How To Build The Perfect In-Law Suite

An in-law suite (sometimes called a mother-in-law suite) or accessory dwelling unit (ADU) is an excellent addition to your home if you want more space. You might want to build an independent space for your parents or other relatives who may need some extra support and want to live as independently as possible. Or you might want some extra space for guests.

Accessory dwelling units are a great choice because they can be constructed in your backyard or on any other open land you might have. You can also convert your garage or attic to add more space to your home.

But creating the perfect in-law suite is a big project, with lots of things to consider. In this post, we’re going to take you through everything you need to know about building an accessory dwelling unit on your property.

Ready to transform your property with an in-law suite? Let’s break down the process into manageable steps so you can move forward with confidence.

1. Research local regulations

Before you start sketching floor plans or picking out backsplash tiles, take a close look at your city’s zoning laws and building codes. Some areas are more lenient than others, and rules often differ for detached, attached, or garage/attic conversions. A quick call to your local permitting office or a visit to your city’s planning website can save you time (and a headache) down the line.

2. Define needs and wants

With the rules in hand, start brainstorming your ideal in-law suite. Make a list of must-haves (like a separate entrance or accessible bathroom) and nice-to-haves (such as a kitchenette or extra storage). Be sure to think about who will use the space—consider both their current lifestyle and future needs, especially if their health or mobility might change over time.

3. Set your budget

Building an in-law suite can range from a modest investment to a major project. Factor in costs for design, construction, permits, and any specialty work like plumbing or electrical. Don’t forget hidden expenses: upgraded finishes, landscaping, or utility connections can add up. Setting a realistic budget now keeps surprises to a minimum later.

4. Find professionals

Unless you’re a DIY superstar, you’ll likely need to bring in some pros. Look for experienced contractors, architects, or designers who have handled accessory dwelling units before. Ask for references and examples of past projects. Depending on the complexity, you may also need specialized tradespeople—think plumbers, electricians, or HVAC experts.

5. Design your space

Once you’ve assembled your dream team, collaborate on the layout and look of your in-law suite. Consider how the space flows, where natural light enters, and how to make it both accessible and comfortable. Many architects now offer 3D renderings so you can “walk through” your future suite before construction begins.

6. Get permits and inspections

Most in-law suite projects require permits, especially if you’re modifying your home’s structure or major systems. Submit your detailed plans (often including architectural drawings) to your local permit office. Be prepared for reviews and inspections at key stages, as well as fees for the permits themselves. Taking care of permits up front helps avoid expensive corrections later.

7. Update insurance and prepare for construction

Once permits are approved, notify your homeowner’s insurance company about the planned addition. This helps ensure your coverage stays up to date. Then, coordinate with your professionals on a timeline, get your financing in order, and start prepping the site.

With these steps checked off, you’re well on your way to a welcoming, comfortable in-law suite that will serve your family’s needs for years to come.

When you're building an in-law suite, you’ll be building it with a specific person in mind. For example, one or both of your parents might be coming to live with you. If this is your plan, you should talk to the people living in the new space when making your plans.

It might be your property, but this new space will soon become their home. They should get to have a say in what they need and how the space will look.

Of course, you can still have your say. For example, you might want the ADU to blend in with your existing home design, and you’ll have the final say on where and how it is constructed. Our best advice is to work together with all the relevant people to come up with a plan that works best for everyone.

Before you go too far with planning your in-law suite, you should think about how much you can afford to spend. Whether your budget is modest or large, you should make a plan that will work for you.

If you're looking to save money on the project, you can save by making your unit smaller, looking at prefab solutions, using affordable materials, and more.

Even if you have more money to spend, it’s always a good idea to understand the costs involved with construction projects and carefully track your budget.

A site plan gives you an overview of your existing home. This is a must-have before you start planning for your expansion. It will help you identify the best place to build your in-law suite and tell you the dimensions of your property.

You might also need a site plan if you need to apply for a building permit before you begin construction. 

Next, you’ll have to decide how you want to add an in-law suite to your property. An ADU is often a free-standing structure that might stand in your backyard or other available spots.

However, in-law suites don’t have to be new, free-standing structures. There are alternative ways to add an ADU to your home, including converting an existing space like a garage. You could also build an addition onto your existing home, which could serve as your ADU.

While planning your in-law suite, don’t forget to think about parking arrangements. Additional residents or frequent visitors may mean extra vehicles at your home, so consider whether your current driveway or street parking can accommodate the increased demand. Check your local zoning and neighborhood regulations to see if there are requirements for off-street parking spaces when adding an ADU.

If space is tight, you might look at options like expanding your driveway, creating dedicated parking pads, or improving access from the street. Accessible parking for older relatives is another factor—level pathways, proximity to the entrance, and safe lighting all help make your property more welcoming for everyone. Careful planning now can prevent headaches and ensure smooth comings and goings for both family and guests.

You might know that you want an in-law suite, but there's a lot to think about in your design. Before you set anything in stone, it's good to get some inspiration and find some ideas.

Take a look at some examples of ADUs to see what you can do with your available space. Ideally, an in-law suite will provide everything that you would need in a home. It should have a bedroom or sleeping area, living space, kitchen, and bathroom. A quick look online can give you some great inspiration for designing your in-law suite inside and out.

With so many options at your fingertips, selecting an interior design style for your in-law suite can be just as fun as planning the layout itself. Start by considering the preferences of the future occupant—after all, this space should feel like home for them. Some people love classic looks with cozy neutrals, while others might gravitate toward clean-lined modern or farmhouse vibes.

