ADU Construction Contractor
We build ADU's in Harford County and Harford County
An Accessory Dwelling Unit (ADU) can be a smart addition for homeowners in Harford County looking to add versatile living space while staying within a single-family lot. Whether you’re thinking of an “in-law suite”, a carriage house, or a detached guest unit, these secondary units help accommodate loved ones, generate rental income, or simply add flexibility to your property.
In Harford County, the zoning code allows one ADU on lots zoned AG, RR, R1, R2, R3, R4, RO or VR. The unit may be attached to, within, or detached from the primary single-family detached dwelling. Key regulatory points include:
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- The ADU must be at least 300 square feet.
- The ADU may not exceed the lesser of 1,500 square feet or 50% of the main house’s habitable space.
- No more than two bedrooms in the ADU.
- It must meet all applicable zoning, building and code requirements — especially important when the primary dwelling is older or has unique system.
- A Zoning Certificate is required, and if the property changes hands, the new owner must re-apply.
At RR Contractor Services, we bring our full design-build expertise to your ADU project. Our in-house design team, led by our Design Director, works with you in our private showroom and design center to plan layouts, finishes, and flow that enhance your home, not just physically, but functionally and visually too. We know how to navigate Harford County’s codes, how to adapt to older home conditions, and how to optimize your investment so your ADU supports your lifestyle and property value.
If you’re considering adding an ADU in Harford County, let’s talk. We’ll guide you through design, zoning, permitting, construction, and the finish touches that make a space feel complete.
What Are The Basic Requirements To Build An ADU?
The demand for Accessory Dwelling Units (ADUs) in Harford County and Baltimore County, has been on the rise in recent years, primarily due to our area's rapid population growth and housing affordability challenges. As a response, Harford County officials have established a basic checklist for homeowners interested in constructing ADUs on their property.
What Are the Basic Requirements to Build an ADU in Harford County, Maryland?
Building an Accessory Dwelling Unit (ADU) in Harford County comes with a few important rules to make sure your project meets local zoning and building standards. These regulations are designed to preserve neighborhood character while allowing homeowners more flexibility and housing options.
Zoning and Eligibility
ADUs are allowed on lots zoned AG, RR, R1, R2, R3, R4, RO, or VR that already contain a single-family detached home. Each property can have one ADU, which can be attached, detached, or built within the existing home (such as a basement or attic conversion). Before planning your project, it’s best to confirm your property’s zoning and eligibility through the Harford County Department of Planning and Zoning.
Size and Layout Limits
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- The minimum size of an ADU is 300 square feet.
- The maximum size is the lesser of 1,500 square feet or 50% of the main home’s habitable space.
- A maximum of two bedrooms is allowed.
- Detached ADUs must meet all setback and lot coverage requirements for the property’s zoning district.
These limits ensure the ADU remains secondary to the main residence and consistent with neighborhood scale.
Setbacks, Height, and Design
Setbacks depend on your property’s zoning, but detached ADUs generally must maintain standard side and rear yard distances. ADUs may not exceed the maximum height allowed for accessory structures in your zone (typically two stories or less). Harford County also requires that exterior design, siding, and roofing materials be visually compatible with the main dwelling.
Parking and Access
An ADU must have safe and adequate access to the primary residence and cannot block existing parking or driveways. Off-street parking may be required depending on the zoning district and layout of the property.
Ownership and Rental Use
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- The ADU must stay on the same lot as the main home and cannot be sold separately.
- It may be rented long-term but not used for short-term rentals.
- A Zoning Certificate is required, and if the property changes ownership, the new owner must reapply.
How We Can Help
At RR Contractor Services, we guide homeowners through every stage of the ADU process — from initial design and zoning review to permitting and construction. Our in-house design team, led by Mark Russell, helps plan layouts that meet county requirements while maximizing comfort and functionality. You can explore layouts, finishes, and materials in our private showroom and design center before the build begins.
Ready to explore your options? Please fill out our contact form to schedule a consultation for your ADU project in Harford County.
