Site and orientation

On a gray Saturday in late January the four students take the bus to Kestrel Point with Visser. The river is frozen and the paths are packed snow. They stand on the upper terrace near the bridge where the house will go, and for a long time nobody says anything useful because it is ten below zero and the wind from the north-west is cutting through every coat. Then Wren notices that, on the south side of the old stone retaining wall at the edge of the terrace, there is a strip of bare ground where the snow has melted, and three park workers are eating lunch there in the sun, out of the wind, with their jackets open. 'That,' says Visser, 'is the whole lesson. Write it down.'

Reading a site

Every building sits in a particular place, and that place has a climate, a shape, a history, neighbors, views, noises and rules. Site analysis is the systematic study of these conditions so that the design can respond to them. In Design Studio I, the students analyzed Kestrel Point for a pavilion that would be used mostly in summer. A house is a different problem: it is lived in through every season and at every hour, and the conditions that matter most are often the ones that last longest, such as winter sun and winter wind.

A site analysis usually records the following, mostly on plans and sections of the site at a suitable scale:

• Boundaries, setbacks and legal limits: the lot lines, easements, zoning rules on height, coverage and setbacks, and any heritage or environmental controls.
• Topography: contours, slopes, high and low points and drainage paths.
• Ground and water: soil type, groundwater, flood levels and existing utilities.
• Climate: the sun path, prevailing winds by season, temperatures, rain and snow, and local microclimates.
• Vegetation: trees with their species, height, spread and whether they are deciduous or evergreen.
• Views: what can be seen from the site, in which directions, and what can see into it.
• Access and movement: roads, paths, parking, deliveries, and the routes people already take.
• Sound, smell and light: noise from the bridge, the smell of the river in spring, streetlights at night.
• History and meaning: what the place was, who used it, and what it means to the people around it.

The upper terrace

The terrace is a level strip about 150 by 65 ft, cut into the slope above the riverside path in the 1930s and held up on its south side by a retaining wall of Kasota stone about 6 ft high. Below it, the bank slopes down to the path and the river. The spring flood reaches only the path, so the terrace is dry. To the north is the park road and a small parking area; to the east the approach to the bridge, with traffic noise at rush hour; to the west, a stand of old cottonwoods and a meadow. The main views are south and south-west, across the river to a wooded bank. The city's zoning requires the house to stay 20 ft back from the road and 10 ft from the edge of the retaining wall, and to be no taller than one story with a roof up to 20 ft, to keep it from dominating the park.

The students' first site plan, at 1 in = 16 ft, records all of this. Wren adds something nobody else drew: the strip of bare ground below the wall where the workers ate lunch. It is a microclimate, a small area with conditions different from its surroundings. South-facing, sheltered from the north-west wind and backed by a mass of stone that absorbs heat, it is several degrees warmer than the open terrace on a sunny winter day.

The path of the sun

The sun's position in the sky is described by two angles. The altitude is its height above the horizon; the azimuth is its compass direction, usually measured clockwise from north. Both change through the day and the year, and both depend on latitude. At noon, when the sun is due south in the northern hemisphere, its altitude equals 90 degrees minus the latitude plus the sun's declination, which varies from about +23.4 degrees at the June solstice to about −23.4 degrees at the December solstice and is zero at the equinoxes.

Minneapolis is at about 45.0 degrees north. The noon sun there is about 21.6 degrees high at the December solstice, 45.0 degrees at the equinoxes and 68.4 degrees at the June solstice. In winter the sun rises in the south-east, stays low and sets in the south-west after a short day. In summer it rises in the north-east, climbs high and sets in the north-west after a long one. This asymmetry is the basis of climate-responsive design in northern places: low winter sun can be let deep into a building through south-facing windows, while high summer sun can be shaded by a modest overhang.

