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How to Build an Accessory Dwelling Unit (ADU house)

May 9, 2024

ADU in Los Angeles

ADU Development Can Be Very Profitable!

Taking a piece of real estate and improving it by adding an ADU house is a relatively easy form of real estate development that even a novice real estate investor or homeowner can accomplish with the right guidance.

Over the course of the next 16-20 weeks, I will take you along as I am building a brand new 1,200 sqft ADU on a property in Hyde Park, Los Angeles. I will be sharing a step-by-step “how to” which covers the entire ADU construction process from the initial design to final inspection.

ADU House

This ADU is being constructed on a property I own, and I am acting as my own General Contractor. Although I am a licensed General Contractor, the information I provide in this guide will benefit anyone who is ready to start designing and building their own ADU.

Planning an ADU house

The first step when deciding to build an ADU is to determine what type of ADU best fits your personal needs, and the physical characteristics of your property.

As most of you reading this already know, the State of Los Angeles has passed laws that make building an ADU fairly easy, and for all intents and purposes all homeowners can decide to build either a detached ADU in their backyard, an attached ADU that is part of a home addition, or an ADU conversion which includes the conversion of part of your existing property into an ADU (including the conversion of an existing garage into an ADU).

The ADU I am building will be used as a rental, so I wanted to maximize my return on investment. With that as my primary motivation I chose to design and build the largest ADU house that was allowed under the City of Los Angeles’ ADU Ordinance.

Larger ADUs tend to rent for more money, and every square foot of new construction you add to your property translates into a higher resale value once you decide to sell.

ADU Drwaing

Why Did I Decide to Build a Detached ADU?

I wanted a 3bd/2ba ADU that I could rent for top dollar. I chose to build a detached unit because I had room in my backyard, and I thought that a detached ADU would be more desirable for a family looking for a home. And as any real estate investor knows, families tend to stay longer which equals less tenant turnover which equals less headaches and lost revenue due to tenant turnover.

Once I settled on the type and size of ADU I wanted to build the next step was to get a design in place and ADU plans, and construction drawings produced.

Do I Need to Hire an Architect to Build an ADU house?

No, in the State of Los Angeles you only need to hire a licensed Architect if you are building residential construction that is taller than two stories. Conveniently, Los Angeles ADU house laws do not allow ADUs over two stories high, so building an ADU house anywhere in Los Angeles typically does not require an Architect. But even though you do not need an Architect, most cities do require that your ADU house plans be reviewed and stamped by a Structural Engineer to ensure they are structurally sound.

Since I did not need an Architect, I was able to save a lot of money on the architectural design and structural work, which added up to tens of thousands of dollars saved.

It is particularly important that you hire a draftsman or Architect experienced in designing ADU houses and processing ADU house plans in the city you live in.

Don’t try to save a few dollars by hiring someone that does not have experience with ADU houses, or an Architect or designer that is not familiar with the ADU house ordinance in your city. An inexperienced designer, Architect, or Engineer can add months to your project timeline if they are not familiar with the ADU house ordinance and how each city treats the permitting process.

Once the designer is done with the ADU house plans, the next step is to submit the plans to the city building department and wait for their comments or approval. In my case, it took the City of Los Angeles about 30 days to review my plans, and after I made a few minor corrections to the plans based on the city’s feedback, I had permits in hand and was ready to start construction.

Construction – Building an ADU

With approval from the city and permits in hand, you can move on to the construction of your new ADU. The following paragraphs detail the construction process for a typical small home in Los Angeles, but the process will be similar throughout ADU in Los Angeles.

