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Glazing can be retained using discrete fixings at intervals on the edges of the panes. The glazing spans one-way against uplift forces (rafter to rafter) but is supported on four sides against inward pressure. This type of glazing can be used for a shallower roof slope than purlins with pressure plates behind which water would be trapped leading to dirt build-up.
#Large glass roof panels Patch
Silicone pointed glazing with patch fittings The elements for this type of roof are usually extruded in aluminium because the profiles required to accommodate pockets for gaskets and to form condensate drainage paths are easily extruded. Condensate drainage channels on the purlins discharge into similar channels on rafters and are drained to the exterior at the bottom of the roof.
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A secondary potential source of water is condensation on the inside surface of the glass which the supporting elements are also designed to collect. Rafters and purlins are designed with drainage channels which interconnect as a secondary drainage path such that any water which passes the gaskets at the edge of a pane of glass is collected and conducted down the roof to discharge at the bottom of a rafter.
![large glass roof panels large glass roof panels](https://i.ebayimg.com/images/g/uccAAOSwS0Jf9gEA/s-l400.jpg)
Cover caps which clip onto the pressure plate provide an aesthetic external finish to the glazing bars. Rainwater will inevitably be prevented from draining freely away by purlin pressure plates but gaps should be provided at the junctions between rafter and purlin pressure plates to allow most of the water to run off. The slope of the roof has to be sufficient to prevent the deflection of glazing and supporting members from causing ponding and to provide sufficient flow velocity to wash dirt away. Water management is fundamental to the proper functioning of the sky light glazing system. Setting blocks are provided on the lower edge of the pane to resist the component of the weight acting in the plane of the glass. Glass panes can be monolithic or insulated glazing units and in simple sky lights are generally clamped on all four edges using a pressure plate which is screwed into the rafter or purlin. Sky lights consisting of areas of sloped glazing in a single plane and atrium roofs may adopt a system of sloping rafters with orthogonal purlins which are designed to retain the glazing by applying a clamping force.