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Windows and Daylighting

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Design Guidance

Overall Strategies

Maximizing the thermal performance of the windows in an office space can drastically reduce the energy spent on heating and cooling. Window upgrades play a key part in a sustainable workplace. A window's energy efficiency criteria is based on the entire window assembly including the frame and the glass. Factors such as heat loss, solar gain, and visible light can be optimized by carefully selecting window coatings and frames. Solar-powered shades can be used to limit solar gain in the summer months or vice versa in the winter months. There are several important factors to consider regarding glazing. The first factor relates to the efficiency of the glass which contributes to the window's U-Factor and Solar Heat Gain Coefficient (SHGC). Typically, a lower U-Factor and SHGC is desired. Additionally, Visible Light Transmittance (Tvis) must be considered. An optimal window system achieves desired efficiency while allowing light penetration.

Fiberglass

Fiberglass glazing is typically only used for skylights and other specialty applications. Fiberglass glazing has excellent thermal properties and is extremely durable. Fiberglass may cost more than standard glass and may turn yellow over time.

Storefront / Curtainwall Assemblies

Storefront or curtainwall assemblies are "built-up" systems of glazing and metal frames that can span full or multiple floors. These systems require careful study of both the quality of glazing and the recycled content of the metal frame.

Interior Light Shelves

Interior light shelves direct daylight deep into a space by bouncing natural light from the light-colored shelves up to the ceiling, where it is reflected down to occupied areas. Blinds and other daylight control devices should be installed as part of a good daylight design strategy because uncontrolled natural light can cause glare.

Clerestory Window

Clerestory windows allow daylight to penetrate into a space. They are designed to allow daylight to penetrate a space, and therefore are located above eye level.

Skylights / Solar Tubes

Skylights/light tubes allow daylight to penetrate into a space. They are typically located in the roof/ceiling and can vary in size. Certain solar tracking skylights have mirrors in them that track the sun in order to maximize the amount of daylight brought into the space. Installation of either exterior baffles or interior shades on skylights provide control of natural light flow allowing for the minimization of heat gain and glare.

Skylights / Solar Tubes

Skylights/light tubes allow daylight to penetrate into a space. They are typically located in the roof/ceiling and can vary in size. Certain solar tracking skylights have mirrors in them that track the sun in order to maximize the amount of daylight brought into the space. Installation of either exterior baffles or interior shades on skylights provide control of natural light flow allowing for the minimization of heat gain and glare.

Green Tips

  • Install double or triple paned glass to increase efficiency and reduce energy consumption.
  • Use interior light shelves to effectively distribute the natural light throughout a space.
  • Consider installing solar powered window shades or blinds to reduce glare and allow control of the daylight entering a space.
  • Use light color schemes such as white or tan painted walls to reflect natural light throughout the space.
  • Select durable, efficient window frames that can withstand exposure to exterior elements and reduce thermal bridging.
  • Consider windows with low-emissivity coatings to prevent heat and ultra-violet (UV) rays from passing through the glass.
  • Consider installing frosted or fritted glass or window blinds to allow daylight to enter the office space while still maintaining privacy.
  • Skylights can provide copious ambient light, minimizing the reliance on electric lighting for portions of the day.
  • Shading devices can be employed to minimize glare and heat gain.
  • Focusing window glazing in a specific direction can assist in either harnessing more direct light (to the south) or providing more diffuse, constant ambient light (to the north).
  • Install daylighting control systems (e.g. photosensors) with zones for electric lights that are dimmed or switched off when there is adequate sunlight.
  • Commission the lighting controls system to make sure it works as designed.
  • Add interior or exterior light shelves to extend the daylighting zone into the laboratory space, while reducing glare. These are most effective on south facades.
  • Specify light-colored interior spaces to help distribute natural light more effectively.

Compare Windows and Daylighting Options

EB = Existing BuildingsNC = New Construction and Major Renovation

Legal Requirements

Guiding Principles

  • Recycled Content ( Guiding Principles, Executive Order 13693 [EB, NC])
    Section: V. Reduce Environmental Impact of Materials

    Per Section 6002 of the Resource Conservation and Recovery Act (RCRA), for EPA-designated products, specify products meeting or exceeding EPA's recycled content recommendations. For other products, specify materials with recycled content when practicable. If EPA-designated products meet performance requirements and are available at a reasonable cost, a preference for purchasing them shall be included in all solicitations relevant to construction, operation, maintenance of or use in the building. EPA's recycled content product designations and recycled content recommendations are available on EPA's Comprehensive Procurement Guideline website.

  • Environmentally Preferable Product ( Guiding Principles, Executive Order 13693 [EB, NC])
    Section: V. Reduce Environmental Impact of Materials

    Use products that have a lesser or reduced effect on human health and the environment over their lifecycle when compared with competing products or services that serve the same purpose. A number of standards and ecolabels are available in the marketplace to assist specifiers in making environmentally preferable decisions. For recommendations, consult the Federal Green Construction Guide for Specifiers.

  • Energy Efficiency ( Guiding Principles, Executive Order <span>13693</span> [NC])
    Section: II. Optimize Energy Performance

    From the Guiding Principles for NC: “Employ strategies that minimize energy usage. Focus on reducing energy loads before considering renewable or clean and alternative energy sources. Use energy efficient products as required by statute.”
    Determining Compliance: “For new construction, ensure energy efficiency is 30% better than the current ASHRAE 90.1 standard. For modernization, ensure: (1) energy use is 20% below the fiscal year (FY) 2015 energy use Baseline, (2) energy use is 30% below the FY 2003 energy use baseline, (3) the building has an ENERGY STAR® rating of 75 or higher, or (4) for building types not in ENERGY STAR Portfolio Manager, where adequate benchmarking data exists, the building is in the top quartile of energy performance for its building type. For new construction and modernization, use energy efficient products, as required by statute.”

