Revitalizing Heritage : Retrofitting a historic residential building to meet future energy standards

Project Type

Energy Retrofit & Building Performance Analysis · Residential

Date

July 2023

Location

Berlin, Germany

This project explores the transformation of a large, abandoned industrial land parcel located in the heart of a dense metropolitan city. Once an active textile mill, the site had been left vacant for years, creating a physical and social void within an otherwise vibrant urban core.

Rather than treating the site as an isolated redevelopment opportunity, the proposal positions it as a city-making intervention, one that reconnects fragmented urban fabric, relieves surrounding pressure points, and introduces new public life into the city center.

WHERE HISTORY MEETS PERFORMANCE

"Preserving the past doesn’t mean standing still—sometimes it’s about upgrading wisely, not replacing recklessly."

Existing Condition of the building

A historic building, out of step with today’s standards.

Tegeler Strasse 35, built in 1910, is architecturally rich but technically outdated. The building suffers from high heat loss, uninsulated walls, and inefficient windows, while natural ventilation and old heating systems dominate energy use. Energy analysis shows that transmission losses account for the majority of its inefficiency, placing the building at Energy Class E with a high primary energy demand.

existing envelop details _11zon_11zon.jpg

Existing building envelope and energy analysis

Existing technical condition of the building

THE RENOVATION GOALS

Balancing heritage with performance

The renovation aims to transform the century-old building into a sustainable, energy-efficient asset while preserving its historic character. The core objectives:

Energy Efficiency: Reduce transmission losses and lower energy demand through envelope upgrades and renewable integration.
Sustainability & Ecology: Minimize CO₂ emissions and implement responsible resource management, including rainwater harvesting.
Technological Integration: Introduce smart systems to optimize heating, lighting, and overall user comfort.

THE RENOVATION CRITERIA

A data-driven approach

Interventions were evaluated through a weighted decision matrix across four categories: Social, Economic, Technological, and Ecological. Key criteria included:

Investment & ROI: Cost-effectiveness and payback period
Flexibility & Tenant Impact: Legally and practically feasible solutions
CO₂ Reduction & Energy Class: Maximize sustainability gains
Durability & Convenience: Long-lasting materials and improved comfort

STRATEGIC INTERVENTIONS

Designing performance, not prescribing it

To reach Energy Class B while maintaining economic feasibility, the retrofit strategy followed a two-layered approach. Rather than relying on standard specifications, each intervention was tested and refined through CAALA simulations, allowing performance, material impact, and return on investment to guide the design.

Reworking the Envelope

Where the biggest losses became the biggest opportunities.

The building envelope emerged as the primary lever for reducing energy demand. Multiple retrofit scenarios were modeled and compared to identify solutions that balanced thermal performance with ecological responsibility.

High-Performance Windows

Different glazing systems were tested to replace the inefficient mid-century windows. Both aluminum and wooden triple-glazed frames achieved a U-value of 0.9 W/m²K, a significant improvement over the existing condition. However, simulations revealed that wooden frames carried a substantially lower embodied carbon footprint. This option was selected to preserve the building’s character while achieving a 12% reduction in primary energy demand.

Façade Insulation Strategy

To address the uninsulated exterior walls, various insulation systems were evaluated. The analysis identified a mineral wool and natural stone assembly (25 cm) as the most effective solution—reducing the wall U-value from 1.40 W/m²K to 0.142 W/m²K. This intervention alone brought the building close to near-passive performance levels.

Roof & Basement Sealing

Closing the thermal envelope was critical. Simulations confirmed wood fiber insulation as the most suitable solution for both the attic floor and basement ceiling. Beyond its ecological benefits, this measure eliminated major thermal bridges, reducing primary energy demand by an additional 5–6% per surface.

Ecological Stewardship

Closing the resource loop:

An 18-ton underground rainwater harvesting system was integrated into the site to collect and reuse rainwater for landscaping and other non-potable uses. This reduces freshwater demand and supports a more resource-efficient building system.

Technological Integration

Optimizing performance through smart systems

While architectural interventions reduced the building’s baseline energy demand, digital systems were implemented to optimize operational performance and integrate renewable energy generation.

A 25.6 kWp rooftop photovoltaic system, designed for the available 124 m² roof area, is paired with battery storage to increase on-site energy utilization and reduce grid dependency. The system is projected to generate over 25,000 kWh annually.

Heating control is upgraded through Bosch digital thermostats connected to a centralized smart building controller. By regulating heating based on real-time occupancy and room conditions, the system prevents overheating and improves thermal efficiency, resulting in estimated annual gas savings of 59,240 kWh.

To reduce standby and auxiliary energy loads, smart sockets and radar-based motion lighting were installed in common areas, ensuring electrical consumption is limited to periods of active use.

PERFORMANCE ANALYSIS AND IMPACT

Heritage preserved. Efficiency unlocked.

The retrofit transforms the building from a century-old energy drain into a high-performance building, delivering measurable ecological, economic, and technological benefits.

Energy & Carbon Reduction

Sealing the envelope and integrating a 25.6 kWp PV system cut primary energy demand by 52%, elevating the building from Energy Class E to B. Combined strategies also reduce annual CO₂ emissions by 47%, contributing directly to Berlin’s climate goals.

Financial Viability (ROI)

Sustainability here is also economically sensible. Operational savings of approximately €33,000 per year from gas reduction and self-generated electricity create a payback period of 12 years, proving that high-performance retrofits can be both responsible and profitable.

Smart Readiness

Digital upgrades prepared the building for future grids. The Smart Readiness Indicator (SRI) increased from 19.4% to 31%, reflecting enhanced building intelligence through automated heating, smart thermostats, and motion-sensor lighting—transforming the structure into a responsive, communicative asset.

DESIGNED TO LAST

The most sustainable building is one that continues to perform.

€600,000 total investment, achieving a return on investment within 10–12 years, demonstrating long-term financial feasibility for historic retrofits.

25% of the building’s total electricity demand is met through on-site renewable generation using the proposed renovation strategy.

Up to 57% reduction in energy losses, resulting in significantly improved overall energy performance and efficiency.

Digital and smart building systems deliver high impact at relatively low cost, offering substantial energy savings with minimal disruption.