Detached ADU
A new standalone residence with its own foundation, structure, utilities, kitchen, bathroom and exterior site work.
PLAPCO RESOURCE CENTER
Your ADU Construction Journey
A complete homeowner guide to what happens from the first feasibility conversation through permits, foundation, framing, utilities, finishes, final inspections and a move-in-ready accessory dwelling unit.
An ADU is a small home, and it requires the same careful coordination as any residential building project. This guide explains the general sequence, the decisions homeowners need to make, the inspections that create normal pauses, and the conditions that can affect the schedule.
1985Established
FamilyOwned
OwnerOperated
California License #987689
B, C-53 & C-27
B, C-53 & C-27
Built with pride. Backed by the Pacheco name.
ADU CONSTRUCTION FROM START TO FINISH
A Small Home With a Full Construction Process
Detached ADUs, attached additions, garage conversions and junior ADUs can follow different approval and construction paths. The approved plans, property conditions and local jurisdiction determine the exact process.
Attached ADU or Addition
A new living unit connected to the main residence, often requiring structural tie-ins, fire separation and careful coordination with the occupied home.
Conversion or Junior ADU
An existing garage, room or accessory structure converted to habitable space, with upgrades needed to meet current health, safety and energy requirements.
HOW PLAPCO WORKS
Approved Plans First. Construction Second.
PLAPCO does not provide architectural design or engineering services. The homeowner selects the architect, residential designer, engineer, surveyor and other professionals required for the property. PLAPCO builds from the approved plans and coordinates construction questions with those professionals when necessary.
Project documents control the work.
This guide is a general overview. Your signed agreement, approved plans,
structural calculations, energy documents, permits, utility requirements,
written change orders and project-specific instructions take priority.
Homeowner-Selected Design Team
Your selected professionals prepare the site plan, floor plans, elevations, structural documents, energy compliance information and responses to plan-check comments.
PLAPCO Construction Coordination
We review the approved construction documents, organize the work, schedule trades and inspections, and coordinate field questions that arise during construction.
Jurisdiction and Utility Review
The city, county, fire district, sanitation agency, water provider and utility companies may each have separate requirements depending on the property.
Decisions and Selections
Homeowner selections for windows, doors, cabinets, plumbing fixtures, flooring, tile, lighting, appliances and finishes must be made early enough to avoid schedule delays.
01Step One
Project Goals and Site Feasibility
The process begins by defining how the ADU will be used, what type of unit is being considered and how the proposed structure fits the property. The design team evaluates zoning, setbacks, height, easements, access, existing structures, trees, slopes, utilities, drainage, fire access and other site constraints.
What to Expect
You may need a property survey, utility research, sewer or septic review, arborist input, geotechnical investigation or preliminary agency conversations before the plans can be completed.
Typical Timing
Highly project-specific. A straightforward flat property may move quickly, while hillside, septic, access or utility issues can require additional investigation.
Start with the property, not the floor plan: A plan that looks perfect on paper still has to fit the actual site, utility capacity and local approval requirements.
02Step Two
Design, Engineering and Construction Documents
The homeowner's selected design team develops the permit set. Depending on the project, this may include a site plan, floor plan, elevations, structural foundation and framing plans, energy compliance documents, utility plans, drainage details and supporting reports.
What to Expect
There will be decisions about room layout, ceiling height, windows, doors, kitchen, bathroom, HVAC, electrical service, water heating, appliances, exterior appearance and how the ADU relates to the main home.
Typical Timing
Often several weeks or longer, depending on design complexity, consultant availability, homeowner decisions and the amount of site-specific engineering required.
Preapproved plans are not automatically site-approved: Even when a jurisdiction offers preapproved ADU plans, the property still requires site-specific review, foundation information and applicable safety approvals.
03Step Three
Planning Approval, Building Permits and Agency Review
The completed package is submitted to the authority having jurisdiction. The exact sequence varies by city or county. Planning, building, fire, sanitation, water, public works, environmental health and utility providers may review separate parts of the project.
What to Expect
Plan-check comments are normal. The homeowner's selected design professionals revise the documents and respond to technical corrections until approvals are issued.
Typical Timing
Frequently the longest preconstruction stage. Timing depends on completeness, jurisdiction workload, correction cycles, outside-agency approvals and utility requirements.
