Landscaping for Energy Efficiency
Can landscaping really make a difference in a home's energy efficiency? If so, what are the key things I need to pay attention to? How do they differ based on location (I live in the U.S. Pacific Northwest)
Answer from Green Energy Efficient Homes
Landscaping can affect the energy efficiency of your home by altering the dwelling's exposure to sun and wind, both of which have a major impact on home energy use.
One of the obvious effects of landscaping for energy efficiency is the impact of planting deciduous trees along the south and west sides of the house. Deciduous trees provide shade during the hot summer and can therefore protect your house from overheating, reducing or eliminating the need for air conditioning. In the cold late fall, winter and spring, the trees allow sunlight to filter through the treeless branches and warm the exterior of your house as well as send solar energy in through windows, reducing your heating expense. Where you plant the trees affects the benefits they provide - deciduous trees to the north won't help as much as those to the south and west, although surrounding your entire house with a forest of deciduous trees will definitely make a difference. I can attest to this - our neighborhood is full of 70 to 90 year old oaks and maples, and on sweltering hot summer days it is always considerably cooler in the shade here than in the full sun of the main drag a block away.
Deciduous trees don't do that much to protect against cold winter winds, but some coniferous trees do. For example, a row of tightly spaced junipers or cedars along the north side of a house can provide a wind barrier that reduces heat exchange between your house and the outside air. In fact, studies in the US have shown that building a windbreak around your house with either trees or a fence can have a huge impact on your home heating bill.
When you hear weather forecasts that talk about wind chill, they are really talking about the fact that wind causes increased heat exchange - since on a calm day, the cold air touching your face or the wall of your house warms a little, stays more or less in place (at least for a second or two), and then has less of a cooling effect on the heat source, while on a windy day that slightly warmed air is quickly moved away and more cold air is brought in to replace it. So a hedgerow or fence along a wind-exposed wall will help reduce heat losses due to cold winter air. In fact, if wind is a big concern in your area, the more disturbances you can add by planting additional trees or adding other landscaping features on the windward side of your house, the less impact the wind will have on pulling heat away from your home.
In terms of land elevation, you can improve the energy efficiency of a new home design by having the land higher at the north end of the home and lower at the south end. By having a house with one storey on the north side and two on the south, you get maximum solar exposure in the south while minimizing heat losses on the north side. Even if you don't bury one side of the house itself in the side of a hill or elevation, you can reduce winter heat loss by raising the land on the north side, in the same way that adding a hedge will help.
I'm not that familiar with the climate in the US Pacific Northwest, but my brother hails from Vancouver, home of the International Rain Festival (September 1 to August 31 each year) so I suspect your climate is rather wet, doesn't get that cold in winter or that hot in summer, and has a fair amount of evergreen trees and few deciduous trees. If you're trying to stick to local plant species, I'd suggest talking to a local tree nursery staff member about suitable deciduous trees that provide good shade in summer. For conifers for a wind barrier you should have plenty of choices!
If it is indeed wet in your climate, you may not need to worry too much about xeriscaping, or creating a landscape that can withstand drought. But in a dry climate, planting thirsty plants is wasteful because water is embodied energy - the energy required to pump, filter, or chlorinate the water is a big part of what you pay for in your water bill. If you have a wet climate but do occasionally need to water plants during a dry spell, one obvious solution in terms of energy efficient landscaping is to install a rain barrel or other rain water retention system. In fact Green Energy Efficient Homes is a proud sponsor of a rain water harvesting tank at Kinu Primary School in Uganda.
Finally don't forget one of the key ways in which landscaping can affect energy efficiency: if you have a green roof on your house, you can significantly cut heating and cooling costs because in winter the green roof acts as a very thick layer of insulation, while in the summer, the garden over your home is getting watered, the plants evaporate the water, and this in turn cools the earth, so instead of your roof being a major source of heat, as it is for most houses, it absorbs and then evaporates the sun's heat, keeping your house nice and cool.
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