- Cost (national average): $73,546
- Return at resale: 51.7 percent
You know from the word "addition" that this project doesn't come cheap.
Anytime you have to add onto the foundation -- and the footprint of your home -- the price climbs, says Michael Hydeck, owner of Hydeck Design Build Inc. near Philadelphia and past president of the National Association of the Remodeling Industry.
With a 200-square-foot room with skylights, low-E windows, automatic shades and a tile floor, "it's a major project," says Alfano.
It can make a big difference in your enjoyment of the home and -- depending on how it's configured -- help heat adjacent rooms, he says. "You can do some pretty creative stuff with this."
At resale: Resale value will vary by region, Phipps says. "You have to look at what your market is."
In Las Vegas, homeowners are more likely to add a roof or cover to the patio -- something with privacy curtains, but no walls, says David R. Tina, president of the Greater Las Vegas Association of Realtors and an owner/broker with Urban Nest Realty.
Whatever you build, if you want to get the biggest bump to your home value, opt for a licensed professional and permitted work, he advises.