The Elements of Architecture

Principles of Environmental Performance in Buildings

Scott Drake

• Publisher: Routledge
• Year: 2014
• ISBN:
  9781317973270
• Edition: 1
• Topic: Architecture
• Subtopic: Sustainability in Architecture

The Elements of Architecture is a clear and well structured introduction to sustainable architecture, which concentrates on general principles to make an accessible and comprehensive primer for undergraduate students.

The author takes a fresh and logical approach, focusing on the way aspects of the built environment are experienced by the occupants and how that experience is interpreted in architectural design. He works through basic elements and senses (sun; heat; light; sound; air; water and fire) to explain and frame effective environmental architectural design - not only arguing that the buildings we inhabit should be viewed as extensions of our bodies that interact with and protect us from these elements, but also using this analogy to explain complex ideas in an accessible manner.

chapter one

SUN

I tried to draw my shadow once, but I couldn’t … My arm kept moving.

Steven Wright

American architect Louis Kahn once remarked that the sun never knew how great it was until it struck the side of a building.¹ Conversely, we might say buildings are never greater than when they are brought to life by the sun. The sun provides warmth and light, and marks the time of the day as it moves through the sky. Even when the sun is overhead, its position can be inferred from the shadows it casts on objects around us, helping us to perceive their shape and texture. The varying intensity of the sun at different points on the Earth’s surface causes differences in climate, which lead to differences in the buildings made to respond to that climate. The sun marks the seasons as its daily path varies through an annual cycle from the heat of summer to the cold of winter, and back again. The sun brings life and energy to plants through photosynthesis, and in turn to the fauna that eat those plants, and each other, along the food chain. The sun forms an essential part of our daily life as we alternately seek refuge from its intensity or revel in its warmth.

In understanding the role of building fabric as an environmental filter, the first thing that must be filtered is the sun. For the most part, buildings do not move, and by remaining in place are exposed to the changing position of the sun through the day and year. Buildings that let sun in may be too hot and bright in summer, while those that keep sun out may be too cold and dark in winter. In general, we prefer buildings to work counter to the prevailing conditions, letting in the scarce winter sun and keeping out the abundant summer sun. But even better is to design spaces in which it is possible to enjoy the sun at all times of the day and year, capturing its warmth or protecting from its heat when appropriate. This requires detailed understanding of the geometry of the sun, so that its position at different times of the day and year can be anticipated and thus incorporated into the design of built space.

Solar geometry

The regular changes in the path of the sun have been understood for many centuries. It is now generally agreed that the monument at Stonehenge is aligned to mark the summer solstice in that region. But mapping the true path of the sun meant dislodging the Earth from its privileged place at the centre of the universe. Since the publication of De Revolutionibus Orbium Coelestium by Nicolaus Copernicus in 1527, the Western world has accepted that that the Earth revolves around the sun, and not the sun around the Earth. But while this model of the solar system is widely accepted, it appears to have diverted attention from the apparent path of the sun in the sky and its very real consequences for the changing environment throughout the day and year. Few people, apart perhaps from astronomers and enthusiastic architects, can actually describe the path of the sun through the sky with any accuracy.

Sun and seasons

Our experience of the rising and setting of the sun each day is caused by the rotation of the Earth around its own axis. Our experience of a year is in turn caused by the revolution of the Earth around the sun. But the reason we experience a circuit around the sun as a ‘year’ is because of the seasons, the cycling back and forth between warm summer and cold winter weather characteristic of temperate zones. What causes seasons to occur is the lack of alignment between the axis of rotation and the axis of revolution of the Earth – there is a slight ‘tilt’, known as the declination, between the two. The declination, currently an angle of about 23.5° (it wobbles back and forth in a cycle that lasts about 41,000 years), was probably caused by a large asteroid colliding with the Earth during its early formation.

Figure 1.1 The Earth’s orbit around the sun

Without the declination, there would be no seasons; the sun would rise and set along exactly the same path each day, and there would be nothing (other than a very subtle change in our view of the planets in the night sky) to mark the passing of the years. The declination causes seasons because it gives rise to changes in the path of the sun throughout the year, with the northern and southern hemispheres taking turns to tilt towards or away from the sun. To understand these changes and their impact on buildings, it is helpful to understand how they are experienced at different points on the Earth.

Annual sun path

Figure 1.1 shows the relation between the rotation of the Earth on its own axis and the revolution of the Earth around the sun. Drawing this with the axis of rotation vertical shows the December solstice (usually around the 22nd of the month), as the highest point reached by the Earth in its path around the sun, while the other solstice, occurring around 21 June, marks the lowest point of the same path. The equinoxes, occurring about 20 March and 22 September, mark the midpoints of the cycle, where the Earth appears to be level with the sun. The apparent path of the sun is affected by whether the Earth is at a low or high point in its journey around the sun. But how this is seen depends on where you are on the Earth’s surface, with the curvature of the Earth causing viewers at different latitudes to see the same solar path from a different angle. This can be understood by imagining how the sun appears when standing at various latitudes.

