When adding an in-law suite or accessory dwelling unit (ADU) to your home, one of the most important considerations is determining the right size. The ideal size for an in-law suite depends on several factors, including the size of your property, local zoning laws, the intended purpose of the space, and your budget. Generally speaking, in-law suites range from 300 to 1000 square feet, with 500-700 square feet being a comfortable size for many homeowners’ needs.
In this comprehensive guide, we’ll discuss the pros and cons of various in-law suite sizes, layout considerations, tips for maximizing space, legal requirements, cost implications, and frequently asked questions to help you determine the perfect size for your needs. With careful planning and design, an in-law suite can provide the ideal living space for aging parents, adult children, long-term guests, or as a potential income suite.
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Small In-Law Suites (300-500 sq ft)
On the smaller end of the spectrum, in-law suites in the 300 to 500 square foot range offer a space-efficient option. Some of the benefits of opting for a smaller in-law suite include:
– More affordable construction costs and permits
– Ability to fit in a smaller backyard or garage conversion
– Less maintenance and utility expenses
– Better potential return on investment for resale
However, the main downside of a smaller in-law suite is limited living space. Here are some tips for maximizing a small suite:
– Opt for an open studio layout to make the most of square footage
– Use furniture that serves multiple purposes such as a sofa bed, folding table, or storage ottoman
– Add high windows, skylights, and light colors to open up the space
– Include a compact or “tiny home” style kitchen with a small fridge, sink, and induction cooktop
– Use space-saving fixtures like a corner shower and wall-hung toilet in the bathroom
– Add thoughtful built-ins like fold-down desks, lofted beds, and cabinet storage
With careful planning, 300-500 square feet can be sufficient for one person as a comfortable living space with all the essentials. But most couples will find this size too small for permanent living.
Medium In-Law Suites (500-700 sq ft)
A medium-sized in-law suite in the 500 to 700 square foot range offers a nice balance of space and affordability. At this size, most couples or a parent/child pair can live comfortably with the following features:
– Combined living/sleeping area
– Compact kitchen
– 3/4 or full bathroom
– Small closet and storage space
This mid-range size gives you flexibility in terms of layouts. For example, you could do a studio, one-bedroom, or open one-bedroom plan. Other advantages include:
– More spacious than a tiny house
– Costs less to build than larger additions
– Easier to heat, cool, and maintain
– Can often be adapted from a garage or basement
The main limitation is that two adults may feel cramped in the long term. But for guests staying for extended visits or live-in help, 500-700 square feet provides suitable accommodations.
Large In-Law Suites (700-1000 sq ft)
On the higher end, in-law suites over 700 square feet offer ample room for multiple people to live comfortably long-term. Some features of a larger suite include:
– True master bedroom and living room
– Full kitchen with dining area
– Full bathroom
– Walk-in closet/storage
– Potential for extras like a laundry room, office space, or two bedrooms
The main appeal of larger in-law suites is having a separate living space that feels like a fully functional home. This makes them ideal for aging parents, adult children with families, au pairs, or permanent tenants. The drawbacks are higher construction costs and potential permitting challenges depending on zoning laws.
If space allows, 750-1000 square feet gives your in-law suite occupants plenty of elbow room with flexible options for furnishings and layouts. But scale the size to suit your actual needs – don’t overbuild for unused space.
In-Law Suite Layout Considerations
In addition to overall size, the layout and design you choose for your in-law suite will impact its functionality. Here are some key considerations:
Open vs. Separate Rooms
– Studio layouts feel more spacious, while separate rooms offer more privacy. Choose based on the occupants and your space constraints.
Doors and Access
– Convenient access to the main home is nice for family interactions. But separate exterior access maintains independence.
Windows and Lighting
– Generous natural light makes a small space feel bigger. Skylights, glass doors, and high windows can help.
Kitchen Features
– Even a compact, galley-style kitchen should include essential appliances, storage, and a sink.
Bathroom Fixtures
– Optimize space with a corner shower, narrow vanity, and wall-hung toilet.
Multipurpose Spaces
– Built-in furniture like fold-down desks, murphy beds, and banquettes add flexibility.
Taking time to think through layout and design considerations will help maximize livability and functionality within the square footage you have available.
