Specifying windows for behavioral healthcare projects

Metropolitan St. Louis Psychiatric Center in Missouri sought exceptionally strong windows, while still offering a symmetrical exterior appearance between secure and nonsecure areas. To meet this challenge, a custom, 152-mm (6-in.) deep system with a hidden ventilator on the exterior and a window on the interior was engineered. The interior security glass was a five-ply, glass-clad polycarbonate glazed into the sash with mechanically fastened, continuous glazing beads. Tamper-proof locks prevent unwanted access to the venetian blinds and ventilators sealed between the panes. For the hospital areas not requiring the high-security windows, a combination of thermal and acoustical high-performance window walls were specified. Photos courtesy Wausau Window and Wall Systems
Metropolitan St. Louis Psychiatric Center in Missouri sought exceptionally strong windows, while still offering a symmetrical exterior appearance between secure and nonsecure areas. To meet this challenge, a custom, 152-mm (6-in.) deep system with a hidden ventilator on the exterior and a window on the interior was engineered. The interior security glass was a five-ply, glass-clad polycarbonate glazed into the sash with mechanically fastened, continuous glazing beads. Tamper-proof locks prevent unwanted access to the venetian blinds and ventilators sealed between the panes. For the hospital areas not requiring the high-security windows, a combination of thermal and acoustical high-performance window walls were specified.
Photos courtesy Wausau Window and Wall Systems

As with selection criteria, additional site-specific pass/fail criteria may apply to drop-tested psychiatric windows. Depending on the furnishings and equipment accessible to the patients, simulation of physical attack with objects may be advisable. Exterior laminated glass should be used at windows at grade, courtyards, or porches with supervised patient access. Codes and standards vary widely by jurisdiction, so there should be consultation with onsite medical and security staff to determine appropriate resistance and necessary security.

It can be challenging to select products and materials that help create a pleasing environment, while enhancing the treatment process and maximizing safety. There are two 2012 resources offering guidance for material selection for inpatient behavioral units:

  • “The Design Guide for the Built Environment of Behavioral Health Facilities,” distributed by the National Association of Psychiatric Health Systems (NAPHS); and
  • the eighth edition of “The New York State Office of Mental Health’s Patient Safety Standards, Materials, and Systems Guidelines,” researched and maintained by Lomonaco and Pitts P.C. (doing business as Architecture Plus of Troy, New York).

These documents help examine the environmental aspects that can have a significant impact on patient safety and healing. The products they recommend have been evaluated to help lower patient risk.

Daylighting: enhance healing environments
AIA’s Guidelines for Design and Construction of Healthcare Facilities notes, “the environment should be characterized by a feeling of openness with emphasis on natural light.” In many new buildings, the design team attempts to maintain high visible light transmittance (VLT or VT) to ‘connect’ the occupants to the outside, provide views, and exploit natural daylighting. It is not only the amount of natural light that is important to building occupants, but also its quality, spectral composition, contrast, variability, and directionality.

Specifying tall windows helps maximize light penetration. Clerestories can be used to increase the effective height of transom lites without increasing window-to-wall ratio (WWR). Even relatively low WWR provides more than ample natural daylighting, when properly oriented and directed.

Within the programmatic limitations of a healthcare occupancy, natural daylighting is most energy-efficient if artificial lighting is automatically controlled. Photosensitive controllers and occupancy sensors can be used to dim or extinguish indoor lights when unnecessary. Artificial lighting accounts for about 40 percent of the energy used in a typical commercial building and generates at least three Watts of heat for each Watt of visible light.

Designers are encouraged to consider the concept of effective aperture (EA), the product of VT and WWR. This can be useful when assessing the relationship between visible light and window size. One should start with an EA of about 0.3 on the north and south elevation, minimizing glazing on the east and west elevations whenever possible. (WWR and EA are described in the article, “Finding the Model Citizen,” by Steve Fronek, PE, LEED GA, which appeared in the October 2012 issue of <i>The Construction Specifier</i>. (Visit www.constructionspecifier.com and select “Archives.”). Essentially, EA is the light-admitting potential of a glazing system, and determined by multiplying the WWR by the VLT. Lawrence Berkeley National Laboratory’s (LBNL’s) “Windows and Daylighting” online resource (windows.lbl.gov) offers additional information on this topic: “Window size and glazing selection can trade off with each other. Use the effective aperture approach when making these decisions: Larger window area requires lower visible transmittance; smaller window [area] requires high visible transmittance. … A good target value for effective aperture is between 0.20 and 0.30.”)

Unless ‘downward’ view is important, vision glass should be eliminated below sill height to reduce solar heat gain that carries no useful daylight. Generally, the window area should be no different in naturally lit buildings than other conventionally lit ones.

In addition to sunlight and views of nature, high-performance window systems can assist with energy efficiency. Thermally broken frames with triple glazing, along with a broad selection of exterior glass options, provide enhanced energy performance and condensation resistance.

American Architectural Manufacturers Association (AAMA) 501.8, Standard Test Method for Determination of Resistance to Human Impact of Window Systems Intended for Use in Psychiatric Applications, involves using a weighted impact device to apply a force simulating shoulder impact from a patient running full-speed into a window.
American Architectural Manufacturers Association (AAMA) 501.8, Standard Test Method for Determination of Resistance to Human Impact of Window Systems Intended for Use in Psychiatric Applications, involves using a weighted impact device to apply a force simulating shoulder impact from a patient running full-speed into a window.

Integral between-glass blinds reduce solar heat gain, offer privacy control without the potential dangers of exposed cords, and minimize the need for maintenance. The tilting of the slats can be keyed for staff operation or to allow patient control with a low-profile ligature-resistant control knob. Raise-lower controls for between-glass blinds are usually limited to custodial access. Controlling raise-lower access allows for uniform blind placement vertically and a resulting consistent exterior appearance.

Many areas in hospitals are required to maintain high relative humidity (RH), as well as prescribed positive or negative internal pressure, for therapeutic reasons or contagion control. Condensation occurs on any interior surface falling below the dewpoint temperature (Tdp) of interior ambient air. Tdp is dependent on temperature and RH, as warm air can hold more moisture than cold air. Condensation can be unsightly, unsanitary, and damaging to adjacent building materials over long periods. For these reasons, condensation should be assessed for both frame and glass in applications where high humidity is maintained.

Finite element computer models and the condensation resistance factor (CRF) test results using AAMA 1503, Voluntary Test Method for Thermal Transmittance and Condensation Resistance of Windows, Doors, and Glazed Wall Sections, can be useful in comparing products or as a basis for performance specifications. The design professional should exercise caution when using these tools to predict or prevent condensation on installed products. Field condensation on interior surfaces is affected by many variables, including:

  • component thermal performance;
  • thermal mass of surrounding materials;
  • interior trim coverage;
  • air flow conditions;
  • weather; and
  • mechanical system design.

CRF applies only to pre-defined configurations under controlled and steady-state laboratory conditions; it assumes some condensation is acceptable under the severest of winter conditions.

Air infiltration through windows and walls is also important to total building energy performance. It not only takes ‘sensible’ energy to heat or cool infiltrating air, but also may require ‘latent’ energy to remove undesirable humidity. Air infiltration performance is usually considered separately from other thermal performance characteristics.

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