Combining adjacent condominium units into a single residence presents unique architectural challenges distinct from ground-up construction or single-unit renovation. Structural walls, existing mechanical systems, shared plumbing chases, and building code restrictions on unit modifications all shape what is possible in high-rise residential conversions. A successful combination project preserves or improves sightlines, natural light distribution, and spatial flow while integrating custom millwork, new mechanical zones, and refined material palettes across what was previously two separate living spaces. Architects and builders working on these projects must balance the client’s desire for open, connected spaces with the physical constraints of existing concrete structures and building-wide systems. Strategies for dual-gable mountain residence design demonstrate how thoughtful structural integration can create unified living spaces from discrete building elements, a principle that applies equally to combining adjacent urban condominium units.
Structural Considerations When Combining Adjacent Units
The first assessment in any unit combination project involves identifying load-bearing walls, structural columns, and shear walls that cannot be removed. High-rise condominium buildings typically use reinforced concrete or post-tensioned concrete slabs with concrete shear walls at the core and around elevator shafts. The wall between two adjacent units almost always contains structural elements that transfer lateral loads, which means full removal is rarely possible. Architects must work within the existing structural grid, opening passages through non-load-bearing walls where possible and using enlarged door openings or partial wall removals to create visual connections between formerly separate spaces. The structural concrete walls in the Oceanside Residence were hidden behind drywall and exposed during renovation to give the apartment distinctive character and a sense of the building’s raw construction. This approach of revealing rather than concealing structure has parallels in modernizing midcentury ranch residences, where exposing original framing and masonry adds authenticity to contemporary renovations while preserving the building’s architectural DNA.
Exposing Existing Concrete for Character
Structural concrete walls hidden behind standard drywall finishes can become defining architectural features when exposed. The process involves carefully removing gypsum board and insulation, then surface-preparing the concrete through grinding, patching voids, and applying a clear sealer. Exposed concrete provides thermal mass benefits, absorbing heat during the day and releasing it at night, which can reduce HVAC load in conditioned spaces. The rough texture and natural color variations of poured concrete create visual contrast against smooth finishes like painted drywall, walnut millwork, and glass partitions. This treatment works best in living areas and circulation zones where the concrete reads as a deliberate design element rather than an unfinished surface. In bedrooms and bathrooms, the cold feel and industrial appearance may be less appropriate, so selective exposure based on room function matters.
Working with Existing Plumbing and Mechanical Systems
Combining two units often requires relocating kitchens and bathrooms to new positions within the combined floor plan. This work involves tapping into existing plumbing risers that serve both units, re-routing supply and drain lines, and coordinating with the building management on shutoff schedules. The Oceanside Residence kitchen was completely relocated and enlarged from its original position, requiring new plumbing, electrical, and gas lines run through the slab or along bulkheads. In post-tensioned concrete slabs, core drilling for new plumbing penetrations requires ground-penetrating radar surveys to locate tension cables and avoid structural damage. Mechanical systems often need zoning changes, as the combined unit may now exceed the capacity of one unit’s HVAC system. Adding a second zone with its own air handler and ductwork distributes conditioned air evenly across the expanded floor plan.
Reconfiguring Floor Plans for Open Sightlines
The primary advantage of combining two units is the opportunity to create long sightlines that were impossible within the original subdivided floor plan. In the Oceanside Residence, the studio apartment was converted into a guest bedroom, and a large sliding wall opens the sitting area of the guest room to the main living space. This flexible partition allows the apartment to function as a larger entertaining space when the sliding wall is open and as two separate zones when closed for guest privacy. The two original bedrooms were combined into a primary suite with an enlarged bathroom, walk-in closet, and direct access to the apartment’s ocean-facing windows. The floor plan was organized so that from all areas, including the primary bath and closet, the view toward the Pacific Ocean and Santa Monica Beach remains visible. Design approaches used in notable residences often emphasize this principle of maintaining visual connection to prized views through strategic room placement and transparent partition systems.
