Building Site Conditions
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The way sunlight moves around a building site influences the way the building is positioned, the size and location of windows and skylights, the amount of day-lighting, and the design of mechanical and natural heating and cooling systems. The distance above or below the equator determines how sunlight moves across the site (Pic. 1, 2). The amount of sunlight that reaches the site depends on its altitude above sea level, how close it is to bodies of water, and the presence of shading plants and trees.
Fountains, waterfalls, and trees tend to raise the humidity of the site and lower the temperature. Large bodies of water, which are generally cooler than the land during the day and warmer at night, act as heat reservoirs that moderate variations in local temperatures and generate offshore breezes. Large water bodies are usually warmer than the land in the winter and cooler in the summer.
Forests, trees, other buildings, and hills shape local wind patterns. The absorbency of the ground surface determines how much heat will be retained to be released at night, and how much will be reflected onto the building surface. Light-colored surfaces reflect solar radiation,while dark ones absorb and retain radiation. Plowed ground or dark pavement will be warmer than surrounding areas, radiating heat to nearby surfaces and creating small updrafts of air. Grass and other groundcovers lower ground temperatures by absorbing solar radiation, and aid cooling by evaporation.
LOCAL CLIMATES
Local temperatures vary with the time of day and the season of the year. Because the earth stores heat and re-leases it at a later time, a phenomenon known as thermal lag, afternoon temperatures are generally warmer than mornings. The lowest daily temperature is usually just before sunrise, when most of the previous day’s heat has dissipated. Although June experiences the most solar radiation in the northern hemisphere, summer temperatures peak in July or August due to the long-term effects of thermal storage. Because of this residual stored heat, January and February—about one month past the winter solstice—are the coldest months. It is usually colder at higher latitudes, both north and south, as a result of shorter days and less solar radiation. Sites may have microclimates, different from surrounding areas,which result from their elevation, closeness to large bodies of water, shading, and wind patterns.
Cities sometimes create their own microclimates with relatively warm year-round temperatures produced by heat sources such as air conditioners, furnaces, electric lights, car engines, and building machinery. Energy released by vehicles and buildings to the outdoors warms the air 3°C to 6°C (5°F–11°F) above the surrounding countryside. The rain that runs off hard paved surfaces and buildings into storm sewers isn’t available for evaporative cooling. Wind is channeled between closely set buildings, which also block the sun’s warm thin winter. The convective updrafts created by the large cities can affect the regional climate. Sunlight is absorbed and reradiated off massive surfaces, and less is given back to the obscured night sky.
CLIMATE TYPES
Environmentally sensitive buildings are designed in response to the climate type of the site. Indigenous architecture, which has evolved over centuries of trial and error, provides models for building in the four basic cli-mate types.
Cold Climates
Cold climates feature long cold winters with short, very hot periods occurring occasionally during the summer.Cold climates generally occur around 45 degrees latitude north or south, for example, in North Dakota.Buildings designed for cold climates emphasize heat retention, protection from rain and snow, and winter wind protection. They often include passive solar heating, with the building encouraging heat retention with-out mechanical assistance.
In cool regions, minimizing the surface area of the building reduces exposure to low temperatures. The building is oriented to absorb heat from the winter sun.Cold air collects in valley bottoms. North slopes get less winter sun and more winter wind, and hilltops lose heat to winter winds. Setting a building into a protective south-facing hillside reduces the amount of heat loss and provides wind protection, as does burying a building in earth. In cold climates, dark colors on the south-facing surfaces increase the absorption of solar heat. A dark roof with a steep slope will collect heat, but this is negated when the roof is covered with snow.
Temperate Climates
Temperate climates have cold winters and hot summers.Buildings generally require winter heating and summer cooling, especially if the climate is humid. Temperate climates are found between 35 degrees and 45 degrees latitude, in Washington, DC, for example. South-facing walls are maximized in a building designed for a temperate region. Summer shade is provided for exposures on the east and west and over the roof. Deciduous shade trees that lose their leaves in the winter help to protect the building from sun in hot weather and allow the winter sun through. The building’s design encourages air movement in hot weather while protecting against cold winter winds (Pic. 3).
Hot Arid Climates
Hot arid climates have long, hot summers and short,sunny winters, and the daily temperatures range widely between dawn and the warmest part of the afternoon. Arizona is an example of a hot arid climate. Buildings designed for hot arid climates feature heat and sun control, and often try to increase humidity. They take ad-vantage of wind and rain for cooling and humidity, and make the most of the cooler winter sun.
