How to specify a structural walk-on roof light

Specifying a structural walk-on roof light correctly avoids costly remakes, thermal bridges and unsafe installations. This guide walks through the decisions in the order a specifier or builder typically faces on site — from use case to ordering.

1. Confirm the use case

Before dimensions or finishes, define how the glass will be used:

• External roof terrace or balcony — foot traffic, weather exposure, thermal performance and drainage matter. Specify thermally broken glass and anti-slip finish.
• Internal glass floor or landing — structural walk-on rating still applies, but thermal insulation is usually less critical. Clear or opaque glass depending on privacy.
• Basement light well — structural rating and weathering if external; consider opaque or anti-slip if accessible from above.

If nobody will walk on the glass, stop here and specify a standard flat roof light instead.

2. Measure the structural opening

Walk-on units are made to measure to the millimetre. Measure the structural opening width and length at multiple points — openings are rarely perfectly square.

Record:

• Clear structural width and length.
• Upstand height and condition on all four sides.
• Any obstructions, falls or drainage channels affecting the glass seat.

At Vant Glass, configurable spans run up to 1320 mm × 2820 mm for walk-on units within rated structural limits. Enter your sizes in the walk-on configurator to confirm feasibility and price.

3. Choose frameless or framed

• Frameless — glass sits cleanly over the prepared opening with minimal visible edge. Best for flush terrace and floor aesthetics.
• Framed — defined external frame and upstand detail; familiar fixing for builders who prefer a visible kerb.

The laminated glass build is the same; only the fixing interface and appearance change.

4. Select thermal performance

• Non-thermally broken — appropriate for internal floors and walkways where the unit does not separate inside from outside conditions.
• Thermally broken — adds an argon-filled cavity and additional pane for external roofs and terraces exposed to weather. Reduces heat loss and condensation risk at the glazing edge.

Match the build to the location before the structural opening is formed.

5. Choose glass finish

• Clear — maximum daylight; typical for internal floors and wells where privacy is not required.
• Opaque — privacy with diffused light; common over bathrooms or sensitive rooms below.
• Anti-slip — recommended for all external terraces and any surface that may be wet. Textured surface improves grip underfoot.

6. Align structure with the fixing detail

A walk-on roof light is a structural element. Before the opening is cast or framed:

1. Obtain the supplier’s edge support and upstand requirements.
2. Confirm continuous bearing on all supported edges.
3. Plan for setting blocks, perimeter clearance for thermal movement and sealant continuity.
4. Coordinate drainage falls on external terraces so water does not pond against the glass edge.

If in doubt, involve a qualified installer or structural engineer before the opening is built.

7. Write the specification

A minimal walk-on roof light specification should include:

• Product: structural walk-on laminated glass roof light / floor light.
• Size: width × length (mm).
• Frame: frameless or framed.
• Thermal: thermally broken or non-thermally broken.
• Glass finish: clear, opaque or anti-slip.
• Manufacturer: Vant Glass (or equivalent rated supplier).
• Guarantee: 20-year glass guarantee.
• Delivery: free UK mainland (if applicable to your order).

8. Order and schedule installation

1. Place the order with confirmed dimensions and options.
2. Do not cut or modify structural openings after the glass is in production.
3. Handle units with edge protection; walk-on glass is heavy.
4. Bed on correct setting blocks and seal per the supplier’s detail.
5. Confirm full perimeter support and level before final seal cure.

9. Handover and maintenance

Record the specification, guarantee documentation and cleaning guidance. External anti-slip surfaces may need periodic cleaning to maintain grip. Inspect perimeter seals during routine roof maintenance.

Vant Glass manufactures every walk-on unit to order in Britain. Use the online walk-on calculator for instant pricing on your sizes, or call 03330 902 592 to review a specification with the team.