Is a solarium a good investment?

Call it what you will, the attached greenhouse, sun room, or solarium introduces a pleasing new dimension to life indoors. That much is now well established. But what is its value as an investment? Is the $8,000 to $16,000 cost of the average quality sun room worth the improved life style and comfort? To make that decision, you need to appreciate a sun room's worth as a space heater and know how a sun room addition compares in resale value with other home remodeling projects.

If the greenhouse is sited on the sunny side of the house and is away from heavy shadows cast by trees or neighboring buildings, it becomes a significant space heater.

Facing solar noon (when the sun is at right angles to the glass at midday) is best of all, but the room can be within 20 degrees of true south and still receive full winter sunshine. Even at 45 degrees to the east or west, the sun room will trap more heat than it uses, particularly if you have good night insulation.

Diane Boas, editor of the Greenhouses for Living directory, assesses the addition's solar heating value this way: If a sun space cuts a home's heating bill by $500 a year, that's the equivalent of earning $500 in interest on a conventional investment. Whatever amount would be needed to earn that $500 would be the immediate value of the sun space to the homeowner. If the interest rate were, say, 10 percent, the investment would have to be $5,000, ``so that would be the immediate investment value of your sun room,'' Ms. Boas points out.

A recent survey by ``Remodeling World'' magazine showed that 90 to 100 percent of the cost of adding a sun room is typically recouped in the increased value of the home. This is often referred to as the short-term recovery cost (when the house is sold soon after the remodeling).

By contrast, the same survey found that a conventional room addition recouped only 57 percent in the short term; a remodeled bathroom, 50 percent; and a remodeled kitchen, 80 percent. On the other hand, adding a new bathroom returned 100 percent of the cost, as did the application of new siding. Top remodeling return (147 percent) came from a fireplace addition.