Directly by the Jakob Church in Döbeln the Lutheran church commissioned a new kindergarten. Similar to a monastery the original kindergarten St. Florian, was intimately connected to the church by the means of a cloister. However, due to the severe flooding of 2002 a replacement kindergarten was required and an architectural competition was run. Architects Reiter Rentzsch won the competition, with the concept of recreating the cloister and the inherent relationship with the church. It was immediately apparent that a modern timber building would require sensitive treatment when placed beside a 19th century church.
When entering the enclosed kindergarten from the street into the foyer, your gaze is immediately drawn towards the church via an expanse of north facing glazing. A curved earthen wall, polished carmine red, with built in wardrobe, separates the circulation space from the south facing group rooms. Stepping through the doors with large glazed elements the children enter their play space complete with timber galleries and bathrooms. From the group rooms it is possible for the four groups of 68 nursery and kindergarten children to access directly the garden. The building has the pleasant aroma of natural building materials, timber and earth, this combined with the controlled mechanical ventilation results in fresh and healthy air quality. The ventilation and heat recovery unit, located above the north wing of ancillary rooms, is expressed and visible though a glass wall. The ecological and Passivhaus concepts have been very well received by the children and clients.
Timber frame on foamglass footing
All external walls and roof are of timber frame construction utilising engineered timber i-beams (360mm Doka), stiffened with OSB panels. An u-value of 0.11 is achieved by filling between the timbers with cellulose insulation. Additionally 4cm of wood fibre board encloses the structure to achieve 30 minute fire resistance and to ensure the construction is free of thermal bridges. This is vital for Passivhaus construction as thermal bridges must be minimised; this is particularly difficult at the corners of timber construction (see illustration). The floor plate is of warm construction and is insulated on the underside (u-value 0.13). Additionally, the the whole of the timber frame is raised on foam glass footings which protects the construction and minimises the thermal bridging.
The internal walls of the group rooms are of timber frame construction with solid timber joists. The children and parents were then capable of building the infill elements of unfired clay bricks. Over this was installed areas of wall heating tubes and straw as a key for the clay plaster, which was then finished in breathable (casein based) natural paint. The earthen construction provides high thermal mass for the building, this regulates not only the temperature swings but also
the internal moisture levels.
Timber frame on foamglass footing
The gallery and ancillary rooms ceilings are solid glue laminated timber. For the glazed facades a Passivhaus glazing system (u-value 0.85, g-value 55%) was installed onto the load bearing timber elements. The external cladding consisted of painted larch timber cladding for the walls, a rear ventilated green roof and timber window complete with material blinds for solar shading. The application of a vapour barrier or waterproof membrane was intentionally excluded, therefore allowing for the walls and roof to be breathable, which is highly desirable for healthy construction. A blower door test achieved the air tightness n50 requirements of a Passivhaus (0.5 internal volume air changes per hour at 50 pascals).
The timber construction including glazing was completed in two weeks. The clients were impressed by the quality and the finish of the construction. The winter erection of a timber building encounter no problems.
60% North facing glazed facade – is that possible?
With passivhaus design it is desirable to have the majority of the glazing in a south facing orientation in order to optimise the solar gains. However central to the architectural concept was a strong visual connection between the church and kindergarten, therefore a highly glazed north facade was essential. The first PHPP (Passivhaus Project Package) calculated that the building was a little over the required 15 kWh/m²a heating load. Through the inclusion of a small windowsill and additional insulation on all external allowed the building was able to achieve the Passivhaus standard. After several years of use it has demonstrated that Passivhaus designs can function effectively as inclusions to the urban fabric.
Internal Planting to remedy dry air
A child requires a minimum of 15m³/h supply of fresh air. With a relatively high occupation of one child per 2.5m², the group rooms require 300m³/h for the 18 children and one adult. Therefore the group rooms with an internal volume of 185 m³ require 1.6 air changes per hour. In winter this could result in low moisture levels and uncomfortably dry air. To remedy the situation, Reiter Rentzsch Architects worked in collaboration with Mr Frantz from Tübingen Botanical Gardens, to design a scheme that would enable them to use internal planting as a means to providing ideal moisture levels.
For example a 2m high plant (Ficus alii) can increase the moisture levels by transpiring around 1.5litres per 24hours. Two large planting troughs were built directly into the floor plate and to ensure air tightness 20cm of clay was laid. The substrate was a special mix of clay, peat, and clay granules. The natural habitat of the selected plants are tropical rainforests, one trough contains African species and the second Asian. The children water the plants themselves and are fascinated by the rate at which they grow.