Next, think about continuity with your main home. Matching— or at least echoing—your existing color palette, finishes, and design flourishes helps the new suite feel like a natural extension rather than an afterthought. Pay special attention to elements like countertops, flooring, cabinet hardware, and lighting fixtures, since these details can tie everything together seamlessly.

If you're stuck, browse design magazines or platforms like Pinterest and Houzz for ideas. Visual inspiration boards can help you land on a style that blends personal taste with practical needs—whether that's durable materials for easy maintenance or soft, calming colors for a restful retreat. With a clear vision, the rest of your decisions—furnishings, textiles, art—will come together much more easily.

If you're planning to have an older relative move in, you’ll need to make the space accessible. People often need more help with mobility as they get older, so it makes sense to add accessible elements to your design. This can include things like wider doorways, grab bars, and an adapted bathroom.

Don’t forget to consider what will happen to your ADU if the intended occupants don’t use it. Maybe they're not ready to move in yet, or maybe they will eventually move into different accommodations. Try to create a flexible design that can be used for multiple different purposes.

You will need to consider some essential features when designing your new ADU. Make sure you plan for some of the fundamentals, such as proper ventilation and exposure to natural light.

In-law suites tend to be small, so you should also think about how you can maximize the space. One way to do this is with high ceilings. It might not give you more floor space, but it does give the impression that your space is bigger.

And don’t forget about storage! Your ADU needs plenty of storage if you want it to be suitable for anyone to live there. Moving into an in-law suite might require getting rid of some clutter, but there still needs to be space for personal things. Adding closets, built-in shelving units, or storage cupboards to your design can help ensure your ADU has enough space to stash everything away. 

Another crucial decision is whether to include a dedicated laundry area in the in-law suite or have everyone share the main home's facilities. Adding a private washer and dryer, even just a compact stackable unit tucked into a closet, can give the suite's occupants more independence and convenience—especially if mobility or privacy is a concern. On the other hand, sharing existing laundry facilities might save on square footage and expense. It's worth weighing your family's needs, space limitations, and future use of the ADU before deciding which setup makes the most sense.

You’ll need some architectural drawings before you get started with construction. These days, it’s easy to find project plans online. One option is to find some project plans online. You can browse plans and buy some that you like that fit your available space.

Or, if you want a more custom design, you can hire an architect to design an in-law suite from scratch. Even if you choose to use existing plans, an architect can adapt them and make adjustments to help the plans suit your needs and fit the space you want to use.

Choosing an architect might seem a little overwhelming at first. Here are some tips to keep in mind when choosing an architect:

• Check their portfolio: Look for architects who have designed this kind of space before. Their portfolio of past projects can give you a sense of their style and what you can expect their design to look like.

• Ask for recommendations: Do you have friends or family that have built similar home additions? Now is a great time to ask them for their recommendations. They might know an architect who is perfect for your project and can tell you what working with them is like.

• Try a design-and-build service: Design-and-build services take care of the whole project. This can be a more cost-effective option and save a lot of time. Beyond the design phase, these services already have a construction team, so you don't need to spend time looking for contractors. This option might not be for everyone, but it is one way to ensure a smooth process.

If you don't want to spend the time finding an architect and designing your ADU, you could consider prefabricated designs. A prefab design will allow you to choose a layout you like and quickly install it on the site where you want it.

You can usually customize prefab designs a certain amount, so you’ll have some control over the final product. One of the benefits of a prefab design is that it makes it easy to control the costs. Installation is easier, too, and it can also often be easy to take apart if you decide you no longer need it.

You will need to make sure that your new in-law suite meets any regulations or building requirements. These can be government regulations or homeowner’s association (HOA) rules. You may need to follow regulations relating to the size of your ADU and its features and materials. Check with your local authority to see what regulations you need to follow.

Once you have the design of your new unit planned out, you will need to find the right contractors. Your architect might be able to help you since they have probably worked with different contractors and can recommend builders for the job.

Just like when choosing an architect, you can also ask friends and family for recommendations to help you find a contractor. You could look for a contractor specializing in ADUs, although it isn't necessarily a priority. A look through a contractor’s portfolio can help you decide if you like the quality of their previous work. And don’t forget to check out online reviews from previous customers.

Want to learn more about hiring a contractor? We’ve put together a handy checklist to help!

Once you’ve hired the perfect contractor, it’s time to start construction. Building an in-law suite or accessory dwelling unit is like building a house on a smaller scale. The My Site Plan blog is a great place to start if you want to read up on all things construction, home additions, and design.

And if you need a site plan for your upcoming in-law suite project, My Site Plan can help. We can help you put together permit-ready plans and get your project in motion. Learn more about our site plan options. 

• An in-law unit (ADU) is a separate living space on your property designed for family members, offering privacy, independence, and flexibility.
• These units can take many forms, including: detached backyard units, home additions, conversions of garages, basements, or attics.
• Planning should start with the people who will live there— their needs, comfort, and preferences should guide the design.
• Budgeting is a key step, and costs can be managed by: keeping the unit smaller, using prefab options, choosing cost-effective materials.
• Financing options like home equity loans or HELOCs are commonly used to fund in-law unit projects.
• A site plan is essential for determining placement, understanding property dimensions, and often required for permit approval.
• You’ll need to decide how to build the unit: convert existing space (most affordable), extend your home, build a new detached structure.
• In-law units are a long-term investment that can increase property value and even generate rental income if not used by family.
• Compliance with local zoning laws, building codes, and permits is critical before starting construction.
• Working with professionals (architects, contractors, or site plan services) helps streamline the process, avoid mistakes, and ensure approvals.