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Lonsdale Roofing

Rooflight & Patent Glazing Glossary

Not all building professionals are familiar with the correct terminology for rooflights and patent glazing. So, let us help with that!

Richard Burgess, Managing Director of Lonsdale Metal Co Ltd with over thirty years industry experience, sets out commonly used terms and their correct definitions below:


Continuous section to retain the glass usually combined with a gasket


Section at foot of the glazing

Curtain Walling

Four edge support cladding system comprising of rafters and transoms for sloped & vertical glazing

Cap / Capping

Screw on or clip in continuous section to retain the glass

Drainage Channel

Water channel integral within a glazing section to discharge any water to the outside the building


Screw or bolt to fasten components


Horizontal section to join two pieces of glass


Raised upstand around the structural opening to provide fixing for roof light.

outlet village glazing


The point where sloped glazing meets the vertical

Fixing Shoe / Slipper

Bracket to fix a glazing bar to the structure which maybe fixed or sliding


Screw or bolt used to fix the glazing system to the supporting structure

Four Edge Support

The system, where the glass is retained on all four sides e.g., sloped curtain walling

thermgard project


Usually a flexible and yielding strip used to provide a water and air-tight seal the glass and glazing bead or capping.

Glazing Bar

Longitudinal supporting member that spans between structural supports & incorporates drainage channels

bmw enfield case study

Patent Glazing

Two edge support glazing system for sloped & vertical glazing


Usually lead or aluminium pressing to provide weather-tight seal with the abutments to the building or at the ridge and hips on a roof lantern


Glass structure usually bonded with silicone without the need of a supporting frame. Sometimes referred to as ‘structural glazing’

Glass / Glazing Stop

Bracket to prevent glass sliding or slipping usually at end of glazing bar


A sloping member providing support to two sloping planes of glass

Keel Bar

A glazing bar with strengthening fin below the glass

Muntin Bar

non-structural horizontal section for joining glass


A parallel structural member providing support to two panes of sloping glass


The vertical triangle formed at the end of duo-pitch glazing

whitgift school thermgard project


Top of sloped glazing


glazing material most commonly glass or polycarbonate, but may be insulated aluminium panel or GRP sheeting

The angle of the glazing to the horizontal

Roof Lantern

Usually hipped rooflight for fitting onto flat roofs


The span between glazing bars i.e. width of panes

Storm Cleat

Clip to improve retention of the glazing bead in exposed locations with high wind loads. Most often used on vertical patent glazing.


The horizontal members in curtain walling and other four edge support sloped glazing systems


The distance from top to bottom of the glazing slope


The vertical part of a glazing bar that gives the section rigidity

Two Edge Support/h2>
The horizontal members in curtain walling and other four edge support sloped glazing systems


Continuous section or bead to retain the glass

Setting Block

Plastic or rubber block to cushion the edge of the glass

lime street plasgard case study

Thermal Barrier

Usually plastic or polyamide section to prevent heat transfer from inside to outside of the rooflight thus reducing risk of condensation


Gasket or sealant to prevent water ingress