The short answer
Walk-on glass has no single thickness. It is built up from several bonded layers, and the total usually runs to a few centimetres, often thicker for wide spans or heavier use. The figure depends on the size of the opening, the load it must carry and whether the pane is single or part of a sealed insulating unit. We calculate it per panel and write it into the quote.
Thickness follows the job, so there is no catalogue number
Ask for the thickness of a window and you will get one number. Ask for the thickness of a glass floor and the honest reply is another question: how wide is the opening, and what will stand on it?
Glass bends under load, and it bends further the longer the span between its supports. Doubling the width of a pane does far more than double how much it deflects, so a wide panel needs to be much deeper in section than a narrow one to feel equally firm. Load matters in the same way. A pane that is only crossed now and then can be lighter than one on a busy terrace with seating on it.
That is why reputable suppliers quote a build, not a single figure, and why you should be wary of anyone who names a thickness before seeing the opening. Our guide to sizing a walk-on rooflight shows how size and build move together.
What the thickness is made of
The total is a stack. Each part has a job, and the job decides how much of the thickness it gets.
| Part of the stack | Role | Typical range |
|---|---|---|
| Top wearing layer | Takes scuffs, carries the grip finish | Around 8 to 12 mm |
| Structural layers | Carry the load in bending | Two or more, each 10 to 20 mm |
| Interlayer, each | Bonds and holds fragments | Around 1 to 2 mm |
| Insulating cavity | Keeps warmth in | Set by the thermal target |
These are general ranges for the market, given as a guide. The real numbers for your panel come from the calculation for its span and load, and they are supplied by the manufacturer. Because each layer is a separate sheet, a walk-on pane of modest size can still add up to something that looks alarming next to a window, and it feels it when someone has to lift it.
The weight follows directly. Glass is heavy, and a thick multi-layer pane is very heavy. Our answer on why walk-on glass is so heavy explains what that means for lifting and for the structure beneath.
Why several thin layers, not one thick sheet
A single very thick sheet might seem the simplest way to make a strong floor. It is also the wrong idea, for reasons of safety rather than strength.
A single sheet that fails does so all at once. A laminated stack behaves differently: the layers are each strong, the interlayer between them holds any broken pieces in place, and a panel with one cracked layer can still carry people while you arrange to have it renewed. The separate layers also mean that a flaw in one sheet does not run through the full thickness. The principle is set out in why walk-on glass is laminated, and the practical side is on whether walk-on glass can crack.
Laminating also lets makers mix layer thicknesses. A stack whose sheets differ is stiffer than one whose sheets are identical, and the mismatch has a useful side effect on sound, which we come to below.
Thick and clear are not opposites
People sometimes assume that all this glass must make the room dark. It does take a little light, but less than you might expect.
Clear glass itself is very transparent, and the loss through a thick stack comes mainly from its slight green tint at the edge of a sheet and from any frit or texture on top. Extra-clear, low-iron glass reduces the tint, and a fine top pattern takes only a modest share of the light. The real daylight penalty is usually smaller than the penalty of a dirty pane. Our page on walk-on rooflight light levels covers this properly.
Seen from below, the edge of a thick pane is sometimes visible as a green line. That is a detail to raise at the survey if the glass will be seen close up, because a low-iron build hides it.
Thickness, sound and the room below
Mass and damping are the two tools for keeping noise out, and a walk-on pane has plenty of both.
A heavy pane with a flexible interlayer damps vibration and does not ring like thin glass. That matters to footfall, to rain on an outdoor panel, and to the aircraft and road noise we hear around Crawley. We describe the result by specification, never by a number: the layers, the interlayer, the cavity and the seat the pane rests on. All of it goes into the quiet spec that comes with every quote. A dedicated page covers keeping the room below a walk-on rooflight quiet.
Questions about how deep the glass goes
A few follow-ups come up every time.
Is thicker always safer?
Not automatically. A pane is safe when it is sized for its span and load and supported evenly. Extra thickness on a poor support achieves little, and extra thickness on a good one is justified only by a bigger load or span.
Will the pane sit flush with my floor?
That is a design choice rather than a fixed fact. Thick panes can be set flush or in a raised upstand, which is compared on our page about flush and upstand walk-on rooflights.
Does more glass cost much more?
Thickness is one of the cost drivers, alongside size, finish and access. The wider picture is in what affects the cost of a walk-on rooflight.
How do I get a thickness for my opening?
Send us the location and rough size, then get a quote. We survey, calculate, and write the build down. The overview sits on our walk-on rooflight installation page.