Accessory Structures

An accessory structure is a secondary building on a residential property that supports the main home but is not physically attached to it. Common examples include detached garages, workshops, storage sheds, pool houses, studios, barns, gazebos, cabanas, and accessory dwelling units (ADUs). These structures are designed for a variety of purposes—from extra storage and hobby spaces to guest accommodations and income-generating rental units.

At The House Plan Company, we offer a wide selection of accessory structure plans to complement your primary residence. Whether you're looking for a garage with a loft apartment, a backyard office, or a multi-purpose shed, our plans are crafted by experienced designers to meet your needs.

Adding an accessory structure is a smart and flexible way to maximize your property’s functionality, value, and curb appeal. Be sure to check with your local building department for zoning regulations, size limits, and permit requirements before construction.

Explore our collection of detached garage plans, ADU designs, and backyard building plans to find the perfect match for your lifestyle.

Accessory Structure plans cover a wide range of building types. With plans for designs ranging from gazebos to accessory dwelling units it can be difficult to zero in on the perfect design for your project. Here are some tips on how to find your dream plan faster!

1. Tip 1: Search FiltersStarting with a plan collection is a great place to start and beginning with our Accessory Structures collection will help you focus on these auxiliary designs. From here Search Filters will help you further zero in on that perfect plan. Applying a structure type filter will add another layer to help you find that perfect pool house plan without having to filter through shops or garages.
2. • Tip 2: Search outside of a CollectionIf you are looking for a plan that offers multiple features or functions, then starting with an open search outside one of our curated collections may be the best starting point. For instance Accessory Dwelling Units come in a variety of configurations.
1. Configuration 1: Detached ADUA detached Accessory Dwelling Unit offers opportunities for rental income or guest accommodations that offer maximum privacy. To search for the perfect detached ADU plan, try searching for Single Family structures in our Accessory Structure Collection or Tiny House Plans.
2. Configuration 2: Garage ApartmentsGarage Apartments offer the ultimate solution for enhancing your property, increasing vehicle storage or space for hobbies while also incorporating an ADU. The perfect Garage Apartment may be found across a handful of collections. Start by diving into our Garage, Garages w/Living, Carports collection. Under the search filters apply the Garage with Living option to see stunning designs that masterfully blend the functions of a garage with attached apartments.
3. Configuration 3: Single Family with Attached ADU or CastiasTo find an Accessory Dwelling Unit design that blends a primary single-family residence with a Casita or attached ADU, start with any of our single-family collections or our duplex/multifamily collection.

While our Accessory Structure collection is an ideal place to start your search for a plan that will enhance your property, jumping outside the collection can open up design options.

Still need help finding the perfect plan for your project? Reach out to our customer service team via email, chat, or phone! They will listen to your design goals and can provide search recommendations or plans to review.

The cost to build an accessory structure—such as a detached garage, workshop, storage shed, pool house, or accessory dwelling unit (ADU)—can vary significantly based on the structure’s size, design complexity, materials, finishes, and location.

According to the 2024 National Association of Home Builders (NAHB) construction cost data, the average cost to build residential space is approximately $153 per square foot. However, accessory structures tend to vary more widely:

1. Basic storage sheds or simple carports: $50–$100 per square foot
2. Detached garages or workshops: $100–$150 per square foot
3. Finished ADUs or guest houses with kitchens and bathrooms: $200–$400+ per square foot

Additional cost factors include:

4. Foundation type (slab, crawlspace, or pier)
5. Utility hookups (plumbing, electrical, HVAC)
6. Insulation and energy code requirements
7. Local labor rates and permit fees

At The House Plan Company, our collection of accessory structure plans ranges from simple and affordable to fully finished living spaces. Many of our designs can be customized to fit your budget and building goals.

To get a more accurate estimate, we recommend choosing a plan, purchasing a plan package, and consulting with a local builder or contractor who can provide a detailed cost breakdown based on your region and specific site conditions. Not ready to commit to a plan? We have partnered with StartBuild to provide Cost to Build reports.

Explore our wide selection of garage plans, workshops, sheds, and ADUs to find the right accessory structure for your property and budget.

Yes, at The House Plan Company, you can absolutely customize any accessory structure plan to better suit your property, lifestyle, or intended use. Whether you’re looking to modify a detached garage, workshop, pool house, or accessory dwelling unit (ADU), our team works with skilled designers who can tailor the plan to your specifications.

