Creating a light well by using glass in the roof is a popular way of introducing light to central areas of a building. In addition to the normal considerations of thermal and solar-control, we need to consider the safety of the overhead glazing. If the glass forms part of an accessible roof area then it may need to be treated as a glass floor.
For overhead glazing there is not a lot of advice in the standards, but we recommend that for single glazing either Pilkington Optilam™ or Pilkington Pyroshield™ 2 is used because of its "break" characteristics. When suitably glazed, both glass types, if broken, hold together. Broken glass should be replaced as soon as possible. Unless the break is severe the risk of the glass falling in is very low. For double glazing the lower pane should be one of either Pilkington Optilam™ or Pilkington Pyroshield™ 2 and the upper pane need not be a safety glass.
The regulations allow the use of toughened glass overhead, however, if toughened glass is used as the lower pane then a safety glass must be used in the upper pane. We also recommend heat soaking of toughened glass when it is used in a safety critical location.
When toughened glass breaks it breaks safe into small particles. When it is overhead the particles can come down locked together forming a mass of glass that may cause injury. To reduce the risk of injury we recommend that the thickness and height above floor level is limited to reduce the risk of injury. For heights up to 5 m above floor level toughened glass can be considered if the other glass products cannot be used. Between 5 m and 13 m above floor level restrict the toughened glass thickness to 6 mm and 3 m2 in one pane. Over 13 m above floor level toughened glass is not recommended.