# Sun altitude and azimuth at the site (simple model, solar time)
import math
lat = math.radians(45.0)
for name, dec in (("June solstice", 23.44), ("equinox", 0.0), ("December solstice", -23.44)):
    d = math.radians(dec)
    print(name)
    for hour in (6, 8, 10, 12, 14, 16, 18):
        h = math.radians(15 * (hour - 12))           # hour angle
        sin_alt = math.sin(lat) * math.sin(d) + math.cos(lat) * math.cos(d) * math.cos(h)
        alt = math.degrees(math.asin(sin_alt))
        if alt <= 0:
            continue
        az = math.degrees(math.atan2(math.sin(h), math.cos(h) * math.sin(lat) - math.tan(d) * math.cos(lat))) + 180
        print(f"  {hour:2d}:00  altitude {alt:5.1f} deg  azimuth {az:5.1f} deg")

June solstice
   6:00  altitude  16.3 deg  azimuth  73.0 deg
   8:00  altitude  37.3 deg  azimuth  93.1 deg
  10:00  altitude  57.5 deg  azimuth 121.4 deg
  12:00  altitude  68.4 deg  azimuth 180.0 deg
  14:00  altitude  57.5 deg  azimuth 238.6 deg
  16:00  altitude  37.3 deg  azimuth 266.9 deg
  18:00  altitude  16.3 deg  azimuth 287.0 deg
equinox
   6:00  altitude   0.0 deg  azimuth  90.0 deg
   8:00  altitude  20.7 deg  azimuth 112.2 deg
  10:00  altitude  37.8 deg  azimuth 140.8 deg
  12:00  altitude  45.0 deg  azimuth 180.0 deg
  14:00  altitude  37.8 deg  azimuth 219.2 deg
  16:00  altitude  20.7 deg  azimuth 247.8 deg
  18:00  altitude   0.0 deg  azimuth 270.0 deg
December solstice
   8:00  altitude   2.5 deg  azimuth 127.3 deg
  10:00  altitude  16.3 deg  azimuth 151.4 deg
  12:00  altitude  21.6 deg  azimuth 180.0 deg
  14:00  altitude  16.3 deg  azimuth 208.6 deg
  16:00  altitude   2.5 deg  azimuth 232.7 deg

The output confirms what the students felt on the terrace. In late December the Minneapolis sun is above the horizon for only about nine hours and never climbs above 22 degrees. A building or tree to the south that is only a little taller than its distance away will shade the house completely at noon. In June the sun is up for more than fifteen hours and shines on the north side of the house in the early morning and evening.

Orientation

Orientation is the direction a building and its rooms face. In a cold northern climate, the classic advice is to elongate the house along an east-west axis, so its long side faces south, and to put the main living spaces and most windows on that side. South windows collect low winter sun and are easy to shade in summer. East windows bring morning light and can overheat on summer mornings; west windows bring evening light and are the hardest to shade, because the late afternoon sun is low and hot. North windows give steady, glare-free daylight but collect no sun and lose heat all winter, so they are kept modest in number and size and placed where views or even light are especially valuable.

For a house, orientation is also a matter of daily rhythm. The students map Margit's day against the sun. She reads at dawn with tea: the reading corner should face east or south-east. She works in the park through the day and returns at noon: the kitchen and dining should catch the midday sun. She works at the wheel in the evening: the workroom can face north for even light, with a west window for the late summer sun. Guests sit outside on summer evenings: the porch should face west or south-west. Elias sleeps late: his bedroom can face north or west, away from the early light.

Passive solar heating

A house can collect a useful share of its winter heat from the sun, a strategy called passive solar design because it uses the building itself rather than mechanical collectors. The key elements are south-facing glass to admit the sun, thermal mass such as concrete, tile or masonry inside the house to absorb heat by day and release it at night, insulation and airtight construction to keep the heat in, and shading to keep the summer sun out. Too much glass without enough mass leads to overheating on sunny days and heavy losses at night; good design balances the two.

In northern North America, the energy crisis of the 1970s produced a wave of experiment. The Saskatchewan Conservation House, built in Regina in 1977, combined very high insulation, an airtight envelope, heat recovery from exhaust air and modest south glazing, and used a small fraction of the energy of a typical house of its time. Its ideas fed directly into the later German Passivhaus standard and into Canada's R-2000 program. The lesson for Margit's house is that orientation helps, but insulation and airtightness matter more in a cold climate than any amount of glass.

