GENERAL INFORMATION RENOVATION PROCESS RETROFIT SOLUTIONS EVALUATION

Railway worker house

via Castel Roncolo

39100

Bolzano, Italy

Owner

Alexandra Troi

User

Alexandra Troi

Contact Details

Alexandra Troi

Eurac Research

alexandra.troi@eurac.edu

Other Information

Related publications
Information comes from the building owner (Stephan Vale and Alexandra Troi) and the architects (in-arte). The documentation of the step-by-step refirbishment for the PHPP conference was done within PNRR project iNEST, Air-tightness testing was done within

Bright, spacious rooms, terrazzo flooring in the corridor, and a veranda with a beautiful, delicate metal structure – from the moment one enters the stairwell of the old railway workers’ house in Bolzano, the atmosphere of the many stories this building can tell becomes tangible. Step by step, one of the apartments has been and is being renovated: first, the distinctive wolf’s-mouth windows were repaired and upgraded; after the crisis winter, the external walls were insulated and a ventilation system installed to protect future occupants from sharply rising heating costs. The next step towards climate neutrality will be the installation of a photovoltaic system.

GENERAL INFORMATION RENOVATION PROCESS RETROFIT SOLUTIONS EVALUATION

Energy performance

94,52 kWh/m2.y

Climate Zone dfa

Altitude 256 m a.s.l.

HDD 2570

CDD 207

Protection level Not listed

Conservation Area:
No

Level of Protection:

Building age 1900-1944

Year of last renovation:
2023

Year of previous renovation:
2017

Building use Residential (urban)

Secondary use:
NA

Building occupancy:
Permanently occupied

Number of occupants/users:
2

Building area Net floor area [m²]: 83,4

Building typology:
One apartment in the apartment block

Number of floors:
1

Basement yes/no:
Yes

Number of heated floors:
1

Gross floor area [m²]:
107,0

Thermal envelope area [m²]:
240,0

Volume [m³]:
375,0

NFA calculation method:
NGF (de)

Construction type

Brick masonry wall

External finish:
Rendered

Internal finish:
Plastered (on hard)

Roof type:
Pitched roof

+ MORE - LESS

RENOVATION PROCESS

Architecture

BUILDING DESCRIPTION

The building is located in the historic centre of Bolzano and was constructed in the late 1920s as housing for railway workers employed by the Italian railway company. It is a multi-family residential building comprising approximately 35 dwelling units, currently organized as a condominium. Although not formally listed, the building exhibits architectural and typological features worthy of preservation and is situated within a historically protected urban context. The intervention concerns a single apartment, undergoing a stepwise refurbishment process aimed at improving energy and comfort performance while respecting the building’s historic character.

State of repair

Conditions of the envelope

Before the intervention, the apartment was in a condition typical of a historic building that had undergone only limited alterations, with most original construction features still intact. Until 2005, the flat had been barely modified and was not connected to the central heating system; an individual gas boiler was added only in 2010. Energy performance and indoor comfort were inadequate, as windows, building envelope, and building services no longer met contemporary standards, although no major structural deterioration was observed.

HERITAGE SIGNIFICANCE

ELEMENTS WORTHY OF PRESERVATION

The building includes several architectural and construction elements of value that are worthy of preservation. In particular, the original typological layout, the historic plastered façades, and the original box-type windows with “Wolfsrachen” detailing, representative of the construction quality of the period, should be conserved. Additionally, historic materials and finishes, as well as the building’s relationship with the historic urban context, are considered key elements contributing to the overall heritage value.

Heritage Value Assesment

The building has notable cultural significance as a representative example of late-1920s residential housing for railway workers in Bolzano. Its architectural value lies in the clear typological layout, balanced façade composition, and preserved original construction details, such as the historic windows. From an aesthetic perspective, the building contributes to the formal continuity of the historic urban fabric, surrounded by buildings protected as ensembles. Its social value is linked to the history of workers’ housing, while its technological value reflects traditional, robust construction techniques that remain durable and adaptable, now enhanced through compatible energy retrofit interventions.

Aim of retrofit

Renovation

The aim of the retrofit is to significantly improve the energy performance and indoor comfort of the dwelling unit while reducing energy demand and related emissions, in full respect of the architectural and typological values of the historic building. The intervention seeks to demonstrate the feasibility of a stepwise energy refurbishment approach applied to individual apartments within historic multi-family buildings, using compatible, reversible, and technically robust solutions that ensure durability, hygrothermal safety, and high indoor environmental quality.

Lessons learned

The project demonstrated that deep energy retrofit is feasible even at the level of a single dwelling unit within historic multi-family buildings, despite decision-making constraints related to multi-ownership. A key lesson is the importance of a stepwise and integrated approach, supported by hygrothermal analysis, detailed thermal bridge assessment, and close coordination between envelope and building services. The use of compatible internal solutions and capillary-active materials proved effective in balancing energy efficiency, building safety, and heritage conservation. The project also highlights the value of in-use performance verification to validate calculated results.

