Toplighting

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Contents

Introduction

De Menil Gallery, A Physical Daylight Model by University of Idaho Students: Image courtesy Kevin Van Den Wymelenberg, University of Idaho
Endeavor Elementary School: Nampa, ID; Design West Architects: Image courtesy Kevin Van Den Wymelenberg, University of Idaho

Skylights, clerestories, and roof monitors are all types of toplighting. The main advantage of toplighting is that is provides access to the brightest part of the sky, the zenith, and has more hours of solar exposure that any other glazing orientation. That means that substantial amounts of daylight are available for long durations. The drawbacks are that toplighting is not available to most areas within multistory buildings, and while this strategy can provide ample daylight illumination, it may or may not be designed to provide any view to the outdoors.

Daylight design using toplighting provides an opportunity to provide illumination in a potent and uniform manner throughout the year and minimizes the concerns related to blind type and patterns of use. In a sense, the perimeter windows can be included to provide views to the exterior while the real work of daylighting the classroom is delivered by the toplighting strategy. When designing toplighting, it is important to consider the size and placement of the apertures, their proximity to adjacent reflective surfaces, line of sight to the apertures so as to avoid glare potential, and ceiling height.


Section Key Resources
  • New Buildings Institute, University of Idaho, University of Washington; Daylighting Pattern Guide, 2011
  • Lechner, Norbert. Heating, Cooling, Lighting 2nd Edition: Design Methods for Architects. 2001 John Wiley & Sons.
Links

Lead Author(s): Kevin Van Den Wymelenberg

Skylights

Camille Beckman: Eagle, ID; BRS Architects: Image courtesy Kevin Van Den Wymelenberg

“Skylights are horizontal or slightly sloped, glazed openings in the roof. As such, they see a large part of the unobstructed sky and, consequently, transmit very high levels of illumination” (Lechner, 2001). In many applications, it is not desirable to have direct sun penetration and because of this skylight openings should usually be glazed with translucent materials or include interior light diffusing elements. Sizing and spacing of skylights is an important design consideration, and the rules of thumb vary by climate zone, building type, and lighting criteria. The term ‘skylight to floor area ratio’ (SFAR) is used to describe the amount of floor area that is represented with skylights. For simple ‘box’ retail applications the desired SFAR may range from 2.5%-7% depending on lighting criteria and climate. For industrial applications the SFAR will vary greatly by climate and lighting criteria as well, but considerations of whether or not the space is heated and/or cooled plays a major role in determining the appropriate SFAR. If spaces are not heated or cooled, it is reasonable to introduce skylights with higher than 7% SFAR, as the heating and cooling loads associated with skylights may not be as important.

Additional design considerations include the detailing of the surfaces adjacent to skylights. Skylights should be placed so that the light distributed washes walls with daylight, while also providing uniform illumination across the floor plate where daylight is desirable. Interior reflectors or ‘clouds’ can also be used to redirect diffuse daylight from translucent skylights or to diffuse direct sun penetration from clear skylights.



Section Key Resources
  • New Buildings Institute, University of Idaho, University of Washington; Daylighting Pattern Guide, 2011
  • Lechner, Norbert. Heating, Cooling, Lighting 2nd Edition: Design Methods for Architects. 2001 John Wiley & Sons.
Links

Lead Author(s): Kevin Van Den Wymelenberg

Sawtooth Roofs

Alum Rock Youth Center: San Jose, CA; BOORA Architects: Images courtesy Joel Loveland, University of Washington
Alum Rock Youth Center: San Jose, CA; BOORA Architects: Images courtesy Joel Loveland, University of Washington

Sawtooth roofs are essentially as series of clerestory windows, or sloped roof monitors, facing the same direction. This strategy allows daylight to wash across the sloping roof surface adjacent to the window and bounce into the space below. The decision for which direction to orient the glazed apertures will depend on the lighting criteria of the space. South openings will provide more abundant daylight year-round. South apertures may also require shading elements to minimize direct sun penetration. However, if solar gain is desired, this minimizing glare while affording heat gain must be balanced. North facing apertures will provide the most constant diffuse daylight but will provide less illumination on an annual basis that south apertures. A combination of apertures may also be desirable. One significant concern with this daylighting strategy is that sawtooth monitors that face all the same direction will be perceived quite differently depending on which direction one is looking. Looking into the openings will produce higher contrast and potential for glare. In large spaces, the illumination provided will be generally uniform, especially if translucent glass or solar shading employed. However in smallers spaces, the side of the room that ‘sees’ the apertures will be substantially brighter than the side that ‘sees’ only the sloping roof surface. The image at the top left reveals this directionality of daylight from a sawtooth application.


