What‘s a sunroom?

The defining feature of a sunroom is the vast amount of glass. Some versions, known as solariums and conservatories, consist of walls and a roof built entirely of windows that are held together by a strong cage of metal, wood, or vinyl.

But the traditional sunroom is built like any other addition — using standard construction techniques and a roof that matches the rest of the house — just with a lot more windows. A sunroom usually has 20 or more windows, plus skylights.

How much will it cost?

A 200-square-foot sunroom addition, including footings and slab-on-grade foundation, post-and-beam construction that’s exposed on the interior, efficient windows, 10 operable skylights, a tile floor, window shades, and a ceiling fan costs an average of $73,546, according to Remodeling Magazine’s 2014 Cost vs. Value Report. You’ll get about $38,000 of that investment (51.7%) back at resale, according to the report.

You’ll need to set aside at least 12 weeks for this project, plus time for planning, and will need the help of an architect or a design-build contractor to create a room that ties in well with the house’s style, flow, and structure.

As with any addition, you’ll need a building permit from the town — and you’ll need to follow zoning rules about how closely you can build toward property lines, how big your home can become, and other restrictions.

Where should it go?

One ideal spot for a sunroom is off of the kitchen, since that’s where so much of a home’s traffic is — and because the sunroom is likely to become your preferred eating spot. But if not the kitchen, make sure it’s adjacent to some major public gathering space, such as the family room, living room, or dining room.

You can knock as much as $8,000 off the cost of the project by using an existing exterior door (or even window opening) to access the new space, since it means almost no changes need to be made to the exterior wall.

Since sunrooms are indoor-outdoor spaces, you’ll also want to consider location from another perspective — the outside world. Take advantage of the best views and the best sunshine. A northern exposure will keep the room partially shaded most of the day, and is ideal for climates where air conditioning is the primary concern.

A room with southern exposure is good for hot climates, since it allows the most sunlight in for natural light and warmth. Eastern exposure provides sunshine in the morning; western exposure yields afternoon sun. A good rule of thumb is that the room should have at least four hours of direct sunlight each day so it’s truly a sunroom.

What about heating and cooling?

You could slash 20% off the cost of the project if you make yours a three-season sunroom instead of a year-round space. Then it wouldn’t need heating and cooling, insulation, or efficient windows. But the savings aren’t worth what you give up in comfort, says Frank Evans, a sunroom builder and designer in Rockland, Mass. You’d wind up with a room that’s a sauna in the summer and an igloo in the winter.

Still, there may be other ways to save on heating and cooling. Instead of expanding your house’s ducts or pipes into the sunroom, which could require replacing the old furnace and compressor with a larger-capacity equipment, you could add independent heating and cooling to the room, using electric baseboard heat, for example, and a ductless air conditioner. That way, you get year-round comfort for a smaller investment.