ADU Builder in Grand Rapids — Accessory Dwelling Units, Designed and Built
Add a self-contained living space to your property — for rental income, family, or flexibility. Detached units, garage conversions, and backyard cottages, protected by fixed-price contracts and expert project management.
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An accessory dwelling unit is a self-contained living space on the same lot as your primary residence. It has its own entrance, kitchen, bathroom, and sleeping area — a complete home, just smaller. Homeowners across Grand Rapids are building ADUs for a range of practical reasons, and the investment pays back in multiple ways.
Rental income. A well-designed ADU generates steady monthly income that can offset your mortgage, fund retirement, or build wealth. In a housing market where rental demand outpaces supply, your backyard becomes a revenue-producing asset.
Multigenerational living. Keep aging parents close without sacrificing anyone's independence. Or give an adult child a real home — not their old bedroom — while they save for their own place. ADUs provide proximity and privacy in equal measure.
Home office or studio. A detached workspace eliminates the commute without sacrificing the separation between work and home. When your needs change, the space converts to a guest suite or rental unit.
Property value. ADUs increase your property's appraised value and expand your buyer pool at resale. A home with a legal, permitted ADU stands apart in every listing.
ADU Types for Every Property
Detached ADUs
A standalone structure in your backyard — often called a backyard cottage, guest house, or casita. New construction from the ground up with its own foundation, utilities, and entrance. Maximum privacy and flexibility for both the occupant and the main household.
Garage Conversions
Transform an underused garage into a fully finished living space. We handle structural modifications, insulation, plumbing, electrical, HVAC, egress windows, and interior finishes. Often the most cost-effective path to a permitted ADU.
Above-Garage Units
Build a complete apartment above your existing or new garage. This approach preserves your parking and storage below while adding a full living unit above — bedroom, bathroom, kitchen, and living area with a private exterior stairway.
Basement ADUs
Convert your basement into a code-compliant accessory unit with a separate entrance, full kitchen, bathroom, and bedroom with proper egress. We address ceiling height, moisture management, natural light, soundproofing, and independent HVAC controls.
Attached ADU Additions
A new addition to your home with its own entrance and fully independent systems — functionally a separate unit, physically connected to the main house. Ideal when zoning or lot constraints rule out a detached structure.
In-Law Suite Conversions
Transform existing interior space into a self-contained suite with kitchen, bath, and private entrance. When the goal is multigenerational living rather than a fully detached unit, an in-law suite conversion delivers independence within arm's reach.
We Navigate the Regulations
ADU regulations in Michigan vary by municipality. Grand Rapids, Wyoming, Kentwood, East Grand Rapids, and surrounding communities each have their own zoning codes governing lot size minimums, setback requirements, maximum ADU square footage, height limits, parking requirements, and owner-occupancy rules. Getting it wrong means fines, forced removal, or a unit you cannot legally occupy or rent.
Before design begins, we research your specific property's zoning classification, identify what's permitted, and advise you on the most effective path forward. We prepare all permit applications, coordinate inspections, and ensure your ADU meets every building code requirement — structural, electrical, plumbing, mechanical, fire safety, and energy code.
Whether you are building a detached backyard cottage, converting a garage, or finishing a basement unit, we ensure your accessory dwelling unit is fully permitted, fully legal, and fully protected by our fixed-price contract.
Everything Handled. No Surprises.
Accessory Dwelling Unit — Design-Build
Our quotes are comprehensive and itemized — every material, every trade, every permit. You see every line item before you sign. The price we quote is the price you pay.
- Fixed-price contract after scope finalization
- In-house 3D design and space planning
- All permits, zoning research, and inspections
- Site work, foundation, and utility connections
- Dedicated project manager — one point of contact
- 2-year workmanship warranty
We'll discuss your goals, your property, and budget range — all on a quick 15-minute call.
Protected From Start to Finish
"We had an amazing experience. I wouldn't hesitate for a minute to recommend Thornapple Construction to anyone. In fact, I already have and each has LOVED the outcome."
ADU FAQ
ADU costs in Michigan vary widely based on type and scope. A garage conversion or basement ADU typically costs less than a ground-up detached unit. Factors include unit size, finishes, plumbing and electrical requirements, foundation work, and site conditions. We provide a fixed-price contract after scope finalization — the price we quote is the price you pay. No change orders, no surprises.
Yes. Accessory dwelling units in Grand Rapids require building permits, and depending on the scope, you may need permits for structural, electrical, plumbing, and mechanical work. Zoning regulations govern what's allowed on your property — lot size minimums, setback requirements, maximum ADU square footage, parking, and owner-occupancy rules all apply. We research your property's zoning before design begins and handle all permit applications, inspections, and municipal coordination.
A typical ADU project takes 4-8 months for construction, with 6-10 weeks of design, engineering, and permitting before that. Detached new-construction ADUs generally take longer than garage conversions or above-garage units due to foundation and site work. We provide a detailed schedule before work begins and share updates through your project portal.
In many Grand Rapids neighborhoods, yes — ADUs can be rented as long-term housing. Local zoning regulations determine whether rental is permitted on your specific property, and some municipalities require owner-occupancy of the primary residence. We research the rental rules for your property during the planning phase so you know exactly what's allowed before you invest. A well-designed ADU can generate meaningful rental income and significantly increase your property's value.
The terms overlap, but generally an ADU (accessory dwelling unit) refers to a self-contained living space — with its own entrance, kitchen, bathroom, and sleeping area — that exists on the same property as a primary residence. ADUs can be detached (backyard cottages, standalone units), attached (additions with separate entrances), or conversions of existing space (garage apartments, basement units). A mother-in-law suite is typically an attached or interior living space within the main house. We build both — the right choice depends on your property, your goals, and local zoning.
Explore Other Ways We Can Help
Home Additions
More space without the moving boxes. Structural expansions that seamlessly match your home's character.
Mother-in-Law Suites
Multi-generational living spaces with private entrances, accessibility features, and independent living areas within your home.
Basement Remodeling
Unlock the full potential of your lower level. Living space, entertainment, guest suites, and more.
What Could Your Property Do With an ADU?
It starts with a free discovery call — a quick phone conversation to discuss your goals, your property, and what's possible. No commitment. No pressure. Just clarity on what you can build and what it will cost.
Book Your Free Discovery CallOr call us at (616) 404-3400
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