What is a Mother-in-Law Suite? (Updated for 2023)

Evelyn Long

Nov 13, 2023

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What is a Mother-in-Law Suite?

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

If you’ve heard more about in-law suites now than ever, there’s a reason. Approximately 23% of adults in the U.S. belong to what is known as the “sandwich generation.” These are adults who live with a parent over 65, raise a child under 18 or financially assist an adult child. In addition, housing activists view these units as a remedy to urban housing shortages — providing more living spaces on previously single-family lots.

How did this trend come about? While there is no official single story about mother-in-law suites, some common jokes about mothers-in-law 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 land purchase 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.

Haven’t you seen any ADUs in your region? That might change in the coming years, especially in higher-density cities where legislators seek ways to decrease housing costs for their residents. Accessory Dwelling Units have recently been explored as a pro-housing policy in 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 65,000 permits for ADUs in 2021 alone. More renters will likely be considering mother-in-law suites in years to come, and they won’t even have to marry into the main household.

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, renting the mother-in-law suite within your home can be a great option. However, ADUs might be the prevailing choice for renters.

Regardless of your structure, you can rent the space, just like you can rent any property 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 June 2023, $410,200 was the forecasted price for the average home in the United States. 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 an intelligent way to afford the home you want while giving everyone 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

People may need help with daily chores like lawn mowing as they age. They may live independently but need someone to check in on them occasionally.

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

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 to a local tenant, providing additional housing on your lot while making up some of your mortgage costs.

Since the in-law suite likely has a different entrance, you can separate living areas. Many people add a sturdy door between the main house and the add-on. You can then lock the door for added safety. as with any home rental, you will want to engage in a vetting process to ensure 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. The property value can rise by up to 30%, and adding an ADU can enhance the resale value by 50% or higher. 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 clients see you, you might want them outside your home amidst your personal belongings.

An in-law suite allows customers to 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 other business purposes. 

How to Build a Mother-in-Law Suite

Once you’ve decided to build a mother-in-law suite, you may wonder where to start building it. One of the first things you must choose is what kind of mother-in-law suite you will create. Once you do that, you can begin 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 you’ll need to build it as an ADU. If making a structure separately is okay, you can start planning your backyard’s ADU. This can even be preferable, as it utilizes space you might not otherwise be using.

Are Mother-in-Law Units Legal?

Zoning laws and building regulations are crucial in constructing a Mother-in-Law Suite. For instance, they might restrict the size or location of the suite on your property. They ensure that your construction project aligns with community standards and safety guidelines.

Every state and municipality will have different rules and guidelines, and it’s essential to pay attention to the regulations and codes of your area. You can often find this information on your city or county’s website. If you’re working with a contractor or builder, they’ll likely know where to guide you for the proper forms and clearances. 

Next, you must submit your building plans to your local government for approval. It’s essential to ensure these plans comply with all local building codes, which cover aspects like safety, design and utility hookups.

Suppose your plans don’t align with existing laws. You might need to apply for a variance, which is an exception to the rule. This process usually requires presenting your case to a local board or committee. Having detailed plans and a clear, reasonable argument for your variance can increase your chances of approval.

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.

Here are budgeting tips and cost-saving strategies to help you in building your mother-in-law suite:

  • Detailed planning: Have a clear plan and budget before starting. It helps in avoiding unexpected expenses.
  • Get multiple quotes: Always get quotes from several contractors to ensure competitive pricing.
  • Prioritize needs over wants: Focus on essentials before considering luxury or non-essential items.
  • DIY where possible: Doing some work, like painting or minor installations, can save labor costs.
  • Repurpose materials: Use recycled or reclaimed materials for construction to save money.
  • Opt for cost-effective alternatives: Choose less expensive materials with durability and aesthetic appeal.
  • Phase your project: If the budget is tight, consider completing the suite in phases rather than all at once.

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

Although every home and every area is different, the 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 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 a favor and meet with experienced contractors before jumping in.

Some attics won’t be suitable for livable space, with codes related to height, square footage, and structural integrity. Having professionals check out the attic space and layout which permits, code requirements and other necessary changes 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, 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 own the land and likely have hookups. 

Made famous by the trend in Vancouver, the Laneway House is one option for a separate space. These dwellings are small. Most Laneways must be at least 9.8 meters wide and typically have one and a half stories with one or two bedrooms and one bathroom.

A stand-alone structure may cost more 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 debate current zoning laws to find more opportunities to provide homes on existing land. Research your municipality and state regulations to get a feel for this discussion in your location.

extended mother-in-law suite

4. Extension to Single-Family Home

This is self-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 an excellent choice for those looking to add a structure to the property without contracting someone or putting in the work themselves.

This can also be an excellent option for those searching for 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, if you are searching for a unique apartment or living situation and are open to renting a mother-in-law suite, you can 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 will likely grow in popularity for American homeowners looking for different housing solutions for their families.

Original Publish Date 7/5/2021 — Updated 11/13/2023

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