The "ADU-First" Strategy: How to Buy a Property with Rental Potential
When my wife and I were looking for houses in 2018, we weren't just looking for a home—we were looking for a business partner.
I knew that building an ADU was the cornerstone of my 15-year plan for Financial Independence (FIRE). So, while other buyers were looking at granite countertops and crown molding, I was looking at side setbacks and sewer lateral elevations.
Buying the wrong property can add $50k+ to your build cost or kill the project entirely.
Here is the framework I used (I’m a PM - I can’t help myself) to evaluate properties, combined with the technical "red flags" my general contractor father taught me to spot.
1. The "Go/No-Go" Checks (Legality)
Before you fall in love with a layout, you have to verify you can actually build. While California state laws (like SB9 and AB68) have overruled many local restrictions, there are still two major deal-killers:
HOAs: Homeowners Associations can still restrict or ban ADUs in some cases. Read the CC&Rs before you offer.
Historic Districts: If a property is zoned as a "Historic Landmark" or in a historic preservation zone, the design restrictions can make an ADU prohibitively expensive or impossible.
The Due Diligence Stack:
Tier 1 (Fast): Use a site like Housable.com. Enter the address for a free, instant feasibility report.
Tier 2 (Official): Call the local planning department. Give them the APN (Parcel Number) and ask specifically about easements and setbacks.
Tier 3 (Expert): If you are serious, pay for a consult with an expert like Ryan from HowToADU to review the specific parcel.
2. The Physical Logistics (The "Contractor's Son" Lens)
Just because a lot is big doesn't mean it's usable. You need to look at the dirt like a builder.
Access is Money: Can a cement truck or excavator get into the backyard? If you have a narrow side yard, you might be stuck digging trenches by hand or paying for a crane to lift materials over the house. Truck access = cheaper builds.
The Slope: Flat land is cheapest. If the yard slopes away from the street, you might need a sewage ejection pump (which I use, and costs ~$12k installed) to get waste up to the main line.
Soil & Trees: Removing protected trees requires permits and arborists. Unstable soil requires deep caissons. Talk to neighbors—if they hit bedrock 2 feet down, you will too.
3. Privacy = Revenue
In the Mid-Term Rental (MTR) market, privacy is your premium product. Executives and traveling nurses pay extra to not feel like they are living in someone's backyard.
Sight Lines: Stand where the ADU would be. Can you see into the main house's master bedroom?
Separation: Can you build a fence or use landscaping to create a dedicated, private entrance?
Parking: A dedicated parking spot is gold for tenants. If you can offer an EV charger, you just unlocked a higher tier of clientele.
4. The Hidden Budget Killers: Utilities
This is where my dad’s advice saved me the most headaches. Bringing utilities (Water, Power, Sewer, Gas) to a detached unit is expensive.
Electrical Panel: Check the main house panel. Is it 100 Amps? If so, you will likely need to upgrade to 200 Amps to support an ADU, especially if you want AC or an electric stove. Budget Impact: $2,500 - $4,000.
Sewer Lateral: Identify where the main sewer line leaves the house. You want to tie into the lateral as close to the ADU as possible without tearing up expensive hardscaping.
Water Line Size: If the main house has a 1/2” water line, it might not provide enough pressure for two homes (especially if you have irrigation). You may need to upgrade to 3/4” or 1” from the street.
Future-Proofing: While the trench is open, run a conduit for hardwired internet (Cat6 or Fiber). "Fast, reliable WiFi" is a non-negotiable for executive tenants.
5. Permitting Friction
Just because the law says you can build, doesn't mean the city will make it easy. We learned this the hard way.
Permitting difficulty varies wildly by city. Some have pre-approved plans and digital portals (fast). Others have antiquated systems and hostile planning departments (slow).
Pro Tip: Look at the city’s building department website. If they have clear "ADU Handbooks" and PDF guides, they are likely pro-development. If their site looks like it’s from 1998 and hides the info, expect a fight.