Bosjes Chapel was designed by South-African-born Coetzee Steyn of London-based architect Steyn Studio for a vineyard setting in South Africa’s Western Cape. Its form alludes both to the silhouette of surrounding mountain ranges, the historic Cape Dutch gables that dot the rural landscapes of the region, and Psalm 36:7 – ‘How precious is your steadfast love, O God! The children of mankind take refuge in the shadow of your wings’.
The six-metre-high building was conceived as a “lightweight, dynamic structure which appears to float within the valley”, an effect accentuated by an adjacent reflective pond.
Constructed from a slim cast concrete shell, the undulating roof rises to form six peaks – one at each corner and one in the middle of each long elevation. It is supported at four points where it falls dramatically to meet the ground. Below, expanses of glazing are framed in timber to give the appearance of crucifixes.
To allow for thermal movement, the roof and floor structures are completely separated by a service channel around the perimeter at the point where the glass meets the floor.
All formwork was purpose-made, and was designed as a system of prefabricated trusses with a bent plywood skin. It took almost five months to construct the formwork on site. A 1:2 scale sample section of the roof was constructed in the contractor’s Cape Town yard to workshop all details and finishes.
Due to the complexity of the roof form, 3D CAD models were used to calculate the required volumes of material. The shell comprises 74 cubic metres of concrete and 8175 kg of high tensile steel reinforcement. It is supported by four hidden reinforced concrete buttresses, each with a vertical load of close to 50 tonnes.
Due to the unusual form of the shell, each reinforcing bar (top and bottom) had to be individually cut and hand-bent to fit. The concrete was poured in the form of shotcrete – pneumatically projected at high velocity through a hose. This had to be done from mobile platforms, and was frequently delayed by strong winds and rain, taking six weeks instead of the two allowed in the original programme.
Rainwater is discharged from the middle of the roof via a submersible pump with sump, through a pipe cast into the concrete whose outlet is hidden under the lowest part of the roof, where it meets the reflection pond.