More and more Americans are keeping it all in the family these days, as multi-generational living—where three or more generations share the same household—continues to rise.

In 2016, a record 64 million people, or 20% of the U.S. population, lived with multiple generations under one roof, according to a recent analysis of Census data by the Pew Research Center.

Maybe it’s because of lingering economic fallout from the recession, increasing lifespans, or different cultural norms in our diverse population. Whatever the reason, sometimes preserving family harmony among cohabiting adults means creating an extra layer of privacy.

Enter the in-law suites, aka granny suites. They’re converted garages, basements, sheds, and attics that contain living, bathing, and cooking quarters that allow Grandma or Junior to live in a separate but connected space. There’s privacy—often a separate entrance or at least a locked door—but there’s also enough togetherness so that help, if needed, is only a holler away.

“Many seniors want to retain their independence but live in a more age-friendly environment,” says Todd Nelson, business development officer at LightStream, an online consumer lender that finances, among other things, in-law suites that can range from $40,000 to $125,000. “While that may seem like a lot upfront, they can save families thousands of dollars in the long run.”

If you’re considering adding your own in-law unit, keep these tips in mind.

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Before deciding where you’re going to create an in-law suite, discuss the remodel with your parents or adult children to find out what they need and want.

Older adults might have trouble climbing stairs, seeing in dim light, or reaching up or down. For them, a suite in a converted attic could be too difficult to access. Adult children, on the other hand, might prefer one large, open, loft-like space.

Whatever you construct for elderly relatives, make sure to incorporate universal design. This includes wide doors and raised cabinets that can accommodate walkers and wheelchairs; lipless shower stalls that eliminate tripping hazards; walls reinforced with plywood that can anchor grab bars; and lever door handles that are easier for old and young hands to grab.

In the best-case scenario, your in-law suite should have a bedroom, sitting room, bathroom, and kitchen area, so whoever’s living there can maintain their independence.

You can go all out and build a 300- to 600-square-foot standalone granny pod in your backyard, which could cost as much $125,000. Or you can throw up an addition, which will cost an average of $20,000 to $72,000.

But you’ll save money if you convert underused space you already have. Here are some options.

Most garages—attached or detached—are uninhabitable in their original state. Although they might have drywall and electricity, most don’t have adequate (or any) heating or air conditioning, enough insulation, the proper number of wall outlets to meet residential building codes, or any plumbing.

On the plus side, garages have foundations, roofs, and framing, and many have separate entrances that provide privacy. So that’s a good starting point.

When converting a garage, you’ll have to install wiring to meet residential building codes for kitchen equipment and wall outlets; plumb a kitchen and bathroom; and condition the space with heating and air conditioning by tapping into the main house’s systems or installing separate HVAC systems.

Depending on where you live, you’ll either have to insulate the garage door to protect against summer heat and winter cold, or replace it with more functional, residential doors—which could require additional framing. Also plan on raising the floor to install insulation.

Cost: $20,000 to $50,000 (add another $15,000 to $25,000 for a bathroom)

If your basement is already finished, turning it into an in-law suite is fairly simple. You can divide a large space into a bedroom and sitting room, and add a simple kitchen that can tap into the pipes and drains already installed.

Unfinished basements present a bigger challenge. You might have to add sump pumps or French drains to guard against flooding, and a dehumidifier to suck moisture out of the air and prevent mold. Also, you’ll probably have to add above-grade windows, window wells, or a door to create an easy exit to meet local building codes.

Your big challenges will be:

When was the last time you ate in your dining room? Or sat in your living room? Or actually hosted a guest in your guest room? If the answer is, “Can’t remember,” then you can convert those hardly used spaces into an in-law suite. You already have exterior walls and windows, sub-flooring, and HVAC ducts in place.

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If you have enough space, carve the big room into a bedroom and bathroom, which will require framing, plumbing, tiling, and electrical work. Or, if a bathroom is nearby, divide the space into sleeping and reading/TV areas.

This converted space might not provide maximum privacy, but it does give everyone a room to call their own.

Cost: Framing a wall costs $2 to $4 per square foot; adding a bathroom can run anywhere from $3,000 to $25,000.

Lisa Kaplan Gordon is an award-winning writer who's covered real estate and home improvement for realtor.com, Yahoo, AOL, and many others.