The client, a housing association founded by the Catholic Church in 1954, considers itself to be “a provider of affordable housing for the socially less privileged”. The aims to satisfy social need have now been supplemented by high environmental goals: the primary energy demand in these new buildings in Ingolstadt is only a third of that prescribed by the German Energy Saving Ordinance 2007 (Energieeinsparverordnung, EnEV) at the planning stage. More than 50 per cent of the buildings’ heat demand is generated by the sun.
Compared to its surroundings, the estate on Albertus-Magnus-Strasse stands out in particular for its high density, which required a differentiated design of the public space. Public and private space alternates between the north-south oriented residential terraces. The flat roofs and terrace ends have been clad in light grey fibre cement panels providing a clear contrast to the grey-brown varnished larch timber cladding of the east and west-facing facades. The architects refer to the roof elements protruding along the long facades as ‘energy racks’ since they support the solar thermal modules as well as the central ventilation systems for the apartments including the air ducts to distribute the supply and exhaust air horizontally along the long blocks.
There are wide access balconies in front of the apartments that are connected by a varied assortment of stairs: straight or dog-legged, cascading or stacked. Two common areas also form part of the scheme: a covered patio on the northern edge of the settlement and a centrally-positioned common room, which can be rented by the residents for parties and other activities.
The four terrace blocks, designed by bogevischs buero, mainly accommodate two and three-room apartments. Sixty-six of the eighty-one dwelling units have been publicly funded, the remaining fifteen, including eight maisonette apartments, are privately financed.
The layouts have been influenced by two fundamental conditions: on the one hand,an upper limit for the total floor area of each apartment; and on the other, the requirement to provide barrier-free access. The bathrooms and bedrooms are therefore fairly spacious, whereas all other rooms are rather compact.
The walls and floors of the two to three-storey buildings consist mainly of load-bearing cross-laminated timber elements. These protrude on the exterior to form balconies, which have been upgraded by simply adding tapered insulation to the upper surfaces. The access balconies, on the other hand, (this is mainly for fire protection reasons) are made of concrete and are thermally separated from the living space. Likewise the underground car park; it is also constructed with concrete and thermally separated from the ground floor apartments in order to avoid thermal bridges.
The fact that the apartments are actually timber buildings is only apparent from the ceilings; particularly on the uppermost levels, where high roof beams bear the considerable extra load of the solar thermal modules on the roof.
The exterior envelope consists of nine-centimetre-thick cross-laminated timber elements. These were prefabricated, connected to form large wall panels and provided with window openings before being brought to the site. The windows were then fitted on site. Finally, a cavity for the insulation was created on the outside of the solid timber walls, the larch timber cladding was fixed and cellulose insulation was blown in. With an insulation thickness of 24 cm, a U-value of 0.15 W/m²K has been achieved for the exterior walls. In order to ensure an airtight construction, blower-door-tests were performed on site at random locations during the completion stage of construction work. According to Matthias Wissmann, project manager at bogevischs buero, it was mainly the conduits for electrical installations in the facades that proved to be a weak point at first. However, the tests gradually made the contracting companies aware of the issue and the results improved significantly.
The heat demand of the buildings in Ingolstadt is only 22.5 kWh/m²a. To minimise ventilation heat loss, all apartments have been equipped with a central ventilation system with heat recovery. A total of six central ventilation units have been erected on the flat roofs. The vertical air shafts, which distribute the pre-heated supply air to the apartments, are located adjacent to the bathrooms. From here, the air is channelled to the living room and bedrooms in the suspended hall ceiling. The exhaust air is extracted in the kitchens and bathrooms and guided back to the central ventilation units on the roofs.
The 863 m² of solar collectors on the roofs are designed to cover 57 % of the annual heat demand for heating and hot water; the remaining heat is supplied by the local district heating grid. In order to achieve the high coverage rate, two solar buffer storage tanks, each with a volume of 273 m³, were integrated into the buildings reaching from the basement to beneath the roof. They are placed in separate, completely enclosed rooms, which were subseqently filled with cellulose insulation. The temperatures inside the tanks are displayed on facade integrated, building high LED diisplays in several colours (red = hot; blue = cold); they can also be checked on a screen in the common room. In terms of heat supply, the four blocks are separated into two sections – one per storage tank. The central heat supply is provided by the heating water with a forward flow temperature of 60 °C. The apartments are heated with radiators. Each apartment has a separate unit with heat exchangers to transfer the heat to the apartment's own heating circuit and the hot-water pipes for the kitchen and bathroom. This solution avoids the need for individual hot water storage tanks in the apartments and reduces the danger of legionella significantly.
