The upstand of a roof lantern: height, materials and insulation

The upstand of a roof lantern is the raised kerb on the roof that the roof lantern sits on. It carries the weight of the glass and frame, lifts the junction above the water running across your roof, and forms the transition between the roof insulation and the frame. A roof lantern on a well-built upstand stays dry and warm. A sloppy upstand is a well-known cause of leaks and of condensation along the edges.

What does a roof lantern upstand do?

Think of the upstand as a frame on the roof, a box without a bottom. On the outside, the roof covering runs up against the upstand. On the inside, you see it as the reveal of the roof opening. The roof lantern frame sits on top.

• Carries glass and frame and transfers the load to the roof
• Keeps the junction above the water on the roof
• Connects the roof insulation to the frame
• Gives the roof lantern a square, level base

How high should an upstand be?

A widely used rule of thumb is that the top of the upstand should be at least around 15 cm above the finished roof covering. The frame then stays dry with a puddle on the roof or a layer of snow, and the roofer has enough height to turn the covering up neatly.

If you are fitting a roof lantern in an existing flat roof, measure from the top of the current covering. If you are adding roof insulation at the same time, those 15 cm move up with it. An upstand that turns out too low after insulating is hard to raise afterwards.

Timber or prefab: building the upstand

A timber upstand is built on site by the contractor or roofer, usually from exterior grade plywood or softwood on a framework. The advantage is that it fits precisely on a roof that is not perfectly level or square everywhere. The downside is that the quality depends on the tradesperson, and the timber must be fully protected on the outside by the roof covering.

A prefab upstand arrives made to measure from the workshop, sometimes already insulated. That saves time on the roof and the size matches the frame straight away. With the wall-abutting lean-to roof lantern, DagLichtDesign supplies the upstand and junction profiles made to measure. For the other types, ask in your enquiry what comes with your situation.

Insulating the roof lantern upstand

An uninsulated upstand is a thermal bridge: a cold strip between the warm roof build-up and the warm glass. In winter, moisture condenses there. If you have trouble with condensation on a roof lantern, the cause is often on the inside of the upstand.

So insulate the upstand all round and connect that insulation to the roof insulation without gaps. Use a vapour control layer on the warm side, so moisture from the house does not get into the timber. If you choose triple glazing, a well-insulated upstand is even more important. Otherwise the edge becomes the coldest point of the entire roof.

The junction with the roof covering

The roof covering runs up over the upstand to just below the frame. With EPDM this is usually one continuous sheet, bonded and neatly folded at the corners. With bitumen, an upstand strip is torched or bonded onto the roof membrane. The details per covering are in connecting a roof lantern to EPDM and in the installation manual, which comes printed and digital with every delivery.

• Check that the upstand is level and square
• Measure both diagonals: equal means square
• Turn the covering up to just below the frame profile
• Fold the corners where possible, without loose patches

Frequently asked questions