What exactly is a mother-in-law suite?

If you watch enough HGTV, you may find yourself hearing a lot about mother-in-law suites when you follow house hunters looking for a new home. A mother-in-law suite is a separate living space that can accommodate in-laws or another family member who wants to visit or needs to move in with you.

An in-law suite, also called a carriage house or second dwelling unit, can cost anywhere from a few thousand to $100,000 or more depending on how creative you get with this additional space. Turning an existing room into a mother-in-law suite will cost less than building a detached mother-in-law suite from scratch.

What do homes with a mother-in-law suite look like?

The term mother-in-law suite refers to a private living area that is typically detached (meaning it does not connect to any other building) from the main structure of a home — or at the very least has a private entrance. Usually mother-in-law suites have their own bathroom, as well as a bedroom. Some may even have additional bedrooms, a small kitchen, and living room. 

These structures are named as such because they’re an ideal spot for in-laws to stay in while visiting or to move into when they get older and need extra support and care. Mother-in-law suites are also called in-law suites, granny flats, and mother-daughter houses. While a mother-in-law suite can preside over a garage, they’re often situated on the ground level, which is another reason they’re a great living situation for aging family members who may have trouble walking up the stairs. 

There is no one-size-fits-all solution to in-law suites. These are a few different types of floor plans and examples of what these suites can look like.

Attached mother-in-law suite

Typically, this is a separate living space built onto an existing home. This acts as an addition to the home and is usually added on to the side or back. Converted garages would also fall under the category of attached in-law-suites.

Think of attached mother-in-law suites as two uses glued together, which means they can serve not only as a dwelling for your in-laws but renters as well. Since whoever resides in the in-law suite and the main house are living in in the same building, this type of dwelling might be called a mother-in-law apartment. 

Detached mother-in-law suites

Detached mother-in-law suites are essentially tiny homes or guest houses that happen to be on the same property as the larger main home and thus provide the most flexibility and privacy. Since it's a separate structure, a detached in-law suite can take up different architecture styles; they might resemble bungalows or log cabins. 

Detached in-law suites can be used to serve a variety of purposes. You may find it suitable for your teen to live while they attend college nearby or you can rent it out to vacationers and use it as an AirBnB property. Some people turn a mother-in-law suite into their “man cave” or “she-shed”. It can also simply act as a guest suite for any visitors who want to stay the night. 

Interior mother-in-law suites

This type of suite is located inside your home, but is separated from the main area of the home in some way. An interior mother-in-law suite could be a converted basement, den, or even an attic. (More on how much it costs to finish an attic here.) In some cases there is even a separate entrance that allows the resident to enter and leave their portion of the home without walking through the main home and using the front door.

Can I build a mother in-law-suite on my property?

Whether you can have a mother-in-law suite on your property depends on the the restraints of your property — including local  laws, and whether or not you belong to an homeowners association (HOA) that would allow this construction project.

Mother-in-law suites are typically considered ADUs, or accessory dwelling units and you'll need to make sure your property is zoned for them. (If it's not, you may face fines.) You'll probably need to get a construction permit when building an in-law suite and make sure the unit is up to code, too. 

3 ways to build a mother in-law suite 

• You can a mother-in-law suite as part of your new custom home.
• You can build a separate structure on your property to serve as a mother-in-law suite.
• You can convert an underutilized space into a mother-in-law suite.

Some people choose to build an in-law suite or apartment as a part of their new construction home, but it’s also very common to add on a mother-in-law suite to an existing home. While you can build a separate structure if your property has the space for it, it’s also possible to turn an underutilized space such as a garage into a mother-in-law suite. 

If you have plans to build any additions to your home instead of renovating an interior space to serve as a mother-in-law suite, then you may also have to navigate adding additional plumbing, electricity, and gas lines to your property. Building a detached mother-in-law suite may require more work, but it depends on the structure of your house.

How much does it cost to build a mother-in-law suite?

How much it costs for you to add a mother-in-law suite to your home depends on a wide variety of factors, including:

• Location of the property
• Size of the suite (square footage, number of bedrooms, etc.)
• Amenities, plumbing, and electric needs

The type of mother-in-law suite can also affect how much you’ll spend. Certain floor plans will cost more than others. For example:

• Interior mother-in-law suites: $5,000 to $200,000 to renovate an existing room, depending on the room. A garage or shed could cost more. 
• Attached mother-in-law suites:  $106,000 or up to $216,000 to build a 500 square foot attached suite. 
• Detached mother-in-law suites:  $50,000 to $125,000 for a prefab pod, but up to $300,000 if you build one yourself.

→ Learn more about how much a major home addition costs

Buying a house with a mother-in-law suite

You also always have the option to buy an existing house with a mother-in-law suite. If this is a must-have for you, tell your real estate agent about this requirement before you start your search for the perfect home. They’ll be able to identify the homes in your area that have this feature. You can specify if you’re looking for a house with a detached mother-in-law suite or if the suite can be attached. 

Should I add a mother-in-law suite?

Homes with mother-in-law suites are convenient (as long as you don’t mind attracting visitors and long term guests) and they can increase your property value. 

One survey found that 41% of Americans buying a home are considering properties that would allow them to support an aging parent or an adult child.¹ With this rising interest in accommodating multiple generations, having a home with a mother-in-law suite can increase your home’s appeal when it comes time to sell. Even if you don’t need to provide a permanent living space for a family member, if you enjoy having frequent visitors, you’ll likely appreciate having a separate place for them to stay during their visit. 

Those who work from home can also turn a mother-in-law suite into a nice, quiet home office away from all the hustle and bustle going on in the main living space. There’s also always the option to rent that space out to a regular tenant or to out of towners. 

4 disadvantages to building a mother-in-law suite

• Up-front costs to build 
• Higher property taxes 
• Paperwork and zoning law hassles
• Potential loss of outdoor space 

If you’re on the fence about whether or not you should add one to your property, you need to think carefully about whether or not the financial investment is worth it and how much use you'll get out of the space. 

Sources: 1. John Burns Real Estate consulting: https://www.realestateconsulting.com/