Building an ADU in Saratoga: Foundation to Framing

We're currently in the middle of an ADU build on a hillside lot in Saratoga, California — and we're documenting the process from the ground up. This post covers Phase 1: site prep, excavation, grade beam foundations, and the challenges that come with building on a sloped lot in Santa Clara County.

The Site: A Hillside Lot in Saratoga

• Saratoga is one of the most desirable cities in Santa Clara County — and one of the most challenging to build in. Hillside lots mean uneven grades, retaining wall requirements, and soil conditions that demand careful engineering before a single form board goes in.
• This project is a detached ADU on a lot with significant grade change from front to back. The city of Saratoga requires full engineered plans for any ADU on a sloped lot, and the building department reviewed our structural drawings closely before issuing the permit. We've been through this process many times — our 40 years of experience in Santa Clara County means we know what the inspectors are looking for before we submit.

Grade Beam Foundations: Why We Use Them on Hillside Lots

• For this ADU, we specified grade beam foundations rather than a conventional slab-on-grade. Grade beams are reinforced concrete beams that sit on drilled piers or spread footings and span between them — essentially a structural frame at grade level that distributes the building's load across multiple bearing points rather than relying on a continuous slab.
• On a hillside lot, this approach has several advantages. It accommodates uneven bearing conditions without requiring massive cut-and-fill earthwork. It provides a rigid, tied foundation system that performs well in seismic events — critical in California. And it allows us to set anchor bolts precisely for the framing above, which matters when you're building to tight tolerances on a sloped site.
• The photos in this post show the grade beams after the concrete pour: anchor bolts set, forms still in place, and the foundation ready for inspection before framing begins.

The Foundation Pour: What Goes Into a Single Day of Concrete Work

• Concrete pour day is one of the most logistically demanding days on any job. For this Saratoga ADU, we brought in a concrete pump truck — necessary because the lot's slope and tight access made direct chute delivery impractical. The pump truck positions on the street and runs a boom over the fence line to place concrete exactly where it needs to go.
• Our crew directed the pour from inside the forms, consolidating the concrete with vibrators to eliminate voids and ensure full coverage around the rebar. Anchor bolts were set to template — their position has to be exact, because the mudsill and framing above depend on them being in precisely the right location.
• After the pour, the concrete cures for a minimum of 7 days before we strip forms and begin framing. During that time, we schedule the foundation inspection with the city of Saratoga's building department.

Retaining Walls: Managing the Grade

• One of the defining features of this project is the retaining wall system required to manage the grade change across the lot. Retaining walls on hillside ADU projects in Santa Clara County require engineered drawings and are inspected separately from the building foundation.
• We formed and poured the stem walls and retaining walls as part of the same foundation sequence, tying them into the grade beam system for a unified structural assembly. This approach reduces the number of separate inspections and keeps the project on schedule.

What's Next: Framing

With the foundation inspected and approved, framing is next. We'll be documenting the wall framing, roof structure, and sheathing as the ADU takes shape above grade. Follow along on this blog or visit our ADU Build gallery for the latest photos as the project progresses.

Thinking About an ADU in Saratoga or Santa Clara County?

If you're considering an ADU on your property, the foundation phase is where most of the complexity lives — and where the difference between an experienced contractor and an inexperienced one shows up most clearly. We've built ADUs throughout Santa Clara County and know the local permitting process, soil conditions, and inspector expectations. Call us at (408) 540-4842 or visit our ADU Construction page to learn more.