Q. I want to build a deck outside the sliding glass door of my family room. I want the deck to be as environmentally friendly and energy efficient as possible. What design and material suggestions can you give me?

A. A deck can actually be energy efficient in several ways. If having a deck allows you to spend more time outdoors, you should be able to set your central air conditioning thermostat higher during the times you are primarily outdoors. Setting the thermostat higher even for just a few extra hours per day can significantly reduce your electric bills.

A properly designed deck with a pergola or some type of tall side wall can also provide shading for your house. This is particularly helpful if the pergola or wall can shade the glass patio door. A tremendous amount of heat is transferred through a large glass door when it is exposed to the direct afternoon sun.

In addition to saving energy, you can make environmentally friendly choices for the decking materials.

For the deck framing, engineered lumber can be used instead of standard solid lumber. Engineered lumber is stronger than standard lumber and is often made from smaller wood pieces, so less prime wood is required overall.

The choice of decking material is the most important factor.

Pressure-treated wood is abundant and is the least expensive material to use. The only environmental drawbacks to wood are its limited life and the harsh cleaning and sealing chemicals that must be applied every year or two to extend the life of the wood.

Trex just developed a new decking material, Transcend, that is the most environmentally friendly material available. Transcend is made from 95 percent recycled materials, primarily from plastic bags and sawdust.

I just replaced my 10-year-old, deteriorated wood decking with Transcend. Transcend is different from other composite decking in that it has a thin polymer top cap. This makes it easy to clean without using harsh chemicals. Also, the material does not stain or support mildew growth, as many composite materials do. Transcend is more expensive than wood, but considering its very long life and minimal maintenance, it is a good long-term investment.

Building a vertical wall on the southwest side of the deck is most effective for shading, and it also provides privacy. The simplest design uses just standard posts covered by lattice. The openings in the lattice allow some breezes to pass through the wall. Planting climbing vines along the lattice will also enhance the cooling by natural transpiration from the plants.

Another option for the shading wall is to install horizontal slats. By tilting the slats at the proper angle, the direct afternoon sun can be blocked while providing ample area for breezes. The best angle for the slats depends upon your area’s latitude and the deck’s orientation to the sun. Make some cardboard slats to test for the best angle.

To block the sun from a more overhead direction, build a pergola over the deck. This is attractive, and by allowing plants to grow up and over it, the pergola can provide additional shading.

The following companies offer alternative decking materials: Azek, www.azek.com; Rhino Deck, www.rhinodeck.com; Timbertech, www.timbertech.com; and Trex, www.trex.com.

Q. My central air conditioner’s outdoor condenser unit is mounted on a concrete slab. The slab was level when it was installed several years ago, but now it looks tilted. Will this reduce the efficiency of the unit?

A. The outdoor condenser unit for a central air conditioner can have a slight tilt and still work fine. Check with your heating and cooling contractor for the manufacturer’s recommendations for the maximum tilt.

Since concrete slabs for condensers are seldom installed on footers, they all will settle and tilt a little. The fact that you noticed it means it might be extreme. Contact a contractor who specializes in leveling slabs and patios.

Send inquiries to James Dulley, Arkansas Democrat-Gazette, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.

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