As El Segundo, Calif., remodeler Bill Simone put the finishing touches on his latest renovation, he checked in with both heads of the household, as usual. Only this household isn’t usual.

The owners are two 60-something best friends, who hired Simone’s company, Custom Design & Construction, to carve dual master suites out of a three-bedroom California bungalow—one upstairs and one on the home’s main level.

“These two ladies have been friends forever, and they have bought many homes together,” notes Simone, who converted two first-floor bedrooms into a suite with a roomy bathroom and a walk-in closet. He also cut French doors into an exterior wall to allow the downstairs occupant access to a private, outdoor deck.

Simone accepts at least one remodeling job every other year that involves adding a second master suite so friends can live together, elderly parents can move in with their adult children, or financially strapped 20-somethings and their young families can bunk with mom and dad while they get on their financial feet.

Across the country, remodelers are fielding similar requests as an uncertain economy, an aging population, and a growing number of immigrants whose cultures embrace multiple-generation households tweak their traditional homes to accommodate a living arrangement that’s becoming more typical.

Sharing—With Boundaries

The job involves more than combining rooms or adding on to the house, however. Remodelers who work with multiple families under the same roof say that the process is as much about protecting privacy and preserving harmony among the home’s diverse occupants as it is about knocking down walls and using space in creative ways.

Here are five recommendations for remodeling a full house whose residents want to share a home without getting too close for comfort.

1. Include every member of the household in the planning—even the kids. The home’s owners might be the paying clients, but their take on what makes their aging parents or children comfortable—or not—might be off-base. The homeowners might not realize, for example, that their aging parents, who love their noisy grandchildren, would like the option to regularly be out of earshot.

2. Build more than a bedroom for the newcomers. Create a sitting room or den where the occupants can close the door and read, watch TV, or have private conversations. Arlington, Va., remodeler David Merrill, of Merrill Contracting & Remodeling, converted two adjoining bedrooms in one client’s house into a master bedroom and a den, and added a small deck outside of the den, where the homeowner’s live-in mother likes to read. The deck leads to a screened porch, which the rest of the family can enter from a larger deck on the other side.

3. Add a bathroom for each age group. Incorporate universal design features, such as a roll-in shower, wide doorways, and grab bars into the bathroom for an elderly parent, suggests Jesse Morado, director of production for the Mosaic Group, an Atlanta design/build firm. Install a bathtub in the kids’ room and dual sinks in the master suite if it’s for a couple.

4. Repurpose unused space. An unneeded formal living room easily converts to a first-floor master suite, says Morado, who bumped out the room’s exterior wall in one ranch-style home and extended the suite into the space once occupied by a large front porch. Among other candidates for conversion to a suite, playroom, or home office as the family expands are an underused finished basement, attic, garage, or formal dining room.

5. Know zoning regulations. El Segundo allows “granny flats”—small, detached bungalows on the property of another house. The catch: The flats may be occupied only by family members, and it’s illegal to rent them out once the relative moves. Simone says that most homeowners who ask for flats opt instead to add onto their homes once he informs them of the restrictions.

Simone also cautions that some communities forbid second kitchens in single-family homes; that’s an effort to prevent homeowners from renting out in-law suites originally intended for family members. Simone often builds a wet bar with a microwave oven and small sink into the second master suite so the occupants can make coffee and snacks without visiting the home’s shared kitchen. —Sharon O’Malley is a writer who lives in the Washington, D.C., area. Follow REMODELING on Twitter at @RemodelingMag.