Climate Effects on Decks
Your deck should offer more than privacy, protection, and plenty of seating. It should take advantage of the natural surroundings—cooling breezes, warm sun, shade, subtle garden fragrances. Paying attention to weather patterns and designing your deck for maximum comfort in a variety of conditions can extend its usefulness.
Off the Axis?
Many homes are not situated on a true north-south, east-west axis, and a deck on such a site will get a combination of sun and shade patterns. For example, a deck on the southeast side of a house will get sun much of the day but escape the hot late-afternoon sun.
To get an idea of how your site will be affected, make a rough sketch of your home and experiment with different deck locations.
Sun and Shade
As the sun travels overhead throughout the day and year, it sends down varying amounts of warmth and light. Shadows cast by trees, walls, and rooflines will also shift throughout the day. Place your deck so these natural patterns correspond to the times of the day and the seasons when you’ll use the space.
Take an inventory of your shade and sunshine. Watch how the sun moves across your property at various times of the day during warm months. Stakes driven in the yard will help you keep track of moving shade patterns. Make notes about the shade patterns and keep them handy when you begin to draw your deck plans on paper.
If your proposed site is already shaded during the times you’ll use the deck, that makes your decisions about location less complicated But even if you don’t have much flexibility in where you put the deck, you can alter the environment. If you need additional shade, you can make some. Add trees and other plants to shade a site that gets too much afternoon sun. A pergola can filter hot sunlight.
So can a roll-out awning, which can be retracted when it’s not needed. Let roses or vines climb up an arbor to create a private shaded spot for outdoor reading—without blocking the breeze. Vines climbing up a lattice wall can cool off a site that gets hot in the late afternoon. Or you could try a compromise— a location that features partial shade and partial sunlight during the hours of greatest deck use.
- Most north-side locations are in almost constant shade and will probably be cool on all but the hottest days. If you’re planning a north-side deck, you may want to build on a detached site, well beyond the shadow line of the house. Or you could extend the surface beyond the shadow line of the house to produce both shady and sunny areas in summer. This site would work well in a year-round hot climate. Southern sites get sun all day and may need added shade from trees or an overhead structure. Although the south side of the house receives sun most of the day, it does so from different angles, depending on the season. Summer sunlight is high in the sky, but in winter the light comes in at a low angle. A south-facing deck with a lattice-covered pergola would have filtered sun in summer and full sun in winter. Outdoor space on the south side will have the best chance of getting any winter sun in mild-winter climates.
- For breakfast in the early light or a cool spot for evening meals, an east-facing deck is ideal. The eastern sun warms the cool morning air. But an east-side site will also be shaded sooner than any other location. For example, by 5 p.m., an east-side location will be shaded for several feet, and by 7:30 p.m., even in summer, it will be engulfed in shade. Depending upon your climate, such early shade can be an asset to your deck, or restrict its hours of use. A west-facing deck will get the hot afternoon sun and, without natural or added shade, may become unbearably hot in the afternoon. The west side starts the day in shade but gets the hot sun from early afternoon until sunset, and deck surfaces will radiate heat long after dusk. To create a deck site that’s enjoyable from early afternoon to evening, you may want to consider a wraparound style that takes advantage of both a western and northern exposure.
The wind will affect your outdoor comfort as much as the sun. A pleasant breeze may bring welcome relief on a hot day, but gusting winds can make it impossible to enjoy the space at all. Study the wind patterns in your yard and learn to make a distinction between prevailing winds (the general direction of wind currents) and seasonal breezes (those localized to a time of day or season). If possible, build your deck in a spot that’s sheltered from strong prevailing winds. If your site is exposed, a slatted fence or windbreak (trees and hedges) can transform a strong wind into a breeze that flows across your deck, cooling and freshening the air.
Trees, Plants, and Microclimates
Unless you’re building a brand-new house, your choice of deck sites will be affected by what you find on the site: It may be either hilly or flat, sunny or shaded. And although you have very little control over the terrain, you can moderate temperature extremes around your deck by carefully planting trees and shrubs.
Trees can provide shade from sunlight and can break up harsh winds. Deciduous trees—such as oaks, maples, and walnuts—are quite bushy in summer but lose their leaves in winter. The leaves will shade your deck in summer but let sun warm the surface in cooler months. That makes trees a practical investment in moderate climates where the deck is in use most of the year.
No matter where in the country you live, your yard will have prevailing winds, and those winds are likely to come from different directions in summer and winter. Watch to see where the wind comes from, and plant to take advantage of it. In summer you’ll want to channel the wind toward the deck; in winter you’ll want to block the wind.
As you design your site, keep the variety of trees and bushes to a minimum to unify the design, and don’t plant deep-rooted trees or bushes near the house, where they can undermine the foundation. You can’t keep the rain from coming down, but you can build yourself some shelter. A solid roof over a part of your deck can keep you dry outdoors in rainy weather. So can a gazebo or retractable awning.
If you live in an area with harsh winters, construct the roof so it won’t be vulnerable to snow buildup or ices dams. And be sure to retract the awning before the first snow. Rain will also affect the relationship of your deck surface to the indoor floor. Build your deck about an inch lower than the floor inside, to keep the rain from seeping in.
In snowy climates, you’ll want to keep the snow from becoming an uninvited guest in your family room or kitchen. That means that you’ll have to build the deck surface 3 to 4 inches below the interior floor. Heavy snowfalls might mean dropping the deck surface to about 8 inches below the inside room, but you can ease this drop with an outdoor landing.
Creating a Microclimate
Did you ever notice that the air on a deck feels a bit different from the air a few feet away? That’s because the materials that go into a deck and the arrangement of those materials create what’s called a microclimate.
Different paving materials, for example, absorb different amounts of heat from the sun each day. They also reflect different amounts of light. A light-colored concrete slab reflects a lot of heat. Although the surface may feel comfortably warm, it may seem harsh and glaring because it also reflects sunlight. By contrast, dark brick won’t reflect the harshness of bright sunlight but will absorb a tremendous amount of heat. This can make the deck surface uncomfortable underfoot during the day, but the stored heat radiates during the cool of the evening, prolonging the daytime warmth.
Likewise, a hilltop deck will feel warmer on a calm day than one at the base of a hill because cooler air flows downhill. What’s more, if you trap the cold air at the bottom of a hill with retaining walls, fences, or house walls, your deck might be quite cool in the evening.
The construction of a wall or fence can also create a microclimate. Don’t expect a solid structure to help reduce winds. Wind-control research shows that solid fences create low-pressure pockets that pull the wind down into the very area you want protected. The wind swirls over the top and drops back down at a distance roughly equal to the height of the fence.
This means that if your quiet site is “protected” by a solid 6-foot wall, the force of the wind on your deck about 6 to 12 feet from the wall is about the same as on the other side. Build louvered fences or walls with open areas on top to filter the wind and let it through instead of causing it to vault over the top and come down with a turbulence.
Frost and foundations
In climates that experience frequent freeze-thaw cycles, a mortared deck requires excavation and concrete footings. Without this extra support, the frost will heave and crack the surface.