Best ADU For · 2026
Best ADU for a Small Lot: Which Model Wins
If your backyard is tight, the Four Fifty is the model to start with. It has a 30 foot by 15 foot footprint, the smallest of any Framework First home, and it’s priced at $180,000 all-inclusive. For lots where every foot of side yard setback matters, that footprint is usually the difference between a project that pencils and one that doesn’t fit at all.
The short version: The Four Fifty (450 sq ft, 30 ft by 15 ft, $180,000) is the best fit for the tightest lots because it has the smallest footprint and the lowest price of any model. If you need an actual bedroom instead of a studio and can spare a slightly higher budget, The 405 (405 sq ft, 27 ft by 15 ft, $237,000) has an even narrower footprint and is the strongest runner-up.
Why a small lot needs a different kind of ADU
Most ADU content talks about square footage like it’s the only number that matters. On a small lot, it isn’t. What actually determines whether a home fits is footprint: length and width, setback clearance, and how much of the buildable envelope is left after you subtract the required distance from property lines, the main house, and any easements.
A tight backyard often rules out anything wider or longer than a simple rectangle before you even get to floor plan preferences. That’s why the models that work best on small lots aren’t necessarily the cheapest per square foot or the most popular overall. They’re the ones with a narrow, simple rectangular footprint that can slide into an oddly shaped side yard or a lot with a shallow buildable zone.
Budget matters here too, but in a specific way. Small lots often belong to smaller primary homes, and a lower total project cost keeps the ADU proportional to the property instead of dominating it. That’s part of why the smallest, most affordable models in the lineup tend to be the right call for tight spaces, not just the fallback option.
The models that fit
All four of these models share the same simple rectangle layout, which is the easiest shape to place on a constrained lot. They’re ranked here by footprint size, smallest to largest.
| Model | Size | Beds/Baths | All-inclusive price* | Why it fits |
|---|---|---|---|---|
| The 405 | 405 sq ft | 1 bed / 1 bath | $237,000 | Narrowest footprint of any model at 27 ft by 15 ft, with a real bedroom instead of a studio layout |
| Four Fifty | 450 sq ft | Studio / 1 bath | $180,000 | Smallest footprint at 30 ft by 15 ft and the lowest price point, our top pick for the tightest lots |
| Five Five Five | 555 sq ft | 1 bed / 1 bath | $267,000 | Still a single narrow rectangle at 37 ft by 15 ft, more room without adding width |
| Six Sixty | 660 sq ft | 1 bed / 1 bath | $287,000 | Largest rectangle before floor plans widen into an L-shape, 44 ft by 15 ft |
*Includes a permitting budget, not final permit costs. Permits and property-specific site work (septic, retaining walls, etc.) vary by property and are confirmed in your feasibility study.
Every one of these keeps the same 15 foot width, which is the number that usually decides whether a home clears a side yard setback. As you move down the table, the length grows but the width doesn’t, so a lot that can fit the Four Fifty can often fit any model above it in the table too, as long as there’s enough length to work with.
The Four Fifty: our top pick for tight lots
The Four Fifty is a studio, which is exactly why it works so well on a small lot. There’s no bedroom wall to fit in, no hallway to a second room, just one open living space and a bathroom inside a 30 foot by 15 foot rectangle. That simplicity is what keeps the footprint small and the price at $180,000, the lowest of any model Framework First builds.
It’s the model we point most small-lot owners toward first, especially for a first ADU, an aging-in-place unit for a parent, or a private studio for one person. If your lot review comes back tight, the Four Fifty gives you the best odds of a workable placement without redesigning the whole backyard around the build. See the full spec sheet at /models/four-fifty/.
The runner-up: The 405, for when you need a real bedroom
Here’s the twist: The 405 actually has an even narrower footprint than the Four Fifty, 27 feet by 15 feet versus 30 feet by 15 feet. If your lot is so tight that even those extra 3 feet of length matter, The 405 is the tightest fit in the entire lineup.
What you get for the higher price, $237,000 versus $180,000, is a true separate bedroom instead of a studio layout. That distinction matters for long-term tenants, a family member who wants a door to close at night, or anyone who just doesn’t want to sleep in the same room they live in. If your lot can only take a small footprint but a studio layout isn’t going to work for how the space gets used, The 405 is the model to look at next. Details are at /models/the-405/.
If your lot has a little more room to give, both the Five Five Five and the Six Sixty keep the same 15 foot width while adding length, which is often the easiest way to gain living space without changing whether the home fits at all.
Pricing, financing, and next steps
Every price in this guide includes a permitting budget along with plans, foundation, the factory build, delivery, utility hookups, appliances, and final inspection. Permit costs are set by each city and county, so your exact figure gets confirmed in the feasibility study. Property-specific site work like septic upgrades or retaining walls isn’t part of the listed model price, but we handle it in-house as part of your contract so one builder still covers the whole project.
Before anything else, the real question for a small lot is whether it can legally and physically fit a given footprint once setbacks, utilities, and access are accounted for. A feasibility study is the fastest way to get a straight answer on that before you commit to a model. From there, you can run your own numbers with the ADU cost calculator or see the full lineup and current pricing at /pricing/ and /models/.
Frequently asked questions
What’s the smallest ADU footprint Framework First builds?
The 405 has the narrowest footprint at 27 feet by 15 feet, followed closely by the Four Fifty at 30 feet by 15 feet. Both are simple rectangles, which makes them the easiest shapes to fit into a constrained side yard or backyard.
Is the cheapest model always the best choice for a small lot?
Usually, but not automatically. The Four Fifty is both the smallest footprint and the lowest price at $180,000, which is why it’s the top pick for most tight lots. But if you specifically need a separate bedroom rather than a studio, The 405’s slightly higher price and even narrower footprint may be worth it.
Can a small-lot ADU still have a real bedroom, not just a studio?
Yes. The 405 (405 sq ft, 1 bed, 1 bath, $237,000) has a true bedroom in a footprint that’s still narrower than the Four Fifty’s studio layout. It’s the clearest option for buyers who need a separate sleeping space but don’t have a wide lot to work with.
How do I know if my lot can actually fit one of these models?
Setbacks, utility locations, and access requirements vary by property, so the only reliable way to confirm fit is a site-specific review. A feasibility study checks your lot against real constraints before you commit to a floor plan.
What if my lot can fit more than just the smallest models?
If your buildable area has more length to work with, the Five Five Five (555 sq ft, $267,000) and Six Sixty (660 sq ft, $287,000) keep the same 15 foot width as the smaller models while adding living space, so they’re worth comparing before you default to the smallest option.
Not sure what will actually fit on your lot? Start with a feasibility study and get a straight answer before you pick a model.