Renovating an interior space within an existing concrete building presents a distinct set of constraints. Unlike new construction, where the architect controls the structural layout from the start, a renovation must accept the existing columns, beams, and shear walls as fixed conditions. The most successful approach treats these structural elements not as obstacles to be hidden but as the foundation of a design strategy. By working with the existing concrete frame rather than against it, designers can create functional, character-rich interiors with minimal material addition and waste generation. This approach connects directly to how architects drive building envelope performance, where the existing structure becomes the starting point for all subsequent decisions.
Understanding the Concrete Wall-Slab Structure
Concrete wall-slab structures, also called reinforced concrete (RC) bearing wall construction, use cast-in-place concrete walls and floor slabs as the primary load-bearing system. Unlike frame structures where columns and beams carry loads to the foundation, wall-slab systems distribute loads through continuous vertical walls that also serve as room boundaries. This method is common in mid-rise apartment buildings constructed from the 1960s through the 1990s in Japan, Europe, and parts of North America.
Why Concrete Walls Constrain Renovation
The defining characteristic of a wall-slab structure from a renovation standpoint is that the concrete walls and beams are structural and cannot be removed or relocated. This creates several constraints:
- Room shapes and sizes are largely fixed by the original structural grid
- Penetrating a concrete wall for new doors or windows requires engineering review and typically permits from the building authority
- Wall surfaces are hard, dense, and cold. Acoustic treatment and thermal comfort require careful planning
- MEP (mechanical, electrical, plumbing) runs must follow existing pathways or be surface-mounted
Rather than fighting these constraints, the renovation strategy that yields the best results treats the concrete structure as terrain (an existing landscape to read and respond to). This philosophy is explored in depth by architects who blend heritage conservation with modern design, where existing fabric is respected rather than erased.
Mapping the Structural Grid
Before any design work begins, the renovation team should document the exact location, thickness, and condition of every concrete wall and beam in the unit. A typical wall-slab apartment from this era has walls 150 to 200 mm thick and beams 300 to 500 mm deep. The following table summarizes common wall-slab conditions and their renovation implications:
| Structural Element | Typical Dimension | Renovation Constraint | Design Opportunity |
|---|---|---|---|
| Bearing wall | 150-200 mm thick | Cannot be removed or opened without engineering | Use as natural room divider, exposed finish |
| Concrete beam | 300-500 mm deep | Creates low headroom zones, cannot be altered | Build low furniture under beam to define zones |
| Floor slab | 150-200 mm thick | Limited recessing for plumbing; no slab penetrations | Surface-mount conduits, use floor steps for level change |
| Sleeve wall (partial wall) | 100-150 mm thick, partial height | Cannot be moved but does not extend to ceiling | Creates visual separation while allowing light and air above |
Furniture as Partition: Low-Height Plywood Strategy
One of the most effective techniques for renovating within a concrete shell without building new walls is to use low-height furniture as space dividers. Rather than constructing new partitions that require fixing into the concrete slab and finishing with plaster, the designer places freestanding plywood cabinetry under existing beams or along interior zones. These furniture pieces serve both as storage and as spatial dividers, defining room boundaries without permanently altering the structure.
Placement Logic: Along the Beam Versus Across the Beam
The placement of low-height furniture relative to the concrete beam determines how it functions spatially.
- Furniture placed along the beam: acts as a partition that divides the space. The beam defines one edge of a zone, and the furniture extends that line to create a distinct room-like area. This arrangement works well for creating private zones such as sleeping areas or study nooks.
- Furniture placed independently of the beam: acts as a switch that redirects circulation. The furniture becomes an island that changes the flow of movement through the room, creating two separate paths around it. This works for living areas where you want defined zones without closed doors.
Shina plywood, a lightweight but strong Japanese hardwood plywood, is a common material choice for these furniture pieces. It can be cut into precise shapes, sanded smooth, and finished with a clear oil or wax to show the natural wood grain. Standard sheets of 12 mm to 18 mm thickness are sufficient for shelving and cabinetry of moderate span. This technique of working with the existing structure’s geometry is a hallmark of how heritage conservation meets high-performance design, where minimal interventions define space without overwhelming the original fabric.
Spatial Zoning Without New Walls
In a typical wall-slab apartment, the concrete bearing walls naturally divide the unit into two zones. On one side of the bearing wall, a large open area can become the primary living space. On the other side, smaller zones defined by the wall automatically serve as private rooms. The renovation challenge is to make the large open space feel organized without building new partitions, while the smaller private zone must accommodate sanitary spaces and bedrooms within tight dimensions.
