Existing Floor ADU — Convert an Underused Floor of Your Home Into a Private Unit
An existing floor ADU conversion takes space you already have — a ground-level floor, basement, or upper story — and redesigns it into a fully self-contained dwelling unit with its own entrance, kitchen, bathroom, and living area.
This approach is one of the most cost-effective ways to add an ADU because the space is already enclosed and often partially finished. At Uni Construction, we design floor conversions that work within your existing structure to create a comfortable, code-compliant unit with minimal disruption to your household.
Why Homeowners Choose Floor Conversions
No new construction footprint — your yard and lot coverage stay the same
Lower cost than new construction — walls, roof, and foundation already exist
No setbacks required — conversion ADUs within existing structures are exempt from setback regulations
Not subject to maximum ADU size limits — California law exempts conversions from the standard 1,200 sq ft cap
Great for homes with unused lower levels, bonus rooms, or oversized layouts
What Our Design Process Covers
Converting an existing floor requires careful analysis of the space and surrounding systems:
Separate entrance design: We identify the best location for an independent entry that provides privacy for both the main home and the ADU.
Kitchen and bathroom placement: Plumbing routing is planned to connect efficiently to existing supply and waste lines.
Fire separation: A one-hour fire-rated assembly is typically required between the ADU and the primary residence. We specify materials and assemblies that meet this standard.
Sound insulation: STC (Sound Transmission Class) rated assemblies are designed between the units for noise separation.
Egress compliance: Windows, doors, and exit routes are designed to meet California residential egress requirements.
HVAC separation: We design independent or zoned heating and cooling so each unit has climate control.
Common Conversion Scenarios
Ground-level conversion: Homes built on slopes often have a lower level that is partially below grade. These spaces typically have good ceiling height and direct exterior access, making them strong candidates for ADU conversion.
Basement conversion: Full or partial basements can be converted into ADUs. We address natural light requirements, moisture control, and egress compliance.
Upper-story conversion: Splitting a two-story home so the upper floor becomes an independent unit. This typically involves adding a separate staircase or exterior entrance.
Each scenario has unique structural and code considerations. Our feasibility evaluation identifies the best approach and gives you a clear picture of cost, timeline, and design options before you commit.
Have unused space in your home? Request a free feasibility report and we’ll show you what’s possible.
