Q. I plan to add some storm windows over my north-facing windows, but I am not sure whether to install acrylic plastic or glass ones. What would be best for a long life and energy efficiency?

From an efficiency standpoint, acrylic plastic and glass storm windows are equivalent. Acrylic windows will be less expensive and last a long time, but they can be scratched more easily than glass.

For indoor storm windows, especially ones on the south and west side, acrylic is the best choice. A natural property of acrylic is it blocks much of the UV (ultraviolet) rays from the sun. It also is lighter weight.

Q. We are planning our energy-efficient dream home. We have heard about "net zero energy" designs. Are they as livable as regular efficient houses? Do they look strange? How much do they cost?

A “net zero” energy house is one in which the house uses no external energy overall throughout the entire year. It may consume some energy at times, such as electricity from a utility company, but it produces extra electricity other times to result in net zero energy use.

This is a fairly new building concept because newer technologies, for both conservation and energy production from renewable sources (solar, wind), have made this possible. Over its life, the savings from a net zero energy house can easily pay back much more than the higher initial cost.

In the past, a rule of thumb was you would have to spend 20 percent more to build a house which used 80 percent less energy than a typical house. To get the addition 20 percent savings, you would have to spend 80 percent more. Today, that extra savings is much less expensive to achieve.

Net zero energy houses do not have to look significantly different than typical houses, although some of the most efficient designs are unique-looking. You may see some hot water solar panels on the roof or large, attractive south-facing windows, but otherwise, these houses often look fairly conventional indoors and outdoors.

There is no reason a net zero energy house should not be as livable as any standard code-built house. In order to attain net zero energy usage, your family should be conscious of typical efficient living habits such as setting the thermostat back at night, not taking 30-minute steamy hot showers, switching off unused lights, etc.

An architect can design a net zero energy house or you can select a pre-engineered net zero house package. Several companies offer these packages. For example, Deltec Homes (www.deltechomes.com/zero-energy, (800) 642-2508) offers circular, panelized net zero energy houses starting at 1,500 square feet, ready to be built on your site.

The package includes double-stud walls, triple-pane vinyl windows, a long east/west axis for passive solar heating, a solar hot water kit, natural summer ventilation, open floor plans, and super-efficient heating and air-conditioning systems and kitchen/laundry appliances.

The circular design of Deltec Homes actually consists of 10 or more eight-foot panels connected together. This near-circular design reduces heat loss (winter) or gain (summer). It also reduces air leakage because the wind flows smoothly around it.

Most of the net zero energy houses in the U.S. are still connected to the electric utility grid for times when external energy is needed. When the solar panels or windmill produce more electricity than the house needs, the utility company may pay you for the extra and it may make your electric meter run in reverse.