attached ADU builder
Attached ADU builder in Sacramento
An attached ADU is brand-new square footage built onto your existing house, sharing at least one wall but functioning as a fully separate dwelling with its own entrance, kitchen, and bath. Unlike a garage conversion it adds new floor area, and unlike a JADU it has independent facilities — making it the middle path between a detached build and an interior unit.
What a Attached ADU is
An attached ADU is the answer when the yard is too small for a detached unit but you still want genuine new living space. By bolting onto the main house, the addition can tap existing utility runs and skip a long trench, which often trims site and plumbing cost versus a freestanding build. You keep more open yard, and the shorter utility distance can speed the rough-in. It is a strong fit on Sacramento's narrower infill lots in Midtown, Oak Park, and Tahoe Park, where a freestanding unit would eat the whole backyard but a wing off the rear or side of the house fits. The trade-off is a shared wall — fire and sound separation and a private entrance set apart from the main door are what make it rent like a real second home.
Best for: Lots where a shared wall saves on utilities and site work.
Not what you need?
These build types are easy to confuse. Here's where to go instead:
- Detached ADU →
Want full separation and the highest rent? A standalone unit is worth the extra cost.
- Garage conversion ADU →
Have a garage to reuse? Converting it is cheaper than building new attached space.
- Junior ADU (JADU) →
Staying inside the existing footprint with shared facilities? That's a JADU, not attached.
Who a Attached ADU is best for
What's included
- Shares one wall and utility runs with the main home
- Independent entrance and full living facilities
- Often lower site-prep and trenching cost than detached
- Keeps more usable yard space
How we build your attached adu
This is the build sequence specific to a attached adu. For what working with Upside feels like start to finish, see how it works.
- Step 01
Tie-in & feasibility
We confirm where the addition can attach, how it connects to existing utilities, and the setback envelope for new floor area.
- Step 02
Design & shared-wall engineering
We design the unit and engineer the shared wall for fire and sound separation, plus its own private entrance away from the main door.
- Step 03
Foundation extension
Attached units need a new foundation for the added footprint, tied into the existing structure — less work than a fully detached slab, but real construction.
- Step 04
Frame, connect & finish
We frame the addition, extend short utility runs from the main service, then complete MEP, insulation, drywall, and finishes.
- Step 05
Inspections & handoff
Milestone inspections tied to your draws, final sign-off, and a separate, rentable unit attached to your home.
Size & layout options
- Most attached units land at 450–850 sq ft
- Studio, 1-bed, and 2-bed layouts; the shared wall usually anchors the kitchen or bath plumbing
- A private entrance on a different elevation than the main door improves rentability
- Single-story keeps cost down; a second-story attached unit is possible on tight lots
Want pre-designed floor plans with fixed pricing? Browse our ADU models.
What a attached adu costs in Sacramento
A attached adu in the Sacramento region typically runs $108,000–$289,000 turnkey in 2026, or roughly $240–$340 per square foot with design, permits, and construction included. Attached ADUs usually cost a bit less per square foot than detached because the shared wall and short utility runs reduce site work — one less wall to build and a far shorter trench to the existing service. But they cost more than a garage conversion, since the square footage is genuinely new: a new foundation for the addition, new framing, and a clean tie-in to the existing roofline all carry real cost.
| Configuration | Typical size | All-in 2026 cost |
|---|---|---|
| Studio / 1-bed | ~450 sq ft | $150,000 – $215,000 |
| 1-bed | ~600 sq ft | $185,000 – $260,000 |
| 2-bed | 750–850 sq ft | $240,000 – $340,000 |
See our full published ADU pricing and what's included, or estimate your specific cost. For a market-wide breakdown, read how much an ADU costs in Sacramento.
Estimate your ADU
Ballpark 2026 turnkey cost, financing, and rental return for your area.
Estimated turnkey cost
$240–$340 / sq ft · incl. design, permits & construction
Estimates only — 2026 regional ranges, not a bid. Your real price depends on site conditions, finishes, and your lot. We confirm with a free feasibility check.
Attached ADU timeline
Expect roughly 6–8 months. Design runs 2–6 weeks and permitting 4–10 weeks; construction is often slightly shorter than a detached build because the addition shares a wall and ties into nearby utilities instead of trenching across the yard.
Permitting notes for this type
Attached ADUs are capped at 50% of the main home's floor area or 1,200 sq ft, whichever is less, and the shared wall must meet fire-separation code. New floor area must respect setbacks. They do not carry the owner-occupancy requirement a JADU can.
Full local rules: Sacramento ADU rules, setbacks & permits · 2026 California ADU law
What to watch for with a attached adu
Sound and fire separation
A shared wall needs proper fire-rated and sound assemblies so neither household hears the other — essential for keeping a rental leased.
Roofline integration
Tying the new roof into the existing one cleanly affects both cost and curb appeal; a poorly matched addition can hurt resale.
Entrance placement
The ADU entrance should be visually and physically distinct from the main home's door so tenants have real privacy and the unit reads as separate.
Attached ADU FAQs
An attached ADU is limited to 50% of the main home's existing floor area, up to 1,200 sq ft. On a 1,500 sq ft house, that's about 750 sq ft. Detached ADUs aren't tied to the main home's size, which is why larger units often go detached.
It can. Attached units often tap the existing water, sewer, and electrical service with short runs, which lowers trenching cost versus a detached build. We can also add separate metering if you want fully independent billing for a tenant.
Usually slightly. The shared wall and short utility runs cut site work, so attached units often run a bit less per square foot than detached. But because the square footage is new construction, they cost more than reusing a garage in a conversion.
An attached ADU shares at least one wall with your main house; a detached ADU is a standalone structure. Attached units can be cheaper to build (shared utilities, less site work) while detached units typically rent higher and add more resale value.
Upside models for Attached ADU
Plan & price your build
ADU services in Sacramento
Explore other ADU types
Ready to build your attached adu?
Get a transparent, all-in attached adu quote and a free feasibility check for your Sacramento-region lot.