Polar sun paths

For a building near the North Pole the path of the sun is always close to the horizon. At the June solstice, the rotation of the Earth makes the sun appear to travel in a low circle around the sky, just above the horizon, as this part of the Earth is tilted slightly towards the sun. The length of a day, 24 hours, is marked not by the rising and setting of the sun, but by the sun travelling one full circle around the sky. As the year progresses, the sun continues to circle around the sky, but its angle above the horizon gradually decreases (see Figure 1.2). By the time of the March equinox, the sun is circling level with the horizon, in a very drawn-out sunset. For the next six months, the sun continues to circle, but now it does so below the horizon, which is experienced as one long period of darkness and cold as this part of the Earth is tilted away from the sun. Thus the poles experience the most extreme form of ‘seasons’ – a long summer of sunshine followed a long winter of darkness – but there are no ‘days’ in the familiar sense of rising and setting sun.

Figure 1.2 Polar sun paths

Tropical sun paths

For a building at the equator, the sun is more intense because it appears higher in the sky. At the June solstice, the rotation of the Earth makes the sun move perpendicular to the horizon, in the northern part of the sky. It rises in the east, sets in the west, and in between follows a high path, with about 12 hours of light and 12 hours of darkness in any single day. As the Earth moves around the sun and reaches the March equinox, the sun still appears to rise and set, but moves gradually from the northern part of the sky to being directly overhead. For the next six months, the days remain unchanged, but the path of the sun gradually moves into the southern part of the sky, and then back again (see Figure 1.3). The amount of sun in any given day is effectively constant; there are no seasons caused by the changing length of the day or by the changing angle of the sun path above the horizon, just a constant rising and setting of the sun, with the day divided evenly between light and dark.

Temperate sun paths

Now imagine standing part way between the poles and the equator, in the temperate latitudes that contain most of the world’s population. Here the path of the sun is part way between the long, drawn-out changes that occur at the poles and the constant cycling of days at the equator. There is still a rising and setting of the sun each day, but the days gradually get longer in summer and shorter in winter, giving rise to the seasons. This is because the path of the sun lifts above the horizon in summer, with more than half of it visible in any given day. In the northern hemisphere, this happens around the June solstice, or summer, which is when the southern hemisphere is having shorter days, or winter. Six months later, at the December solstice, the northern hemisphere has shorter days, marking winter, while the southern hemisphere has longer days of summer (see Figure 1.4). In the temperate zones, the heat of summer results less from overhead sun than from the long, low light of the sun as it circles around the sky.

Figure 1.3 Tropical sun paths

Sun angles

At any point on the Earth’s surface, the path of the sun appears to change throughout the year by an amount equal to the declination, or 23.5°, either side of a midpoint that occurs during each equinox (see Figure 1.5). At the poles, where the latitude is 90°, the sun will be level with the horizon, or 0°, during the equinox, and then rise and fall above and below this point to a maximum of 23.5°. At the equator, where the latitude is 0°, the sun will be directly overhead, or 90°, at solar noon on the equinox, and will then vary by 23.5° either side of this point, to be at a maximum angle at solar noon of 66.5° in the northern sky for the June solstice or in the southern sky for the December solstice. For all points in between, the sun reaches an angle of 90° minus the latitude at solar noon during the equinox, and then varies by 23.5° either side of this for each solstice. The maximum sun angle at solar noon for summer and winter solstice can thus be found by the equation (90 – latitude ± 23.5°).

Figure 1.4 Temperate sun paths

Since the sun can only be directly overhead within a narrow band (± 23.5°) either side of the equator, the sun appears from the temperate zones to be in that part of the sky that is towards the equator. In the northern hemisphere, the equator is towards the south, so the sun, rising in the east and setting in the west, travels through the southern part of the sky.² Thus, in the northern hemisphere, south-facing windows will receive sun during the day, and north-facing windows will receive light from the sky, but not sun. In the southern hemisphere, the equator is towards the north; the sun still rises in the east and sets in the west, but here travels through the northern part of the sky. In the southern hemisphere, sun will enter through north-facing windows during the day, while south-facing windows receive light, but not sun. To avoid this confusion, the term equator-facing window is sometimes used to describe a window that will receive sun for much of the day, whether in the northern or summer hemisphere.

The cycles that mark the path of the sun throughout the year are also the source of the imaginary lines that define the globe. The Tropic of Cancer (23.5° north) is the latitude where the noon sun is directly overhead at noon during the June solstice; the Tropic of Capricorn (23.5° south), is where the noon sun is directly overhead at noon during the December solstice. The Arctic and Antarctic circles (23.5° away from the poles) are the latitudes where each solstice is experienced as either one day of full darkness or one day of full sunshine. These lines also mark the boundaries between the broad climate zones: the tropics, occurring between the Tropic of Cancer and the Tropic of Capricorn at latitudes below 23.5°; the polar regions, occurring within the Arctic and Antarctic circles, at latitudes above 66.5°; and the temperate zones, at all other latitudes between the tropics and the polar circles.

Figure 1.5 Apparent change in the sun’s position throughout the year

Climate zones

The shifting of the sun back and forth each year from its midpoint above the equator helps to disperse the heat of the sun out towards the poles, assisted by atmospheric and oceanic currents. But even with this dispersal, the tropics remain the warmest part of the Earth...