Windows and outdoor spaces are shaded from the sun, and summer shade is provided to the east and west and over the roof. Enclosed courtyards offer shade and encourage air movement, and the presence of a fountain or pool and plants increases humidity. Even small bodies of water produce a psychological and physical evaporative cooling effect. Sites in valleys near a water-course keep cooler than poorly ventilated locations. In warm climates, sunlit surfaces should be a light color,to reflect as much sun as possible.
Hot Humid Climates
Hot humid climates have very long summers with slight seasonal variations and relatively constant temperatures.The weather is consistently hot and humid, as in New Orleans. Buildings designed for hot, humid climates take advantage of shading from the sun to reduce heat gain and cooling breezes. East and west exposures are minimized to reduce solar heat gain, although some sun in winter may be desirable. Wall openings are directed away from major noise sources so that they can remain open to take advantage of natural ventilation. If possible, the floor is raised above the ground, with a craw space under the building for good air circulation.
THE SITE
The climate of a particular building site is determined by the sun’s angle and path, the air temperature, humidity, precipitation, air motion, and air quality. Building designers describe sites by the type of soil, the characteristics of the ground surface, and the topography of the site.
Subsoil and topsoil conditions, subsurface water levels, and rocks affect excavations, foundations, and landscaping of the site. Hills, valleys, and slopes deter-mine how water drains during storms and whether soil erosion occurs. Site contours shape paths and roadway routes, may provide shelter from the wind, and influence plant locations. Elevating a structure on poles or piers minimizes disturbance of the natural terrain and existing vegetation.
The construction of the building may alter the site by using earth and stone or other local materials. Construction of the building may bring utilities to the site,including water, electricity, and natural gas. Alterations can make a positive impact by establishing habitats for native plants and animals.
The presence of people creates a major environ-mental impact. Buildings contribute to air pollution directly through fuel combustion, and indirectly through the electric power plants that supply energy and the incinerators and landfills that receive waste. Power plants are primary causes of acid rain (containing sulfur ox-ides) and smog (nitrogen oxides). Smoke, gases, dust,and chemical particles pollute the air. Idling motors at drive-up windows and loading docks may introduce gases into building air intakes. Sewage and chemical pollutants damage surface or groundwater.
Other nearby buildings can shade areas of the site and may divert wind. Built-up areas upset natural drainage patterns. Close neighbors may limit visual or acoustic privacy. Previous land use may have left weeds or soil erosion. The interior of the building responds to these surrounding conditions by opening up to or turning away from views, noises, smells, and other disturbances. Interior spaces connect to existing on-site walks,driveways, parking areas, and gardens. The presence of wells, septic systems, and underground utilities influences the design of residential bathrooms, kitchens, and laundries as well as commercial buildings.
Traffic, industry, commerce, recreation, and residential uses all create noise. The hard surfaces and parallel walls in cities intensify noise. Mechanical systems of neighboring buildings may be very noisy, and are hard to mask without reducing air intake, although newer equipment is usually quieter. Plants only slightly reduce the sound level, but the visually softer appearance gives a perception of acoustic softness, and the sound of wind through the leaves helps to mask noise.Fountains also provide helpful masking sounds.
As you move up and down a site or within a multistory building, each level lends itself to certain types of uses. The sky layer is usually the hardest to get to and offers the most exposure to wind, sun, daylight, and rain. The near-surface layer is more accessible to people and activities. The surface layer encourages the most frequent public contact and the easiest access. The sub-surface layer confers isolation by enclosure and provides privacy and thermal stability, but may have ground-water problems.
Wind and Building Openings
Winds are usually weakest in the early morning and strongest in the afternoon, and can change their effects and sometimes their directions with the seasons. Ever-green shrubs, trees, and fences can slow and diffuse winds near low-rise buildings. The more open a wind-break, the farther away its influence will be felt. Al-though dense windbreaks block wind in their immediate vicinity, the wind whips around them to ultimately cover an even greater area. Wind speed may increase through gaps in a windbreak. Blocking winter winds may sometimes also block desirable summer breezes.The wind patterns around buildings are complex, and localized wind turbulence between buildings often in-creases wind speed and turbulence just outside building entryways.
Openings in the building are the source of light,sun, and fresh air. Building openings provide opportunities for wider personal choices of temperature and access to outdoor air. On the other hand, they limit control of humidity, and permit the entry of dust and pollen. Window openings allow interior spaces to have natural light, ventilation, and views. Expansive, restricted, or filtered window openings reveal or frame views, and highlight distant vistas or closer vignettes.
