Granny flats are becoming more popular in many cities as rent and housing costs rise. They offer more space that you can convert to suit your unique needs. Granny flats can make an excellent addition to your property and increase your resale value.
This article can help you determine if you can build a granny flat on your property. We also cover the pros and cons of granny flats and why you should consider making the addition to your home.
Granny flats are accessory dwelling units (ADUs), also known as in-law suites, backyard cottages, bonus units or guest houses. Granny flats are self-contained living areas built on the property of a single-family home. These units can be attached to the main property or stand independently.
Granny flats have the name because they are often inhabited by aging parents who might need additional care. Rather than putting your parents in a nursing home, you can use these units to keep your family close by and offer them the care that they might need from the comfort of your own home while still maintaining your privacy and theirs.
More than 25% of Americans live in multigenerational homes, and the number continues to grow. With more people living at home with their families, granny flats are a popular choice for expanding your living space and providing housing for your loved ones.
You can also rent out your ADU, reducing your housing and mortgage costs while living in your dream home. These units can be used to house nannies or young adults looking for an affordable place to live, especially since rent costs continue to rise in nearly all major cities.
Building a granny flat is worth it for most property owners in 2026, providing 20-30% property value increases and $1,500-$4,000 monthly rental income. Here's the financial breakdown:
| Investment | Annual Return | Payback Period |
|---|---|---|
| $150,000 granny flat | $18,000-$48,000 | 3-8 years |
| $300,000 granny flat | $36,000-$60,000 | 5-8 years |
Worth it if: You plan to stay 5+ years, need rental income, or house family members
Not worth it if: Planning to sell soon, tight budget, or can't manage tenants
If you are trying to decide whether or not you want to build an in-law suite on your property, you will need to consider some essential factors before making your in-law suite addition plans.
Constructing a granny flat on your property can be expensive, from the design process to the completion of construction. You should consider the costs and your available budget before making any final decisions. A granny flat often costs between $300-$600 per square foot.
If you want to build a smaller unit around 300 square feet, your final costs will range from $90,000 to $180,000. If you are looking to construct a more extensive unit at or above 600 square feet with more available amenities, costs can range from $180,000 to $360,000 to complete. You need to know the approximate size and finish grade you want with your new unit so you can estimate what the final costs will be to complete construction.
Every city and state has different regulations for ADUs regarding where they are allowed and how big they can be. There may be additional regulations or restrictions if you live in an area with a homeowners association (HOA). Some locations may not allow a dwelling that's separate from the main house but will allow a granny flat conversion inside the existing structure.
Once the city or state has approved you to build your ADU, you will want to hire a contractor to assist with the design and construction process. Look for a contractor with a good reputation, licensure and plenty of experience. Some contractors can even help you with the paperwork and permits required to start your project.
An additional structure on your property means you will add more to your monthly utility bill to cover electric, water, heating and cooling costs. Before you start construction, consider these costs and add them to your budget to ensure you can make these additional payments each month.
A new addition to your property means additional maintenance. You will need to keep up with upkeep, repairs and replacements to keep your new unit in working order. The additional maintenance will take more time than before, and you need to determine if you can handle the workload or the costs of paying a professional before you start construction.
Not all insurance providers will cover granny flats or ADUs. Without insurance, your new unit is at risk for damages that you will have to pay out of pocket. If you want to rent out your unit or house a loved one, you will need to find additional insurance to protect your tenants, family members and yourself. Insurance can also potentially cover repair costs if your unit gets damaged in a storm or other event.
Building a granny flat on your property comes with many benefits. Here are some of the most popular reasons people choose to construct a granny flat on their property:
While there are many advantages of a granny flat, there are also some disadvantages to be aware of before you start construction.
In California, most people can build a single ADU on their property. It can take up to 60 days for approval. New legislation in California specifies the sizes for different types of granny flats. The maximum size of an attached unit is 50% of the main home. Detached units can be built to a maximum size of 1,200 square feet.
If your new property does not comply with these regulations, your approval process will be more extensive, and you may need to make changes to the floor plans of your granny flat.
Building costs can be higher than expected if you do not keep a careful eye on your budget plan, requiring more out of your pocket. Many people do not consider the additional maintenance and utility costs until after they have already completed construction.
No, well-built granny flats typically increase property value by 20-35%. However, poor construction quality or unpermitted work can decrease value. Key factors include professional design, proper permits, and quality materials that match your main home's aesthetic.
Short-term rental regulations vary by city. Many Bay Area cities allow ADU short-term rentals with proper permits and registration. Airbnb income potential is $100-$300 per night depending on location and amenities, but requires active management and higher insurance costs.
Separate meters are recommended but not always required. Separate utilities cost $5,000-$15,000 extra but simplify tenant billing, prevent disputes, and allow accurate expense tracking for tax purposes. Shared utilities can work for family members but complicate rental situations.
The granny flat stays with the property and typically adds $50,000-$200,000 to your home's value. Most buyers view permitted ADUs as valuable assets for rental income or multi-generational living. Unpermitted units can complicate sales and reduce offers.
A granny flat can give you extra space on your property to suit your individual needs, whether that is keeping your family close or providing additional room for your hobbies or home business. At Valley Home Builders, we can help you construct your dream granny flat with our expert knowledge and quality craftsmanship. Our three-phase process walks you through the process from design to construction.
If you are interested in building a granny flat in the South Bay area, contact Valley Home Builders to learn more about our services.
