Glass floors and walkways explained

The applications

Walk-on rooflight. In a roof, bringing daylight into the space below while the surface above stays usable. A terrace over a kitchen extension is the classic.

Glass floor. An internal floor panel between two storeys, passing daylight down from a rooflight above through to a lower level. Used in narrow houses and basement conversions where daylight has to travel vertically.

Glass walkway or landing. A bridge or landing in a double height space, letting light through to the level below rather than casting a shadow across it.

Pavement lights. The historic version: small thick glass blocks in a cast frame over a vault or cellar. Still the right answer where vehicles are involved.

What they share

A laminated stack of toughened plies with redundancy built in, an anti slip fired surface, continuous even bearing around the perimeter, and structure designed to tighter deflection limits than an ordinary opening.

What differs

Weathering. An internal glass floor has no weather to keep out, so there is no drainage design and no sealed double glazed unit. That makes it simpler and cheaper than an external walk-on rooflight of the same size.

Privacy. Far more pressing internally. A glass floor between two occupied storeys usually wants an obscured interlayer.

Combining them

The most effective use is stacking: a rooflight in the roof, a glass floor at first floor level beneath it, delivering daylight to a ground floor room with no external wall.

Expensive, and sometimes the only way to light the middle of a deep narrow house.

What separates a glass floor from a rooflight

The loading case, and everything follows from it.

A rooflight is designed to resist wind, snow and the weight of a person falling onto it. A glass floor or walkway is designed for people to stand and walk on repeatedly, which is a completely different specification and a completely different price.

The build up

Structural glass flooring is laminated: three or more plies of toughened glass bonded with structural interlayers. Where the unit also has to insulate, that stack sits over a sealed cavity and an inner pane, making it thick and heavy.

The reason for lamination rather than one thick pane is failure behaviour. Toughened glass, when it breaks, breaks completely and instantly. A laminated stack that loses one ply retains the others and stays in place as a surface you can walk off. That is the entire safety case.

The top surface

Always treated for slip resistance, either a ceramic frit fired into the glass or an etched pattern. It is a wearing surface, it is what makes the difference between a floor and a hazard when wet, and it slightly obscures the view from below. That is the trade.

Internal against external

Internal glass floors between storeys need no weathering and no thermal performance, so they are a simpler build up: laminated structural glass in a frame or on a structural bearing. The considerations are loading, slip resistance, privacy from below and how the edges are supported.

External walk on rooflights have to do all of that plus keep the weather out and insulate. Hence the sealed cavity, the perimeter drainage and the thermal detailing at the kerb.

Support and structure

Glass floors are heavy and the opening has to carry them. On a new build that is designed in. Retrofitting means a structural engineer, frequently steel, and that is usually the largest line on the quotation rather than the glass.

Getting large panes to position is its own problem: several hundred kilograms cannot be manhandled, so crane or glass robot access and a route to the position have to be established before anything is ordered.

Privacy

The question everybody asks about an internal glass floor and nobody asks in time. A clear floor between storeys is a view in both directions, and the anti slip pattern obscures less than people hope.

Options are a heavier frit, an interlayer with a translucent film, or switchable glazing. All are specified with the panel rather than added later.

When not to

Where nobody will actually walk on it, a non fragile rooflight does the safety job at a fraction of the cost. Where maintenance access is the only requirement, that is an access planning question rather than a glazing one.

The family of products

Walk on rooflights. A single unit set into a terrace, courtyard or light well, giving light below and usable surface above.

Glass walkways. A run of units forming a path, frequently across an atrium or between two parts of a building. The structural principles are the same; the spans and the framing are more demanding.

Glass floors. An internal application, a section of floor made of glass to let light down through a building, typically from a rooflight above through to a lower storey.

Pavement lights. The traditional version: a cast metal frame holding many small glass blocks, historically used to light coal cellars and basements below pavements. Still made, still the right answer in a period setting, and good at carrying load.

What they all share

A laminated build up with a sacrificial walking layer on top and structural plies bonded with interlayers below. A slip resistant treatment, fired ceramic frit being the durable one. A structural engineer, because the load case is calculated for the actual use. And a bespoke unit with a lead time of weeks.

What varies between them

Weathering. An external unit needs a full drainage strategy. An internal glass floor does not, which makes it considerably simpler and cheaper.

Thermal specification. An external unit over a heated space needs insulating glass and an insulated frame. An internal one within the thermal envelope needs neither.

Privacy. Anything horizontal and clear allows sightlines in both directions, and internal glass floors between storeys raise that more sharply than a terrace does.

The common thread

The engineering comes before the order, and the opening is built to confirmed dimensions rather than the unit made to fit an opening already built.