Tools used

Was the renovation process done following a specific methodology? PHPP, Delphin, ProCasaclima HT, Thermcalc

RETROFIT SOLUTIONS

External Walls

Brick masonry

The solid brick wall, 60 cm thick and plastered on both the interior and exterior sides, was upgraded as part of the energy retrofit by applying 16 cm of internal wood fiber insulation. This was achieved by combining a 10 cm panel with a 6 cm panel. Particular attention was paid to ensuring a full-surface adhesive installation of the insulation in order to completely avoid any rear ventilation and to allow the wood fiber insulation to fully exploit its capillary-active properties. The airtight connection to the floor slab was also carefully executed. At the junction with the floor, where heating pipes run (previously installed surface-mounted), the inner 6 cm insulation layer was omitted over a height of 10 cm, creating a recess for routing the services, which was subsequently finished with plaster.

The wall was insulated from the inside, not only because, in the renovation of a single apartment within a multi-family building, this is effectively the only feasible approach, but also because it allows the characteristic external plaster to remain visible and unchanged.

U-value (pre-intervention) [W/m2K]: 1,185 W/m²K U-value (post-intervention) [W/m2K]: 0,2 W/m²K

More Details

Original wall build-up

Plaster - Plaster:
50 mm

Brick - Full bricks:
570 mm

Plaster - Plaster:
50 mm

Retrofitted wall build-up

Plaster :
50mm

Brick - Brick masonry:
570 mm

Plaster - Plaster:
15 mm

Other - glue:
5 mm

Insulation - Woodfiber:
160 mm

Plaster :
50 mm

Windows

Standard WIndow

The renovation upgraded the windows’ performance through repair and retrofit while preserving their historic character (e.g., box-type windows with the “Wolfsrachen” detail). It significantly reduced overall Uw (e.g., box-type windows from 2.1 to 1.05 W/m²K) without changing the original typology.

The intervention is conservation-compatible because it preserves the building’s historic features by refurbishing and upgrading the original windows (e.g., box-type windows with the “Wolfsrachen” detail) rather than replacing them.

03_BZVALEpdf230602_Detail Fenster.pdf

Existing window U-value Glass [W/m2K]: 2,1 New window U-value Glass[W/m2K]: 1,25 Existing window U-value Frame [W/m2K]: 2,1 New window U-value Frame [W/m2K]: 1,25

More Details

Existing window type	Casement window
Existing glazing type	Single
Existing shading type	Outer shutter
Approximate installation year	1900

New window type	Casement window
New glazing type	Double
New shading type	NA
New window solar factor g [-]	0,56

Other interventions

ROOF

The intervention insulated the ceiling towards the attic with about 20 cm of insulation, achieving a final U-value of about 0.16 W/m²K.

The intervention is generally conservation-compatible because it is carried out from the inside and does not change the roof geometry or exterior appearance. Compatibility mainly depends on correct installation and detailing that avoids discontinuities or interference with valuable elements.

U-value (pre-intervention) [W/m2K] 1.185 U-value (post-intervention) [W/m2K] 0.2

More Details

Original roof build-up

Brick :
450 mm

Plaster :
50 mm

Retrofitted roof build-up

Brick :
450 mm

Insulation - Woodfiber:
200 mm

Plaster :
15 mm

HVAC

VENTILATION

The renovation involved changes to building services, including the installation of a mechanical ventilation system to complement the internal insulation retrofit. This upgrade aims to ensure adequate air exchange and better control of humidity and indoor air quality.

The intervention is generally conservation-compatible because it adds an internal building-services system without changing the building’s exterior appearance or key architectural features. As this is a conventional solution, compatibility mainly depends on discreet integration and minimally invasive service routes.

More Details

Original roof build-up	New ventilation system
Type ventilation system	Decentralized
Type flow regime	NA (Natural)
Heat recovery	No
Humitidy recovery	No
Nominal power	- kW
Electric power	0,02 kW
Control system	-

Energy Efficiency

Energy Performance

Energy performance certificate: Italian EPC, "Attestato di Prestazione Energetica"
Voluntary certificates: No

Energy Use

Heating
Primary Energy 94,52 kWh/m2.y

Documents:

231229_APETroiRunkelsteinstraße.pdf

Italian EPC

Consumption_estimation_After: 94,52 kWh/m2.y

Primary Energy
Consumption_estimation_Calculation_method: Steady state simulation (e.g. EPC, PHPP)
Consumption_estimation_Including_DHW: Yes
Consumption_estimation_After: 94,52 kWh/m2.y

Costs

Financial Aspects

Final cost of the retrofit: 59.000€

Investment Costs

Total investment costs
59.000€ (total)

Running Costs

Lifecycle cost
No

Environment

Greenhouse Gas Emissions

Methodology_used: LCA

Life Cycle Analysis

Methodology_used: One-click LCA tool