ADU Construction Done Right, Nationwide
ADU construction is a big project to take on, and the company you pick decides how it feels from the first phone call to the last inspection. Seedling ADU Builders has been building accessory dwelling units since 2001, and we do it with a written price before any tool is picked up, a crew that keeps your home and yard clean, and a 365-Day Done Right Promise on every completed job. If it is not done right, we make it right. Call (707) 383-5338 and a live person will talk through your project, any hour, any day.
What ADU Construction Includes
ADU construction is the full build of a second, self-contained home on your property. That means site work, foundation, framing, roof, windows, plumbing, electrical, heating and cooling, insulation, finishes, and the final inspection. A true ADU has its own entrance, a kitchen, a bathroom, and a place to sleep. Families build one for aging parents, a grown child, a renter, or a quiet home office, and they want it to last as long as the main house. Seedling ADU Builders handles the whole job under one written price, so you are not juggling a designer, a foundation crew, and a finish carpenter who each point at the other when something goes wrong.
One Builder, One Phone Number
When a single company is accountable for the whole build, questions get answered fast. You call (707) 383-5338, a live person picks up, and the answer comes from the people who are actually on your lot. That is how we have run projects since 2001.
Built to Local Code
Every city and county has its own rules on size, height, setbacks, parking, and utility connections. We build to the code where your lot sits, not to a generic checklist, and we pass inspections before anything gets covered up.
Types of ADUs We Build
Most homeowners start with a picture in mind and then learn that their lot only allows one or two of the options. We walk you through each type honestly, with the tradeoffs in plain words.
Detached ADU
A detached ADU is a separate building in the backyard or side yard. It offers the most privacy for the person living there and the most freedom in layout. It also needs its own foundation and its own utility runs, so it usually costs the most. Expect roughly $190,000 to $420,000 depending on size and site conditions.
Attached ADU
An attached ADU shares a wall with the main house, often built as a side or rear addition. Utilities are closer, which can trim cost, but you need to think carefully about sound between the two homes and a separate entry.
Garage Conversion
If you have a garage you no longer park in, converting it into a living unit can be one of the faster paths. The slab, walls, and roof are already there. The work is in insulation, new plumbing, a proper bathroom and kitchen, and replacing the garage door with a wall and windows.
Junior ADU
A JADU is a small unit, capped at 500 square feet in most places, created inside the existing footprint of the house. It has its own entrance and a compact kitchenette. A JADU conversion generally runs $60,000 to $130,000.
Site Work and Foundation
The first weeks on a lot matter more than most families expect. Before concrete goes in, we check setbacks, grading, drainage, and where water, sewer, and power will tie in. We protect the path from the street to the work area so your driveway and lawn stay in one piece, and we mark every trench line so you know exactly where the work will happen.
Soil conditions change the foundation plan. A level lot with firm soil is straightforward. A sloped lot, a high water table, or fill soil can call for a deeper or reinforced foundation, and we tell you that in the written price, not halfway through the dig. Utility runs are the other big variable. A short run from the main house is inexpensive. A long run across the yard, or an old panel that cannot carry the added load, adds real cost, and you deserve to see those numbers before you commit.
Framing, Systems, and Inspections
This is the stage where the building takes its shape. Walls go up, the roof goes on, windows are set, and the plumbing, electrical, and HVAC are roughed in. Our crews are background-checked and uniformed, and each visit starts with the same habits: shoe covers and drop cloths wherever people walk inside your main home, pet-safe products where there is a choice, and a photo of the clean-up before we leave for the day.
We schedule and meet every required inspection. Framing, rough plumbing, rough electrical, insulation, and the final all have to pass, and we do not cover work that has not been signed off. You get a straight update after each one, so you always know where the project stands.
Permits and Plans
Permits slow more ADU projects than any other single step. Jurisdictions reject drawings for setbacks, height limits, fire access, and missing structural details all the time, and every round of corrections costs weeks. We prepare the submittal package, answer plan-check comments, and track the permit through approval. If you already have drawings from an architect or an online source, we will review them and tell you honestly whether they will clear your local office.
Plan design and permit preparation commonly run $4,000 to $12,000 depending on the unit and local requirements. We list it as its own line in the written price, so nothing about it is a surprise.