  • Daylighting and Lighting Controls ( Guiding Principles, Executive Order <span>13693</span>&nbsp;[EB])
    Section: IV. Enhance Environmental Quality

    Guiding Principles for NC & EB: “Maximize opportunities for daylighting...except where not appropriate because of building function, mission, or structural constraints. Maximize the use of automatic dimming controls or accessible manual lighting controls, task lighting where life cycle cost-effective, and appropriate shade and glare control.”
    Determining Compliance: “Maximize opportunities for daylighting in regularly occupied space, automatic dimming controls or accessible manual controls, task lighting, and shade and glare control.”

  • Energy Efficiency ( Guiding Principles, Executive Order <span>13693</span> [EB])
    Section: II. Optimize Energy Performance

    From the Guiding Principles for EB: “Employ strategies that minimize energy usage. Focus on reducing energy loads before considering renewable or clean and alternative energy sources. Use energy efficient products as required by statute.”
    Determining Compliance: “Ensure: (1) the building has an ENERGY STAR rating of 75 or higher, (2) energy use is 20% below the FY 2015 energy use baseline, (3) energy use is 30% below the FY 2003 energy use baseline, or (4) energy efficiency is 30% better than the current ASHRAE 90.1 standard. Use energy efficient products, as required by statute.”

  • Indoor Air Quality ( <span id="docs-internal-guid-f1e45d2e-bf74-2656-0c1b-777092dd54a0"><span>Guiding Principles, Executive Order <span>13693</span> [NC&amp;EB]</span></span>)
    Section: IV. Enhance Indoor Environmental Quality

    Guiding Principles for NC&EB: Take actions to ensure optimal indoor air quality, including:
    (i) “Test for radon in buildings and mitigate high levels.”
    (ii) “Establish policy and implement a moisture control strategy to prevent building materials damage, minimize mold growth, and reduce associated health risks.”
    (iii) “Use low emitting materials for building construction, modifications, maintenance, and operations. In particular, specify the following materials and products to have low pollutant emissions: composite wood products, adhesives, sealants, interior paints and finishes, solvents, carpet systems, janitorial supplies, and furnishings.”
    (iv) Establish a policy and implement necessary protocols to protect indoor air quality during construction, renovations, repairs, and alterations, and during occupancy.
    (v) “Prohibit smoking in any form within the building and within 25 feet of all building entrances, operable windows, and building ventilation intakes.”
    (vi) “Use integrated pest management techniques as appropriate to minimize pesticide usage.”
    Determining Compliance: “Develop and implement an indoor air quality policy that considers the following: moisture control, use of low emitting materials and products with low pollutant emissions, necessary protocols to protect indoor air quality during construction and in the finished building, prohibition of smoking in any form inside and within 25 feet of all building entrances, operable windows, and building ventilation intakes, and use of integrated pest management techniques.”

  • Occupant Health and Wellness ( <span id="docs-internal-guid-f1e45d2e-bfa3-fe9d-96f4-ff81811a5b68"><span>Guiding Principles, Executive Order <span>13693</span> [NC&amp;EB]</span></span>)
    Section: IV. Enhance Indoor Environmental Quality

    Promote opportunities voluntary increased physical movement of building occupants such as making stairwells a desirable option for circulation, active workstations, fitness centers, and bicycle commuter facilities. Support occupant health by considering options such as providing convenient access to healthy dining options, potable water, daylight, plants, and exterior views where possible.
    Determining Compliance: Where feasible, “promote opportunities for voluntary increased physical movement of building occupants such as making stairwells an option for circulation, active workstations, fitness centers and bicycle commuter facilities; and support convenient access to healthy dining options, potable water, daylight, plants, and exterior views”

  • Material Content and Performance ( Guiding Principles, Executive Order <span>13693</span>&nbsp;[EB])
    Section: V. Reduce the Environmental Impact of Materials

    From the Guiding Principles for EB: Procure construction materials, products, and supplies that have a “lesser or reduced effect on human health and the environment over their life cycle when compared with competing products or services that serve the same purpose”, including:
    (i) “Use Resource Conservation and Recovery Act (RCRA) section 6002 compliant products that meet or exceed EPA’s recycled content recommendations for building construction, modifications, operations, and maintenance.”
    (ii) “Per section 9002 of the Farm Security and Rural Investment Act (FSRIA), for USDA-designated products, use products with the highest content level per USDA’s biobased content recommendations.”
    (iii) “Purchase products that meet Federally Recommended Specifications, Standards and Ecolabels or are on the Federal Green Procurement Compilation.”
    (iv) Eliminate, to the maximum extent practicable, “ozone depleting compounds and high global warming potential (GWP) chemicals where EPA’s SNAP has identified acceptable substitutes or where other environmentally preferable products are available” during construction, repair, or replacement at the end of life.
    Determining Compliance: “Procure products that meet the following requirements where applicable: (A) RCRA section 6002, and (B) FSRIA section 9002, and (C) Federally Recommended Specifications, Standards and Ecolabels or are on the Federal Green Procurement Compilation for other green products, as appropriate, and (D) Avoid ozone depleting compounds and high GWP chemicals.”