BUILDING GREEN - Step 3. Design for Your Conditions.

BUILDING GREEN - Step 3. Design for Your Conditions.

Before you design your house—before you even choose a site—you need to know the conditions of your region. These conditions include such things as the climate, topography, and soil type. They determine what kind of a building will be durable, comfortable, safe, and efficient in that area. For example, in a very cold climate a lot of insulation is needed to keep you comfortable and exterior materials need to be able to withstand freezing and thawing. In a hot region freezing won’t be a problem, but ultraviolet rays from the sun may be very destructive to some materials.

u HIGH RISK v MODERATE RISK w LOW RISK
This map shows the termite risk in different parts of the country. Are they a special problem where you live? If so, maybe you should choose construction materials termites won’t want for their dinner.

The better you understand the conditions in your region, the more you can maximize the positive ones and minimize the negative ones—by your choices of site, design, materials and systems. It’s easier and cheaper to work with nature than against her.

A. Understanding your region

This map shows 15 different climate zones in the U.S. The kind of building that is comfortable, efficient, and durable in one zone might not be in a different zone.

Here are some things you need to consider about your regional conditions.

1. Temperature
a. Severity of winter and summer temperatures
How much of the time and when is it too cold to be comfortable? How much of the time and when is it too hot? Knowing this precisely will help you decide matters such as the best house shape and placement on the site, how much window area to have and where to place windows, how much insulation you’ll need, whether you’ll need a heating or cooling system, and if so, how efficient it should be. For example, if you need a lot of heat in winter, a sunroom may be a good idea. It heats up due to the green house effect, and can provide free heat to the rest of the house. In a hot climate, sunrooms tend to overheat the house.

b. Temperature differences between day and night
Understanding temperature shifts from night to day helps you determine the best building materials for your region. For example, in the desert southwest, where there are warm days and cool nights, masonry materials, such as adobe walls and tile roofs and floors, work well. Masonry can store a lot of heat but it changes temperature very slowly. In the cool night it gives off the heat it stored up in the hot day, just when the occupants need it. This process works in reverse during the day to help keep the home cool. In a region with both a cold night and cold day, masonry would get cold and stay cold.

c. Ground temperature
Understanding ground temperature helps you decide what foundation type and flooring materials will work best in your area. For example, in a hot climate with a constant comfortable ground temperature, an uninsulated concrete slab provides both a serviceable foundation, and an energy-efficient, comfortable finish floor. As long as occupants don’t cover the floor with an insulating material like carpet, they’ll benefit from the cool ground temperature, and won’t need as much air-conditioning. In a cold climate, such a floor would get too cold for comfort.

2. Sunlight
Notice that the arc of the sun is higher in the summer than in the winter. Fortunately this arc is entirely predictable, unlike the weather. By knowing exactly where this arc is in your region at the hottest and coldest times of the year, you can place and size windows and overhangs to let in just the amount of heat you need to make your home more comfortable.

In the U.S., the sun makes a high arc in the sky in summer and a lower arc in winter. We can take advantage of this difference by designing buildings that keep out the sun’s heat in summer and let it in in winter.

For example, in a hot climate, a west facing window without a large overhang would take in too much solar heat. However, the same window in a northern climate would help make the most of heat gain and help lower winter heating costs.

Notice how the overhang of this house will shade the windows on the south side in summer, but not in winter, when the sun’s heat is needed.

3. Rainfall
Knowing average annual rainfall, volume in a short period, and time of year that rain typically falls helps you make choices about landscaping, roof pitch, and building materials that will reduce landscape failures, leaking, erosion, rot and mold. For example, in regions with torrential rains, it’s important to get water off the roof as fast as possible, so it doesn’t drive back up under the roofing and leak into the house. A steeply pitched roof does this much better than a flatter one.

4. Relative humidity
Low humidity encourages the growth of viruses, and high humidity encourages mold growth, which causes problems with rot and allergies. Both extremes are uncomfortable and unhealthy. Understanding relative humidity in your area enables you to choose the proper construction methods, materials, and ventilation systems to avoid these problems. For example, in an area with long cold winters, a vapor barrier must be installed on the inside of the exterior walls. This keeps the warm, moist interior air from entering the wall, where it could cool down, condense, damage the insulation, and rot out the wall. In warm areas, sometimes it’s more humid outside, sometimes inside. There’s no ideal way to build for this, so it’s best to install no vapor barrier and let the vapor move freely through the wall. The wall is not likely to be under any one condition long enough for damage to occur.

