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Can Quality Daylight and Views be Prescribed?

Qualitative and quantitative approaches in rating systems

Alan Scott

From the beginning, LEED recognized the important health benefit of exposure to sunlight and connection to the outdoors in a pair of Indoor Environmental Quality credits for Daylight and Views. The inclusion of these measures was based on decades of pioneering research on the health and productivity benefits of daylight, catalogued in publications like "Greening the Building and the Bottom Line" by Joseph Romm and Bill Browning, and reinforced by numerous subsequent studies.

Through multiple versions of LEED these credits changed little, maintaining their simplicity and the corresponding limitations to ensuring that the desired benefits would be achieved. Good daylight design requires finesse and is hard to boil down to a simple metric that applies to all projects. LEED v4 introduced some significant changes to the Daylight and Views couplet, and concurrently, newer rating systems like WELL Building, the Living Building Challenge (LBC), and FitWel offered different means to prescribe and measure quality daylight and views.

Let's explore the requirements side-by-side and consider the virtues and challenges of quantifying these fundamental attributes of healthy buildings. LEED v4 still has one credit each for daylight and views. In contrast, WELL includes two preconditions (like LEED prerequisites) and six optional optimizations (like LEED credits) that cover aspects of daylight and views, while the LBC has just one Imperative addressing both, and FitWel's checklist includes three related line items.

 

Daylight

Up through LEED v2009, the Daylight credit was usually achieved with simplified prescriptive calculations (based on window area/floor area ratio and visible light transmittance of the glazing). Compliance was also possible with less common options using daylight simulation models or field measurements. LEED v4 retained the field measurement option, but dropped the prescriptive calculations in favor of two daylight simulation options. The first option requires demonstration that spatial daylight autonomy (sDA, percentage of occupied floor area receiving adequate daylight) is achieved for 55 percent (2 points) or 75 percent (3 points) of regularly occupied spaces, and that annual sunlight exposure (ASE, percentage of occupied floor area with excessive direct sun exposure) does not exceed 1,000 lux for more than 250 hours per year in more than 10 percent of regularly occupied spaces (ASE1000,250). The analysis must show that the interior illuminance level is at least 300 lux for more than 50 percent of operating hours (sDA300/50%). The second option requires demonstration of illuminance levels between 300 and 3,000 lux between 9 a.m. and 3 p.m. on the spring and fall equinox, under clear sky conditions, for 75 percent (1 point) or 90 percent (2 points) of regularly occupied spaces.

WELL has an optimization (Feature 62, Daylight Modeling) identical to the first simulation option in LEED, and adds another optimization (Feature 63, Daylight Fenestration) that prescribes window to wall ratios, percentage of daylight glass (glass >7 feet above the floor), and the visible transmittance (VT) and uniform color transmittance of the glass. If daylight is consistently available from 9 a.m. to 1 p.m., it can contribute to the melanopic lux for a critical WELL precondition (Feature 54, Circadian Lighting Design).

In contrast, FitWel simply requires that daylight be provided in at least 51 percent of workspaces, and an LBC imperative (Civilized Work Environment) requires appropriate daylight in all occupied spaces, leaving it to designers to propose the best approach, within the constraints of the Net Positive Energy imperative that will require optimized daylight, shading and glazing performance.

 

Glare

While daylight is highly desirable, the benefits are undermined by excessive glare. The LEED v4 Daylight credit requires automatic or manually operable glare control on all transparent glazing in regularly occupied spaces, and identifies acceptable means including interior blinds or shades, or movable exterior louvers, screens or awnings.

WELL addresses several different aspects of glare, starting with a precondition (Feature 56: Solar Glare Control) similar to the LEED Daylight credit requirement, but with unique requirements for operable shading of vision glazing (including shades, blinds or dynamic glazing) and fixed or operable daylight management for daylight glazing (including fixed exterior shades, interior light shelves or dynamic glazing). WELL also includes three optimizations focused on glare reduction:

  • Feature 57: Low Glare Workstation Design, requires workstations within 15 feet of windows be configured with computer screens within 20 degrees perpendicular to adjacent windows.
  • Feature 59: Surface Design, which prescribes average light reflectance values (LRV) for ceilings, walls and furniture to reduce contrast ratios and glare.
  • Feature 60: Automated Shading and Dimming Controls, which requires automated shading for glare control on windows larger than 6 square feet.

FitWel requires only that operable shading be provided for windows in at least 51 percent of workspaces, while the LBC reminds designers to address visual acuity and comfort, but does not prescribe glare reduction solutions.

 

Views

From inception, the LEED Views credit addressed quantity of views (90 percent of regularly occupied spaces), but did not stipulate what should be visible outside the windows. This has shifted with the v4 Quality Views credit, dropping the minimum floor area to 75 percent, but now requiring that views be available from multiple lines of sight, or offer several view types (e.g., flora and fauna, sky, movement or distance). WELL takes a different approach with a views-focused optimization (Feature 61, Right to Light), which limits lease depth (75 percent of occupied spaces within 25 feet of a window), and requires space planning that gives workstations views to windows or atriums (75 percent of workstations within 25 feet of a window or atrium, and 95 percent within 41 feet).

By contrast, FitWel keeps it simple (at least 51 percent of workspaces with views to the outside), and the LBC's Civilized Environment imperative stipulates that all spaces must have windows on at least 10 percent of one wall, and all workstations must be within 30 feet of an operable window or skylight.

Is it better to set specific prescriptive and performance standards for daylight and views, or to describe qualitative outcomes and expect that architects will do the necessary analysis to design spaces with daylight that functions well? I have seen excellent examples of daylit buildings, and others that were well intentioned, but poorly executed. Whether seeking certifications and applying the specific requirements of the rating system, or simply working to design healthy, productive indoor environments, the consideration of both the qualitative and quantitative requirements of the various rating systems is advised, as well the application of increasingly accessible simulation tools. Good design for daylight and views can start with the designer's intuition, but needs to be reinforced with careful analysis. Tweet me with your thoughts.

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Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with 30 years of experience in sustainable building design. He is a senior associate with YR&G, a WSP company, in Portland, Ore. To learn more, visit www.yrgxyz.com and follow Scott on Twitter @alanscott_faia.