Compaction (construction)

Densification (Construction) - Architectural densification (in-place densification) refers to the intensification of development on already developed plots or in existing residential areas. It includes adding stories, converting attics, building on vacant lots, filling in gaps between buildings, and repurposing existing structures. Densification is the central tool of inner-city development and enables the creation of additional living space without sealing off new areas on the city outskirts.

Forms of infill development

The most common forms of densification are: Adding stories - Adding one or more stories to an existing building. Attic conversions - Converting an unused attic space into living space. Rear development - Construction of a new building behind an existing one, with access via the front property. Filling in vacant lots - Development of undeveloped plots between existing buildings. Side extension - Lateral expansion of an existing building. Conversion - Conversion of commercial space into residential space. Each type has specific building code requirements and economic potential.

Particularly interesting for property owners is the combination of multiple densification measures: An apartment building with an unused attic, an underutilized backyard, and an oversized garage offers three densification opportunities that-individually or in combination-can create significant additional living space. The challenge lies in meeting all building code requirements simultaneously: setback distances, parking space requirements, and development obligations are the most common bottlenecks.

Building Code Framework

The permissibility of infill development depends on planning law: Within the scope of a zoning plan (§ 30 BauGB), the floor area ratio (FAR), floor space index (FSI), and building lines determine the extent to which densification is permitted. In unplanned inner-city areas (§ 34 BauGB), the project must blend in with the character of the immediate surroundings-adding stories is permitted if comparable building heights exist in the neighborhood. Adding stories and attic conversions may be exempt from approval if they fall under the simplified procedure according to the Bavarian Building Code (BayBO). Setback distances, parking space requirements, and fire safety are the most common hurdles.

Since 2022, the Building Code has also allowed for expanded opportunities to develop vacant lots in inner-city areas (Section 13b BauGB - Inner-City Development Zoning Plan). This enables municipalities to develop vacant lots more quickly and through simplified procedures under planning law. For owners, this means: It is worth checking with the municipal administration to see if a planned infill project can be supported or expedited by current urban planning programs.

Economic Considerations of Infill Development

The economic viability of an infill project depends on three factors: construction costs, the achievable added value, and financing costs. As a general rule: The more expensive the location, the more attractive infill development becomes-because the increase in value resulting from new space in sought-after neighborhoods often significantly exceeds the investment.

A practical calculation example: An owner in Nuremberg’s Südstadt district owns an apartment building with an unused attic space. Converting this space creates 120 m² of living area. Construction costs are around 300,000 euros. The finished attic space can be sold for 5,000 euros per square meter-yielding 600,000 euros. The net profit before taxes is around 300,000 euros; additionally, the property remains in the owner’s possession, and the total building value increases permanently.

Alternatively, an addition can be used for rental purposes: Two new 60-square-meter apartments in central Nuremberg command base rents of approximately 1,100 euros per month per unit-equivalent to an annual base rent of 26,400 euros. With construction costs of 280,000 euros, this results in an initial gross rental yield of around 9%, which is very attractive in the current market environment. Important: This calculation must be adjusted for taxes, reserves, and financing costs.

Practical Tip for Property Owners in Nuremberg

We recommend that owners in the Nuremberg metropolitan region have the densification potential of their property assessed. Particularly in neighborhoods such as Gostenhof, Johannis, Südstadt, and Maxfeld, there are numerous buildings with unused attic space or backyard lots that could be developed. Adding a floor can increase the building’s value by 20-30%. The City of Nuremberg actively promotes infill development as part of its inner-city development strategy.

Submit a preliminary building inquiry to the Building Regulations Office (cost: approx. 200-500 euros) to determine with certainty whether your infill project is eligible for approval. This preliminary inquiry is a sensible investment before the actual planning phase-it provides legal certainty and prevents expensive architectural and engineering services from being performed for a project that is not eligible for approval. We support property owners in identifying and economically assessing densification potential.

Frequently Asked Questions

Do I need a building permit for an addition?

Generally, yes. An addition changes the building’s height and is therefore subject to approval. In Bavaria, the addition can be processed through the simplified approval procedure (Art. 59 BayBO) if the building is not a special-purpose structure. The approval process takes approximately 6-10 weeks in Nuremberg. Check the following in advance: setbacks from neighbors, proof of parking space (or waiver if applicable), and the structural load-bearing capacity of the existing building.

How much does an addition cost?

The costs depend on the construction method and scope: An addition using wood-frame construction costs approx. 1,800-2,500 euros/m² of living space, while solid construction costs approx. 2,200-3,000 euros/m². Added to this are planning costs (architect, structural engineer: approx. 10-15% of construction costs) and permit fees. For an 80 m² addition in Nuremberg, the total costs are approx. 200,000-280,000 euros - the achievable increase in value is often higher, especially in sought-after inner-city locations.

Does the neighbor have to agree to the densification?

The neighbor does not have a right of veto, but their rights must be protected: setback distances (Art. 6 BayBO), lighting, and ventilation must not be unreasonably impaired. The neighbor is involved in the permitting process and may raise objections. If setback distances are not met, the developer needs a waiver (Art. 63 BayBO) or the neighbor’s written consent. Early communication with the neighbor avoids conflicts and delays-a cooperative approach is almost always faster and cheaper than a legal dispute.

What funding is available for infill development projects?

Several funding sources are generally available for infill development measures: The KfW supports energy-efficient construction for building extensions and attic conversions if the new section meets specific energy efficiency standards (KfW Efficiency House 40 or 55). The Bavarian Housing Support Program subsidizes the creation of new rental housing under certain income and rent control requirements. The City of Nuremberg offers its own advisory services as part of the municipal housing construction support program. We recommend checking all three levels (federal, state, and municipal) for current subsidy programs before construction begins-an experienced architect or energy consultant can help you put together the optimal mix of subsidies.

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