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Dear Jim: I can feel the intense heat from the driveway and concrete walkway. I want to reduce my air-conditioning costs in an environmentally-sound manner. How can I block this afternoon heat? - H. K.
A: One of the most environmentally-sound methods to control the heat from driveways, sidewalks and patios is proper landscaping. Plants both block the direct summer sun and act as natural air conditioners.
On a typical summer day, the air temperature around plants is about 10 degrees cooler than the outdoor air. It can be as much as 20 to 30 degrees cooler than the air around a concrete or asphalt driveway or walkway in the sun.
Plants primarily cool the air by a process called transpiration. This is similar to our perspiration. As moisture from a plant's leaves evaporates, it absorbs heat and thus cools the surrounding air. The hotter the day is, the greater the plant's cooling effect.
On a hot sunny day, an average-size deciduous tree will evaporate about 100 gallons of water. This provides the equivalent cooling of 660,000 Btu. As a reference, a three-ton central air conditioner provides 36,000 Btu/hour.
Choosing the proper types of plantings can reduce the sun's heat in three ways. First, taller trees and plants can block the sun's direct rays from striking the driveway, walkway or patio. This reduces heat buildup. Choose deciduous trees on the south side so the winter sun is not blocked.
Second, medium-height plants can block heat reradiated from a hot driveway to your house walls and through windows. A solar-heated concrete driveway or walkway continues to radiate heat well into the evening.
Third, low ground cover creates a cool buffer zone immediately next to your house. This is where the transpiration cooling process is particularly effective. If you sometimes rely on natural ventilation, this cooler air will be refreshing.
When choosing ground cover, consider the plant's height, spread, texture, foliage and whether it is deciduous or evergreen. Keep in mind that in the winter, you will welcome any extra radiant heat, so select ground cover that will not block it from your house.
Consider the coloration of the foliage so it complements your other landscaping. Many ground covers have attractive flowers and are very fragrant. I planted pachysandra outside my office window and the fragrance is wonderful in the spring. Lilyturf with dark mulch is also attractive.
Instant Download Update Bulletin No. 451- list of 55 ground cover plants, types (perennial, deciduous, evergreen), hardiness zones and U.S. map, height, spacing, preferred soil, propagation methods (division, cuttings, seeds), chart to estimate number of plants required for specific are in square feet and a mulch selector guide.
Dear Jim: I have caulked and weatherstripped all the leaky spots that I found in my house, but I still feel drafts. Where is the most likely location of the air leaks? - A. B.
A: The most likely location of the leaks is at the sill plate. This is where the walls rest on the top of the foundation. Tests have shown that it is the area of greatest air leakage in most houses and often overlooked.
If your house has a basement, go into the basement at night and have a helper shine a flashlight at the foundation from outdoors. You will see the light shine through gaps. Expandable urethane foam caulk from a can works well. If you do not have a basement, just caulk the entire area from outdoors.