Climate Control: Design Your Home So the Weather Works for You

Designing a house to work with the weather

A building’s indoor spaces are warmed in winter, cooled in summer, freshened when stale, and otherwise made comfortable by devices that create the opposite effect of the weather outdoors no matter how it rages every hour of the year. Making these devices serve their masters comfortably well, however, begins by analyzing what happens ninety-three million miles away.

The sitesun angles

As the Earth tilts on its axis during its annual rotations around the sun, at any latitude this bright orb crosses the sky at a significantly higher altitude in summer than in winter. In summer it also rises earlier well north of east and sets later well north of west, and in winter it rises later well south of east and sets earlier well south of west. There are clever ways to manipulate these solar trajectories to your advantage.

For example, by building an overhang over a south-facing window, you can keep the high summer sun from entering the window, lower your air-conditioning bills and allow the low winter sun to pass through the window and lower your heating bills. Such an overhang appears in figure 8-1. And by locating masses of foliage outside an east-facing window, you can block the summer sun from throwing a lot of heat and glare into the room behind. But in winter, the rising sun would shine only obliquely on the glass during the morning and you wouldn’t want to block what little light it could add to the room behind. Such a window appears in figure 8-2. A mirror image of these conditions exists in windows facing west.

This is how architects design a building’s openings to save you money. By knowing how high above the horizon and what direction the sun will be every hour of the day during the year around a planned building, they can design overhangs over south-facing windows and locate barriers in front of east- and west-facing windows in ways that will appreciably reduce the building’s cooling bills in summer and heating bills in winter.sun and windows

However, the sky doesn’t always cooperate in these matters. Summer days can be cool, winter days can be warm, and clouds can hide the sun any time all year round. And the sun’s highest trajectories across the sky don’t occur on the average hottest days of the year, nor do its lowest trajectories occur on the coldest days. As a sample, on August 20 and April 20 the sun’s trajectories across the sky are the same; but where I live, the average noonday temperature on August 20 is 78° F while on April 20 it is only 56° F. In early September I normally wouldn’t want the sun shining on my windows, but in early April I would want all the free heat I could get. This shows that however well a fixed overhang may work, a movable overhang will work considerably better. But movable overhangs cost more. This is the kind of balancing act one must perform when designing a building to take advantage of the weather: either spend some money for a solution that will work some of the time, or spend more money for a solution that will work more of the time. Hence, when you design for climate, you are gambling. But unlike the wagering that occurs in Las Vegas, where the “house” odds are always against you, when wagering against the weather, if you know the prevailing probabilities and bet on them, the “house” odds will be in your favour.

Deciduous foliage is one kind of movable “overhang” over southerly windows that automatically allows the sun to shine on them in April and shade them in September. Such trees rising on the south side of a house or low commercial building will shade its windows in summer and let the sun shine through them in winter. This device is also pleasant to look at, and does anything but despoil the environment in its making.

Nearer than the sun but still some distance from a planned building is another climatic factor: wind. These air currents flow over land much the way water flows over the bed of a stream. Where the terrain is smooth, the air flows evenly; where the terrain is rough, the air flows fast over the high spots and slow over the low. Over low depressions these drafts often form stagnant “air ponds” that are clammy as a cave compared to the air fifty feet away: you wouldn’t want to locate a building here, in warm weather or cold. Breezes also speed up when they slide down hills, fall over bluffs, or sluice though city streets and other narrow openings; and they slow down when they flow up hills, run into cliffs, and spread into parks and other open areas. Breezes are also slowed by masses of foliage, which cool the air below during the day and warm it slightly at night. How forest foliage affects air speeds and temperatures appears in figure 8-3.

Prevailing winds also tend to bring cooler air from the northwest and warmer air from the southwest. In northerly latitudes during most of the year these breezes are unwelcome when cold and welcome when warm, and in southerly latitudes the reverse is true. The smart thing to do here is open a building to local prevailing breezes where they are desired, and shield them when they are not. Desirable openings are flat terrain, low ground covers, tall shade trees around a building, large casement windows located in facades where their opened sashes can scoop passing air indoors, and roof-mounted belvederes that can draw stuffy indoor air up from below. A lot of houses in warm climates are built this way. Desirable shields are rises in terrain, tall solid fences and other windbreaks, clusters of evergreen trees around a building, small high-silled windows, and recessed entrance doors. A lot of houses in cold climates are constructed this way. A few such openings and shields appear in figure 8-4. In temperate climates where temperatures are usually hot in summer and cold in winter, one can locate high-branched deciduous trees and other openings around a two- or three-story building’s southern half, and place low-branched evergreens and other shields around the northern half. These natural strategies can lower a building’s heating and cooling bills as much as adding one or two inches of insulation in its roof and outer walls. In fact, our old friend Frank Lloyd Wright said: “I think it far better to go with the natural climate than try to fix a special artificial climate of your own.”

Nearer than prevailing winds from a planned building is another natural element that affects life indoors: the ground. A marvelous tool exists for analyzing this: topographic or topo maps. The government publishes these for nearly everywhere in the country. They are generally drawn to a scale of 1 inch equals 2,000 feet, and they show forests in green, water in blue, elevation contours in brown, and roads, railroads, buildings, and other landmarks in black. Part of a USGS map appears in figure 8-5. Where topographic contours are far apart, as at A, the land is flat or nearly so, and where contours are close together, as at B, the land is steep. Flat land may seem like a good place to build, but water sometimes doesn’t drain well in these places. The steeper the slope, usually the nicer the view downhill, but the more you will likely pay for a foundation and a driveway. Gentle slopes, like the one at C, usually offer the best of both worlds. Rugged terrain, as around D, can cause all kinds of trouble unless they are carefully analyzed. And see the grassy symbols in the flat area around E? That’s a marsh. You probably couldn’t build there if you wanted because most building codes won’t let you. In this map are several streets, an interstate highway, a railroad, a river, and the corner of a lake. See if you can find them. When designing a building, an architect usually obtains the USGS map where the building will be located, enlarges the area around the planned building, and draws the enlarged contours on the site plan.

