The Best Way to Build an ADU Home and SB9—And How to Avoid All the Headaches in Construction
“The time to repair the roof is when the sun is shining”
It was the beginning of 2022. I was in my studio, settling into the second year of my solopreneur journey, enjoying my morning coffee when Shawn called me.
“I have this property, but I’m not sure what to do about it,” Shawn explained. “I want to invest back in it.” I finished gulping my coffee and cleared my throat.
“Well…what’s your address? I can take a look,” I offered. Once he provided me with the address, I started checking his zoning regulations. That’s when I realized he’s in a single-family zone located in the heart of LA.
“Lucky for you, you can build a Jr ADU, a regular ADU, and a new SB9,” I confirmed. Shawn contemplated my suggestion for a second before he replied.
“What’s the best option for me?” He asked. I took a look, knowing that I would have to do a bit of research before I could give him a firm answer.
“Let’s check out the site and try to plan to make sure we get it right the first time,” I offered.
Plan Ahead and Weigh Your Options Carefully
That’s the first lesson: to plan ahead. So, we got to work. I got my things ready and met Shawn on the site. While at the site, we checked his available space in the back and the best way to plan this out. We asked ourselves the important questions:
Is this new ADU home for his family or for rent? Was Shawn willing to use up all the space you can for it?
“If I build anything, it would be for family. My younger brother is coming back home, and my mom is getting older. I want to take care of my mom on my property rather than in a retirement home. I do know I want to keep my backyard open,” he told me as we gazed out at his property.
Given his situation, creating two units would be ideal. I thought about the best way to build the two of them. It was easier to make them detached since we could build both simultaneously while Shawn lived in the main home. It would also make it easy for him to add a Jr. ADU home later because they need to be made from an existing space attached to the main home, which caused a little bit more of a problem than what we needed then.
“Considering everything you're telling me, I think we should do a second-story addition to your garage. We can do one unit on the bottom and one unit above,” I told him. Then, I drew up a quick floor plan and broke it down with Shawn; we talked about everything and anything until he asked me the biggest eye-opening question:
“So, what’s the best way to start building this anyway?” The only thing that came to mind immediately when he asked me was two words: plan ahead!
Use a Checklist to Prepare All the Important Stuff for an ADU Home
Before submitting for permits, you should always plan how to do everything to avoid any issues later on. We started by checking out the garage so we could plan what we needed to do for the second-floor addition. I ran through my checklist for the important stuff:
Foundation
What’s the depth of the footings? Are the footings made of concrete? Yes, you should check. Back in the day, they built footings out of cinder blocks! Crazy, I know!
We need to check these things to see the best way to Underpin. Conventional underpinning is from the exterior of the building, but sometimes, doing it from the interior is needed.
What’s the difference? If we do it from the outside, we only need to remove dirt to place the concrete, which makes it easier. If we do it from the inside, we must reinforce the slab we broke to add more concrete. Both have pros and cons, and both are used in different situations.
Framing
We then check the framing to see if it works. Whatever framing may not be up to par, we can always sister new framing to it. But what’s most important is checking the height of the top plate.
This will determine where our second story starts and let us know how many steps we need. Pro Tip: plan for one foot higher than the top plate as the finished floor of the second story. All second-story additions must have a shear wall connecting from the second story to the first and pinned to the foundation using hold-downs.
So, plan for the best places to do so. Usually, it’s the corners of the building, but it’s important to check each site. Things like windows & doors would also determine where we can place shear walls as they can’t have any openings. This will save some money because the alternative is a strong wall.
That covers the big structural stuff, but what about the rest behind the walls for the new ADU home?
Check Behind the Walls to Confirm Important Details Before Building
Where is the Sewer Line on the Property?
Identifying the sewer line's location on the property helps us find the best place for bathrooms. This will also keep any hard costs down, like having to excavate more or adding a sewer line in the alley. Trust me when I say that you want to avoid doing any work in a public right of way.
Find the Gas and Water Lines, Too
Detached ADUs and SB9s can hook up directly to the main water and gas lines. The only thing is that they have to hook up where the meter is. They can’t hook up anywhere else or share any line with any other building. Each unit needs to have a separate water heater and HVAC but does not need to have separate meters. Fortunately, those are optional.
Locate the Electrical System and Wires
The same rules apply for electrical: we do not need to add another meter. However, some cities have changed requirements, and all new construction needs to be electric and not gas. So, with this in mind, we also have to make changes when designing our ADU home. We should also plan out every light and outlet beforehand so we know how many amps a new sub-panel would need.
Are the Walls and Ceilings Fire-Rate?
A thing that usually surprises people is the need to fire-rate walls and ceilings between units and any wall close to the property line. How close you are to the property line determines your fire rating and if you can have any windows or doors on a specific wall.
Fire-rated ceilings and walls are where we make sure to halt as much fire that can pass through as much as possible by adding two layers of type x drywall and fireproof foam around any conduits and such.
Pro Tip: You cannot have any ventilation openings within fire-rated walls.
Do a Title 24 to Determine the Insulation Needed
What about insulation? Currently, in CA code, we need a Title 24 to determine what energy rating your insulation needs. Especially if you decide to do a vaulted ceiling—that’s when things get tricky!
Many people think you can just add regular batt insulation in that area, but that creates air gaps within since batt insulation is permeable. This would allow for condensation and cause dry rot in ten or more years… that’s a big no in construction because we need to plan to build and have this last at least fifty years.
So, what we do in that situation is use spray foam insulation, which makes that area non-permeable. The problem is solved by planning!
Consider the Best Way to Waterproof the Existing Slab
Since we are dealing with an existing slab, we must now think about how to best waterproof it. When we pour a new slab, we add vapor barriers underneath it to mitigate any water vapors. Unfortunately for us, this is something that a lot of old homes do not have.
So, what’s the modern-day cure? Remove the slab? No. The solution is to add epoxy coating above the slab. The epoxy acts as a way to enclose the porous nature of concrete, making it impossible for water vapors to seep through.
Pro Tip: Slope the dirt or concrete around the building with a 2% slope away from it. This would ensure proper water flow around the building when it rains. Just make sure your garage is higher than the street because if not, we may need to add a sump pump.
The Key is Planning Ahead and Solving Issues Early On
What’s the best way to build an ADU home and SB9? It comes down to thinking ahead and solving issues in the early stages of planning your project. If you’re eager to explore your options and want to build an ADU home, we’d love to collaborate with you. Contact our team today to have us visit your property to conduct an assessment.