Do not schedule construction from an estimated permit date: Construction can be firmly scheduled only after the required approvals, issued plans and permit conditions are available for review.
04Step Four
Preconstruction, Site Setup and Demolition
Before building begins, the approved plans and permit conditions are reviewed, required notices are posted, access and staging areas are established, utilities are marked, and the work area is protected. Existing concrete, landscaping, fencing or structures included in the scope are removed.
What to Expect
Temporary fencing, material deliveries, portable facilities, dumpsters, equipment and crews may occupy part of the property. Expect noise, dust, truck traffic and changing access routes.
Typical Timing
Usually several days to a few weeks, depending on demolition, tree work, access, utility coordination and grading requirements.
Occupied-home reminder: If the main residence remains occupied, construction will still affect parking, privacy, noise, dust, utilities and portions of the yard.
05Step Five
Grading, Underground Utilities and Foundation
The building pad is excavated and prepared according to the approved plans. Underground plumbing, electrical conduit, grounding, drainage components and utility sleeves are installed before the foundation is placed. Forms, reinforcing steel and required moisture or energy components are inspected before concrete.
What to Expect
The site may look more disturbed before it begins to look like a building. Trenches, soil stockpiles, formwork, reinforcing steel and utility piping are normal during this phase.
Typical Timing
Often two to four weeks, including preparation, inspections, concrete placement and initial curing. Complex foundations, piers, slopes or utility work can take longer.
Hidden-condition warning: Rock, unsuitable soil, groundwater, undocumented utilities or buried construction may not be discovered until excavation and can require added work or design review.
06Step Six
Framing and Structural Construction
Floor, wall and roof framing create the shape of the ADU. Structural hardware, posts, beams, shear walls, hold-downs and roof components are installed according to the approved structural plans.
What to Expect
The building takes shape quickly. Door and window openings become visible, room sizes become easier to understand, and structural inspections occur before work is concealed.
Typical Timing
Often one to three weeks for a straightforward detached ADU, with additional time for complex roofs, engineered beams, existing-house tie-ins or inspection corrections.
Field dimensions become real: Framing is when homeowners often fully understand room proportions. Changes at this stage may affect engineering, permits, cost and schedule.
07Step Seven
Roofing, Windows, Doors and Weatherproofing
The structure is dried in with roof underlayment and roofing, exterior sheathing, weather-resistive barriers, flashing, windows and exterior doors. The goal is to create a weather-protected shell before sensitive interior materials are installed.
What to Expect
Exterior details receive careful attention around windows, doors, roof transitions, penetrations and wall assemblies. Siding or stucco preparation may begin during this phase.
Typical Timing
Often one to three weeks, depending on roofing, window lead times, exterior finish system, weather and inspection requirements.
Material lead times matter: Windows, doors, roofing and specialty exterior products should be selected and ordered well before this phase.
08Step Eight
Mechanical, Electrical and Plumbing Rough-In
Plumbing supply and drain lines, electrical wiring and panels, lighting, HVAC equipment and ducting, ventilation, water heating, fire-safety components and low-voltage systems are installed before the walls are closed.
What to Expect
The framing fills with wiring, pipes, boxes, vents and equipment connections. Required rough inspections occur before insulation and drywall.
Typical Timing
Often two to four weeks, depending on utility capacity, service upgrades, HVAC type, fixture count, solar or battery scope and inspection sequencing.
Utility coordination can control the schedule: New meters, service upgrades, sewer connections and utility-company work may require separate applications, fees and lead times outside the contractor's control.
09Step Nine
Insulation, Drywall and Interior Finishes
After rough inspections, the building envelope is insulated and sealed. Drywall is installed, taped and finished. Interior doors, trim, cabinets, countertops, tile, flooring, paint, plumbing fixtures, lighting, appliances and finish hardware are installed in a coordinated sequence.
What to Expect
This phase contains many separate trades and depends heavily on completed homeowner selections. The ADU begins to look finished, but touch-ups and adjustments are normal.
Typical Timing
Often four to eight weeks or more, depending on finish level, cabinetry, tile complexity, product availability and inspection timing.
Selections must be complete: Late changes to cabinets, tile, fixtures, appliances or lighting can affect rough-in locations, ordering, cost and multiple following trades.