Water
Rainwater falling on steeply pitched roofs with over-hangs is collected by gutters and downspouts and is carried away as surface runoff, or underground through a storm sewer. Even flat roofs have a slight pitch, and the water collects into roof drains that pass through the interior of the building. Drain leaders are pipes that run vertically within partitions to carry the water down through the structure to the storm drains. Interior drains are usually more expensive than exterior gutters and leaders.
Rainwater can be retained for use on site. Roof ponds hold water while it slowly flows off the roof, giving the ground below more time to absorb runoff. The evaporation from a roof pond also helps cool the building. Water can be collected in a cistern on the roof for later use, but the added weight increases structural requirements.
Porous pavement allows water to sink into the earth rather than run off. One type of asphalt is porous, and is used for parking lots and roadways. Low-strength porous concrete is found in Florida, but wouldn’t with-stand a northern freeze-thaw cycle. Incremental paving consists of small concrete or plastic paving units alternating with plants, so that rainwater can drain into the round. Parking lots can also be made of open-celled pavers that allow grass or groundcover plants to grow in their cavities.
Sites and buildings should be designed for maxi-mum rainfall retention. In some parts of North America, half of residential water is consumed outdoors, much of it for lawn sprinklers that lose water to evaporation and runoff. Sprinkler timing devices control the length of the watering cycle and the time when it begins, so that watering can be done at night when less water evaporates. Rain sensors shut off the system, and monitors check soil moisture content. Bubblers with very low flow rates lose less water to evaporation. With drip irrigation,which works well for individual shrubs and small trees,a plastic tube network slowly and steadily drips water onto the ground surface near a plant, soaking the plants at a rate they prefer. Recycled or reclaimed water, including gray water (wastewater that is not from toilets or urinals) and stored rain, are gradually being allowed by building codes in North America
Animal and Plant Life
Building sites provide environments for a variety of plant and animal life. Bacteria, mold, and fungi breakdown dead animal and vegetable matter into soil nutrients. Insects pollinate useful plants, but most insects must be kept out of the building. Termites may attack the building’s structure. Building occupants may welcome cats, dogs, and other pets into a building, but want to exclude nuisance animals such as mice, raccoons,squirrels, lizards, and stray dogs. You may want to hear the birds’ songs and watch them at the feeder while keeping the cardinals out of the kitchen.
Grasses, weeds, flowers, shrubs, and trees trap precipitation, prevent soil erosion, provide shade, and deflect wind. They play a major role in food and water cycles, and their growth and change through the seasons help us mark time. Plants near buildings foster privacy,provide wind protection, and reduce sun glare and heat.They frame or screen views, moderate noise, and visually connect the building to the site. Plants improve air quality by trapping particles on their leaves, to be washed to the ground by rain. Photosynthesis assimilates gases, fumes, and other pollutants.Deciduous plants grow and drop their leaves on a schedule that responds more to the cycles of outdoor temperature than to the position of the sun (Pic.. 4, 5). The sun reaches its maximum strength from March21 through September 21, while plants provide the most shade from June to October, when the days are warmest.A deciduous vine on a trellis over a south-facing window grows during the cooler spring, shades the interior during the hottest weather, and loses its leaves in time to welcome the winter sun. The vine also cools its immediate area by evaporation. Evergreens provide shade all year and help reduce snow glare in winter.
The selection of trees for use in the landscapes should consider their structure and shape, their mature height and the spread of their foliage, and the speed with which they grow. The density, texture, and color of foliage may change with the seasons. For all types of plants, requirements for soil, water, sunlight, and temperature range, and the depth and extent of root structures are evaluated. Low-maintenance native or naturalized species have the best chances of success. To support plant life, soil must be able to absorb moisture,supply appropriate nutrients, be able to be aerated, and be free of concentrated salts.
Trees’ ability to provide shade depends upon their orientation to the sun, their proximity to the building or outdoor space, their shape, height, and spread, and the density of their foliage and branch structure. The most effective shade is on the southeast in the morning and the southwest during late afternoon, when the sun has a low angle and casts long shadows.
Air temperatures in the shade of a tree are about3°C to 6°C (5°F–11°F) cooler than in the sun. A wall shaded by a large tree in direct sun may be 11°C to 14°C(20°F–25°F) cooler than it would be with no shade. This temperature drop is due to the shade plus the cooling evaporation from the enormous surface area of the leaves. Shrubs right next to a wall produce similar results, trapping cooled air and preventing drafts from in-filtrating the building. Neighborhoods with large trees have maximum air temperatures up to 6°C (10°F) lower than those without. Remarkably, a moist lawn will be6°C to 8°C (10°F–14°F) cooler than bare soil, and 17°C(31°F) cooler than un shaded asphalt. Low growing, low-maintenance ground covers or paving blocks with holes are also cooler than asphalt.
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