5. Prevailing winds
Understanding the wind patterns of your region helps you design to take advantage of refreshing breezes and avoid harsh winds. This will affect your choices about window size and placement, and roof shape. For example, in areas that get a lot of pleasant gentle breezes, windows can be placed to maximize cross ventilation. In areas with cold winter winds, window area can be reduced on the side of the house the wind hits the hardest. In most places that’s the north side.

6. Special conditions
A good design also requires a deeper knowledge of the special conditions of your area, such as the risk of earthquakes, hurricanes, radon gas buildup, termites, soil stability, and the effects of nearby bodies of water or mountains. For example, in a region where tornadoes are prevalent, it’s a good idea to have a storm cellar. In some parts of the U.S. there is evidence of radon gas in the soil. It may pose a health concern to occupants if it gets into buildings. If you build in these areas, you may want to use building methods that keep radon gas out.

B. Choosing a site and design
Once you understand the conditions of your region, you’ll be able to pick a site that minimizes negative conditions and maximizes positive ones. Your site might be quite different from its neighbors. The City of Austin, Texas, for example, is split down the middle into two markedly different geographic regions (bioregions). Soil, plants, and even weather conditions are quite different in these two areas. Once you know your site thoroughly, you’ll be able to make a design that exactly suits it—one that further enhances regional and site assets and reduces problem conditions. Think of your region, site and design as a single unit, working together to keep you comfortable. Focus on getting the biggest bang for your building buck. Spend your time, effort and money on what matters most in your region and on your site. If you live in Minnesota, your main concern is staying warm. Choose a site that is protected from northern winds and gets plenty of sun. Choose a design which lets in plenty of radiant heat from the sun. Stop heat loss with well insulated walls, ceilings, and floors. Invest in a high-efficiency heating system, since it will run many months of the year. If you live in Florida, the sun is your enemy much of the time. Your focus should be on keeping the sun out with shade trees, overhangs, and covered porches. Invest in solar screens or southern low-e windows, a roof radiant barrier, and good ceiling insulation. Since losing heat in the winter is not a big concern, wall insulation, floor insulation, and heater efficiency are not where you should spend a lot of money. A high-efficiency cooling system, especially one that dehumidifies well, should be a top priority, however.

What site and design features work best in your conditions?

It is helpful to look at the historical styles of buildings in your area to see how people got comfort passively from the building design and site, in an era before they could get the additional comfort of modern heating, cooling and humidity control systems. You don’t have to build a home in a historical style to take advantage of the design features used. For example, a high ceiling works the same way whether a home is contemporary or Victorian. Heat will rise above the occupants. In a hot climate, that’s a plus, but in a cold one, it’s not. Here are some samples from three different climate regions, that show you some smart site choices and design features for that region. The zone numbers correspond to the climate map above.

Zone 1: Very Cold (Severe cold in winter; moderate summer with brief hot spells)
Site:
1. South side of slope to get warmth of winter sun
2. Evergreen trees on north/northwest to protect from winter wind
House:
3.Compact shape for less exterior surface area to lose heat
4. Most windows on south for sun’s warmth, fewest on north
5. Sunroom for solar heating
6. Roof slope to deflect winter winds

Zone 6: Hot Dry (Summer hot and dry, both day and night; winter moderately cold)
Site:
1. Southern exposure for best sun control (hot west-facing slopes avoided)
2. Evergreen trees on the north side to protect from winter wind
House:
3. Masonry materials which change temperature slowly
4. Courtyard with fountain or pool for cooling effect
5. Overhangs or thick walls to protect windows from sun
6. Windows placed for good cross ventilation
7. Light exterior colors to reflect sun’s heat

Zone 10: Hot Humid
(Summer hot and humid both day and night; moderate winter)
Site:
1. North and south exposure (hot west-facing slopes avoided)
2. Deciduous trees on east and west for sun protection
House:
3. Long, narrow shape; long walls and most glass facing north and south so smallest area faces east and west sun
4. Large overhangs and covered porches on east and west for sun protection (skylights and sunrooms avoided)
5. Operable windows placed for good cross ventilation and heat exhaust
6. High ceilings, so hotter air rises above occupants
7. Light exterior colors to reflect sun’s heat

Consider this....
• What are the dominant conditions of your region that affect building?
• What kind of a site would mitigate the most negative conditions and maximize the positive conditions of your region?
• What basic house type would do the same?