lighting:

We provide a number of aisle light accessories that are intended to illuminate the edge of an aisle and provide a pool of light on the adjacent floor or step. Often, aisle lights are turned off during a performance so as not to distract performers and can not be used as emergency lighting. Aisle lights are NOT designed to provide code compliance across the entire width of an aisle, they should be considered a part of a comprehensive lighting plan. Communication and coordination between the architect, general contractor, electrical contractor and Irwin Seating Company is key to proper installation of aisle light accessories.

In recent years, the use of 120 volt incandescent lights has been replaced with low voltage LED lights which are brighter, last longer and are more safe than lighting used in the past.

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Junction Boxes:

Location of aisle light junction boxes that supply power to aisle lights is important to good auditorium design. As part of the seating layout and field check process for each project, Irwin Seating Company produces a drawing which locates the aisle light junction boxes in conjunction with the seating to be installed. Junction boxes must be located to prevent them from obstructing traffic flow and creating a trip hazard. The photo below shows poor placement of a junction box. This is often the result of poor dimensional information being supplied when the layout is being drawn.

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The proper position for a floor box or stub-up serving an aisle light is between the aisle standard and the first center standard directly below the seat. Ideally it is placed 8” inboard from the aisle line - then centered, front-to-rear on the standard’s mounting foot. The drawings below illustrate two of the most common aisle light conditions.

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Please Note: connection of 120 v aisle lights and our E-Link power system are different from what is shown above, please contact us if you have questions for accessories other than LED aisle lights.

Junction boxes and connectors can vary by local code or contractor preference (see photos below). The pre-wired standards with LED lights from Irwin Seating are always supplied with 3/8" flexible conduit and contractor supplied components must accommodate that.

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What you want to be sure of when you're in the beginning of your project, you want to be sure you find experienced, trustworthy, and reliable individuals to help you through the process. I can help guide you through the complexity of seating design and placement, coding considerations, guest comfort, and sight lines.

Everything You Need To Know - 4 Part Series: Seating Configurations

We're in Part 3 in our 4 part series of everything you need to know about educational seating. This week, we're going over seating configurations. If you missed the past two weeks, be sure to catch up on last week's post on coding considerations. Week 1 we discussed common industry terms and expressions that you need to know while working with vendors and architects on your project. If you missed it, you’ll want to go read it first to familiarize yourself with the language.

Seating Configurations:

The configuration of a space used for public assembly is usually determined by desired capacity and use - For example: house of worship, school, arena, concert venue, etc. A small space may be fine with straight rows on a flat or sloped floor but as the need for capacity increases, the use of radii, treads and risers, or balconies (or some combination) is often used to improve the patron experience, safety, sight lines and to save space.

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Straight Rows:

In the past, seating spaces were often installed in banks of straight rows, and the best theaters had sloped floors or a balcony. Usually, chairs were all the same size (width) which hurt sight lines. In addition, little consideration was given to persons with mobility issues. Access to exits was also limited. As I talked about last week, code considerations now are extremely important as well as regulated.

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Historic safety code for conventional layouts specified there could be a maximum of 14 chairs between legal aisles, and a maximum of 7 chairs between an aisle and wall. Rows had to provide clear passage of 12".

This type of layout is still used today from time to time, but often in very small spaces. Modern design and construction techniques, and an awareness of patron comfort make this type of layout the exception and not the norm.

Continental Seating:

Another common configuration was a continental arrangement with aisles along the outside of the seating area. This arrangement is not widely used any longer because patrons prefer quicker access to an aisle, but it is still seen from time to time, particularly in large performance venues.

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Historic safety code for continental layouts specified there could be no more than 49 chairs to an aisle - maximum 99 chairs per row. In addition, code requires additional exits at the end of rows to a ratio of one exit for each five rows. Clear passage requirements are greater than those required for a conventional layout up to a maximum of 24".

Mixed Design:

Current design frequently uses a combination of sloped floors, radii and risers. This provides patrons with easier access to aisles and exits while helping to improve sight lines.

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It's not uncommon to see the seating closest to the stage arranged in a continental arrangement while the back rows are installed on risers.

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Often seating sections will be in straight rows but the banks are angled toward the stage - this is very common in places of worship.

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Depending on your guest's needs and the needs of your space, whether it's straight rows, continental seating, or a mixed design, there is something for every need and every space.

Come back next week for the final part in our 4 post series - sight lines.