Creating Hierarchy in the Open Zone
Within the large studio space, four techniques create spatial hierarchy without walls:
- Floor steps: raising or lowering a section of flooring by 150 to 300 mm signals a change in use. A stepped-up area becomes a dining zone; a sunken area becomes a living room. No walls needed.
- Ceiling height variation: the existing beams create natural zones of lower headroom. Placing the dining table or desk under a beam uses the reduced height to define that zone as functional rather than lounging.
- Sleeve walls: where they already exist, these partial-height concrete walls provide visual separation between zones while allowing light and air to pass over the top. Painting or finishing them differently than the full-height walls emphasizes their role as zone markers.
- Furniture alignment: arranging sofa, shelving, and cabinetry along a consistent sightline creates an implied wall that the eye reads as a boundary even though the space remains physically open.
These strategies allow the large space to accommodate living, dining, work, and sometimes sleeping functions within the same volume without feeling cluttered. The approach mirrors how civic design integrates with high-performance building principles, defining zones through spatial cues rather than solid barriers.
Material Reduction and Future Renovation Cycles
A guiding principle of working within an existing concrete structure is minimizing the addition of new materials. Every new wall, layer of drywall, or built-in cabinet represents materials that will eventually need removal, disposal, or replacement during the next renovation cycle. The less you add to the existing shell, the less waste future renovations will generate.
Concrete as the Finished Surface
Leaving concrete walls and beams exposed eliminates the need for drywall, plaster, paint, and the labor to install them. The concrete becomes the finish material, with its texture, color, and formwork marks serving as decorative features. This choice reduces renovation material use by an estimated 15 to 25 percent compared to a full finish-out. The concrete surface must be cleaned and sealed, but this is a one-time treatment rather than a layered system that will need replacement.
| Renovation Approach | New Materials Added | Waste at Next Reno | Labor Intensity | Design Flexibility |
|---|---|---|---|---|
| Full wall cover with drywall | High (all surfaces concealed) | High (all must be demolished) | High | Low (hard to change layout) |
| Partial wall cover with selective finishes | Moderate (some surfaces exposed) | Moderate (partial demolition) | Moderate | Moderate (some walls movable) |
| Furniture-as-partition (minimal approach) | Low (only freestanding elements) | Low (furniture relocatable) | Low | High (reconfigurable layout) |
The furniture-as-partition approach reduces waste at the next renovation cycle because nothing is permanently attached to the structure. Furniture can be reused, donated, or disposed of separately from the building fabric. This aligns with the material reduction priorities documented in the architects’ role in passive house design, where minimizing material use and embodied energy are central performance goals.
Designing for Lived-In Environment Rather Than Static Layout
The most ambitious goal of working with an existing concrete structure is to create an environment-like living space (a place where the inhabitants can read the terrain of the interior and adapt their use of it over time). Unlike a conventionally finished apartment where every room has a fixed function, a concrete-exposed interior with freestanding furniture invites the occupants to reinterpret the space as their needs change.
This approach requires a shift in how the designer thinks about storage. Instead of built-in closets and cabinets that lock the floor plan into specific uses, freestanding storage furniture that reminds inhabitants of where they are within the larger volume creates a more flexible environment. A tall cabinet in one position defines a dressing area; moved to another position, it becomes a room divider for a guest sleeping zone. The entire small living space becomes usable in different configurations at different times.
Soft furniture (upholstered seating, curtains, rugs, cushions) is placed against the hard concrete terrain to create pockets of warmth and comfort. This juxtaposition of hard and soft, permanent and movable, structural and applied, is what gives the interior its character. The concrete provides the constant; the furniture provides the variable. The synthesis of these methods is explored in urban architecture that integrates passive standards and sustainable design, where the existing structure is leveraged rather than replaced.
Renovating within an existing concrete wall-slab structure does not require fighting against the constraints. By reading the concrete walls and beams as terrain, placing low furniture strategically under beams, using floor steps and sleeve walls to define zones, and leaving the concrete exposed as the finished surface, designers create interiors that are materially efficient, spatially rich, and adaptable to future needs. The furniture-as-partition strategy reduces both first-cost and end-of-life waste, making it a sound approach for anyone renovating an apartment in an older concrete building.