Designing Easy to Use Operable Windows

By Steven Watchorn, LEED AP BD+C & Jenne dos Santos

In addition to a window’s primary function of letting natural light into buildings, operable windows also provide a stronger connection to the outdoors allowing users to control natural ventilation and, in some cases, provides a means of emergency egress. 

So, operable windows must be just that:  Operable.  The Merriam-Webster Dictionary defines the term “Operable” as the “ability to perform a function: exert power or influence,” but the ability to perform these functions varies greatly from window to window.  In judging a window’s ability to perform the function of opening, we must assess how much power the user must exert to achieve this result. 

This assessment of the window’s ability to open becomes especially critical when designing windows in public spaces and buildings occupied by elderly and/or physically-disabled persons.  Designers must pay particular attention to the various components of windows and to the applicable codes and standards that may have certain requirements that must be met.  For instance, the Americans with Disabilities Act (ADA), Appendix A4.12.2 (Window Hardware) recommends that operable windows require no more than a 5 pound force to open or close, and that locks, cranks, and other hardware comply with set reach ranges.  However, this section is only an advisory, and many other accessibility codes fall short of assessing a maximum allowable force for the operation of windows. 

In Massachusetts, the Massachusetts Architectural Access Board (MAAB; 521 CMR) reserves a section for windows to be included in a future edition.  The 5 pound force maximum is set for the operation of doors and controls; however, whether windows are included may be open for interpretation.  One school of thought may be that doors and operable windows have a lot in common.  But windows are, in fact, much more complex and have many more variables than doors, such as size, weight, and availability of hardware options.  Windows can be located anywhere on a wall and can hinge on any side or slide open in almost any direction.  So, the ability to define an opening force that applies to all windows is much more complex than it is for doors.

A review of other codes and standards reveals that standards for window operability remains vague or undefined; many codes cross-reference each other, often raising questions regarding interpretation.  The following is a list of just a few of the codes or guidelines that set certain parameters and that may be applicable, depending on the jurisdiction, building use, and/or funding source. 

  • ICC/ANSI  – American National Standards Institute (non-governmental organization)
  • ADA – Americans with Disabilities Act (U.S. Department of Justice) Civil Rights Antidiscrimination Statute
  • ABA – Architectural Barriers Act
    These accessibility standards closely matchADA, and are required for federally-funded facilities open to the public, in accordance with the UFAS standards (see below)
  • UFAS – Uniform Federal Accessibility Standards
  • Federal Fair Housing Act – Design Manual; U.S. Department of Housing and Urban Development (HUD)
  • IBC – International Building Code (2009)

In addition to abiding by the applicable codes and standards, architects must consider the many options that will impact a window’s ease-of-use, no matter who it is intended for.  Operable windows such as double-hung, single-hung, awnings or hoppers, sliders, and casements each require a different movement and/or muscle group to operate and are all available with numerous handle and hinge options.  The glass components, opening size, and the height of the window above the finished floor, as well as the weight of the window, all play a vital role in how easily they operate.  Windows also come with a variety of hardware options to select from, including locks and lifts and their intricate mechanisms.

These intricacies, and the multitude of options combined, must be considered using a wholistic approach.  Currently, window manufacturers lack any standard tool to predict or determine the opening force, in part because of all of these options, but also because the glass, frame material, locks, and balances are each provided by third party suppliers and assembled by the window manufacturer. 

Compounding the difficulty to provide a standard tool to assess whether a window is “accessible” are additional requirements that may come into play such as hurricane and blast resistant glass, energy code requirements, and/or sustainable products that are increasingly stringent and can have a drastic impact on the overall weight of a window.

Designers must rely on best-practice standards, current regulations, and the knowledge of window manufacturers to select the most appropriate window for each space and the people it is intended for.