Gym Zlatar Bistrica / Studio NOP
Text description provided by the architects. Zlatar Bistrica is a small town located on one of the few otherwise hilly plains of Hrvatsko Zagorje in northwest Croatia. The western perimeter of the school square in Zlatar Bistrica once bordered a sports hall that had been destroyed by fire, and the new hall project inherited its former orientation as an important parameter to be incorporated into the new configuration external and internal of the building.
The hall was placed on a westerly sloping plot and configured to respond to given urban and topographical determinants. The perimeter around the hall is designed to establish a link between the school square and the lower plateau with an open courtyard and school parking for the school bus and vehicles bringing children from neighboring villages. From here starts the main pedestrian access configured as a stair and ramp system.
The interior mirrors this sloping exterior pedestrian configuration. The facade that opens onto the school square with a glazed ground floor and an entrance allows the space of the public square to enter inside, then to cascade down the staircase of the grandstand to the lower sports level, which is why the square has a clear view of what is happening in the hall and vice versa. The square and the interior of the hall complement each other and exchange views in an almost continuous and direct shift between what is happening in the hall and outside. The outer layer of the hall is made of translucent polycarbonate, which at night transforms the entire volume of the building into a lantern illuminating the school square and its surroundings.
This lantern motif points to the problem of shaping the volume of the room. The author considered several variants that would be both pragmatic and innovative in form. Much attention has been paid to the incorporation of custom prefabricated elements which have only recently been introduced into construction and tested in Croatia. Instead of using generic precast panels, the author worked with concrete precast company Beton Lučko to develop a unique type of panel with the outer and inner layers of black pigmented concrete and thermal insulation in between. .
Although their section is standard, their design required research into production technology. The way the panels are mounted is also innovative. The author decided to abandon a conventional design with a completely walled lower part and light openings in the upper part and replace it with horizontal panels placed at an angle to the vertical like shutters to let in diffuse light. . The panels are mounted on a steel structure attached to precast concrete pillars, and their lower, gaping end is closed with polycarbonate. The lowest row of panels opens at the widest angle from the vertical, which gradually decreases with each new row upwards.
Such a configuration provides enough diffused light inside, avoids glare and provides better protection against the sun and western heat in the hot season. The exterior, in turn, has a dynamic and rhythmic texture thanks to the angled panels. These panels are made of a diabase of dolomitic aggregates of an original green hue mixed with a black pigment added in production, which is why smooth “black” concrete is never entirely black.
Additional tints and uniform colors are obtained with different inclinations of the rows of panels because they reflect the color of the sky differently. At average overcast noon, these hues and colors range from leaden gray to dull dark green, while during a clear sunset, the colors can even become warm. At night, the west facade is distinguished by horizontal strips of light emitted from the interior onto the sidewalk along the sports field.
The panels on the gable walls are not as polished as the west facade and give a greenish texture of the aggregate diabase referencing the greenstone slates from the nearby mountain of Medvednica, which was once a popular local building material, now completely exhausted. The matte color palette is complemented by black iron plates and sheets from which the fences and protective window panels are made. The interior space and surfaces, including the ceiling, are configured to reflect the precise geometry of the load-bearing precast elements.
The vertical and horizontal load-bearing beams are made of precast concrete, also in black. They carry the grid structure of the roof made up of glued laminated wood supports, whose light material contrasts with the heavy concrete frame. Along the western roof, the area extends light domes that provide additional natural lighting. The author paid much attention to the modular configuration of the building and the infrastructure elements, having carefully integrated the artificial lighting and the elements of air conditioning and ventilation into the geometry of the whole.