The term ‘patent glazing’ refers to a non-load bearing, two-edge support cladding system. Its name relates to the number of patents that were taken out in the 19th and 20th centuries for different versions of the system.
Patent glazing bars provide continuous support along two edges of glazing infill panels, and are fixed back to the main structure of the building. This system supports its own weight, and provides resistance to wind and snow loading, but does not contribute to the stability of the primary structure of the building.
Patent glazing is a dry glazing system in which the patent glazing bars are drained and ventilated.
The earliest systems were typically manufactured from a steel section, covered with lead. However, the development of aluminium manufacturing during the second world war, and the clear advantage of the material in terms of weight and cost resulted in aluminium becoming the main manufacturing material in the 1950’s and 60’s.
Modern patent glazing systems are typically formed by aluminium T or box section patent glazing bars which provide continuous support along two edges of infill panels such as single or double glazing or composite panels. The glazing bars are fixed back to the main structure of the building.
Channels within the patent glazing bars collect rainwater that penetrates through the outer bead, or condensation that accumulates within the bar, and drain this to the outside.
Typically, aluminium patent glazing bars are available in lengths up to 7 or 8m, but beyond 3 to 6m, they generally need intermediate support, depending on their section size, anticipated loads and the weight of the infill panels.
Guidance for the design and installation of patent glazing is provided in BS 5516-1:2004 Patent glazing and sloping glazing for buildings. Code of practice for design and installation of sloping and vertical patent glazing.
Design and installation considerations might include:
- Maximum required span.
- Supporting structure.
- Access for maintenance.
- Requirement for opening roof lights to allow natural ventilation and smoke ventilation.
- Use of laminated glass to prevent glass falling in the event of breakage.
- Drainage (typically, a pitch of at least 15° is required to ensure rainwater run-off).
- Acoustic performance.
- Heat accumulation and shading.
- Wind, snow and maintenance loads.
- The pressure difference across the patent glazing.
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