10Step Ten
Exterior Finishes, Access and Site Restoration
Exterior siding or stucco, paint, gutters, downspouts, landings, walkways, patios, utility equipment, address numbers and required exterior features are completed. Final grading directs water away from the ADU and disturbed areas are restored according to the contracted scope.
What to Expect
Concrete, pavers, drainage, fences, gates, landscaping and exterior utility work may overlap with the interior finish stage. Site access can remain active until near completion.
Typical Timing
Often two to six weeks, with weather, curing, utility work, drainage details and landscape scope affecting the sequence.
Drainage is part of the building: Finished grades, roof runoff and hardscape drainage must work together to move water away from the ADU and neighboring improvements.
11Step Eleven
Testing, Final Inspections and Project Closeout
Systems are tested, fixtures and appliances are checked, finish corrections are completed and required final inspections are scheduled. Inspectors may identify corrections that must be completed before final approval or occupancy authorization.
What to Expect
A final walkthrough addresses contracted punch-list items. Manuals, warranties, keys and project-specific operating information are assembled for turnover.
Typical Timing
Often one to several weeks after major construction is complete, depending on correction items, utility releases and final-inspection availability.
Do not occupy the ADU early: The unit should not be occupied until required final approvals and any occupancy authorization are issued by the governing jurisdiction.
HOMEOWNER DECISIONS THAT PROTECT THE SCHEDULE
Your Most Important ADU Checkpoints
A well-built ADU still depends on timely decisions, complete information and realistic expectations about permits, utilities and inspections.
Confirm selections before the affected trade begins, respond promptly to questions, keep the construction route clear and avoid directing changes to individual workers in the field. Scope changes should be documented and priced before the changed work proceeds.
Construction schedules are sequences rather than uninterrupted daily activity. Inspection holds, curing time, material lead times and outside-agency work can create normal gaps between visible stages.
Before Construction Starts
Confirm the approved plans, finish selections, owner-supplied items, appliance specifications, utility responsibilities, access limitations and any work excluded from the contract.
The least expensive time to make a decision is before the affected work is installed.
Changes after foundation, framing or rough utilities can require demolition, revised plans, engineering, permit updates and work by several trades.
ADU PROJECT CHECKLIST
What Homeowners Should Track
Plans and Permits
Keep the current approved plan set, permit card, agency conditions and design-team contact information available.
Selections and Lead Times
Approve products early and confirm whether items are contractor-supplied or owner-supplied.
Utility Applications
Track utility-provider applications, meter or service requirements, fees and release dates separately from the building permit.
Documented Changes
Use written change orders for scope, cost and schedule changes instead of informal field instructions.
Access and Safety
Keep children, pets and visitors away from the work zone and preserve clear access for crews, deliveries and inspections.
Final Approval
Wait for required final approvals before moving furniture into the unit or allowing occupancy.
Local requirements vary. ADU rules, permits, inspections, utility requirements, fees and approval sequences differ by jurisdiction and property. The approved project documents and agency requirements always control.
COMMON HOMEOWNER QUESTIONS
ADU Construction Guide FAQs
No. The homeowner selects the architect, residential designer, engineer, surveyor and other design professionals. PLAPCO constructs the project from the approved plans and coordinates field questions with the selected professionals when needed.
Possibly. Availability and eligibility depend on the jurisdiction. Preapproved plans generally still need a site-specific plan, foundation information, utility coordination and applicable planning, building, fire and safety approvals.
There is no single reliable duration for every property. Design, permits, utility coordination and material procurement occur before construction. The field-construction schedule then depends on size, type, access, foundation, finish level, inspections, weather and outside-agency work.
Incomplete plans, correction cycles, utility-company lead times, late selections, owner changes, special-order products, hidden soil or utility conditions, inspection availability and weather are common schedule variables.
Often yes, especially for a detached ADU, but expect noise, dust, deliveries, temporary access changes and occasional utility interruptions. Attached additions and conversions can be more disruptive to the occupied home.
That is project-specific. The approved plans, local agency requirements and utility provider determine meter, service, connection and capacity requirements. Utility applications should be started early.
Only after the required final inspections, utility releases and any occupancy authorization required by the jurisdiction have been completed.
HAVE APPROVED PLANS OR A PROJECT IN DEVELOPMENT?
Start With a Phone Conversation
Tell us about the property, the type of ADU, the current plan or permit status, and the construction scope you are considering.