April 18, 2024

ADU Laws and Regulations in St. Louis - 2024

Steadily's blog cover page for information around landlord insurance.

Overview of ADU Laws in St. Louis

In St. Louis, Missouri, the regulations governing Accessory Dwelling Units (ADUs) have evolved to address the city's housing needs. These units, often referred to as secondary houses or granny flats, allow property owners to maximize the use of their residential lots.

Zoning Regulations: ADUs in St. Louis are permitted in residentially zoned areas, subject to specific guidelines that ensure these structures comply with the city's planning objectives.

Size and Placement Requirements:

  • ADUs must adhere to established size restrictions and setback requirements.
  • The design of an ADU must be compatible with the main residence.
  • Owner occupancy is typically required for either the primary or the ADU.

Permitting Process: Prospective builders need to secure the requisite permits, and they must comply with the Missouri State Building Code. As of recent legislation, St. Louis has made strides to streamline the ADU application process, providing more clarity to property owners.

Ensuring that all structures are safe and do not detract from neighborhood character is a priority for the city. Those interested in constructing an ADU must engage with local building authorities to understand specific local regulations.

By updating ADU laws, St. Louis demonstrates their commitment to providing flexible and affordable housing options within the United States. The intention behind such regulations is not only to increase housing availability but to ensure neighborhood integrity and design consistency.

Zoning and Location Requirements in St. Louis

In St. Louis, the development of Accessory Dwelling Units (ADUs) is subject to specific zoning laws and location restrictions. Both zoning regulations and location criteria play crucial roles in determining where ADUs can be constructed.

Zoning Laws for ADUs

Zoning in St. Louis dictates the type of buildings allowable in each district. The recent amendments in the City of St. Louis zoning code permits the construction of ADUs in all districts that allow residential use. These units must comply with the existing zoning regulations, which govern aspects such as unit size and additional requirements for single-family homes.

ADUs are generally allowed in the rear or side of a lot, but must adhere to setbacks defined by zoning laws. Setbacks ensure that structures keep a certain distance from property lines, maintaining space between neighboring properties.

Specific Location Restrictions

Location requirements often revolve around ensuring proper egress, privacy, and safety for both the primary and secondary residences. Regulations typically specify that ADUs:

  • Be built on the same lot as a single-family home.
  • Are not allowed on lots with multi-family buildings, except in specific approved zoning districts.
  • Follow strict placement rules, including the minimum distance from the main residence and borders of the property to meet setback and egress specifications.

In conclusion, navigating ADU development in St. Louis requires a comprehensive understanding of both the zoning laws and location-specific restrictions, which are designed to promote orderly growth and maintain community standards.

Types of ADUs in St. Louis

In St. Louis, accessory dwelling units (ADUs) add value and versatility to properties, diversifying housing options. These come in several forms, including detached structures, expansions of the existing home, or conversions of existing spaces.

Detached ADUs

Detached ADUs are standalone structures separate from the main residence. Commonly known as granny flats or carriage houses, these units offer privacy and independence. They must comply with Missouri's guidelines, which mandate minimum lot sizes and dimensions.

Attached ADUs

Attached ADUs involve an addition to an existing home, such as an in-law suite that is build onto the side or rear of the main house. These units are integral to the main structure but function as separate living spaces with their own entrances.

Converted Existing Structures

Some homeowners opt to convert parts of their home into ADUs. This includes basement apartments or the transformation of a garage apartment. These conversions make efficient use of the space within the existing footprint of the property, often requiring adherence to the local building code for St. Louis Park.

Planning and Permitting Process in St. Louis

In St. Louis, preparing for the construction of an Accessory Dwelling Unit (ADU) involves a detailed planning and permitting process. Homeowners must navigate specific guidelines and resource availabilities to ensure compliance with local regulations.

Pre-Application Planning

The initial phase of creating an ADU in St. Louis centers on thorough planning. Before applying for a permit, homeowners should familiarize themselves with zoning ordinances and building codes, which dictate the feasibility of their project. Essential resources such as OneSTL's toolkit offer valuable guidance on local regulations and practices, laying a solid foundation for a successful application.

Permit Application and Approval

Once pre-application planning is complete, homeowners may proceed to the permit application stage. This involves submitting detailed construction plans and documentation in accordance with the stipulated guidelines. Procuring a building permit is contingent upon satisfying local requirements; therefore, it is crucial to ensure all paperwork accurately reflects the proposed ADU project. The ADU Laws and Regulations in Missouri provide insights into this structured process, aiming to make the journey to permit approval as smooth as possible. After submission, the local building department reviews the application before granting permission to initiate construction.

Building Standards and Regulations in St. Louis

St. Louis has specific building standards and regulations that apply to the construction and design of Accessory Dwelling Units (ADUs). These regulations ensure safety, functionality, and adherence to zoning laws.

