What is a Mother-in-Law Suite?

Evelyn Long

Jul 5, 2021

what is a mother-in-law suite

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What is a mother-in-law suite? The term refers a guest house or apartment space attached to a dwelling. Also called a granny flat or in-law suite, the size varies depending upon local regulations. Traditionally, these were installed so extended families could move in with loved ones and still have some separation and independence.

If you’ve heard more about in-law suites now than ever, there’s a reason. More households are turning to multigenerational living, with about 24% of those between 55 and 64 living with their children. Plus, some housing activists see additional units as part of a solution to urban housing shortages — opening up more homes on previously single-family lots.

How did this trend come about? While there is no official single story about mother-in-law suites, there are some common jokes about mothers-in-law that make you realize why people build a granny flat instead of just using a spare room. Here’s what you need to know.

Are They the Same as Accessory Dwelling Units?

They can be! Accessory dwelling units (ADUs) are often synonymous with mother-in-law suites. These dwellings are small, cost-effective homes that can be built on the same lot as single-family homes. They are cheaper to build and inhabit because they don’t require the purchase of land and often use more affordable and sustainable construction techniques.

ADUs are growing in popularity as an affordable housing option for single-person or small households — and can also be a great way to house extended family members, too.

Haven’t seen any ADUs in your region? That might be changing in coming years, especially in higher-density cities where legislators are looking for ways to decrease housing costs for their residents. Recently, Accessory Dwelling Units are being explored as a pro-housing policy in the state of California. This is particularly critical in cities like San Francisco, where housing supply crunches contribute to a high cost of living that pushes out lower-income residents.

Thanks, at least in part, to loosening regulations on building ADUs, California issued 12,392 permits for ADUs in 2020 alone. More renters are likely to be considering mother-in-law suites in years to come, and they won’t even have to marry into the main household to do so.

Can You Rent Out a Mother-in-Law Suite?

Whether or not your mother-in-law suite is an attachment to your home or an ADU, you can rent out the space to someone looking for housing. If you don’t mind housing a tenant within your home, renting the mother-in-law suite within your actual home can be a great option. However, ADUs might be the prevailing choice for renters.

Regardless of the type of structure you have, you can absolutely rent the space, just like you can rent any property that you own.

Reasons to Build a Mother-in-Law Suite

If you’re considering building a mother-in-law apartment or choosing a home with one attached, there are many benefits to adding this detail to your home:

1. Overcome Rising Housing Costs

In April 2020, $246,334 was the forecasted price for the average home in the United States. Obviously, the cost varies widely depending upon location and demand in your area — but the truth remains that homeownership can be a stretch for many households.

Pooling resources with the in-laws is a smart way to afford the home you want while still giving everyone their own space. Elderly family members with income limitations and young families can reside together instead of fending for themselves in the real estate market.

multigenerational family in an in-law suite

2. Help an Aging Parent or Family Member

As people age, they may need help with daily chores, such as mowing the lawn. Perhaps they can live on their own but need someone to check in on them occasionally.

A granny flat offers the convenience of having family on location to provide support to elderly family members. This can also cut down on the cost of alternative solutions, like assisted living, which can often be challenging for families to financially support.

3. Add Rental Revenue

This is where the concept of an in-law suite intersects with discussion around ADUs more generally. Your mother-in-law suite doesn’t necessarily have to house your family. You can also rent the space out to a local tenant, providing additional housing on your lot while making up some of the costs of your mortgage.

Since the in-law suite likely has a different entrance, you can keep living areas completely separate. Many people add a sturdy door between the main house and the add-on. You can then lock the door for added safety. Of course, as with any home rental, you will want to engage in a vetting process to make sure you and your tenants agree on the basic courtesies and laws of sharing a lot.

4. Increase Your Property Value

Another argument for this addition is that in-law suites are desirable. Around 33% of house hunters say they’ll pay up to $3,000 more for a home with a bonus apartment. You’ll gain the added value of the square footage plus extra money for having an independent space.

5. Invite Clients to Your Home Office

If you run a home-based business where you have clients see you, you might not want them in your actual home amidst your personal belongings.

An in-law suite affords the opportunity to have customers visit you via a separate entrance and in a professional space. You can use this type of space for salon services, accounting, construction meetings and any number of other business purposes. 

How to Build a Mother-in-Law Suite

Once you’ve decided to build a mother-in-law suite, you may be wondering where you should even get started with the process of building it. One of the first things you need to decide is what kind of mother-in-law suite you’re going to build. Once you do that, you can start laying out plans and searching for the right contractor for your project.

Can You Build a Mother-in-Law Suite in Your Backyard?

