The timber frame gridshell is constructed from four layers of alternating lath, finger jointed to enable the use of locally sourced small section green chestnut. The requirement for the gridshell to support the frameless glazing meant that the usual method of construction which allows the gridshell to ‘find its own form’ and to be able to flex was inappropriate. This timber frame grid needed to be predictable and rigid while specially designed node clamps allowed for small amounts of settling in movement, A further complication was that the design required the laths to bend over tighter radii than they would naturally go.
The roof had to be designed within the confines of the existing listed structure. Loading had to be transferred to the new foundation under the stone floor below, not to the existing structure. While similar to a number of other structures we’ve previously completed Chiddingstone was unique in that it had to support a frameless glass roof.
The initial concept required the laths to bend to radi far in excess of the accepted engineering tolerances, meaning the risk of breakage was high.
To inform the design process we carried out numerous tests on the cable and clamping system and bending tolerances of the laths, this provided the data that dictated the curvature of the roof. Excessive curvature was designed out wherever possible but was unavoidable where the laths interfaced with the ring beam.
Our designers worked in close collaboration with the glass manufacturers to develop a node that would clamp the chestnut lath, the cabling and support the 12mm toughened glass panels, allowing the glazing to float over the frame while accommodating small amounts of movement of the laths.