Custom Millwork and Built-In Integration
Custom-designed built-ins are central to making combined units feel cohesive rather than like two apartments awkwardly joined. In the Oceanside Residence, the walk-in closet was positioned within the primary suite with a lower division wall that serves a dual purpose: it separates the closet from the sleeping area while supporting audio equipment and light distribution above and a custom credenza and television mount facing the bed. Every built-in element, from the closets and vanities to the kitchen cabinetry and bathroom fixtures, was designed specifically for the combined floor plan. A custom limestone tub was carved from a single piece of stone in Portugal and installed as a centerpiece in the primary bathroom. The kitchen cabinetry from Boffi was paired with custom thin aluminum shelves and a support system for a completely cantilevered kitchen counter, creating a one-of-a-kind workspace. Modern design-build approaches for American foursquare homes similarly demonstrate how custom millwork tailored to existing floor plans produces better spatial outcomes than off-the-shelf cabinetry.
Material Selection for Cohesive Interiors
Material continuity across the expanded floor plan prevents the combined unit from reading as two separate apartments with different finish treatments. Walnut flooring installed throughout the primary suite and walnut veneer applied to all doors and select kitchen cabinets provide a consistent warm tone that unifies the living, sleeping, and dressing areas. The primary bathroom and closet feature spandrel glass and limestone finishes, materials selected to complement the exposed concrete structure while adding refined surfaces where tactile quality matters. Acid-etched glass sliding doors enclose or open the bathroom area to the bedroom, providing privacy when needed while maintaining visual flow. The material palette balances three distinct categories: raw concrete for structural honesty, warm walnut for residential comfort, and cool glass and limestone for the wet areas. This three-material strategy creates visual hierarchy without competing finishes. Lessons from designing smaller family homes emphasize that disciplined material palettes of three to four materials produce more coherent interiors than broad selections of competing surfaces.
| Design Element | Original Condition | Post-Combination Solution | Material | Key Benefit |
|---|---|---|---|---|
| Floor plan | 2 separate units | Single open-plan residence | N/A | Continuous ocean views |
| Guest room | Studio apartment | Guest room + sliding wall | Sliding wall system | Flexible open/closed zones |
| Primary suite | 2 separate bedrooms | Combined bed + bath + closet | Walnut floor, glass, limestone | Ensuite spatial continuity |
| Bathroom | Standard bath | Enlarged with acid-etched glass | Spandrel glass, limestone | Privacy + visual openness |
| Kitchen | Original location | Relocated and enlarged | Boffi + custom aluminum | Cantilevered counter feature |
| Structural walls | Hidden behind drywall | Exposed concrete | Poured concrete | Industrial character + thermal mass |
Lighting, Views, and Spatial Continuity
The most successful unit combinations preserve or enhance natural light penetration across the entire expanded floor plan. The Oceanside Residence, located on the seventeenth floor, captures panoramic views from the city skyline across Santa Monica Beach to the Pacific Ocean and Malibu. The floor plan was arranged so that the primary suite, living area, kitchen, and even the bathroom and closet all have direct or angled sightlines toward these views. Interior partitions use transparent or translucent materials rather than solid walls wherever possible to allow daylight to travel deeper into the plan. The bathroom’s acid-etched glass sliding doors transmit light while obscuring direct sightlines, and the sliding wall between the guest room and living area permits borrowed light to reach what would otherwise be an interior zone when closed. Designers of contemporary mountain home designs apply the same principle of maximizing view corridors and natural light through strategic placement of glazing and open-plan organization, proving that the strategy works across dramatically different geographic settings.
Combining two condominium units requires coordination between the design team, structural engineer, building management, and local permitting authorities. The Oceanside Residence was completed in 2015 by a Los Angeles and Paris-based architecture firm with extensive experience in renovation, restoration, and adaptive reuse of existing structures. The project covers 155 square meters or approximately 1,665 square feet, a common size for combined units in high-rise residential buildings where two smaller apartments are merged into one larger residence. The same principles of structural assessment, open floor plan design, custom millwork integration, disciplined material selection, and view optimization apply whether the project is a beachfront condo combine or a lakeside home design and construction project where site conditions, existing structure, and client requirements shape the final architectural solution.