The answer is yes, absolutely! Of course, deciding to put the structure in the backyard means that you’ll need to build it as an ADU. As long as building a structure separately is okay with you, you can get started on planning your ADU for your backyard. This can even be preferable, as it utilizes space you might not otherwise be using.

Are Mother-in-Law Units Legal?

If you’re wondering about the legality of mother-in-law units, everything depends on your specific situation, project and location. Every state and municipality will have different rules and guidelines, and it’s important to pay attention to the regulations and codes of your area. If you’re working with a contractor or builder, they’ll likely know where to guide you for all of the proper forms and clearances. 

How Much Does It Cost to Build a Mother-in-Law Suite?

The answer to this will likely depend heavily on your specific home and the details of the suite or structure you’re adding. Usually, adding a suite can run you somewhere in the neighborhood of $40,000-$100,000, but an ADU will likely hit much closer to the top of that range. Of course, this is all subject to change, as every home is different, and only you know the details of your space.

How Much Value Does a Mother-in-Law Suite Add?

Although every home and every area is different, the general consensus is that mother-in-law suites overall add to the value of a home. Assigning a specific dollar amount to the value added can sometimes be a bit of a gamble, however, most research shows that the appraised value of properties with mother-in-law suites added tends to be 7-9% higher.

Types of Mother-in-Law Suites

Mother-in-law suites can come in many shapes and sizes. Sometimes they’re a converted room in the main household, and sometimes they’re an attached or completely separate unit on the same lot.

converted attic into mother-in-law suite

1. Attic Conversion

Converting an attic into a livable suite can seem appealing. After all, an attic can often be completely wasted space in a house’s floor plan. Yet if you’re thinking about converting your attic into an in-law apartment, do yourself some favors and meet with experienced contractors before jumping in.

Some attics won’t be suitable for livable space, which have codes related to height, square footage, and structural integrity. Having professionals check out the attic space and lay out which permits, code requirements and other changes will be needed can help you budget the project and decide if it’s worthwhile.

2. Basement Conversion

Does a renovated basement apartment sound perfect for a second dwelling? Roomy basements are great for in-law apartments, particularly if renovated to include a kitchenette, bathroom and comfortable aesthetic. Homeowners might prefer to turn an underutilized and finished basement into a rentable home for their multigenerational family or a local tenant.

Basement suites should have at least one window, ideally a private entrance and upgraded walls and flooring to create a comfortable space. With some finishing touches, a basement will feel like a natural extension of the main living area.

3. Laneway House

Although traditionally, mother-in-law suites are an addition to an existing structure, they can also be a detached space on the same property. Think of them more like a guest house. You’ll still save money as you already own the land and likely have existing hookups. 

Made popular by the trend in Vancouver, the Laneway House is one option for a separate space. These dwellings are small. Most Laneways are between 600 and 800 square feet and have one and a half stories with one or two bedrooms and one bathroom.

A stand-alone structure may cost a little more to build than an addition, but you gain extra privacy. The size of the quarters and building costs in your area determine how much the in-law suite costs. 

One limitation for homeowners considering a Laneway House is zoning regulations. Many U.S. cities, facing urban housing crises, are debating current zoning laws to find more opportunities to provide homes on existing land. Research your municipality and state regulations to get a feel for what this discussion looks like in your location.

extended mother-in-law suite

4. Extension to Single-Family Home

This is pretty aelf-explanatory; rather than creating a detached space, adding an in-law suite can involve building an extension to the existing house. This unit may still have separate entrances but will be designed and built to align with the style of the main structure.

5. Prefab Mother-in-Law Suites

Another option for mother-in-law suites is using a prefab structure to set up an ADU — or an accessory dwelling unit. This can be a great choice for those looking to add a structure to the property without having to contract someone out or put in the work themselves.

This can also be a great option for those on the hunt for a bit more privacy for their additional space — especially if you plan to have someone consistently living there.

How to Find a Mother-in-Law Suite for Rent

On the flip side of things, if you are on the hunt for a unique apartment or living situation, and you are open to the possibility of renting a mother-in-law suite, you can certainly find plenty out there.

You can start by looking up mother-in-law suites for rent in your area. Many rental sites even have an option to filter through them so you can find exactly what you’re looking for.

What is a Mother-in-Law Suite?

Whether you’re interested in multigenerational living or taking in additional rent payments, there’s a lot to love about the in-law suite. Your reasons for building a granny flat may vary widely from another person’s.

The story behind the mother-in-law suite is an interesting one. In years to come, the trend is likely to continue to grow in popularity for American homeowners looking for different housing solutions for their families.

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