Cut Your Energy Bill: Shade Your Windows & Shading w/ Landscaping
Posted in Home Improvement on March 13, 2019
Summer is here and it’s hot. It’s the kind of heat that makes tomato plants droop, barefoot kids hip-hop across paved sidewalks, and your ice cream cone drip before you can give it a lick.
It’s hard to imagine that not many generations ago, before air conditioning, shading was the best defense against summertime heat.
In those days our parents and grandparents worked inside if they could, near open windows. After work, they headed for the nearest covered porch, where they sat and fanned themselves, waiting for a cool breeze or simply sweating it out. Indoors, electric fans worked overtime.
And once commercial air conditioning arrived in town, they escaped to the air-conditioned theater for the afternoon matinee or shopped in an air-conditioned department store on weekends.
Today, years later, shading has taken a back seat to air conditioning, which has become a standard fixture in homes, in our workplaces and in our cars.
But don’t dismiss shading strategies as outdated. While porches are no longer so common, good shading at home is still important for energy conservation and comfort. It will reduce the time you run your air conditioner, thereby cutting your monthly electric bill by as much as a third.
And shade will make your yard cooler and more pleasant too.
In this article, I'll describe the ways shading can help your house escape the sun's heat. I'll also mention other cooling strategies like insulation and ventilation, which most homes, but not all, already have in place.
To begin, let’s follow the sun through a typical summer day and describe how it heats your house, and then describe the shading strategies you can use to block it.
- 1 Following The Sun’s Path
- 2 Window-Shading Devices
- 3 Shading with Landscaping
- 4 Landscaping by Region
- 5 Final Thoughts: The Payoff
Following The Sun’s Path
As every gardener, construction worker, and farmer knows, sunrise is the coolest time of the day and the best time to get the heavy work done. All night long, while the summer sun bakes folks on the other side of the globe, air temperatures drop around your home. At sunrise, the process reverses and the air begins to heat up again.
While the morning sun usually won't affect you, it does affect your house. The massive walls, ceilings, and floors slowly, but steadily, absorb heat on the outside and radiate it to the inside. Morning sunlight that directly strikes the east wall of your house begins the day-long warming process.
Unfortunately, houses don’t sweat, so once this heating begins, there's almost no way to reverse the process until sundown, except by turning on an air conditioner.
Fortunately, most homes now have at least one good defense. The same insulation that keeps your home warm in winter keeps it cool in the summer too, trapping most heat in the exterior part of a wall so it’s slow to reach the inside surface.
However, even a well-insulated house has key weak spots — the windows. Morning sunlight that pours through the eastern windows rapidly accelerates the heat buildup inside. To keep cool, it’s critical that you shade these windows.
I'll discuss shading methods later.
By noontime, the sun’s rays are hottest, because they're most intense, beating down from directly overhead. However, unlike what happens in the morning, the walls and windows of your house absorb much less heat during this period, because the sun hits them at such a sharp angle during summer months (Fig. C).
Actually, the noontime sun perches slightly to the south side of your house. Good architectural design should provide roof overhangs or porches to shade the walls during the middle of the day. Window shading on the south side can help too.
Your roof and attic catch the brunt of the noontime heat. Roof temperatures can soar beyond 160°F/70°C (egg-frying temperatures!). And attics become ovens.
Fortunately, most homes have a thick blanket of insulation in their attics, usually twice as much as in walls. Good attic ventilation helps too, but insulation is the main defense.
Before the widespread use of ceiling insulation, hot weather sometimes forced entire families to cook, eat and sleep on the covered back porch, so they could escape the stifling heat indoors.
The sun continues to heat your house all afternoon, especially as it swings over to the west. In most regions, your air conditioner switches on by this time to counteract the heat buildup from morning and noon.
The outside air temperature usually peaks around 4 PM, then begins to drop.
In most regions, the day feels hottest around 6 PM. By now, the air temperature has dropped slightly, but rising humidity in the early evening creates a more intense sensation of heat.
So the evening sun can feel especially hot. If your kids are going to grumble, they'll probably do it at this time, and you can bet that evening shade will feel especially welcome.
The evening sun heats your home just like the morning sun, except that it strikes the west wall instead of the east wall. And the temperature inside your house will continue to rise even after sunset since the heat already in the exterior walls slowly works its way inside, where it radiates off the walls.
The evening is the hottest time of day inside. That's why it's more pleasant to relax outdoors or on a screened porch in the evening and into nightfall, rather than sweating it out inside.
After sunset, your house slowly cools down until morning, when the process begins again.
The path of the sun dictates the best placement for shading devices. Fig. A shows a variety of ways to shade windows, especially those east- and west-facing windows that catch direct sunlight.
Blinds and curtains are perhaps the most popular because they also provide privacy. The outer-facing side should be light-colored so it reflects sunlight and heat away from the window. Dark-colored shades are somewhat self-defeating because they absorb heat and draw it inside.
Outside blinds work better than inside blinds because they block the heat before it gets into the house. But few people use them because it's so inconvenient to run outside every time you want to raise and lower them.
Unfortunately, blinds, curtains, and shades block your view and cooling breezes if you want to keep your windows open.
One shading product particularly popular in the South is a densely woven insect screening, sometimes called shade cloth. This screening, made from fiberglass or aluminum, blocks up to 75 percent of sunlight.
Another option is a plastic film in various densities that you apply to your window glass to reflect or filter out some of the heat. These films are particularly useful if you want to prevent rugs and furniture fabric from fading under intense sunlight. Don't apply these films to double-pane windows, however, because they can cause a temperature imbalance that cracks the glass.
