Are walk-on rooflights slippery?

How it is done

Ceramic frit is the usual method. A ceramic ink is printed in a pattern of dots, lines or squares and fired in during toughening, so it fuses into the glass surface.

Because it is fired in, it cannot peel, wear off or be scratched away. It will outlast the installation.

Acid etching textures the surface chemically for a uniform frosted finish. Also permanent, generally slightly less grippy when wet than a good frit.

The rating to ask for

Manufacturers quote a pendulum test value. Ask for the wet figure, not the dry one. A wet value of 36 or above is generally regarded as low slip risk for pedestrian surfaces.

What reduces grip over time

Not wear on the frit, but what settles on it. Algae and moss build up in shaded damp positions, and that is genuinely slippery regardless of the surface beneath.

Cleaning two or three times a year, more in a shaded position, keeps it as designed.

The transparency trade

A denser frit gives more grip and less transparency. That is the actual decision, and most people resolve it towards grip once they have stood on a wet panel.

A completely clear walk-on panel is available and we would not recommend one for an outdoor surface people use.

Barefoot

Worth mentioning if the terrace will be used barefoot in summer. Some frit patterns are coarse enough to be uncomfortable, and there are finer patterns that still meet the slip rating.

Not if the anti slip surface is intact

Every walk on rooflight carries an anti slip treatment on its top surface, and it is not an optional finish. Without it, wet glass is genuinely dangerous, and that is exactly what the treatment exists to prevent.

Two types are used.

A ceramic frit, a pattern of ceramic material fired into the surface of the glass during toughening. It becomes part of the pane, it is durable, and it will normally outlast the sealed unit beneath it.

An etched or sandblasted texture, which roughens the surface mechanically. Effective, and it wears more visibly on a heavily used route.

Fritted is the more durable and slightly the more visible from below.

How well it works

Properly specified glazing is tested for slip resistance and rated in the same way as flooring. A good walk on unit compares with a decent external paving surface wet, which is the sensible benchmark: not carpet, but not a hazard either.

What it will not be is grippy in the way a textured rubber surface is. Anybody moving quickly across wet glass in smooth soled shoes should expect to take care, and that is true of wet stone and wet decking too.

What makes it slippery

Wear. Grit underfoot is what actually abrades the anti slip surface, more than any cleaning method does. A doormat at the door onto the terrace does more for the life of the surface than anything else.

Wrong cleaning. Wire brushes, scouring pads and close range pressure washing all damage the treatment. Water and a soft brush is the method.

Algae and organic film. On a shaded terrace this builds up and it is genuinely slippery. Regular cleaning removes it; leaving it does not.

Frost. Ice on glass is ice, and no anti slip pattern changes that. A terrace with a glass panel in it needs treating like any other hard surface in freezing weather.

Choosing the pattern

Coverage varies between products. A heavier pattern gives more grip and obscures more from below; a lighter one lets more light and detail through and gives less grip.

Where the unit sits on a route people use in all weathers, take the grip. Where it is over a formal room and rarely walked on, a lighter pattern is defensible.

When it has worn

The treatment cannot be renewed in place. Where an anti slip surface has worn to the point of being a hazard, the unit is replaced.

Keeping grit off it and cleaning it properly is what prevents that, and it takes minutes.

Wet glass is slippery, and that is why treatments exist

Untreated glass underfoot in the rain is genuinely hazardous, and any walk on unit in an external position should be specified with slip resistance from the start. It is not an upgrade.

The treatments, and how they differ

Fired ceramic frit. Ceramic applied to the surface and fired into it during toughening. It becomes part of the glass, so it does not wear off, does not need renewing, and cannot be scraped away. This is the specification to insist on outdoors.

Etched or acid treated. A textured surface produced chemically. Durable, and it diffuses light and view more than a frit pattern does.

Applied coatings. Cheaper, and they wear under foot traffic. On a terrace that means renewing them periodically, at height, which is a recurring cost and a recurring risk of it being deferred.

The trade against light

Every slip treatment reduces light transmission and obscures the view. On a unit that is the only daylight source for the room below, that matters.

The usual resolution is a pattern rather than full coverage: dots or lines giving grip on the treated areas with clear glass between them. Enough texture underfoot, most of the light preserved.

That same pattern resolves privacy and the vertigo some people feel looking straight down through clear glass, so it frequently earns its place three times over.

What else helps

Keeping it clean. Algae and organic film on glass are far more slippery than the glass itself, and on a shaded terrace that builds up quickly.