Accessory dwelling units come with tighter setbacks, smaller footprints and often less equipment access than a standard new-home build. We pour ADU foundations specifically, not a scaled-down version of a full-home job — and most clients book us for the framing too. See Home & ADU Framing for that combined option.
ADU projects usually mean working in a backyard or side yard with limited access for equipment, existing landscaping and utilities to work around, and a foundation footprint that has to match state ADU allowances and your city's specific setback and lot-coverage rules exactly. Garage-conversion ADUs bring a different problem: an existing slab that may or may not meet current code for a habitable space. We treat each of these as its own foundation problem instead of applying a standard new-home approach to a project that doesn't fit it.
Slab-on-grade or raised foundations for standalone backyard units, sized to your approved ADU plans and sited correctly relative to setbacks and your existing home.
New foundation sections tied into your existing home's foundation for attached ADUs, engineered so loads transfer correctly between old and new construction.
Assessment of an existing garage slab for a JADU or ADU conversion, with repair or supplemental footings where the existing slab doesn't meet current structural requirements.
Equipment and pour methods suited to tight side-yard and backyard access — a common constraint on infill ADU lots that a standard foundation crew isn't always set up for.
Foundation placement coordinated with utility lines, property setbacks and your civil/site plan so the poured foundation matches what was actually permitted.
Based in the Bay Area, working throughout Santa Clara, San Mateo, Alameda and Contra Costa counties.
Most detached ADUs on level lots use a slab-on-grade foundation, which is typically faster and less expensive. A raised foundation may be needed for drainage reasons, sloped lots, or if your city or soil report requires it. We'll confirm which applies once we've reviewed your site and plans.
Yes — this is a large part of what we do. We use smaller equipment and adjusted pour methods for side-yard and backyard access that a standard foundation crew built around full-size equipment often can't accommodate.
Sometimes, but not always. Garage slabs are often built to a lighter standard than a habitable-space foundation requires. We evaluate the existing slab as part of the process and recommend repair or supplemental footings if it doesn't meet current structural requirements for the conversion.
We work from your approved ADU plans and site survey. If you're still finalizing plans with a drafter or architect, we can review the foundation design with them before it's submitted, which can save a correction cycle at plan check.
A straightforward detached ADU slab-on-grade foundation is often completed in a matter of days once excavation starts. Attached ADUs and raised foundations take longer. We'll give you a specific timeline after reviewing your plans and site.
Tell us what you're building — a new home, an ADU, an addition — and we'll get back to you with next steps, usually within one business day.
(925) 592-7162
ProHomeFoundation