Common customizations include:

• Changing the dimensions or footprint of the structure
• Adjusting rooflines, door and window placements
• Adding or removing living space, lofts, or storage areas
• Converting a garage into a guest suite or rental unit (ADU)
• Modifying the plan to meet local building codes and zoning requirements

Customizing your accessory structure ensures that it fits seamlessly with your existing home design, complies with local regulations, and serves your specific needs—whether it’s for extra parking, a hobby space, or a private retreat.

To get started, simply choose your favorite accessory structure plan and request a modification quote from the designer. We’re here to help you bring your vision to life with flexibility and expert guidance.

Many of the accessory structure plans available through The House Plan Company are well-suited for conversion into an Accessory Dwelling Unit (ADU) or guest house. Whether you're looking to create extra living space for family, a private guest suite, or a rental unit for additional income, converting an existing structure plan can be a smart and cost-effective solution.

Plans commonly adapted into ADUs or guest houses include:

• Detached garages with lofts or finished upper levels
• Workshops or studios with open floor plans
• Pool houses with plumbing-ready layouts
• Compact cottages and backyard cabins

When converting a plan to an ADU, you may need to incorporate key features such as:

• A full bathroom and kitchen
• Insulation and HVAC systems
• Windows and doors that meet egress requirements
• Utility hookups for water, sewer, and electricity
• Compliance with local ADU zoning laws and building codes

Our team at The House Plan Company can connect you with designers who offer modification services to help transform your chosen plan into a fully functional ADU or guest house. We recommend reviewing your local ADU regulations before starting the conversion process, as requirements vary by municipality.

Explore our growing collection of ADU-ready plans and let us help you find the perfect design for your property and lifestyle.

All accessory structure plans available through The House Plan Company are designed to meet widely accepted national building standards. However, because local building codes, zoning ordinances, and permit requirements can vary significantly by city, county, and state, it’s important to understand that additional adjustments may be needed to ensure full compliance in your area.

Factors that may affect code compliance include:

• Snow loads, wind zones, and seismic activity
• Zoning restrictions, such as height limits, setbacks, and maximum square footage
• Requirements for plumbing, electrical systems, or living space (especially for ADUs)
• Local mandates for energy efficiency and sustainability

To ensure your chosen garage, workshop, ADU, or backyard structure plan meets local requirements, we strongly recommend consulting with your local building department and having a licensed engineer or architect review the plans if needed. Many of our designers also offer modification services to help tailor the plans for regional code compliance.

At The House Plan Company, we’re committed to helping you build with confidence. Browse our collection of accessory structure plans and contact us to discuss customization options that fit your location and project goals.

The concept of a garage apartment, mother-in-law suite or granny flat is not a new one. This type of residential unit was popular in the 1930s, 40s and even 50s as a way for homeowners to bring in additional income. By the housing sprawl of the 70s and 80s, however, local municipalities and planning commissions began to remove zoning allowances for high density and accessory dwelling units (ADU) in favor of trim, spacious suburban neighborhoods.

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When it comes to enhancing the appeal and functionality of your property, few additions offer the versatility and charm of a detached garage with living space. Not only does it provide practical storage for your vehicles and tools, but it also offers the potential for additional living quarters or recreational spaces.

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Discover the variety of accessory structure plans here!

Plan Details	Plan Image
Pool House Plan Steamboat Springs 82180 477 sq ft 0 bedrooms 1 bathrooms 1 story floor plan outdoor kitchen View Floor Plan
Detached Workshop West Coy Workshop 23171 200 sq ft 0 bedrooms 0 bathrooms 1 story floor plan workshop with office View Floor Plan
Barn Plan 82931 864 sq ft 0 bedrooms 0 bathrooms 1 story floor plan horse stalls with turn outs, tack room, and storage View Floor Plan
Hazel Detached Garage with Apartment 90605 965 sq ft apartment 1 bedrooms 1 bathrooms 3 car garage 2 story design View Floor Plan
Juniper Two ADU 3005 834 sq ft 2 bedrooms 2 bathrooms 1 car garage 1 story design View Floor Plan

Looking for more great Accessory Structure plans? Explore the full collection here: Accessory Structure Plans