Also affecting the climate around a building is the temperature of the ground’s surface. As appears in figure 8-6, on a sunny day when the ambient air is 80° F, since light surfaces are more reflective and cooler than dark, the air over a meadow may be 75° F, above bare earth 88° F, over a pond 73° F, above a lawn 78° F, over rocks or concrete 98° F, above asphalt 120° F, and over a wood deck 85° F.

Knowing these things can indicate the best location for turnarounds, terraces, decks, yards, and gardens around a building. As a sample, in warm regions you wouldn’t want to locate hot surfaces around the south side of a building. Also, the difference in temperature between a shady area and a sunny area only a few feet away is about 12 degrees. If it is 80° F on a sunny day, a thermometer will read 80 in the shade and 92 in the sun. Hence, a sunlit side of a building will be 12 degrees warmer than if shaded. This consideration is how well-placed foliage, especially deciduous foliage, can reduce a building’s cooling bills in summer and its heating bills in winter.

Another important ground temperature is the one twenty feet below. All year round at this depth the temperature is approximately that of the local annual temperature and the local groundwater. Hear what a noted engineer says about this: “In wells 30 to 60 feet deep, the water temperature is 2° F to 3° F above the annual mean temperature of the area. Well water decreases in temperature about 1° F for every 64 feet in depth.”

If you come across a text that says the temperature of the ground several feet below its surface is ”always about 50 degrees” or “55 degrees” (as have three texts I’ve recently read)—give it a cold shoulder and seek your information elsewhere; because if it doesn’t have this fact right it probably has others wrong too. Groundwater in Miami is obviously warmer (about 74° F) than in Minneapolis (about 43° F), which means a house in Miami requires only about 60 percent of the energy to heat to 120 degrees water drawn from a drilled well as does the same house in Minneapolis. An engineer needs to know these things before sizing a hot water heater, a furnace boiler, or any number of industrial operations. If you know these things, you can make sure an architect or engineer knows them too, and even inform your friends.

Speaking of water, one landscape feature that buildings should stay away from is streams. A whispery brook may seem the epitome of tranquility, but it can rise up and steal a house during a rare superstorm. If you consider building along a stream, see if the ground extending back from each bank is fairly level a few dozen feet or so to a second bank that slopes steeply uphill. That second bank was created by a few thousand years of once-a-century superstorms. Always remember that the stream owns the first mortgage on the level land between the outer banks. And here’s a well-kept secret about America’s most famous creekside residence: Frank Lloyd Wright’s Fallingwater. Its foundation rising out of the creek absorbs water via capillary action, the way a towel draped over the side of a bathtub sucks water from inside the tub, and in the rooms upstairs the moisture in the air condenses on the cold stone walls the way it condenses on the side of a cocktail glass. At least one of my architecture school professors said this around 1960 (this defect may have been remedied by now). This historic house also experiences floods. Once during a violent storm the creek rose so high that it submerged the cantilevers on the second floor. The architecture above looked like a houseboat on a lake. It’s a testimony to Wright’s structural genius that the building didn’t wash away. But the owners lost a lot of furnishings and had to scoop tons of mud from the flooded floors. So the moral here is: Keep your house away from creeks and streams, and they will keep trouble away from you.

With this insight it would be pertinent to say a word about the familiar expression, “once-a-century superstorm.” A nebulous concept if there ever was one. In 1986 I built a pond below my house. Meticulous analysis on my part indicated I should install a big 36-inch-diameter culvert below the pond’s outflow basin to carry the drainage of a once-a-century superstorm. Then in 1989—only three years later—came Flood Floyd. At the height of this hurricane’s rainfall the culvert was filled with thundering outflow and spilling over one side of the pond was a 7 inch deep sheet of water 70 feet wide! Fortunately I had “disobeyed” the building department’s order to build a three-foot wide spillway beside the pond and instead made a 75 x 30 foot area of ground alongside the pond 12 inches lower, covered it with a layer of softball-size rocks, covered the rocks with 4 inches of topsoil, and seeded the soil with hardy meadow grass. Here the designer, instead of whining to the authorities about a seemingly excessive order, allowed it to give power to his imagination to create a “soft path” solution that carried six times more water than the culvert.

A building’s designer should also consider the nature of the ground up to several hundred feet away. Large areas of pavement around shopping centres and factories (roofs too if they are flat and dark) increase temperatures in the wake of prevailing winds. And the air on the lee side of expressways and airports is slightly more toxic. Here you wouldn’t want to locate an elementary school playground, or maybe even one in your backyard. Also regarding any property you may buy, before writing a check pay it a lengthy visit and see if any noises bother you. Thirty years ago I inspected a house for a couple who wanted to buy it. The place was a gem. But during the three hours we were there, we continually heard the drone of vehicles on an expressway hidden behind a grove of trees beyond the backyard. When the wife said, “I can’t stand that traffic,” I knew the noise had killed the sale.

[ background=”#b6c4b3″ color=”#000000″ border=”0px solid #cccccc” shadow=”0px 0px 0px #eeeeee”]After graduating from the Cornell School of Architecture in 1964, Robert Brown Butler has worked as a carpenter, contractor, and registered architect. Through the years Mr. Butler has received a variety of honors for his creative work. He is the author of The Ecological House, which introduced many ideas that are further advanced in this volume, among other books. This excerpt reprinted with permission from Architecture Laid Bare!: In Shades of Green, by Robert Brown Butler. © 2012, Robert Brown Butler.
image: horvathgab
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