Does walk-on glass get hot underfoot in summer?

Glass absorbs some of the sun that lands on it, and that energy has to go somewhere.

Sunlight passes through clear glass, but not all of it. A share is absorbed by the glass itself and warms it, and the surface of a pane in direct sun ends up warmer than the air around it. Laminated walk-on glass is thick, and thick glass holds more heat than a thin sheet does. It takes longer to warm and longer to cool. So on a bright afternoon the pane feels warm, and in the evening it gives that warmth back slowly.

Underfoot, the effect depends on the finish. A pane with a fine anti-slip pattern fired into its top surface has a slightly different feel from smooth glass, and a pale or frosted pattern reflects a little more light. Our page on anti-slip finishes for walk-on glass describes the options. Colour matters as well, because dark surfaces warm faster than pale ones. A light terrace surface beside the glass helps, and a dark composite deck beside a clear pane will often feel hotter than the pane does.

In the British climate the extremes are short. A few hot weeks a year is the real test, and most days the glass sits at a pleasant temperature. Bare feet in the middle of a heatwave are the situation to plan for.

Surface warmth is a small matter. The larger one is solar gain into the room below.

A room under a terrace or a flat roof receives sun from above, and on a hot day a large area of clear glass lets in a great deal of it. The room warms faster than it cools, which is most noticeable in a loft bedroom or a kitchen extension with a lot of glass overhead. Part O of the Building Regulations deals with overheating in new homes in England, and it looks at glazing area and solar gain. That rule is aimed at new dwellings, but the physics applies to any room.

Walk-on glass has limits that ordinary rooflights do not. It must be thick, laminated and fixed, so you cannot add an external shade or open it to vent. That makes the glass itself the place to control solar gain, which is why we raise it at survey stage for any south-facing or west-facing terrace. Our page on how walk-on rooflights affect light levels explains the balance between daylight and solar control.

A solar control layer is a thin coating, invisible from most angles, that reflects part of the sun's heat away from the pane.

The coating sits on an inside face of the glazing build, and some of the solar energy is reflected back up before it reaches the room. The top pane still warms a little, but less heat is passed downward, so the room stays more comfortable. The trade is a slight change of tone. A solar control unit can look a touch cooler or greyer than clear glass, and it passes marginally less daylight. We show you a sample so you can judge it against the room.

A tinted interlayer is the other route. It absorbs more of the sun inside the pane, which can make the top surface warmer than a reflective coating would. For a terrace people use in bare feet, a reflective coating is usually the more comfortable choice. The manufacturer's datasheet gives the solar factor for each build, and we read it with you rather than quoting numbers from memory.

Because the panel is part of a wider glazing build, the heat choice and the noise choice are made together. A laminated acoustic pane is already part of a walk-on unit, and our page on why walk-on glass is laminated covers what the laminate does. The coating is added on top of that build, not instead of it.

A few small habits make a sunny terrace easier to use, whatever the glass.

• Shade from the side. A pergola or a parasol on the surrounding deck shades the glass at midday without touching the pane.
• Pale surfaces around it. Light decking or stone stays cooler than dark, so the whole terrace feels less harsh.
• Internal blinds. A blind below the glass cuts what reaches the room, though it does nothing for the top surface.
• Cool, not cold, water. Never pour iced or boiling water on hot glass to cool or clean it. A sudden change in temperature stresses any glass.

That last point connects to our page on whether walk-on glass can crack, where thermal stress is one of the causes described. For cleaning in summer, wait until the glass is shaded or has cooled, which also avoids streaks. Our guide to cleaning and caring for walk-on glass sets out the routine.

We specify the glass for light, for quiet and for comfort together, and the quiet spec records all three.

A solar control coating and a laminated acoustic build combine in one unit, so you do not have to choose between a calmer room and a cooler one. Our page on whether walk-on glass is energy efficient covers the winter side of the same coin. If you want the heat and the sound both considered, get a quote and tell us which way the terrace faces.

Can walk-on glass burn bare feet?

It gets warm, not hot enough to burn for normal contact on a British day. A dark composite deck around it is likely to be hotter, and a few seconds' test with your hand tells you before anyone walks out barefoot.

Does the anti-slip pattern make the glass hotter?

The pattern changes how the surface reflects light a little, and the effect is small. The finish is chosen for grip, and the coating underneath does the work on heat.

Will solar control glass make the room dark?

It slightly reduces the light passing through, and the room stays bright. We compare samples in the room, so you see the tone before committing.

Where can I read more about walk-on glass?

Our walk-on rooflight installation page covers the full range, and the page on energy efficient rooflights covers thermal performance in more depth.