and use of stock items, nor the reprocessing of manufacturing techniques, but rather the investigation of a raw product – the wood lath. 5 In a series of design-build projects over the past decade Coastal Lab has investigated simple vault structures that shelter a variety of community activities. There is a progression of vault form from the 2010 Ross Creek lamella – a 120m barrel vault, to the 2012 Camera Obscura brick shell in Cheverie – a 20m 2 decreasing catenary vault, to the 2014 Cheticamp Farmer’s Market 80m 2 wood gridshell, to the 2015-present 300m 2 gridshell for Cape Breton Highlands National Park. Each project has been an exploration of material, structural principles and construction within an architectural program of unserviced shelter from rain and wind, in particular, southeasterly suettes which blow from plateau to coast, often at 200 kilometres an hour.
all images:dalcoastalstudio.com
Ross Creek lamella, 2010
Camera Obscura brick shell in Cheverie, 2011-12
Farmer’s Market grid shell in Cheticamp 2014-15. top: overlay of survey, engineering and architectural models
The 2012 vault is masonry and is less constrained than the lamella vault, moving from semi-circle to a catenary form and from a constant cross-section to a shrinking one. The repetitive material unit is face-brick, three layers thick that with mortar creates a three-inch thick shell that works in compression. It is based on a nineteenth technique developed by Rafael Guastavino 7 and has been updated by the use of digital modelling. This parabolic brickshell frames the tidal landscape, acting as a camera obscura, a device which records the rising tides of the salt marsh at the mouth of the river.
Gridshells are structures made of thin wood members. There is a reiterative process of calculation that creates structural hybrids between grid and shell, allowing the thin laths, the material of the grid, to act like a shell. Underpinning gridshell construction is a set of simple premises: each lath is continuous in cross section, the wood grain is straight, each lath spans the entire distance, each lath is locked where it crosses another lath, the lath is restrained at each end. It is simple carpentry. While lath was occasionally used in the twentieth century, it required complex mathematics and intricate physical models. The advent of three-dimensional structural software has allowed more complex visualisation and form-making within the time limitations of a design-build studio with a different cohort of students each summer. Wood lath as a structural material depends on the type of wood, the cross-sectional profile of the lath (the strength of wood along its grain is aligned to act extremely efficiently), node connections, the structural performance of the overall form, the springing of the shell and the roof-to-wall connection.
The first barrel vault was made from a thousand similar metre-long pieces made from locally harvested full-dimension 1” x 6”. The one- inch thickness for each piece was the minimum dimension to prevent wobble at its butt joints. Zollinger designed this technique in the 1920s, reconsidering nineteenth century material in a twentieth century way. 6 Our twenty-first century update was made thinner and lighter using a hand-held circular saw, a double-mitre chop saw and CNC-made bolt holes. The length and degree of angle at the end of each piece pre- determines the overall width of the vault and thus the building. It is interesting how dimensional lumber limits building form. In this case, a semi-circular cross-section is the only possibility with this construction technique.
6 German engineer, Friedrich Zollinger, 1880-1945, who developed the lamella roof. 7 Spanish engineer and builder, Rafael Guastavino, 1842-1908, who introduced a version of the Catalan tile to the United States in 1885. 8 Wood with rectangular cross-section bends easily in one direction. Planking occurs when trying to twist or force curvature in the other direction.
On Site review 35 : the material culture of architecture
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