  • Site Clearing & Building Pad Preparation
  • The main house was built in 1914 and was an old craftsman-style bungalow. At the time it was built, it apparently had a two-car detached garage space, but at some point over the last 100 years, the garage had been demolished or destroyed. I am not sure what happened to the original garage, but it wasn’t standing when I bought the property in the summer of 2019. The only evidence that a garage once existed was contained in old building permits from 1914 that showed the size and location of the original construction. It was the existence of these old building permits that led to the first delay in the construction of my new ADU house. Since the building department’s records showed the existence of a garage on the property, I was required to pull a demo permit to remove the garage. A garage that no longer existed on the property. And to top it all off, the City of Los Angeles required that I send all my neighbors within 500 feet a notice notifying them that I was going to demolish the garage and give them 30 days to voice any concerns regarding the demo to the city.
  • Wait, what?!?! You want me to apply for a demo permit, send my neighbors a “notice of pending demolition,” and wait for 30 days to start my project so that my neighbors can protest the demolition of my garage that doesn’t exist? Yes, that is what the City of LA required. A complete waste of time and money since I had to pay 30 days’ worth of mortgage expenses and taxes while waiting for a demo permit for a garage that had long ago been demolished. Oh well. Unfortunately, these types of delays are inherent in the construction process and are why a contingency of 10-15% of your construction budget is so important. I finally had the permits complete and was ready to start building my ADU house.
  • The backyard is almost completely flat, so my engineer designed a slab-on-grade foundation for the ADU house. This is the least expensive foundation to build and is perfect for an ADU house foundation on a flat property. But slab-on-grade foundations require a clear and flat surface to build on, so I went to work clearing out all the trees and vegetation that were in the footprint of my new ADU house. You will see from the picture below that there was one old tree that was the biggest obstacle. A quick call to a tree trimmer I found on Craigslist, and the tree was removed and hauled away for $1,100. The tree removal was a bargain and much less expensive than the $3,500 I had originally budgeted for this line item.
  • Foundation Footings
  • The engineer designed a 6″ thick slab with 18″ wide and 18″ deep footings for the ADU house. Since the dirt was relatively soft and the foundation area relatively small, I decided to hand dig the footings as the cost of renting equipment would have doubled the overall cost of the footings. I used two hard-working construction laborers to help, and with my guidance, I was able to dig the entire foundation and prepare the footings in a little under 16 hours of work. Now that we have the footings dug, it is time for the next step: underground utilities.
  • Underground Utilities
  • At this point in the build, it is necessary to run any underground utilities that will run underneath the foundation slab of the ADU house. For this building, I have chosen to run the property entirely on electric power. I chose to use electric-only for two reasons. First, to save a little money. Running only electric to the ADU house meant I did not need to run gas lines, which saved about $3,500. Second, with an all-electric home, we will be powering the ADU house with a renewable resource and not natural gas. In the long run, the State of Los Angeles will require all new homes to be built with all electric power, so I’m a little ahead of the curve with this ADU house. The decision to use electric power means that the only underground utilities I have running under the foundation slab and through the footings were my plumbing waste lines. At this point, we called the city inspector to come out and approve the foundation pad and footings, and to perform a water test and approve the underground plumbing. With the inspector’s blessing, we backfilled the sewer trenches and started progress on preparing the slab for our concrete.
  • The next step in the ADU house construction process is the Rough Framing. This is when the construction of your ADU house gets fun as you see the new home rise out of the ground. Us builders refer to this stage as “going vertical.”
  • I specifically designed this ADU house to be inexpensive to build by using off-the-shelf products and traditional dimensional lumber with no structural steel framing or large structural beams. As such, my framing crew will be able to complete the rough framing portion of this ADU house project in about 12-14 working days. My job now is to make sure the framers have the lumber and materials they need and to ensure my windows are ordered, as we’ll need the windows after the rough framing is complete.
  • The video below shows the progress after 3 working days. It’s amazing how fast a small ADU house like this can be built with an experienced crew of framing carpenters.

Who We Are

KN Remodeling is a certified and qualified renovation company that provides renovation services to all people of Los Angeles, Woodland Hills, Simi valley, Thousand oaks, and its environs. As a full time company, we offer a wide range of services and products tailored to make your home beautiful. From replacement of kitchen counter-tops to bathroom flooring, KN Remodeling, does it all. We take pride in what we do and we are always glad to put a smile on your face each time you ask for our services. That is why we have a showroom with certified designers and kitchen remodelers who guide you in deciding what’s best for your bathroom or kitchen. We make our customers feel at home by giving them a wide range of remodeling designs to choose from and we always renovate your home with your needs and wants in mind.