Prefab and Modular ADU Construction
Factory-built units can shorten the time crews spend on your property, and they suit some lots well. We work hands-on with Dvele, Mighty Buildings, Boxabl, Plant Prefab, and Cover, and we use James Hardie materials for durable exteriors. The factory builds the unit, but your site still needs a foundation, utility hookups, a crane or delivery access, and finish work, and those costs are real. We help you compare a prefab unit against a site-built one using actual numbers for your lot, not the product the builder prefers to sell.
Signs You Are Ready to Build
- Your family needs more room, and moving is not the answer. A parent who cannot live alone, a young adult who needs a first place, or a growing household can all be solved on the lot you already own.
- You are renting out space that is not a legal unit. An unpermitted apartment can create insurance and liability trouble. A permitted ADU protects your property and your family.
- You want rental income without buying another property. A well-built unit can carry its own weight, and it adds a second living space that stays with the house.
- Your garage or basement is sitting empty. Existing space is often the lowest-cost route to a legal unit, and a builder can tell you quickly whether it qualifies.
- You want one company accountable for the whole project. One written price and one written promise means one phone call if anything is not right.
How ADU Construction Works With Us
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Call and talk with a live person. You reach a person at (707) 383-5338, not a voicemail tree. We ask about your lot, your goals, and your budget range.
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Site walk-through and honest assessment. We look at access, panel capacity, utility locations, and setbacks, and we tell you what is realistic on your lot and why.
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Written price and scope. Before construction starts, you receive a written price for the scope we discussed. The estimate is free, and no surprise line items appear after crews arrive.
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Permits, site prep, and construction. We pull permits, protect the inside of your home, build, and keep you updated through every inspection.
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Final walk-through and 365-Day Done Right Promise. We walk the finished unit with you, handle any items, and hand over the written promise. If it is not done right in the first year, we make it right.
How Much Does ADU Construction Cost?
A JADU conversion inside your home typically runs $60,000 to $130,000. A full ADU construction project, whether detached, attached, or backyard, usually lands between $180,000 and $420,000 depending on square footage, utility runs, and finish level. A custom unit with high-end finishes on a difficult lot can go above that, and we will tell you if your project is heading that way before you spend anything on construction.
What moves the price most: whether the unit is inside the house or separate, how far utilities have to run, the condition of your electric panel, soil at the foundation, and the materials you choose. The best way to avoid overpaying is a written, fixed scope before work starts and a builder who does not lean on change orders afterward. A free estimate from Seedling includes a walk-through and a written price, so you know your number before you commit. Call (707) 383-5338 to schedule yours.
Where We Work
Seedling ADU Builders serves homeowners across the United States through local crews who know the housing stock, soil, and weather in their area. Wherever your lot is, the same written pricing and the same 365-Day Done Right Promise apply. Looking for the full-service overview? See our home page or our ADU builders page. If you are weighing other ways to add space, we also cover room addition contractor work and second story addition contractor projects. Call (707) 383-5338 and a live person will connect you with the crew who covers your area.
Frequently Asked Questions About ADU Construction
Most ADU projects take six to twelve months from first conversation to final inspection. Design and permitting often take the longest, and the speed of your local permit office plays a big part. Actual building time is shorter, and prefab units can cut it further. We give you a realistic schedule in writing before work begins.
A JADU conversion typically costs $60,000 to $130,000, and a detached or attached ADU usually runs $180,000 to $420,000. Size, utility runs, soil, and finishes drive the number. Call (707) 383-5338 for a free estimate with a written price for your lot.
Yes. We prepare the permit package, respond to plan-check comments, and follow the permit through approval. If you already have drawings, we will review them and tell you whether they are likely to pass in your jurisdiction.
Yes. We work with Dvele, Mighty Buildings, Boxabl, Plant Prefab, and Cover. A prefab unit still needs a foundation, utility hookups, and finish work, so we compare it against a site-built option with real numbers for your lot.
Every project is covered by the 365-Day Done Right Promise in writing. If it is not done right within the first year, we make it right. During the build you also get shoe covers and drop cloths inside your home, pet-safe products where there is a choice, and a photo of the clean-up before the crew leaves.
Yes. A live person answers calls 24/7 at (707) 383-5338, including during an active build. You will not wait through a voicemail tree or for a next-day callback.
Schedule Your ADU Construction Today
A new home on your lot starts with one phone call. Call (707) 383-5338 to talk with a live person about your ADU, garage conversion, or home addition. You get a free, no-obligation estimate with a written price before any work starts, and every job is backed by the 365-Day Done Right Promise. Building since 2001, we answer 24/7, so call whenever it works for your family.
Written by Ben Ortega, Owner at Seedling ADU Builders.