Efficient Replacement for Sliding Doors

QUESTION: We bake in the summer and are chilly in the winter near our old sliding glass patio door. What are the most efficient replacement sliding glass doors? I need one that slides open easily, yet is secure when locked.

ANSWER: An old, poor-fitting sliding glass patio door is one of the worst energy guzzlers in most homes. With the drafts it causes, you often have to adjust your air conditioner or furnace thermostat several degrees up or down, just to stay comfortable. This can push up your utility bills by 5% to 10%.

When selecting a sliding glass door, you should consider the type of frame material and the type of high-efficiency glazing (glass). These effect both the amount of heat wasted through the door and the air leakage around it. Many new doors have multiple hook locking points for security.

One of the most efficient and maintenance-free frame materials is pulltruded fiberglass. It has all the advantages of other frame materials with none of the drawbacks. In my own home, I installed a sliding glass door with a fiberglass frame and low-e, argon gas-filled thermal glass.

Fiberglass expands or contracts very little with seasonal temperature changes, so it stays airtight year-round. It is also strong and durable. It comes in several colors, but you can paint it like wood to match your interior and exterior. Real wood interior veneer is also available.

Fiberglass material itself is a good insulator. As with vinyl door frames, there are many internal ribs for rigidity. These ribs create many small dead air spaces to increase the insulation level and block noise. A lap joint where the slider meets the stationary half provides a good seal.

Wood frames also provide natural insulation value and is attractive. Solid wood does require periodic maintenance. Selecting a wood frame door with exterior vinyl or aluminum cladding minimizes maintenance and painting.

Aluminum frames are very durable and provide a long-term good fit and smooth operation. It is difficult to paint aluminum, so you are generally limited to several stock colors. In cold climates, a vinyl thermal break separates the indoor and outdoor sections to reduce condensation.

You should select low-e double pane glass at the very minimum. Filling the air gap with inert argon gas increases the insulation R-values and greatly reduces outdoor noise transmission. The most efficient glazings--Heat Mirror, multi-low-e coatings and triple panes--are used more often in severe climates, but are also effective in your milder climate. To block more of the summer sun’s heat and glare, order high-efficiency tinted glass.

You can write to me for Utility Bills Update No. 555 listing manufacturers of the highest-efficiency sliding glass doors, frame materials and types of glass options for each, a chart showing typical energy efficiency ratings for comparing doors, and information on a fiberglass door. Please include $1.50 and a self-addressed business-size envelope. Send your requests to James Dulley, c/o Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.

Should Foundation Insulation Be Covered?

Q: I recently had a house built and the exterior foundation foam insulation is exposed. Should I cover it?

A: The ultraviolet rays from the sun can quickly degrade the extruded polystyrene insulation. Exposed foundation insulation also looks bad.

You can cover it with panels such as cement board, vinyl or pressure-treated lumber. Nail it directly to the foundation wall. There are several brush-on foundation paint coatings available. Another choice is brushing or troweling on stucco or plastic stucco-like materials.