Courtyard and Daylighting

Some rough daylighting guidelines for courtyard proportions are based on the daylight factor (defined in Chapter 7; the ratio between the daylight available at some point within a room, and the daylight available outdoors at the same moment). Because daylight coincides with the sun’s heat, rooms in colder climates benefit from higher daylight factors, while rooms in hotter climates are often content with lower daylight factors. Recommended DF for specified tasks are shown in Table 12.1.

Table 12.1. Recommended Daylight Factors (DF)

18 The higher the top of the window above the floor, the deeper the daylight penetration into a room.

19 The larger the window relative to the floor area, the higher the daylight factor (DF).

The diagram in Figure 12.10 is based on the assumption that, at a distance into a room that exceeds 2.5 times the height (H) of the daylight opening, there will be so little daylight relative to the daylight just inside the opening that electric lights will probably be routinely used. In courtyard buildings with arcades, this 2.5H distance must be measured from the face of the arcade at the courtyard edge. Clearly, the arcade intercepts daylight that would otherwise serve the room beyond.

DFav =	(0.2) window area
	floor area

DF min =	(0.1) window area
	floor area

(Based on Stein and Reynolds 2000; drawing by Michael Cockram.)

You can purchase Courtyards: Aesthetic, Social and Thermal Delight by John Reynolds from the Oikos Bookstore. Follow the link above to see a detailed description of the book and a complete table of contents. See also: Courtyard Characteristics: Exposure.

20 Aspect ratio influences the available DF.

Figure 12.11 charts the relationship between buildings with a square, white-walled “atrium” of given aspect rations, and the expected DF in surrounding rooms. Note that three floor-level positions are listed: top floor, middle floor, and bottom floor. For each position, there is a range from most light (0 percent windows) and least light (50 percent windows); these refer to the opposite walls of the atrium that act as light reflectors toward the windows being evaluated. A light-colored wall without windows reflects more daylight, since any openings in such a wall will be darker in color, especially if they are arches with walls in shadow behind them.

Using this graph requires some additional judgment. Figure 12.11 assumes the contemporary office building atrium, with continuous horizontal strip windows that begin at the ceiling and take up 50 percent of the wall area. The typical arcade, however, reaches toward but rarely touches the ceiling, and then only at the center of the arch. On the other hand, the arches typically constitute well over 50 percent of their wall area.

I believe that this graph predicts the DF in the arcades rather well. But for spaces beyond the arcades, even using the “bottom floor” position might overpredict the DF available.

Apply this graph to the room facing the shallow courtyard in Figure 12.10. The square courtyard has the proportion 3 units width to 2.5 units height, therefore

aspect ratio =	3 x 3	= 1.38
	2.5 x 2.5

Use the “top floor” (T) range, and the “50% windows” lower line; the three dark arches and the tree will not be reflection much daylight! According to Figure 12.11, within the 2.5H floor area, the average DF = about 4.2. The DF in the arcade will be more; the DF within the room itself will be less than 4.

Fig. 12. 11
Daylighting and the aspect ratio. (a) Daylight factor (DF) estimates for spaces adjacent to courtyards. For arch range (top floor, middle floor, bottom floor), the upper boundary curve “no windows” assumes a light-colored wall (70 percent reflectance) across the courtyard, while the lower boundary curve “50 percent windows” assumes a light colored wall with opening half its area (40 percent average reflectance), across the courtyard. (b) Daylight factor (DF) estimates for courtyard floors. Plan growth demands sufficient daylight; under overcast skis, up to 40 percent DF is needed, while under clear skies, a considerably lower DF is adqequate. (Reprinted by perrmission from Brown and DeKay 2001).

21 Light-colored courtyard surfaces diffuse daylight to the surrounding arcades and spaces.

The courtyard admits, absorbs, and reflects daylight according to its proportions and surface colors. When the courtyard floor is very light in color, a substantial amount of reflected light is cast onto walls and ceilings of the arcade. Thus, elaborately carved ceilings can be appreciated for their subtlety and complexity, as in the courtyards of the Alhambra and the Alcazar at Seville (Figure 12.12a).

22 Provide daylight openings with filtering options.

When a light floor surface is also specular (*as with white marble)., the sheen of light can become glare. White walls quickly become glare when direct sun strikes them, because they are directly in one’s field of vision. In the Muse Archeologic in Cordoba, an ancient glare-mitigation technique from Islam, the mashrabiya breaks the sheet of glare into many sparkling components (Figure 12.12). It also provides privacy along with the filtered view, and the wood conducts heat slowly, tending to keep the heat on the outer surface where winds might better carry it away.

Fig. 12.12

(a) Daylight reflected from a white marble floor illuminates the detail around the arches in the Patio delas Doncellas (courtyard of the Maidens), Reales Alcazares, Seville.

(b) Strong relections from the white marble floor at Cordoba’s Museo Arquologico are filtered by a dark wooden mashrabiya.

23 The interior surfaces around daylight openings can ameliorate glare.

(Examples: plans in Figure 1.4, and Figures 1.2, 1.10, 2.3, 2.12, 3.4, 3.12, 4.2, 5.3, 7.3, 10,8, 11.9, 12.6).

Glare is excessive contrast, as between a bright window and dark surfaces in a room. One strategy for glare reduction is to work with the surfaces immediately adjacent to the bright window. In the thick-walled courtyard buildings of Seville, most windows and doors are surrounded by surfaces placed diagonally in the wall; that is, the opening on the interior surface is much wider and taller than the opening in the exterior surface. Such surfaces not only help “spread” the daylight to the interior, but become a”brightness mediator” between the window and interior wall surface, as in Figure 12.13.