Piedmont Lower Level Addition - Amiari | Bay Area General Contractor for Remodels, ADUs & Custom Homes

Finished Los Altos custom home exterior at dusk with warm interior lighting.

A lower-level expansion built beneath an occupied home, adding new living space while supporting the floor above and creating a new deck at the backyard level.

Lower-Level Addition

Piedmont Lower Level Addition

PIEDMONT, CALIFORNIA

Year

Duration

Size

Project Type

Location

PROJECT SNAPSHOT

PIEDMONT, CALIFORNIA

Lower-Level Addition

1,200 sq ft

7 Months

2024

THE STORY

New living space had to be built beneath the existing home.

The goal was to create new space below the existing house while the family continued living upstairs. That meant the second floor had to remain fully supported as the ground beneath it was excavated and rebuilt.

The work happened in stages. We first constructed a retaining wall and installed drainage behind it to control the soil below the house. The slab and remaining foundation followed in separate pours once the structure and site were stable.

Rain made the sequence more difficult. As the soil softened, temporary support and daily site conditions had to be watched closely. By working in controlled sections, we kept the home supported and the construction moving safely through the wet season.

The construction story.

BEHIND THE BUILD

Existing rear deck and lower area before excavation work.

Lower-level slab preparation with reinforcing steel and forms.

Concrete placement for the new lower-level slab.

Rear structure opened and temporarily supported during foundation work.

New wall framing taking shape under the existing home.

Sheathing and roof tie-in work at the lower addition.

Interior drywall and paint preparation in the new lower level.

Exterior sheathing and window work near the upper wall.

New stair connection framed inside the lower-level addition.

PHASE 01

Support, Excavation & Drainage

We shored the occupied floor above, excavated beneath the house, and built the retaining wall and drainage system needed to hold back the surrounding soil.

PHASE 02

Foundation & New Structure

We poured the foundation in stages so the soil, retaining wall, slab, and existing home stayed stable throughout. New framing then created the lower-level rooms and the interior stair connection.

PHASE 03

Interior Build-Out & Deck

We completed two bathrooms, a flexible bedroom and office, interior finishes, and a new deck above the addition. The finished layout connects the lower level directly to the main home and backyard.

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The completed addition gives the home a new lower level with two bathrooms, flexible bedroom and office space, an interior stair connection, and direct access to the backyard. Above it, the new deck restores the outdoor space and gives the family a natural extension of the main floor. What began as difficult construction beneath an occupied house now feels like a permanent part of the original home.

Bringing It Together