Q: Dear Jim: My concrete patio is cracked and I thought about building a deck instead. 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.

A: Dear Bob: An over-heated concrete patio can create a lot of energy problems in addition to being uncomfortable under the intense summer sun. Your thoughts about 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 your air-conditioning bills and peak electricity demand.

A hot concrete patio radiates its heat back to your home's walls and into the house through any uncovered windows. This increases the air-conditioning load. Concrete has a very high thermal mass, so it continues to give off heat into the air above it and to adjacent structures well into the evening as it slowly begins to cool.

Anything you can do, such as eliminating an uncomfortably hot patio or building an efficient wood deck, that allows you to be outdoors more often will save energy. Whenever you are outdoors you will not have to keep your house as cool indoors and this reduces air-conditioning costs.

Also, it is a well-accepted fact that 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 best and most efficient design. Try to build the deck floor high enough so at least one side is several inches above the ground of the old patio. If it is built too close to the ground, air will not be able to 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 the natural breezes through. The design of the vertical wall on the deck will vary somewhat depending on which direction the deck faces. The sun is highest in the sky when it is shining from

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the south at noon. For designing your vertical barriers, you can find simple solar charts (sun's position) at your library, 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 six-or eight-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.

Another 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 it will still allow a breeze through it and a reasonable view of the yard. This may be important if you have children.

The best way to install the screening is with a do-it-yourself screen-framing kit. When installed, these are often used to screen in a porch and have a truly professional appearance. A support strip is screwed into the posts and the top and bottom cross pieces. The screen is placed over this strip and a finishing cap is snapped over it to trap the screening in place. You can easily remove the screening during the winter for more sun if you wish.

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. Precut kits include all the pieces ready for assembly. Modular kits already have the eight or 10 roof, wall and floor sections completed for assembly.

Write for (instantly download - www.dulley.com) Utility Bills Update No. 732 - DIY instructions and diagrams for attractive energy-saving, two-level decks (east, south, west locations), and a buyer's guide of 15 screening/frame and gazebo kit manufacturers. Please include $3 and a business-size SASE. James Dulley, Illinois Country Living, 6906 Royalgreen Dr., Cincinnati, OH 45244.

James Dulley is a mechanical engineer who writes on a wide variety of energy and utility topics. His column appears in a large number of daily newspapers.

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