Why Choose RR Contractor Services for Your ADU Project
Building an Accessory Dwelling Unit (ADU) is a major investment, and choosing the right contractor makes all the difference. Here’s why homeowners across Harford and Baltimore County trust RR Contractor Services:
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- Local expertise. We understand Harford County’s ADU zoning, size, and permit requirements and handle the details for you.
- In-house design team. Led by Design Director Mark Russell, our design staff helps plan layouts, materials, and finishes that fit your home and lifestyle.
- Private showroom and design center. See finishes, fixtures, and design ideas in person before construction begins.
- Full design–build service. We manage everything under one roof — design, permitting, and construction — for a smooth, coordinated process.
- Open communication. You’ll always know what’s happening, what’s next, and who’s handling it.
- Craftsmanship that lasts. Our experienced team builds ADUs that blend naturally with your home and stand the test of time.
Ready to explore what’s possible? Contact us today to schedule a design consultation and start planning your ADU project.
How Much Does An ADU Cost?
The cost for accessory dwelling units can vary depending on many different factors
Attic ADU
This would be for the complete conversion of your unused attic space into a fully functional and rentable ADU.
Cost $45k-$75k+
Depending On Size and Scope.
Above Garage ADU
This would be for converting that unused space above your garage into a functional ADU.
Cost $75k-$150k+
Depending On Size and Scope.
Detached ADU
This would be for a completely detached, stand-alone, ADU on your property. This is entirely new construction.
Cost $75k-$250k+
Depending On Size and Scope.
Frequently Asked Questions About Accessory Dwelling Units
What is an Accessory Dwelling Unit (ADU)?
An Accessory Dwelling Unit (ADU) is a small, secondary home located on the same property as a single-family residence. It can be attached to, built within, or detached from the main house. Many homeowners use ADUs as in-law suites, guest houses, or rental units for extra income.
Are ADUs allowed in Harford County?
Yes. Harford County allows one ADU per lot in most residential and rural zones — including AG, RR, R1, R2, R3, R4, RO, and VR zoning districts — as long as the property already has a single-family detached dwelling.
How big can an ADU be in Harford County?
According to county zoning regulations:
- Minimum size: 300 square feet
- Maximum size: The lesser of 1,500 square feet or 50% of the habitable space of the main home
- ADUs may include up to two bedrooms
These limits ensure the ADU remains secondary to the primary home and fits the character of the surrounding neighborhood.
Can my ADU be a detached structure?
Yes. ADUs can be detached, attached, or built within the existing home (such as a basement or attic conversion). Detached units must follow all required side and rear setbacks based on your property’s zoning district.
How tall can a detached ADU be?
Detached ADUs cannot exceed the maximum building height for accessory structures allowed in your zoning district — typically two stories or less.
Do I need extra parking for an ADU?
Possibly. ADUs must have safe and adequate access, and off-street parking may be required depending on your zoning district and site layout. The county reviews parking availability during the permit process.
Can I rent out my ADU?
Yes — ADUs in Harford County can be rented long-term, but they cannot be sold separately or used for short-term rentals such as Airbnb. The property owner must retain ownership of both the main home and the ADU.
What permits or approvals are required?
You’ll need to apply for a Zoning Certificate and a building permit through the Harford County Department of Planning and Zoning. If the property is sold, the new owner must reapply for the zoning certificate.
Can I convert my garage, basement, or attic into an ADU?
Yes — internal ADUs are allowed. Converting existing space, such as a garage, basement, or attic, is often the most cost-effective way to create an additional dwelling unit, as long as the finished space meets all building and safety codes.
These prices are only ball park figures to give you a rough idea as to what you should expect for the cost of design/build ADU construction project completed by a team of craftsman. Your particular ADU project may vary depending on the site, any zoning issues, the size and scope of the ADU, the specific materials you've chosen, and the overall scope of work. If you need a firm price please request a consultation so we can view your potential project, listen to your ideas, and determine the actual scope of work required to complete your ADU project. After our on-site consultation we'll be able to provide you with a firm estimate to build your new ADU the right way.
