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Internal ADU Lower Level

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Expert Internal Lower-Level ADU Conversions in Los Angeles

For many Los Angeles homeowners, the solution to the housing crunch isn’t in the backyard, it’s right downstairs. Whether you have a hillside home with a walk-out lower level, a finished basement, or an underutilized ground floor in a two-story residence, you are sitting on valuable square footage. At Ground Up Builders, we specialize in Internal ADU (Accessory Dwelling Unit) conversions, specifically transforming lower levels into high-yield rental units or comfortable suites for extended family.

Unlike building a new detached structure, an internal conversion works within your home’s existing envelope. This often means faster permitting, lower construction costs, and the preservation of your precious yard space. However, converting a “lower level” comes with a unique set of technical challenges, from waterproofing to soundproofing, that require the seasoned expertise of a general contractor familiar with California’s rigorous building codes.

Modern industrial-style internal ADU lower-level living room with exposed wood ceiling beams and black-framed glass doors in Los Angeles.

What is an Internal Lower Level ADU?

An Internal ADU (often called a conversion ADU) is created by partitioning off a portion of the existing primary residence to create a fully independent living space. When we talk about a “Lower Level” conversion in Los Angeles, we typically encounter two scenarios:

  1. The Walk-Out Basement: Common in hillside properties (like those in Silver Lake or the Hollywood Hills), where the lower floor has at least one wall open to the exterior.
  2. The Ground Floor Conversion: In traditional two-story homes, converting a rec room, garage, or guest suite into a self-contained unit.

Because the structure is already there, the focus shifts from framing and roofing to refinement and separation. We turn “dead space” into a legal apartment with its own kitchen, bathroom, and private entrance.

JADU vs. Standard ADU: Knowing the Difference

Before we swing a hammer, we must determine how your lower level will be classified. This distinction affects everything from the kitchen design to owner-occupancy requirements.

Junior Accessory Dwelling Unit (JADU)

If your lower level conversion is 500 square feet or less and contained entirely within the existing walls of the home, it often qualifies as a JADU.

  • Kitchen: Requires only an “efficiency kitchen” (plug-in appliances allowed, standard stove not required)
  • Bathroom: Can technically share a bathroom with the main house, though we highly recommend adding a private one for rental value.
  • Owner Occupancy: Crucially, JADUs generally require the property owner to live in either the main unit or the JADU.

 

Standard Conversion ADU

If the space is over 500 square feet (up to 1,200 sq ft or 50% of the main home’s living area), it is classified as a standard Attached ADU.

  • Kitchen: Must have a full kitchen with a stove, oven, sink, and prep space.
  • Bathroom: Must have a dedicated, private bathroom.
  • Owner Occupancy: Currently, state law does not strictly require owner occupancy for standard ADUs permitted between 2020 and 2025, offering more flexibility for investors.
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Modern internal lower-level ADU with exposed wood ceiling beams, a compact kitchenette, and an integrated bedroom area in Los Angeles.

The Technical Challenges of Lower Level Conversions

To ensure your internal lower-level ADU is safe, legal, and comfortable, Ground Up Builders focuses on four critical technical pillars:

  • Egress and Fire Safety: We install code-compliant egress windows (minimum 5.7 sq. ft. opening) and Type X fire-rated drywall to ensure safe exits and prevent fire spread between units.

  • Soundproofing and Privacy: To eliminate noise transfer, we use high-density Rockwool insulation and resilient channels to decouple the ADU ceiling from the main floor joists.

  • Moisture and Waterproofing: We apply moisture mitigation barriers to concrete slabs and optimize exterior drainage to prevent “musty” odors and protect your flooring.

  • Ceiling Height Compliance: We ensure all habitable rooms meet the 7-foot height requirement by relocating ductwork or, when necessary, performing structural excavation.

Our Design-Build Process

At Ground Up Builders, we handle the entire project from concept to keys.

Phase 1: Feasibility Study – We measure your lower level to the inch. We check the plumbing stack locations (for the new kitchen/bath) and assess the electrical panel’s capacity to handle a second kitchen.

Phase 2: Architectural Plans & Permitting – We draft the floor plan, ensuring the flow works for independent living. We handle the submission to the Los Angeles Department of Building and Safety (LADBS), ensuring all Title 24 energy standards are met.

Phase 3: Construction – Since we are working inside your home, we prioritize cleanliness. We set up dust barriers and designated entry points to minimize disruption to your daily life upstairs. We handle all rough-ins, inspections, and high-end finish work.

Modern internal ADU featuring white cabinetry, recessed lighting, and a smooth architectural flow between the kitchen and living room.

EXPERT INTERNAL LOWER-LEVEL ADU CONVERSIONS

Transform your underutilized basement or lower floor into a masterfully crafted living suite with our custom internal ADU conversion services. Whether you are seeking a high-end rental unit or a private guest retreat, we turn your home’s existing footprint into a functional reality.

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Compact Lower-Level ADU Studio
Modern industrial-style internal ADU lower-level living room with exposed wood ceiling beams and black-framed glass doors in Los Angeles.
Modern internal lower-level ADU with exposed wood ceiling beams, a compact kitchenette, and an integrated bedroom area in Los Angeles.
Spacious basement ADU conversion featuring polished concrete floors, large factory-style windows, and a full modern kitchen.
Modern internal ADU featuring white cabinetry, recessed lighting, and a smooth architectural flow between the kitchen and living room.
Bright contemporary internal ADU with custom light wood built-ins, a neutral color palette, and an open-concept living area.

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Why Choose Ground Up Builders?

We are Los Angeles natives who understand the intricacies of local zoning.

  • Expertise: Our team includes seasoned project managers and structural experts who understand the physics of hillside and lower-level construction.
  • Transparency: We provide detailed, itemized contracts. You will know exactly what the cost of moving a sewer line or upgrading a sub-panel will be before we start.
  • Quality: We don’t cut corners on the “invisible” stuff like waterproofing and fire safety. We build units that last.
Bright contemporary internal ADU with custom light wood built-ins, a neutral color palette, and an open-concept living area.

Monetize Your Square Footage Today

Don’t let your lower level remain a storage area for holiday decorations. Transform it into a high-value asset that pays your mortgage. Whether for rental income or housing a loved one, an Internal ADU is a smart, sustainable investment.

Ready to see what’s possible in your lower level? Contact us today for a free on-site feasibility consultation.

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What Our Clients Are Saying

“I Recommend Ground Up Builders to my family and friends”
Received consistent updates about everything that was going on. Always had someone to call if I had a question. Everyone involved was very nice. I would recommend Ground Up Builders to my family and friends. Thank you again. Phyllis J.
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Love them! I was referred to them by a friend and am so happy I never have to look for another contractor again. Very professional team, were able to answer all of my questions very kindly and professionally. Morin Z.
“Very satisfied with the work”
Workers were very friendly and worked in a timely manner to make sure job was done on time and every task completed. We were very satisfied with the work, professionalism and attention to detailed offered us. I would highly recommend Ground Up Builders for your next home project.Terrina S.
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Really loved the customer service and efficiency, especially since I have 2 young children. I have already recommended them to my family.Annie G.
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