How Much Does an In-Law Suite Cost?

Having a whole extra apartment in your home — or a cottage in the backyard — might seem like a luxury you don't need. However, families with aging loved ones often see the need for such arrangements as they consider how to best support older parents or others. Even if you aren't planning to move an older adult in with you soon, an in-law suite offers other benefits.

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If you don't yet have a space with a kitchenette, extra bathroom or the other amenities necessary for a second dwelling, the first step in building them is researching costs. Learn about the cost to build a mother-in-law suite below.

What Is a Mother-in-Law Suite or Granny Flat?

A mother-in-law suite, also called a secondary suite or granny flat, is a space in your home that provides independent and separate living for an older relative, guest or renter. Usually, these additions include a living space, kitchen or kitchenette, bedroom and bathroom. Some are designed with multiple rooms, while others take a studio and open-concept approach.

When the secondary living space is outside your home, such as a cottage in the backyard, it may be called an accessory dwelling unit or guest house.

Common uses for these types of spaces include:

Living space for aging parents. They're called mother-in-law cottages or in-law suites because, traditionally, these secondary dwelling areas provided a way for families to support somewhat independent elderly relatives.

Living for adult children or other relatives. Many people rent the spaces to adult children or other relatives or let loved ones live in the suites for free if they are moving, are seeking a new job or otherwise need a place to stay.

Guest housing. Secondary living spaces let you put up guests in style, allowing you to be hospitable without disrupting the rhythms of your home.

Rental income. A detached in-law suite or apartment in your house can be rented on a monthly basis or listed on apps like Airbnb to increase your household income.

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

The cost of building an in-law suite depends on whether you convert existing space in your home or build a new structure on your property. According to HomeGuide, can cost $5,000 to $100,000 (CAD 7,025 to CAD 140,516) to add a secondary suite using existing space in your home, such as an unfinished, partially finished or finished basement. If you need to build from the foundation up on your property, a detached mother-in-law cottage could cost $30,000 to $280,000 (CAD 42,154 to CAD 393,444)

What Are the Cost Factors of Building a Secondary Suite?

The average costs for the mother-in-law suite construction above cover a wide range for a reason. Numerous factors go into determining the cost. For example, are you planning to do most of the work yourself, or do you need to hire a general contractor? Experienced DIYers might cut down on overall costs by handling some work, but it's important to balance safety and the functionality of outcomes with the need to protect your building budget.

Other factors that impact the cost of an in-law addition include size and type of construction, materials, design features, labor needs, utility work and your location.

Size and Type of Construction

A detached unit typically costs more to build than an interior one, as it requires a separate foundation, walls, roofing and utilities. Inside your home, converting an unfinished space such as a basement can be more expensive than converting two extra bedrooms into a small suite. Generally, the more that's already there, the less expensive the overall build will be.

Costs for building in-law additions are usually quoted in square feet. The larger the space, the more it's likely to cost, particularly with other factors like material and design choices.

Materials

How you finish the space impacts overall costs. You can save (or spend more) based on counter, flooring, fixture and even paint choices.

For example, here's how different flooring options can impact the cost of an in-law suite:

Carpeting and laminate are often the cheapest flooring options, starting at just $1 (CAD 1.41) per square foot and topping out around $5 or $6 per square foot (CAD 7.03 or CAD 8.43). For a 500-square foot space, this translates to $500 to $2,500 (CAD 702 to CAD 3,513) for carpet installation or between $500 and $3,000 (CAD 702 to CAD 4,215) for laminate flooring installation.

On the upper end, you could install luxury vinyl plank flooring for $1,000 to $5,000 (CAD 1,405 to CAD 7,026) for a 500-square foot space. Hardwood is often the most expensive option: $2,000 to $7,500 (CAD 2,810 to CAD 10,539) for a 500-square-foot room.

Design Features

Design choices also impact overall costs. Big and more obvious choices include whether you build a full kitchen or bathroom. Adding any type of plumbing increases the cost of the space, but without some of these elements, it's not true secondary living quarters. You might save by adding a kitchenette, which is a small space with a sink, counter and room for a fridge. You can add a microwave and skip the range and oven.

Where you put the bathroom and kitchen spaces also matters. If you can add them close together or near an area of the home that's already plumbed, you cut down on plumbing labor and pipe materials.

Other design choices that impact the cost of mother-in-law suite construction include:

• What appliances you add to the space

• Whether you want custom cabinets and built-ins or can buy ready-to-assemble options

• A preference for upgraded bathroom features, particularly for accessibility

• Recessed or custom lighting

• Adding ductwork for heating or cooling

Labor Needs

Hiring a general contractor to manage the project can help ensure a more efficient build, support compliance with codes and safety requirements and reduce how much work you have to do yourself. While a general contractor may increase the initial cost of the project, you might save money later because work is well-managed and done right the first time.

Even if you don't use a general contractor and manage the project yourself, you'll likely need to bring in skilled laborers. Plumbers and electricians may charge a flat rate or by the hour for work on an in-law addition. Consider getting several quotes to find an affordable professional who meets your quality and safety requirements.

Utility Work

If you're building a unit separate from your existing structure, you may need to pay for foundation and utility work. The land may need to be graded, new electricity and water lines run and other utilities set up. Even in your own home, you may want to consider the most efficient way to set up an in-law suite. For example, are you using existing ductwork, or do you need to install a mini split to heat and cool the space?

Your Location

Geographic location plays a role in the cost. Construction costs vary in different areas, so obtain quotes from contractors and other professionals in your city or area to understand the potential cost of building an in-home or detached in-law suite.

All CAD conversions are based on the exchange rate on the date of publication.