Shading

A horizontal overhang above a south window can be sized so that it shades the glass at the summer solstice and lets the sun through at the winter solstice. If the overhang projects a depth P and the bottom of the glass is a height H below it, the glass is fully shaded when the sun's altitude is above the angle whose tangent is H divided by P.

# Size a south overhang at the site (noon sun)
import math
lat = 45.0
summer = 90 - lat + 23.44
winter = 90 - lat - 23.44
H = 7                     # top of overhang to bottom of glass, ft
P = H / math.tan(math.radians(summer))
print(f"Noon altitude: summer {summer:.1f} deg, winter {winter:.1f} deg")
print(f"Overhang to shade the whole window at summer noon: {P:.2f} ft")
# how far the winter sun reaches into the room through a window 7 ft tall
print(f"Winter noon sun reaches about {7 / math.tan(math.radians(winter)):.1f} ft into the room")

Noon altitude: summer 68.4 deg, winter 21.6 deg
Overhang to shade the whole window at summer noon: 2.77 ft
Winter noon sun reaches about 17.7 ft into the room

The overhang works at noon on the solstices, but the sun does not follow the calendar of human comfort. In mid-September, when it is often still hot, the sun is as low as in late March, when it is often cold. Designers use deciduous trees, adjustable awnings, exterior blinds or vines on a trellis to give flexible shading where the fixed overhang cannot. The cottonwoods to the west of the terrace already shade the evening sun in summer and let it through in winter, after the leaves fall.

Wind, snow and shelter

In Minneapolis the coldest winter winds come from the north and north-west, and the summer breezes more often from the south. Wind increases heat loss from a building and makes outdoor spaces bitterly cold. Snow drifts form in the lee of buildings and fences, where the wind slows down, so entrances and parking on the downwind side can be buried after every storm. The students place the house so that its long, low north wall, with few windows, faces the wind; the garage-sized storage shed and a row of evergreen shrubs extend the shelter to the north-west; and the main entry is on the east side, out of the worst wind but away from the drifts that form on the south-east of the house.

Summer breezes are welcome. Windows on opposite sides of a room allow cross-ventilation, and a high window on the north side, opposite low south windows, lets warm air escape by the stack effect. The terrace's exposure to the river is an advantage here: on summer evenings a cool breeze often moves up the valley.

Views and privacy

The view of the river is part of Margit's program, but a view is best when it is framed and partly withheld. A whole wall of glass shows everything at once and soon becomes wallpaper; a carefully placed window that frames a bend of the river or the tops of the cottonwoods can be enjoyed every day. The students also consider the reverse view: walkers on the riverside path below will look up at the house, and the city wants it to sit quietly in the park. A low profile, a roof that follows the terrace, natural materials and windows set back under deep eaves help the house belong to the landscape rather than stand on top of it.

Precedent: the Magney House

The Australian architect Glenn Murcutt's Magney House at Bingie Point, New South Wales, completed in 1984, is a long, narrow house on an exposed coastal headland. Its orientation, its curved, wing-like corrugated metal roof, its adjustable louvers and blinds and its plan, one room deep, are all driven by the sun, the wind from the sea and the view. Murcutt often quoted an Aboriginal saying, 'touch this earth lightly', to describe his approach. His houses are in a very different climate from Margit's, but his method is the same one Visser asks the students to follow: study the site, the sun and the wind first, then let the building become an instrument tuned to them.

Exercise 5: site and sun

This exercise takes about eight hours.

• Draw a site plan of the terrace at 1 in = 16 ft showing setbacks, contours, trees, views, wind, noise and access.
• Draw a sun path diagram for the site and plot the sun's position at 9:00, 12:00 and 15:00 on the solstices and equinoxes.
• Place three massing options on the site plan and draw the noon shadow of each at the December solstice.
• Draw a section through the south wall and overhang of your preferred option, showing the summer and winter noon sun angles.
• Deliverable: the site plan, sun path, three shadow studies and the section, with a short note explaining your choice.

Self-critique checklist

• Have I recorded conditions in every season, not just the day I visited?
• Do the living spaces face the winter sun?
• Is the entry sheltered from the prevailing winter wind and out of the drifts?
• Does the house frame the view rather than simply exposing it?