Water Drainage for Structural Glass Roofs

When installing a structural glass roof, you must consider where any water run off will go. The most suitable drainage solution will depend on the other planned interfaces of the glass roof, its size, and the design of the structure. Here we go through some of the most common ways water drainage is dealt with in glass roofs however many others are possible. Always speak to the experts if you have a specific requirement.

Glass to Glass Connections with Overhang

When you have a glass roof draining towards a vertical elevation of glazing, the external pane of the glass roof unit is elongated and ‘stepped’ creating a drip edge. This glass overhang steps over the vertical face of glass below and allows water to safely drain off the glass roof into whatever ground drainage is detailed for below.

This detail is very minimal, allowing for a frameless glass to glass connection between the fixed roof glazing and the fixed vertical glazing.

A similar detail can be used when the glass roof is meeting opening doors on the vertical elevation. Caution must be taken however when the opening below is a pivoting opening. Due to the nature of a pivot having no rebated frame additional water protection such as a drop edge or canopy is recommended to protect the opening element from water ingress.

glass to glass edge to glass link
glass roof with cotswold stone wall

Glass Supported by Solid Wall Structures

A glass roof can be supported on its draining edge by a solid structural glass wall. The glass roof unit sits and is fixed at the top of this wall and sails over the outer edge.

Water from the glass roof then drains from the roof and over the edge of the glass wall into whatever ground drainage has been detailed.

A stepped glass unit is often used for this method as well to provide an effective water drip edge, forcing the water off and away from the structural glass connections.

A Structural Gutter

A structural gutter is an extremely useful solution for high specification glass roofs where the glass roof is required to drain towards a wall.

The structural gutter both supports the weight of the glass unit, connects the glass roof to the wall structure and provides a high-volume water drainage system all in one.

There are various applications where a structural gutter may be useful. One such application is a side infill extension. With party wall issues it may be advantageous to drain the glass roof of the side infill extension back towards the existing property and away from the party wall. A structural gutter at this junction will provide the structural connection to the building and drain the water run off from the roof.


pencil sketch of a structural gutter
glass roof over basement extension

Structural Gutters in Glass Extensions

Structural gutters can be used to create effect on glass extensions.

In many glass extension designs we see the glass roof is designed to drain towards the rear elevation of glass. That means the glass doors to the rear must be shorter to allow for the fall of the roof.

By pitching the glass roof from the glass doors back towards the building connection the glass doors can be taller, creating the appearance of a taller and bigger glass extension. In addition, the rear elevation is more minimal with the bulk of the structural support located at the connection with the existing building.

Internally structural gutters can be covered by the internal building finishes such as plaster board. This creates a frameless internal design with only the glass on show.

The glass roof on Eton Villas was pitched back towards the existing building. A structural gutter was used here to connect the glass extension to the building and provide water drainage for the roof. As the roof was pitched this way the rear sliding doors could be taller which created the appearance of a much large glass extension.

glass extension in London
a glass extension to a house in London

glass extension in London

What Next?

If you are looking to specify a structural glass roof on your next project, contact the team at IQ who will be happy to advise on the possible design solutions. You can contact the team by calling our head office on 01494 722 880 or visit the contact us page for all the ways you can get in touch.

Visit the contact us page for all the ways you can get in touch.

Rebecca Clayton
Technical Sales

Rebecca is the Communications Director at the IQ Group and has worked in glazing specification for many years. She has a broad range of technical knowledge about all our glazing products and offers technical advice and guidance to architects for specification. Her easy to digest technical advice is often quoted in magazines and publications. You might also recognise her as one of the IQ Glass CPD presenters.

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