Zoning Regulations and Permitting
Local zoning ordinances and permitting requirements will determine the maximum size and height allowances for your in-law suite. Building codes also dictate construction specifications like:
– Foundation
– Electrical and plumbing
– HVAC/ventilation
– Fire safety
– Means of egress
Many areas limit detached in-law suites to 800-1000 square feet. Attached units may have more flexible limits but will need to comply with rules for the main dwelling size. Getting your plans approved by the local permitting office early in the process will prevent headaches down the road.
Some key questions to investigate include:
– Is an in-law suite allowed on your property?
– What are the size limits for your zone?
– Is there a limit on occupancy numbers?
– What are the setback requirements from property lines?
– Is there adequate space for parking/driveways?
– Will you need special permits for plumbing or HVAC?
Navigating permit approvals takes time, so build that into your project timeline. Most jurisdictions require that the in-law suite is a permanent addition – not a temporary structure. Know the regulations before designing your ideal layout and submitting plans for approval.
Budget Implications of In-Law Suite Size
On average, you can expect to spend $100-$200 per square foot to build an in-law suite addition. This covers planning, permits, demolition, construction labor and materials, electrical, plumbing, finishes, and contingency costs.
For a 500 square foot addition, a reasonable budget would be $50,000 – $100,000. The larger and more luxurious the suite, the higher your total costs will be.
Here is an overview of how size impacts your construction budget:
| Size | Low End Cost | High End Cost |
| 300 sq ft | $30,000 | $60,000 |
| 400 sq ft | $40,000 | $80,000 |
| 500 sq ft | $50,000 | $100,000 |
| 600 sq ft | $60,000 | $120,000 |
| 700 sq ft | $70,000 | $140,000 |
| 800+ sq ft | $80,000+ | $160,000+ |
As you can see, your total budget can rise quickly for larger suites with high-end finishes. Make sure to factor in ongoing expenses too like utility costs, maintenance, and furnishing the space.
Creating a detailed budget before starting your project will keep costs on track. Prioritize must-have features over unnecessary luxury finishes to maximize value.
Return on Investment
One consideration for adding an in-law suite is resale value. Well-designed ADUs are growing in popularity and can increase interest from buyers.
According to one study, the average return on investment for adding an ADU is about 10% of the home’s total value. However, the recouped value depends on factors like:
– Overall demand in your real estate market
– Desirability of the neighborhood
– Construction quality
– Size and layout
A permitted in-law suite shows future owners the addition was done legally and properly. Smaller suites around 500 square feet tend to offer the best ROI compared to larger, more elaborate additions.
Think about long-term flexibility too. An ADU could potentially be rented out or repurposed as a home office or teenage retreat in the future. Multi-use spaces add value for resale.
Frequently Asked Questions
What’s the minimum size for an in-law suite?
The absolute minimum is usually around 300 square feet, but not ideal for permanent living. Aim for at least 500-600 square feet for comfortable functionality.
What’s the largest legal size in most areas?
Zoning laws typically limit detached ADUs to 800-1000 square feet maximum. Attached units may have more flexible upper limits.
Should I build the biggest suite I can afford?
Not necessarily – right-sizing the space for your actual needs helps optimize use and cost efficiency. Avoid overbuilding empty square footage.
How much space is needed per person?
100-200 square feet per person is a reasonable estimate. But your layout and furnishings also impact livability within a given footprint.
Can I include a washer/dryer or full kitchen?
Most zoning laws allow full kitchens and laundry facilities as part of a legal in-law suite, provided sufficient space.
How do I add light to a smaller suite?
Strategies like skylights, glass doors, windows placed high on walls, and minimizing interior walls help open up a small footprint.
What are the best furnishings for small spaces?
Look for multifunctional, space-saving pieces like murphy beds, fold-down desks, sleeper sofas, and ottomans with storage.
Conclusion
When designing your in-law suite, carefully weigh the pros and cons of size based on your family’s needs, budget, available space, and local regulations. A well-planned layout can make even a modest footprint feel spacious and welcoming. With some creative thinking, 300-1000 square feet can comfortably accommodate your in-laws, adult children, a rental unit, or multi-generational living space.