To Flex or Not to Flex? And How to Flex?

by Denelle Wrightson


Modern libraries are asked to be many things to many people many times each day. While space needs for collections have remained static or decreased, the need for areas of varying sizes for events, programs, meetings, collaboration and creating content has exploded.

Spaces of different sizes are required to accommodate:

  • Large community meetings and events programmed for up to 300 people and held a few times each year
  • Weekly programs for 30 – 50 children or adults and special events for 100 or more
  • Alternative uses of spaces intended for events and programs when none is being held
  • Diverse user behaviour and the need for collaborative and quiet spaces
  • Speedy transformations to suit a variety of purposes

Flexible Spaces can be Greener and Less Expensive

In addition to providing for a variety of uses, flexible spaces have other advantages. They support aims of greater sustainability and are usually less costly and faster to build and maintain than spaces with solid walls. For example, a design for a meeting space that includes three separate rooms for meetings of 50, 100, or up to 300 participants would require approximately 5,000 square feet (465 square metres). A project like this would typically cost about US$250 per square foot (approx.US$2325 per square metre), or US $1,250,000 for the total project.

In contrast, one large divisible room for 300 would take 3,200 square feet (297.3 square metres) of space. Assuming the use of the highest performance and cost of movable walls to allow the room to be easily divided three ways into alternative configurations, the cost would be US$1,000,000. Reducing the size has a very positive impact by lowering the footprint required for the building and its overall cost. At the same time, the environmental impact would be less with a more efficient use of the site, lower demand for building materials and reduced energy consumption. Movable walls can be introduced into existing or new spaces.

Creating Flexible Spaces

There are many ways to create flexible spaces. Mobile furniture can be used to rearrange areas and is often found in children’s sections in libraries to create room for presenting programs or in open library areas to accommodate exhibitions or special events.  Portable dividers, movable partitions and even curtains can be used to create space separation. Acoustical or sound separation between spaces is very important when there are simultaneous events, meetings, programs or collaborative activity adjacent to each other. Creating movable (sometimes known as operable[1], mobile or flexible) walls has become a more effective solution to the creation of separate spaces when sound containment is required.

Too many Choices? Deciding Which Approach is Best

The variety of flexible wall solutions available can be very confusing and the advantages and disadvantages of each difficult to assess. Demountable walls can be used. Garage-type opening doors are also used to segregate spaces. Sliding glass doors, folding walls or accordion partitions and side-stacking mobile walls are also possibilities. The following describes some of the options.

Demountable Walls

Most of the major office furniture manufacturers offer some type of demountable wall which can be installed in any open space.  If sound separation is important, the space will need a ceiling ideally no higher than 12 feet (3.66 metres). The modular panels rest on the floor and anchor to the ceiling. They can be made of many materials, ranging from glass to markerboard, with fabric or painted surfaces. They are very effective for changing large open areas into several smaller spaces. Installation is quick and efficient.  They can be cost competitive with conventional fixed walls, with reduced downtime while providing the ability to reconfigure. The end result of using demountable walls is as close as possible to standard wall construction with some level of flexibility. The solution does not provide for day to day reconfiguring of the walls. This class of premanufactured wall is intended for occasional use and movement when there is a change to the normal use of the building. The Sound Transmission Coefficient (STC) is 50 for solid walls and 45 STC for walls that include glass.

Garage Doors

Many libraries have started to use garage or overhead coiling doors to provide a way to open interior space easily to the exterior or to open one space into an adjoining space.  This solution is most cost-effective and provides the option of using glass panels or more standard opaque doors. The size of the opening is limited but multiple doors can be combined. As these doors do not seal well to their adjacent fixed walls, the acoustical and climate separation is on the low end for flexible partitions. The other cautionary note is that garage-type doors require tracks suspended from a ceiling and when in the open position cover any items in or suspended from the ceiling including lights, sprinkler heads, supply and return heating, ventilation and air-conditioning, and smoke detectors. A coiling overhead door eliminates the tracks, but requires space for a large box above the opening to hold the retracted door. A garage-type door is the least expensive solution but provides the least amount of sound separation. The Sound Transmission Classification (STC) for this kind of separation is approximately 15.

Sliding Glass Doors

Sliding glass doors are offered by many manufacturers such as Modernfold and Hufcor. Both these companies operate internationally. Sliding glass doors provide good visual connection between spaces as well as transparency of activity and facilitate the use of natural light. Some require a floor track and rail for the panels to slide along. Others use ceiling tracking systems. The maximum standard height is 10 feet (6 metres) with the width of the panels varying according to various international standards and practices (24 – 48 inches in the United States). The glass panels when open can stack to either one or two sides. Panels are single or paired. With single panels, each panel pivots and slides to the stacking location. With paired panels, two panels fold before sliding to the stacking location. Some manufacturers offer these systems with manual or electric operation. Pass doors can be included. The STC varies greatly from manufacturer to manufacturer.  Some include seals typical of outdoor, weather resistant models and achieve very high STCs similar to those for demountable walls. These high-performance walls usually require a raised threshold and may not be suitable for some spaces, due to disability concerns. Changes in the installation will limit the STC value to about 30.

Accordion Partitions

Accordion or folding partitions have been used for many years. They provide a visual separation between two spaces and are very quick to open and close, and almost as easy as opening a curtain. Folding partitions can be used to create an enclosure around a corner and provide for greater design flexibility. They function in openings up to 12 feet (3.66 metres) high and 60 feet (18.3 metres) wide. They provide useful sound attenuation if the sound separation type is specified appropriately. The least expensive type provides no rated STC, while the highest rated can provide up to STC 40.

