The Downland Gridshell
Conservation Store and Workshop

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Constructing the Ribbon Roof

July 2001 

Construction of the ribbon roof begins.

Support frames consist of a 7 metre horizontal rafter 125mm x 25mm clamped between pairs of vertical members which are attached to each of the vertical laths in the gridshell.  

Six longitudinal members 80mm x 12mm are let in to notches in the frame to support the ribbon roof, below each of these, the rafter is supported by a post with a simple lap joint at the top and a hemispherical turned base which is drilled for a bolt to be inserted and glued.  This bolt then passes through the vertical lath on the gridshell and is secured with a stainless steel nut.  The rafter is then supported at six points across the structure.  The vertical member shown on the right of the following photo form the frames for the polycarbonate glazing.  

Ribbon roof construction

The ribbon roof consists 100mm x 12mm longitudinal timbers laid at 200mm centres across the support frame, a waterproof reinforced polythene barrier backed with foil, , then a multilayer insulation material is laid into a void, then a 12mm ply board and a further layer of 12mm ply which will be covered with Roofcrete.

Where the underside of the roof is outside the structure a plywood soffit replaces the 100x12 longitudinal members.  The roof layers are clearly visible in the next picture

Stages in the roof construction.

September 2001

The finished roof.  Small section laths were fixed to the roof boards running diagonally from high to low points to distribute the run-off water to the sides of the roof.  The whole was covered with three layers of 10mm galvanised mesh extending over the side of the roof and finishing with a metal bead at the soffit.  The Roofkrete material was trowelled over the whole roof to cover the mesh layers.

[Next: Clerestory glazing]