If you have to replace your windows anyway, buy double-pane glass with tinted or "low-e" coatings, which also block some of the sun's heat.
All of these shading methods (except buying new windows) are relatively inexpensive and can do a good job. You can install most of them yourself, using materials from well-stocked home centers.
Awnings are a good alternative if you want to catch cooling breezes because they shade without blocking the wind and only partially block the view. They're semi-permanent, you don't have to open and close them, and you can leave them up until cooler weather arrives in the fall.
If you have a good sewing machine, you can even make them yourself from canvas or reinforced nylon and inexpensive hardware parts you can buy from an awning dealer.
Awnings should extend about halfway down the window and have fabric sides to block the sun at all but extremely low angles.
No matter which ideas you use, remember to shade your east-facing windows to block the morning sun, and your west-facing windows to block the evening sun. Shading can be effective over south-facing windows too.
In all regions except Florida and the extreme southern United States, you should remove the shading devices in winter to allow maximum heat gain from the sun in cold weather.
Awnings, interior and exterior shades, shade screens, dark films, and tinted glass help shade windows and keep the sun's heat outside. Other shading features, like roof overhangs, covered porches, arbors, trellises and trees, shade both the roof and walls of your house as well as the windows.
Shading with Landscaping
Landscape shading blocks the sun before it hits your house in the first place. So it's a great strategy, assuming you can alter the area around your house.
Of course, landscaping makes your yard cooler and more attractive too. The general idea is to place trees and other foliage in such a way as to shade the house in summer, yet not in the winter.
In Figs. A and B you can see low foliage on the east and west sides to block the early morning and late evening sun. Moderate sized trees block late morning and early evening sun, and tall trees placed fairly close to the house cast shade over the roof during midday hours.
These are all broadleaf deciduous trees, which conveniently lose their leaves in winter, allowing more sunlight to hit the house when you welcome its heat.
In stormy areas with frequent high winds, you might not want to plant trees close to your house. Ask experts at your local nursery for their advice on which trees to plant and where to plant them.
In general, plant trees to shade the east- and west-facing walls of your home. Leave the south side open to receive the sun's warmth in winter. In regions with cold winters, plant dense evergreens on the north side to block the wind.
However, even the branches of leafless trees can block 30 to 40 percent of the sunlight. Because the winter sun hangs so low in the southern sky (Fig. C), the south-facing windows are by far the most important to keep as unobstructed as possible for winter heating.
Plan landscape shading to block the summer sun, but not the winter sun, which follows a lower arc in the winter sky.
Obviously, to develop the ideal shading pattern by landscaping is a long-term proposition. After all:
- trees don't grow to the right height over-night;
- the longest side of your house might not face south (which is ideal);
- a neighbor's house could block your southern exposure; and
- you won't want to cut down a beautiful tree because it's in the wrong place.
So use Figs. A and B as models and choose ideas you can apply to your own situation.
Landscaping by Region
Of course, the best shading strategy must take account of your local climate. The best shading trees and plants vary too, so rely on your local nursery to help you choose.
Fig. D illustrates four zones, all of which have somewhat different cooling requirements. The climate in these zones can vary, so plan shading strategy according to local conditions. Hawaii's climate is moderate year-round.
Zone 1: Warm Summers & Cold Winters
In Zone 1, summer cooling isn't nearly as important, or expensive, as winter healing.
So a good landscaping plan would position trees and evergreens on the northwest side, the direction of cold north winds in Zone 1 while keeping the south side completely clear to gain as much heat as possible in winter.
For example, in Zone 1 you'd want to modify Figs. A and B by moving the large shade trees away from the south side of the house and by shifting the arbor at least 30 ft. from the south wall so it won't block the winter sun.
And you could add more evergreens on the north side to block more wind.
Zone 2: Hot Summers, Cold Winters, And (Sometimes) High Humidity
Without modifications, the landscape plan in Fig. A works best in Zone 2.
This zone is a region of hot and cold extremes, so the cooling shade of the arbor against the house makes sense.
The arbor also shades the patio, which would otherwise reflect sunlight and heat into the house.
Closely spaced trees and shrubs on the north side still block the cold north wind, but the foliage on the other three sides should be open enough to channel cooling summer breezes around the house.
Zone 2: Hot Summers, Mild Winters, And High Humidity
The principles in Zone 2 also apply to Zone 3 except that you don't have to worry about the cold north wind.
Shade trees with high canopies (leaves and branches) work best here because they allow the breezes to circulate easily beneath them.
High humidity in this zone becomes a critical factor because it makes summer days feel even hotter.
Since dense foliage produces a lot of humidity, you'll want to move vines and arbors away from the house and rely more on awnings, porches, roof overhangs, and other architectural devices for window shading.
Zone 4: Clear, Hot, And Dry Summers And Mild Winters
In Zone 4, the hot/arid region, you can move the shading vines, arbors and other foliage right back against the house, because the extra moisture these plants produce helps cool the air in this dry region.
Your plant choice will be more limited in this climate, so you might have to rely on awnings, window shades, porches and other features of your house to shade the east and west walls and windows.
Final Thoughts: The Payoff
As you can see, no one shading device or landscaping idea is best for every home. But basic shading principles will help you choose what fits your home's style, your local climate (sometimes different from the regional climate), and certainly your budget.
The payoff will be a better looking, more comfortable, and more energy-efficient home.