ADU Process

Discover the Process of How to Build an ADU

Discover the process of how to build an ADU. Planning to completion, we give insights and realistic timelines for constructing your tiny home.

3 Steps to Get Your ADU Project Started!

Assess Your Lot
Understand what size ADU you can build and where you want to place it
Select an ADU Design!
Choose an ADU design you love and fits on your lot
Hire a General Contractor
Your GC will be your ADU project manager until completion

Initially, the process may seem daunting, but there’s no need to feel overwhelmed!

Your actual role throughout the project is minimal. You can think of your involvement as a three-step process once you have decided to build an ADU.

1.Conduct a Basic Assessment of Your Lot

Assess your available space for an ADU by considering legal boundaries, zoning regulations, topography, nearby structures, and potential encroachments such as easements on your lot.

Understanding this information will help you determine the optimal location for your ADU.

Much of this information is available in your official lot survey, including your property’s zoning district. If you don’t have an official survey, search for the zoning map of your jurisdiction using the terms [“City of (your city name)” and “zoning map”]. Once you determine your residential code, search your local zoning ordinance using [“City of (your city name)” and “zoning ordinance”]. This will help you understand applicable development regulations, including permissible location and maximum size for your ADU.

You can also choose to have any of these tasks completed by us or your general contractor!

2. Select an ADU Design

When contemplating your ADU, consider the desired square footage, number of bedrooms and bathrooms, its compatibility with your buildable area, as well as the overall design and aesthetic preferences.

3. Hire a General Contractor

First, reach out to multiple general contractors and present your desired ADU design and project objectives. Consulting with several contractors is vital as pricing may vary significantly among them.

Shortlist your options to about three contractors and request cost estimates. Consider factors such as experience, pricing, timeline, communication, and the workload of their team.

For further guidance on finding a general contractor, refer to the FAQs.

Select a contractor when you’re ready to commence the project. Securing a contractor early on is advantageous due to fluctuating material costs, labor availability, and high demand. Your GC not only transforms the drawings into a physical building but also serves as the ADU project manager throughout.

Once you’ve hired a contractor, they will manage the remaining steps. However, we’ve listed them here to help you understand the build process.

Your GC should review and organize as soon as your project is initiated to prevent construction delays.

The following are a few key areas in the design that should be reviewed from the get go.

Aside from understanding where on your lot your ADU should be built, the project site also has implications for other factors such as the ADU’s foundation and project planning.

Our ADU designs recommend an energy-efficient and cost-effective system: a three or four-zone (your choice) ductless mini-split system for heating and cooling. Though locations and product selection have already been suggested, the actual system should be planned by a licensed HVAC contractor.

The drawings specify appliances, equipment, and light fixtures with various power requirements which must be confirmed and coordinated by a licensed electrician.

A selection of plumbing fixtures and their respective locations are specified within the drawing package. The fixtures, the piping, and the rough-ins must be confirmed and coordinated by a plumbing engineer.

Pre-order building materials with extended lead times. Certain construction items may require several weeks to a few months for delivery. For example

  • Structural Insulated Panels: Up to 12 weeks
  • Manufactured Foundation System: Up to 8 weeks
  • Windows and Exterior Doors: Around 6-8 weeks
  • Anything that may be out of stock when you start your project.


For any given parcel, the City will require a review of the ADU project for land use and zoning codes. (This step is necessary even if you purchase a Fast Track pre-reviewed design.) Since every site is unique, a Site Plan must be prepared in order to complete the permit application.

A survey contains the legal boundaries of your property, road frontage, topography, utility locations, flood hazard areas, location and capacities of stormwater management, hard surfaces, and the footprint of the existing structures on the property. You might already have this document if you had a recent mortgage closing.  The legal lot survey is necessary in order to develop a site plan that meets all the requirements of the City.  A land survey generally costs a few hundred dollars.

A residential site plan is a detailed drawing that outlines various aspects of a property and its surroundings, including existing and new building, driveways, landscaping, and utility connections. It provides an overview of the property’s layout and spatial relationships. Site plans are essential for ensuring compliance with zoning regulations, setback requirements, and other land use regulations.

Either your contractor will coordinate the Site Plan or you can hire Atmos Arc to create this necessary document for your project. This process should only take a couple weeks to complete.

Get Your Soils Tested & Have The Foundation Design Confirmed

Every project site possesses unique soil characteristics and topography. While our construction documents include a foundation design and layout, a site-specific foundation must be confirmed by a structural engineer.

For the Ascension Home design, the foundation manufacturer will coordinate with your lot’s geotechnical report to assess soil compatibility with Ascension Home’s design and structural load. They will then confirm the foundation based on this data.

Expect an additional project service fee of approximately $1,500 to the foundation manufacturer for this service. While the installation of a manufactured foundation is swift, taking only a couple days (as opposed to the weeks a traditional concrete foundation may require), the lead time for confirming and delivering the foundation components can extend up to eight weeks. Therefore, it is advisable for the contractor to order these parts while preparing other aspects of the building.

For ADU designs utilizing a slab-on-grade foundation, your GC will manage the coordination of geotechnical professionals and the engineering required for confirming the foundation design. The cost for an engineering seal on a conventional foundation should typically be a few hundred dollars.


Your contractor initiates the permit process.

Along with your application, the site plan and the complete ADU drawing set will be required for submission. Your contractor will also submit some documents such as a certificate of workers’ compensation insurance.

During the review, the City may seek clarifications or corrections on the site plan or ADU design for final approval and permit issuance. Your General Contractor will manage this process, handling communications with the City. The duration of this procedure can range from one to two months.

construction begins

This process can take anywhere from three to eight months depending on the GCs project load and the City’s inspection schedule.

At this stage, hopefully, your GC has already ordered materials that have long lead times and the items are being stored at or near your project site.

Once the construction gets going, your contractor and you will need to schedule key rough-in inspections with the City before moving forward with each phase of construction. Your contractor will coordinate these.

During the review, the City may seek clarifications or corrections on the site plan or ADU design for final approval and permit issuance. Your General Contractor will manage this process, handling communications with the City. The duration of this procedure can range from one to two months.


Once inspections have been successfully passed, and you or another agent have walked through the site to ensure your contractor’s work aligns with the drawings and design, an occupancy certificate is filed, allowing you to move into your new space!

Once you or another agent have inspected the project and the site to ensure alignment between the contractor’s work and the drawings and design, you can initiate the project close-out process.

Only after scheduling and passing all final inspections can you apply for a Certificate of Occupancy. Once the ADU passes all necessary inspections, the city will issue the certificate, legally permitting you to move into and reside in your new space!