Best financial decision we ever made. HSP found savings we didn't know existed.
Attached ADU
An ADU attached to your home — designed, permitted, and built as one project.
Attached ADU construction for San Diego and Washington homeowners — addition-style ADUs sharing a wall with the main structure. One contractor for design, permits, structural work, and finish.
- Structural work in-house
- In-house permitting
- Dedicated project manager
What we handle in an attached ADU project.
From a side-yard addition to a rear attached unit:
- Site and zoning assessment — lot coverage, setbacks, and structural attachment requirements reviewed on-site before design begins.
- Design and floor plan — attached ADU layouts that optimize the connection point with the main home and maximize usable sqft within the buildable envelope.
- Structural design and permitting — attachment to the existing structure requires engineering; we coordinate the engineer and pull all permits in-house.
- Foundation and framing — new foundation and framing designed for the attachment detail and site conditions.
- Separate entrance — private exterior entrance required for legal ADU designation; designed into the floor plan from the start.
- Utility separation — separate electrical meter, water sub-meter, and individual address coordinated with the utility and city.
- Interior finish — full kitchen, bath, flooring, cabinets, and fixtures scoped to the design direction in your written proposal.
Attached ADU projects begin with a free feasibility consultation. You leave with a written proposal covering structural engineering, permits, and build cost.
How it works
Our 3-step process.
STEP 01
Feasibility & design
On-site walkthrough. We assess attachment options, setbacks, and structural considerations. You leave with design direction and a written proposal — scope, engineering plan, permit timeline, and total cost.
STEP 02
Engineering & permitting
Structural engineering coordinated for the attachment detail. City and county permits pulled in-house. Utility service upgrades scheduled. You have a firm start date.
STEP 03
Build & final inspection
Foundation, framing, structural attachment, MEP rough-in, inspections, insulation, drywall, finish, and final inspection. Your dedicated project manager is on-site through every phase.
What sets us apart for attached ADU construction.
Structural work handled in-house
Attaching a new structure to an existing home requires engineering. We coordinate the structural engineer, pull the permits, and manage the attachment as part of the project — not as a separate contract you have to coordinate.
In-house permitting
ADU permits — including the structural elements unique to attached units — are pulled and managed directly. No third-party expediters. Your PM owns the timeline.
One proposal, full scope
Engineering, permits, structural work, MEP, and finish — in one written proposal. Every line item visible before anyone picks up a tool.
FAQ
Frequently asked questions.
What's the difference between an attached ADU and a detached ADU?
An attached ADU shares at least one wall with the main home. A detached ADU is a fully separate structure on the same lot. Attached ADUs typically cost less to build (shared wall, no separate foundation perimeter) and are better suited to lots with limited yard space. Detached ADUs offer more privacy and are often preferred for rental income.
Does an attached ADU require a separate entrance?
Yes — a private exterior entrance is required for legal ADU designation in both California and Washington. We design the entrance location into the floor plan from the start.
Do you handle the structural engineering for an attached ADU?
Yes. We coordinate a licensed structural engineer for the attachment detail and integrate their drawings into the permit set. The engineering cost and timeline are included in your written proposal.
Are you licensed for ADU construction in California and Washington?
Yes — licensed in California and Washington, bonded and insured. Documentation available on request.
What does an attached ADU cost?
Attached ADU construction typically runs $140,000–$280,000 depending on size, site conditions, and finish level — generally less than a comparable detached ADU due to the shared wall. Your written proposal gives a line-item breakdown.
Reviews
What our customers say.
on Google · 298 reviews
Service area
Where we work.
HQ in San Diego, CA
Ready to plan your attached ADU?
Start with a free feasibility consultation. We'll walk the site, assess attachment options, and follow up with a written proposal.