My concrete patio is cracked and I thought about building a deck over it. The patio sometimes gets too hot to use. How can I design the deck to stay cooler and shade the house for lower air-conditioning bills?—Bob M.
An overheated concrete patio can create a lot of energy problems in addition to being uncomfortable. Building a deck to help shade your house makes a lot of sense. When properly designed for the specific location on your lot, a deck can reduce air-conditioning bills and peak electricity demand.
A hot concrete patio radiates heat back to your home’s walls and into the house through uncovered windows. This increases the air-conditioning load. Concrete has a high thermal mass, so it continues to give off heat well into the evening.
Anything you can do—such as eliminating a hot patio or building an efficient deck—that allows you to be outdoors more will save energy. When you are outdoors, you will not have to keep your house as cool indoors and this reduces air-conditioning costs.
Also, people who spend more time outdoors in the natural heat are more comfortable indoors at a higher room temperature. If you can set your central air conditioner just two degrees higher, the energy savings can be 5 to 10 percent.
Building a wood deck with a sun-deflecting side is your most efficient design. Build the deck floor high enough so at least one side is several inches above the ground or the old patio. If it is built too close to the ground, air will not freely flow beneath it to keep it cooler.
The key to a solar-efficient deck design is creating a vertical barrier that shades the deck and the house wall while letting natural breezes through. The design of the vertical wall on the deck will vary somewhat depending on which direction the deck faces. For designing your vertical barriers, you can go to your library to find simple solar charts showing the sun’s position. Or just hold up a stick at several times of the day and measure the shadow length.
Install vertical posts along the side of the deck in the direction of the most sun. Using 6- or 8-inch-wide lumber, position pieces horizontally on the posts to create louvers. Tilt them so the most intense summer sun is not striking the deck and some of your house wall. Also, space them far enough apart so natural breezes will freely flow between them. If you tilt them properly for your area, the lower winter sun will shine through the spacing.
A simpler option is to install sun-control screening across the vertical posts. This type of screening will block up to 70 percent of the sun’s direct heat, yet will still allow a breeze through it and a reasonable view of the yard.
The best way to install the screening is with a do-it-yourself screen framing kit. When installed, these have a truly professional appearance. You can easily remove the screening during the winter for more sun.
For greater efficiency, especially for shading the house, cover the top of the deck with additional tilted wooden louvers or just flat, narrow wood strips. These can be spaced closer together because they will not impede any breezes. Tilt the louvers properly so the lower winter sun shines through.
Another way to enjoy more non-air-conditioning outdoor time is to build a do-it-yourself screened gazebo kit. Many are made of cedar or white vinyl and are available in precut or modular kits.
Write for Utility Bills Update No. 4732, for a buyers’ guide of gazebo kit manufacturers. Include $3.00, a business-size SASE, and Update number. Mail requests and questions to James Dulley, Kentucky Living, 6906 Royalgreen Drive, Cincinnati, OH 45244. Go to www.dulley.com to instantly download.