![]() They work twofold: as well as facilitating drainage, they assist in connecting the glass to the structure, providing added support to the glazing. There are a few instances when a structural gutter can be installed – notably, when the glass roof is attached to a wall that is higher than the glazing panels, in the case of a party wall, or when there are no other means of removing the water. In instances where heavy rainfall is expected the glass may need to be altered slightly or stepped, to guide the water towards the lip, to make sure that the system can cope and to ensure that the water doesn’t simply fall in sheets at the other edges, although this is only a possibility on projects with smaller pitch angles. (Otherwise, it will need to be built upwards). If the rooflight is to be built on an upstand, this will need to be weathered usually it will need to rise to at least 150mm, and the glass placed on a 3 degree pitch, usually over the smaller dimension. The workaround typically involves inserting a steel channel. This creates a completely minimal visual appearance, but involves the challenge of effectively removing a brick course, and in many cases the structure won’t be sturdy enough to handle this on its own. In the case of new builds, however, it’s possible to chase the glazing into the brickwork. If you’re face-fixing an aluminium angle to a wall, for instance, this should be covered with lead flashing to ensure the installation will last. There are a few options that can be designed into the structure to ensure longevity. This is one of the easiest scenarios to fix water drainage on a flat glass roof (as it can take advantage of the existing drain system in place for the rest of the building), but if your glazing is going to sit directly up against a solid wall, it’s going to be more weathering compared to other drainage systems. This isn’t to say a drip edge is inherently a bad thing, but it tends to give a more Victorian appearance, compared to the sleek visual impact of a flush edge.Īnother consideration for glass to glass drainage would be if the glass below the lip has installations in place which could be damaged by runoff water, such as pivoting opening doors or windows, in which case a structural gutter may need to be used or the glass pitched in another direction. For that reason, in many modern installations, a fully flush edge is preferable both practically and aesthetically. It is possible to design a glass roof with an extended overhang of the horizontal pane, but in these cases it’s vital to be aware of capillary action: water rolling over and under the overhang edge. Without effective planning, the water would splash in sheets down the sides of the glass or harshly onto surfaces below, which would create unpleasant visual deluges, and can lead to water marks after the fact. When glass is connected to glass, whether it is a vertical glass wall, or another pane of flat glazing further down, it is vital to control where the water travels, even before it gets to a gutter. There are a few available design choices for fixed glass roofing (opening rooflights can also suffer from water pooling, but they have different ways of dealing with the issue) where a lower pitch is preferred, and these depend on how your roof is attached to the rest of the building. These decisions affect not only which direction you want to pitch your glass, but also what kind of drainage system you will utilise. Put simply, the bigger the pitch the better, but for a glass roof to be considered ‘self cleaning’, and for water to drain away effortlessly off the panel, the pitch should be at least 15 degrees.Īlong with the pitch of the roof, you also need to consider where exactly you want the water to go. Picture a car windscreen in the rain – even with a pitch closer to 45 degrees, water droplets still form. It’s also important to note that while a pitch of 3 degrees will prevent ponding, it doesn’t necessarily mean that water will simply run off the roof. ![]() In the case of glass specifically, water and other debris need to run off smoothly and quickly to ensure visibility and natural light aren’t impacted. ![]() At best it could leave stains and smearing, at worst: leaking and damage to the components of the structure, caused by a build up of silt over time. Pooling, or ‘ponding’, of water on a flat roof (whether glass or not) is never a good thing. To counteract this, glass roofs are designed at a pitch of up to 3 degrees – any less than that, and there will be a problem with ponding. To understand why roof water drainage is so crucial, it’s first important to note that glass bows under its own weight.
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