school extension and renovation gröhrmühlgasse

analysis of the competition site
the building ensemble of gröhrmühlgasse impresses with two dominant structures from different construction and stylistic periods, harmoniously located along the jointly adjacent park.
the burkhard villa, a listed building designed in the “style of” [historical reference], features generous ceiling heights and almost stately room dimensions. for its use as school space, this room offer raises questions regarding the “proper” allocation of uses.
the 1980s school building, designed as a hall school, is considered architecturally valuable due to the conceptual clarity and the aesthetic dominance of the structural system, aside from certain structural modifications likely added during prior adaptations.
the existing plot is just large enough to geometrically accommodate the newly required triple gymnasium. the additional required volume demands an exact and respectful positioning and articulation of the new building, ensuring the independence of the two existing structures and maintaining a harmonious scale transition to the neighboring houses.

concept 81><20
the ensemble—burkhard villa, 1981 school building, and park—remains unchanged. the schoolyard, important for breaks and events, continues to serve as the main access to the school grounds.
the villa is repurposed as a pedagogical “control center,” connected to the school buildings via a first-floor bridge. existing spaces are used without substantial intervention as work areas for teachers and administration.
the 1981 building undergoes refurbishment: spatial organization is reorganized to follow the structural system. skylight bands are removed according to the concrete structure and glazed to provide natural light to central areas. bright surfaces reflect light and alter the currently somewhat dark character of the multi-storey hall.
part of the basement of the 1981 building is modified via a structural intervention, lowering the floor in the former ancillary gym rooms by 50 cm to increase ceiling height.
demolition of the existing gym areas clears the site for the future triple gymnasium and additional pedagogical spaces in the new building.
the fully underground yet naturally lit new gym areas are overbuilt by a three-storey volume, designed with respect for the surrounding single-family houses. with forward terraces, the large volume steps back from the street and northern boundary over three floors, a respectful gesture to the neighbors.
the new building is deliberately one floor lower than the 1981 structure, responding to the differentiated height sequence of the two existing buildings, including on the west side.

functional arrangement
school access remains unchanged.

level 0 (former basement)
locker rooms are organized within designated fire compartments.
all artistic and scientific areas are located in the lowered existing building and the adjacent new building around a shared workshop yard.

level 1
entrance and public zones of the school are located here.
old and new buildings are integrated into a continuous functional sequence.
library, multipurpose room with adjacent music room, dining hall, etc., provide space for readings, events, it courses, music lessons, and after-school care.
staircases and bridges allow areas to be separated and used externally.

levels 2 + 3
spaces for humanities and language labs are accommodated in both existing and new buildings.
reorganization of the historic building offers open core zones as additional pedagogical space.

open space and parking
the ensemble of burkhard villa, 1981 school building, and park remains unchanged; the schoolyard continues as the main access and central gathering area.

terraces and courtyards
terraces of the new building allow outdoor teaching directly adjacent to classrooms.
for the 1981 building, outdoor classrooms are created on level 3, with additional activation of level 2.
a lowered west section provides natural daylight to the triple gym and invites outdoor play and bouldering.

parking
most required parking spaces are located in the northern part of the plot. additionally, two barrier-free spaces are positioned between the main and accessible entrances.
bicycle parking is proposed in the schoolyard near the main entrance.

gymnasium overbuild
the new triple gym is located west of the existing building and below ground level. a continuous excavation support using bored piles is planned; for this reason, the gym is set back 1.75 m from the existing building.
the three-storey overbuild of the gym (span approx. 22.30 m) uses staggered transverse partition walls (approx. 8.85 m spacing) to form load-bearing “truss structures,” spanning the gym without beams. vertical loads from slabs are suspended into the wall panels and transferred “via diagonals” to side columns of the gym; resulting horizontal tensile forces within slabs are short-circuited. this allows gym overbuilding with minimal structural height and economic efficiency.

intervention in the existing structure
in part of the existing building, floors of the workshop rooms (level 0) are lowered by 48 cm to achieve desired ceiling heights. this requires new foundations for the supporting columns.
individual foundations for the existing columns are constructed using dsv methods. after temporary shoring, the existing columns are removed at level 0, and new, deeper reinforced concrete foundations and longer columns are installed according to the existing grid. the floor structure, including insulation and sealing, is then constructed.
this method allows reuse of the existing structure, being more economical than a complete rebuild.

fire protection
fire safety planning considers the specific use of the school with attached staff facilities. applicable regulations include oib guideline 2 (2019 – fire protection), oib guideline 4 (2019 – accessibility and safety), and the workplace regulations (astv).
the building is classified as class 4 school building under oib 2019 criteria, based on height and number of floors.

energy concept
heating is supplied via district heating. well water can be used for cooling.
heat is distributed via low-temperature underfloor heating; the same system can provide cooling without the heat pump (change-over).
during heating, supply air is pre-tempered via high-efficiency heat recovery.
to prevent summer overheating, supply air is cooled directly via well water, and partial building activation can be applied. air is supplied pre-tempered (warm/cold) to classrooms, preventing drafts, then flows via transfer openings to corridors and is extracted in locker and sanitary areas.
this ensures optimal air exchange and low co₂ concentration.
high-efficiency insulation prevents cold surfaces, ensures comfort, and minimizes energy use. glazing achieves 0.6 w/m²k; slender frames and large panes yield uw/ucw < 1.0 w/m²k.
compact design with massive concrete slabs (no suspended ceilings) provides sufficient thermal mass to prevent rapid heating and store nocturnal coolness. mechanical ventilation can operate as night ventilation during heat periods; alternatively, window ventilation can be used, with classroom-wise system shutdown. cantilevered balconies, roofs, or building elements combined with external shading prevent overheating, protect facades, and allow easy cleaning.
large trees shade significant facade areas in the schoolyard. a photovoltaic system can be installed on the roof of the 1981 building within existing solid parapets to partially offset electricity demand.