Section Key Resources
  • New Buildings Institute, University of Idaho, University of Washington; Daylighting Pattern Guide, 2011
  • Lechner, Norbert. Heating, Cooling, Lighting 2nd Edition: Design Methods for Architects. 2001 John Wiley & Sons.
Links

Lead Author(s): Kevin Van Den Wymelenberg

Clerestories

Detroit Airport NWA Terminal – Detroit, MI: Image courtesy Joel Loveland, University of Washington
Mt. Angel Abby Library: Mt. Angel, OR; Alvar Aalto: Image courtesy Kevin Van Den Wymelenberg, University of Idaho

Clerestory windows are often considered a form of ‘toplighting’ but can also be interpreted as ‘sidelighitng’. If windows are located high in the wall, in roughly the top 1/3 of the wall, they are referred to as clerestories. These windows can provide daylight illumination deep within interior spaces because of their high location in a perimeter wall as shown in the Detroit Airport image. The clerestory shown in the Mount Angel image puts daylight directly to the middle of the volume through a step up in the roof structure, almost approaching a roof monitor or skylight.

Clerestories do not see the brightest part of the sky and are therefore not as effective as skylights in terms of light provided per unit area of opening, however they are useful for several reasons. For example, in very hot climates, clerestories can be used with shading devices and proper orientation to provide daylight with less solar heat gain than might be associated with some skylight designs. In some buildings, extra roof penetrations are not permissible and clerestories provide another option besides skylights. Furthermore, incorporating natural ventilation can be done effectively with operable clerestory windows.

As with any toplighting application, a decision must be made whether to install clear or translucent products in the aperture. This decision is largely related to the specific indoor activity, orientation and other design attributes so it is difficult to generalize which most appropriate. However, it is always important to consider how often direct sun may penetrate a clerestory window and whether direct sun is an asset or a liability. If blinds are warranted, they will likely need to be on motorized drives or have long extension hand crank operations.

One common challenge with clerestory designs is that the area of the wall directly beneath the clerestory can be the darkest area in the room while the clerestory itself is the brightest area in the filed of view. This can cause unwelcome contrast and a perception of glare. This concern can be mitigated though he use of reflective interior baffles, lightshelves or otherwise deigning the space so that daylight from clerestory windows washes other surfaces near the window. This can be seen in the Mt. Angel image where the clerestory washes another reflective interior surface and bounces daylight back underneath the aperture.



Section Key Resources
  • New Buildings Institute, University of Idaho, University of Washington; Daylighting Pattern Guide, 2011
  • Lechner, Norbert. Heating, Cooling, Lighting 2nd Edition: Design Methods for Architects. 2001 John Wiley & Sons.
Links

Lead Author(s): Kevin Van Den Wymelenberg

Monitor Roofs

Yesler Community Center: Seattle, WA; Mithun: Image courtesy Kevin Van Den Wymelenberg, University of Idaho and Chris Meek, University of Washington
Mt. Angel Abby Library: Mt. Angel, OR; Windows Live Maps

Roof monitors a raised section of the roof that is composed of vertical, horizontal or sloped daylighting apertures, such as clerestories and skylights. They are a hybrid between skylights and clerestories and can therefore have some of the benefits of each. Sawthooth monitors are a repeated sloped surface with a vertical clerestory window and sometimes have a skylight on the sloped surface. Clerestory windows designed into monitors can provide easy relief for stack ventilation. They can also be more effective at providing daylight to the middle of large span spaces than clerestories from the perimeter wall. However clerestories are by their nature a directional light source and therefore spaces designed with clerestory monitors tend to be brighter on one side of the space than the other. This can be mitigated by including clerestories that face multiple directions or through a combination of monitors and skylights as shown in the images of Yesler Community Center.

Skylights designed into monitors perform very similar to traditional skylights except they may have a longer ‘well’ or ‘throat’ and this may slightly reduce the spread of daylight distributed to the floor. Many of the same design principles discussed in the skylighting section apply in this case.


Section Key Resources
  • New Buildings Institute, University of Idaho, University of Washington; Daylighting Pattern Guide, 2011
Links

Lead Author(s): Kevin Van Den Wymelenberg

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