It's not just your parents moving back into an in-law suite - more often these days, it might be your adult children.

In-law suites are more popular than ever among homeowners. These suites add value to the home and might allow three generations to live under one roof.

Contractors and builders say they're having trouble keeping up with demand for in-law suites - renovations, say, of a porch or a garage, or for an addition to customers' existing homes.

Dave Martin, president of Remodeling Concepts in Langhorne, hears this from his clients.

"[They] are spending more money on in-law suites and staying longer in their homes," said Martin. "Years ago, they would add an in-law suite, expecting to sell within a few years. Now, they plan to stay, so they want all the bells and whistles." Those might include step-in showers and higher-end kitchens.

In the past, Martin would be contracted to build perhaps one in-law suite per year, but now he's working on three to four a year. A garage conversion runs between $40,000 and $60,0000, while a full addition may run $80,000 to $120,000, he estimates.

And Martin's last two jobs haven't been for elderly in-laws, but for younger people. Many can't afford a down payment on their own home yet and return to the nest to live with their parents and grandparents.

At Martin's latest in-law suite project on Pebblebrook Road in Warminster, "the mother owned the house and built the in-law suite for her son and his wife to occupy. They're expecting a child soon, which allows the grandmother to be close with her grandchild."

At another project in Huntingdon Valley, Martin explained: "The parents have a son who is newly married and just had a baby. We built an addition as an in-law suite. The couple both work. The grandma helps take care of the baby. So it's a three-generation in-law suite."

Harriet and Larry Kessler of Glen Mills converted their detached garage into a 750-square-foot suite for their grown children, who were expecting a baby.

That squares with demographic data. During the housing recession from 2007 to 2011, America had a rise in the number of multigenerational households, according to 2012 U.S. Census data.

But those households, defined as three or more generations living together, started to gain ground in the last 10 years.

According to Census Bureau data, the share of multigenerational households, among a total of 80.5 million family households in 2012, was 4.6 percent, compared to 3.9 percent in 2000 and 3.2 percent in 1990. The reasons? Economic and cultural: a high unemployment rate and the prohibitively high cost of owning and renting for new households.

Explains David Hagen, founder of Hagen Construction & Design in Lower Gwynedd: "For baby boomers, their parents are moving back in with them, especially if there's only one parent left. For the younger boomers, they can't get their kids to leave. Whenever we do a renovation, there's a different frame of mind than 15 years ago among clients."

But do in-law suites always add value? In certain areas, yes. In others, no.

For houses in the $400,000 to $750,000 range, suites add value, Hagen said.

"Those people are adding on and increasing the square footage. And it's a desirable trend. Fifteen years ago, it was undesirable. Now they look at it as either a home office or an in-law suite or a potential rental unit," Hagen said.

Basement renovations for in-law suites are different. "They don't always add a lot of value," Hagen said. "Spending $40,000 for a real nice renovation in the basement, you only get $10,000 more in value. Forget about making money on it, unless you the homeowner do the renovation. Then they come out even."

In-law suites in general add resale appeal.

"If you look at houses for sale, you'll see that at least some of them advertise in-law suites as a selling feature. It's more of an economic trend than any other time," Hagen says.

For a client in Schwenksville, contractor and builder Dennis Gehman turned an attached two-car garage into an in-law suite, then built a detached garage, as well.

In East Norriton, "We enclosed the side porch as an office and created a pass-through connection to the in-law suite addition," Gehman said.

But there is sometimes a catch: Not all towns and townships will allow in-law suites to include a full kitchen, for fear the homeowner is creating a hidden rental unit.

Gehman advises to make sure the homeowner complies with local zoning laws.

"My parents moved in two years ago. We put in a walk-out basement and an extra driveway," says Gehman. "We also put in a 10-foot stretch of kitchen, as the township said we could put in a kitchen, but with no stove."

215-854-2808

@erinarvedlund