Size and Design Standards

Square Footage:When it comes to the size of ADUs in St. Louis, Missouri regulations stipulate that the lot must be at least 50 feet in width and encompass a minimum of 5,000 square feet. For the ADUs themselves, there are guidelines that dictate the proportion of living space in relation to the primary dwelling.

Design Standards:Design standards focus on maintaining the aesthetic and structural integrity of neighborhoods. This encompasses the architectural design of ADUs, including the external appearance, materials used, and overall compatibility with the primary residence.

Utilities and Services Requirements

Utilities:Each ADU must have independent or shared utilities to ensure they are functional living spaces. This includes connections to water, sewer, electricity, and gas. Proper implementation ensures safety and sustainability standards are met.

Kitchens and Bathrooms:An ADU must contain its own kitchen and bathroom facilities to qualify as a separate living space. These facilities must comply with local building regulations concerning the safety and sanitation to accommodate residents adequately.

Economic Aspects of ADUs in St. Louis

Accessory Dwelling Units (ADUs) offer economic benefits and potential hurdles that property owners in St. Louis should consider. These considerations include upfront costs, long-term value addition, and the potential for rental income.

Cost Considerations

When evaluating the cost of constructing an ADU in St. Louis, property owners must account for a variety of expenses. Initial costs can be significant, encompassing:

  • Land preparation: Making sure the land adheres to Missouri ADU guidelines regarding lot size and dimensions.
  • Construction: Expenses to build the ADU, which includes materials and labor.
  • Permitting: Fees associated with obtaining the necessary permits to comply with local regulations.

Considering these expenditures, the potential return on investment becomes an essential calculation, as ADUs can increase rental housing supply and generate steady rental income over time.

Value Addition to Property

Investing in an ADU not only fulfills housing demand but also adds considerable value to the property itself. Property owners can expect:

  • Appreciation: An ADU can boost the overall property value, as it creates a versatile living space that can accommodate additional residents or be used for rental purposes.
  • Marketability: Homes with ADUs tend to be more attractive to buyers looking for properties with rental income potential or additional space for relatives.

In the context of the St. Louis area, where strategic growth is encouraged, initiatives like OneSTL recognize the role of ADUs in creating a sustainable and economically vibrant future. Property owners should be aware that the precise value added by an ADU can vary depending on several factors, including the current state of the housing market, the quality of the ADU construction, and its integration with the primary dwelling.

ADU Impact on Communities in St. Louis

Accessory Dwelling Units (ADUs) introduce a dynamic element to housing in St. Louis, offering diverse accommodations while presenting a mix of logistical and legislative hurdles for the region.

Housing Options for Diverse Needs

In St. Louis, ADUs provide a range of housing options catering to multi-generational living and the needs of seniors. As detached entities like backyard cottages, they afford privacy and independence within established neighborhoods. This expansion in housing typology benefits those seeking accessory apartments—apt for those downsizing or families desiring proximity.

Challenges and Opportunities

The introduction of secondary dwelling units, such as granny flats, in St. Louis, comes with its own set of complexities. Zoning laws require strict adherence to guidelines concerning lot size and dimensions, as informed by Missouri accessory dwelling unit guidelines. The careful calibration of these regulations is necessary to avoid overcrowding and maintain the character of neighborhoods. On an upswing, ADUs can provide homeowners with additional income, aiding with mortgage payments or retirement, thereby adding an economic incentive to tackle these challenges.

Regulation Compliance and Enforcement in St. Louis

In St. Louis, property owners interested in creating an accessory dwelling unit (ADU) must navigate a series of regulations and local ordinances. Compliance is not optional; rather, it's a legal requirement for the lawful construction and maintenance of an ADU within city limits.

Lot Size and Dimensions:

  • ADU construction requires adherence to specific zoning requirements, including minimum lot sizes and width restrictions.
  • For example, lots must generally be no less than 50 feet wide and cover an area of 5,000 square feet or more as stated by the guidelines for Missouri accessory dwelling unit.


  • St. Louis often enforces an owner-occupancy requirement, signifying that one of the units, either the primary or the ADU, must be owner-occupied.


  • The city's ability to enforce these rules comes through routine inspections and the potential for penalties or fines for non-compliance.

Regulation adherence is monitored by the City of St. Louis, with potential recourse laid out in the City Code and Revised Code.

City ordinances also cover wider aspects of property use, including operating short-term rentals, which have their own set of rules as can be seen in a specific ordinance pertaining to the zoning code.

Property owners must be diligent in following these guidelines to not only ensure the legal standing of their ADUs but also to contribute to the orderly development of their communities. Compliance ensures a uniform approach to urban planning and the maintenance of local standards.

