Courtyard Characteristics: Exposure

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: Courtyards, Daylight and Aspect Ratio

Aspect ratio =	area of the courtyard floor
	(avg. height of surrounding walls)2

The greater the aspect ratio, the more exposed is the courtyard to the sky. This exposure allows heating by the sun by day, cooling by radiation to the cold sky by night, and some entry to the wind. (Aspect ration used in daylighting design is found in Baker, Fanchiotti and Steemers [1993].)

Conversely, the solar shadow index deals with winter sun exposure (Figure 1.9b).

Solar shadow index =	south wall height
	north-south floor width

The greater the solar shadow index, the deeper the well formed by the courtyard, and the less winter sun reaches the floor, or even the north wall, of the courtyard.

Example: Return to the courtyards in Figures 1.6 and 1.7. These courtyards have wall heights that are 1.5 times the shorter floor dimension. The floor length is 2.5 times the floor width. Assume height = 6m, width = 4m, length = 10m.

Both the courtyard elongated east-west and the one elongated north-south have

aspect ratio =	4 m x 10 m	= 1.15
	[6 m]2

However, their solar shadow indices are quite different. For the courtyard elongated east-west,

solar shadow index =	6m	= 1.5
	4 m

, not promising of winter sun at noon.

For the courtyard elongated north-south,

solar shadow index =	6m	= 0.6
	10 m

, much more winter sun at noon.

In houses that look towards the south, the sun penetrates the portico in winter, while in summer the path of the sun is right over our heads and above the roof so there is shade. To obtain this result, the section of house facing south must be built lower than the northern section in order not to cut off the winter sun. Socrates Xenophon, Memorabilia, III, viii, 8f.

While in general a square courtyard with large aspect ration will have a small solar shadow index, sometimes the south wall is of a height markedly different from the other walls around the courtyard. Thus, this index concerning solar access from the south is important, especially in colder climates.

In Part Two, forty-three courtyards in Mexico and Spain can be compared for both aspect ration and solar shadow index. See Table 7.1.

Fig. 1.9 Bird’s-eye views of a square courtyard

(a) A high aspect ratio indicates greater courtyard exposure to the sky.

(b) A high solar shadow index indicates more winter shadow on the courtyard’s north (most sunny) face.