Why We’re Building an ADU in Our Own Backyard

This is the first post in the Corner ADU series, where I’m documenting our own build from planning through move-in. I’m a licensed architect, and this time the client is my own family. I’ll share the design decisions, the permit process, the timeline, and the numbers as they happen.

Our baby started crawling all over the house a few days ago. That was the moment our home officially got too small, with all the baby equipment, toys, and activity centers claiming whatever floor was left.

My husband Daniel and I live in a 400 square foot garage conversion ADU we built back in 2021 in the City of Whittier. We left Los Angeles for Whittier when we found out we were expecting. We loved our place in LA (our East LA triplex), but it was too busy and noisy for a baby.

400 square feet was fine for a newborn. A newborn doesn’t need much space (a bassinet, you, and a hundred burp cloths). But we had to get creative with storage and ruthless about what we bought, for the baby and for ourselves (auto-subscribe was a lifesaver). A garage conversion inherits the garage’s footprint, and ours didn’t leave room for closets, so the floor holds what the closets can’t.

Crawling changed everything. A baby on the move needs open floor, and ours was already spoken for. Every square foot in our place is doing two jobs, and now there’s a small person who wants all of them.

So we’re building a new ADU. From the ground up this time, in the backyard of our other property.

The Corner ADU

The new ADU is going on a corner lot we bought in late 2021: a 1,600 square foot house with a large backyard that has both street and alley access. We fixed up the house and partially converted it into two units. 1,200 square feet stayed the main house (2 bedrooms, 1 bathroom) and 400 square feet became an attached ADU (1 bedroom, 1 bathroom).

When we did the split, we left the backyard open on purpose. The yard faces a street on one side and an alley on the other, and for a lot like this, that’s worth more than it sounds. A detached ADU built back there gets its own entrance from its own street. Nobody walks through anyone’s yard to get home, which is the difference between a backyard ADU that feels like a rental behind a house and one that feels like its own address.

The ADU law makes this possible: a single-family lot is allowed 1 attached and 1 detached ADU, so this build can sit alongside the conversion we already did. We could have added 2 more units, but we decided against it. We wanted a standalone home with no shared walls or floors for our growing family.

We’ve been saving for this build for 3 years, and we’re paying for it with a combination of cash savings and a HELOC we’ve had open since 2021. The target size is 1,200 square feet with an attached garage (three times the space we live in now), and we’re budgeting $240,000 for the build. We’re going to subcontract everything ourselves, so we’ll see if we keep to that number.

Why another ADU, and not the house

You might expect an architect to skip straight to the single family home. That’s the usual script: stretch for the house first, then maybe add an ADU someday. We’re running it in the other order. We’re building the units first and letting the units carry us to the house.

Part of it is simple math. We already own the lot, and building is much cheaper than buying. The $240,000 build cost is about what a down payment on a house runs these days. And once we move in, we’ll live mortgage free, because the rent from the main house and the attached ADU covers our housing and utility costs.

So the plan looks like this. We build the new ADU and move in. We live there for two to three years while the other units earn, and we save. Then we buy a single family home with no shared units and no tenants, a house that’s only ours. The new ADU is the stepping stone that gets us there, and when we move out, it keeps earning as a rental. The property ends up with one more unit than it started with, which raises both what it brings in and what it’s worth, long after we’ve moved on.

There’s also a simpler reason we’re building new instead of converting again. We’ve lived inside a garage conversion for five years, so we know exactly where it pinches. A conversion inherits its walls. New construction lets us choose everything: the storage we’ve been living without, a layout that works with a toddler underfoot, new plumbing and electrical instead of whatever the old garage allowed, and a design that’s actually ours from the first sketch. I draw these for clients all the time. I’ve been waiting a long time to draw one for us.

What’s coming in this series

Right now we’re under planning review with the city. We’ve also submitted to Southern California Edison, because a power pole and cables run through the alley behind us, and we need their clearance before we can build near their lines.

I’ll post as the project moves: the design and the trade-offs behind it, the permit process step by step, what things cost (the part nobody publishes), and eventually the build itself, through to the reveal.

If you’ve been circling the idea of an ADU in your own backyard, for family, for income, or as your own version of this plan, follow along. And if you have a project in mind and want to talk it through, get in touch. I’d love to hear what you’re planning.

Thank you for reading!