Local Resources and Assistance in St. Louis

In St. Louis, individuals seeking to build or retrofit Accessory Dwelling Units (ADUs) can look to several local resources for guidance and support. The City of St. Louis provides crucial legal information through its city codes, which outline the standards and requirements for ADU construction.

Planning Departments: Homeowners may consult with municipal planning departments, which offer expert advice on zoning ordinances pertaining to ADUs. For instance, the St. Louis City Planning Commission can facilitate the understanding of such regulations and assist with the relevant application processes.

At Counties and Local Jurisdictions: The rules for ADUs can vary depending on the location, making it important for homeowners to reach out to county offices or local jurisdiction authorities. These entities ensure that residents are well-informed about the specific laws applicable to their area.

For Homeowner Resources:

  • Workshops and Seminars: Local organizations often host events to educate homeowners on the benefits and processes of ADU development.
  • Permitting Help Desks: Some planning departments provide help desks to navigate the permit application, making the procedure more accessible.
  • Online Toolkits: Accessible guides and online toolkits, such as those provided by OneSTL, detail the steps involved in creating an ADU.

Local assistance resources for Accessory Dwelling Unit (ADU) projects include legal advice on zoning and compliance, available through local government offices; step-by-step guides accessible on the OneSTL website; support in obtaining necessary permits from local planning departments' help desks; and educational workshops offering guidance on the benefits and processes of ADU construction, which can be found through community event listings.

In summary, St. Louis provides comprehensive resources to assist homeowners through each stage of the ADU process, from initial planning to final construction. These local resources are instrumental in supporting community members as they navigate the complexities of ADU development.

Comparative Analysis

This section provides a detailed look at Missouri's ADU regulations in comparison with other states and discusses the impact that varying rules have on ADU development.

ADU Laws in Missouri vs. Other States

Missouri ADU regulations require a lot size of at least 5,000 square feet for the construction of an Accessory Dwelling Unit, with the property needing to be at least 50 feet in width. In contrast, states like California and Oregon have more permissive ADU laws, which have been instrumental in promoting ADU developments For example:

  • California: No minimum lot size for ADUs, allowing for varied development across cities such as San Francisco.
  • Oregon: Statewide easing of regulations allows cities like Portland and Bend to embrace ADUs, leading to a surge in development.

Impact of Different Regulations on ADU Development

The regulatory environment significantly influences ADU development. In states with lenient laws, construction of ADUs is more common:

  • Vermont: Allows ADUs by right, which means homeowners can construct them without needing special permission.
  • Washington: Cities like Seattle and Spokane have seen increased ADU development, as Washington's regulations encourage multiple forms of ADUs.

These contrasts highlight how regulations can facilitate or hinder the expansion of ADUs, reflecting directly on the availability of affordable housing options.

Frequently Asked Questions

Navigating accessory dwelling unit (ADU) regulations requires clear understanding of local laws. St. Louis has specific requirements affecting construction, size, and use of ADUs.

How do zoning regulations in St. Louis impact the construction of ADUs?

Zoning regulations in St. Louis permit the construction of accessory dwelling units in residentially zoned districts. This includes any area that allows for residential use, but adherence to zoning codes is mandatory.

What are the size and occupancy restrictions for ADUs in St. Louis County?

In St. Louis County, a lot must be a minimum of 50 feet in width and cover an area of at least 5,000 square feet to qualify for constructing an ADU. Occupancy laws may further dictate the number of inhabitants.

Can ADUs be used as rental properties in St. Louis, Missouri?

Yes, homeowners in St. Louis may rent out their ADUs. These rental arrangements are governed by landlord-tenant laws, including regulations related to eviction, even though a business license is not required for renting an ADU.

What are the building code requirements for ADUs in St. Louis?

The construction and occupancy of ADUs in St. Louis must comply with the city's building code requirements. These codes dictate the technical specifications and safety standards that have to be met.

How does the approval process for ADUs work in St. Louis County?

Owners looking to build an ADU must go through the appropriate approval process, which entails submitting plans and applications in accordance with St. Louis County’s ordinances and obtaining necessary permits before construction can commence.

Are there any specific design standards for ADUs in St. Louis?

While the design standards for ADUs in St. Louis are not prescribed at a granular level, they must be in alignment with the existing neighborhood character and comply with the city’s zoning and building codes.

Download your free resource

Table of Contents

Get coverage in minutes

One of America's best-rated landlord insurance services. No hidden cancellation fees. Competitive rates nationwide.

Get a quote
Get Appointed

Delight your clients with one of America's best-rated landlord insurance services nationwide.

Apply Today

Video Library

View all videos

Other Resources

Get coverage in minutes

No hidden cancellation fees. Competitive rates nationwide.

    Thank you! Your submission has been received!
    Oops! Something went wrong while submitting the form.

    Get Appointed

    Become a Steadily appointed agent and start selling one of America's best-rated landlord insurance services.