Acoustical Side-Stacking Mobile Walls

Several manufacturers make high quality side stacking mobile walls.  Two of the largest in the United Sates include Modernfold and Hufcor. As already noted, these companies operate worldwide and both offer hinged walls which operate electrically and employ top and bottom sound seal systems. These panels can be up to 40 feet (12 metres) high and have openings up to 230 feet (70 metres) wide. They are available in a wide variety of finishes and design and are primarily intended for large convention centres, hotels and ballrooms. They stack in a variety of ways. The important issue to remember when selecting this solution, similar to the sliding glass partitions, is the space necessary to store the stacked panels when open. In a typical multi-purpose meeting room where the flexible opening is 40 feet (12 metres) wide, a storage area of approximately 5 square feet (.5 square metres) would be required, resulting in a reduction in seating capacity of up to 60 seats, or reduced sightlines within the building. The STC ranges from 28 to 56.

Manual operation of the panels is available at a reduced cost. The panels inevitably require more time to open and close manually and tend to have maintenance issues with alignment and sound seals, especially at the bottom.

Acoustical Vertically Stacking Mobile Walls

The Cadillac of flexible wall solutions is the acoustical vertically stacking mobile wall system.  It is the only mobile system that does not need floor space to store the panels and is available in an electric version only since it raises the panels vertically and stores them in the ceiling.  It requires adequate space and structural support.  The leader in producing this type of partition is Skyfold who offer glass as well as opaque panels.  The company is based in Canada but operates worldwide. All the options available with demountable walls and side stacking panels are offered.  This solution is the most expensive but does not require the additional floor storage space associated with other mobile solutions.  This system is the only one capable of providing a mobile partition with the highest STC of 60.

Sound Separation and STC Rating

Sound Testing Classification (STC) measurements have been provided for the various options outlined. Some qualifying remarks about STC values are needed. The ones quoted are the manufacturers’ laboratory test values. In the laboratory, the sample is installed and sealed as perfectly as possible, yielding better results than would be typically received in field construction, even with good workmanship. Acousticians typically lower the published laboratory-tested value by at least 5 STC points to provide a more realistic assessment for the expected performance in real life. What does an STC of 40 versus 60 mean? Below is a general guideline of what the real results of the different STC ratings mean.

The following Sound Transmission Class (STC) ratings provide the described subjective noise isolation.  The isolation provided is highly dependent on quality of construction and level of detailing, but is a good baseline from which to select different partition types.  We recommend these be reviewed with the Owner to determine which level of isolation is required as specific noise sensitive areas[2]

Table 1. STC Rating

STC Subjective Noise Isolation
  40 Normal Level voices can be heard with some effort including some individual words and phrases. Raised level voices and music could be heard with little effort.
  45 Normal level voices could be heard with great effort — subjectively heard as a murmur. Raised voice conversations could be heard with some effort including some individual words or phrases. Music, especially low frequencies, could be heard easily.
  50 Normal level voice conversations effectively blocked. Raised voice conversations heard with effort — subjectively heard as muffled voices.  Music heard, especially low frequencies.
  55 Loud speech heard faintly. Music audible with low frequencies considered disturbing.
  60 Loud speech effectively inaudible. Music faintly heard, but low frequency sounds still disturbing.
  65 Loud music heard faintly which is problematic if adjoining spaces are highly sensitive to noise. Sound flanking limits most partitions to STC 65 on suspended floor slabs.
  70 Most noises effectively blocked. STC 70+ may not be achievable in the field due to sound flanking paths. Exceptional detailing and QC is required to achieve high noise isolation.


Cozby Library
Cozby Library and Community Commons, Coppell, Texas


The need for greater flexibility in library buildings has become apparent, with changing user behaviour and the provision of additional services to meet wide-ranging community needs. Movable partitions and walls provide the opportunity for constant reconfiguration of library spaces. The higher quality (and more expensive) movable partitions can allow for simultaneous events in adjacent rooms. The STC of the chosen solution is relevant to the type of use. Compatibility from a noise standpoint will always be an issue. It would not be wise, for example, to locate the Jane Austen Club meeting next to the Hip Hop Club gathering or the Bridge Club next to the Teens’ Homework Group. Even the best demountable or moving partition is not designed to isolate loud, low frequency sounds, and the same would be said for standard gypsum board as well. However the Jane Austen Club next to the Mystery Writers’ Club should be able to coexist just fine. The use of movable walls and partitions within libraries provides for greater flexibility, space optimization and effective and efficient operations.

[1] An operable (movable) wall is a system of individual solid or glazed panels that can moved independently from each other which when fitted together end to end form a continuous flat, faceted or curved wall. Operable wall panels are designed to be easily maneuvered and operated. They are top hung from either a surface or recessed mounted head track and no floor track is required. Various head track formations are possible to provide different stacking options. Each panel is provided with interlocking seals to each vertical profile, retractable top and bottom seals are either manually or electrically operated. The seals pressure close against the ceiling channel and floor to provide a continuous seal. Individual panels can incorporate single or double door sets and junction panels to form various configurations. Final closure of the wall can be by a telescopic panel, extending wall jamb or full height door.

[2] STC chart created by Texan acoustical consulting firm WJHW 

Author details

Denelle Wrightson is the President of Library Planning & Design. She is based in Dallas, Texas, and provides advice and assistance to libraries, specializing in the areas of master planning and programming for public libraries. She has been involved in over 250 library projects and worked on all types of libraries. She is a LEED Accredited Professional and was Chair of the ALA LAMA Library Interiors & Furniture Committee from 2011 to 2017. Denelle is the ALA representative on the IFLA Library Buildings and Equipment Section Standing Committee from 2015-2019.

Photo credits: Lara Swimmer, Dirtt, Haworth, Modernfold, Hufcor, Skyfold, Cozby Library and Community Commons, Coppell, Texas.



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