Walk-on rooflights and where they make sense

Where it earns its cost

A terrace over a habitable room. The classic case. A first floor terrace above a kitchen extension, where the room below would otherwise have no daylight at all and the terrace cannot be given up.

A light well that is also a route. Where the only path to a garden crosses the light well serving a basement, a walk-on panel gives you both.

Basement conversions. Where the alternative is a habitable room with no natural light, and a light well at ground level is the only route daylight can take.

A pavement or courtyard light. Occasionally in a period property where an original coal hole or vault light is being reinstated in modern glass.

Where it does not

Anywhere the roof is not actually walked on. If the surface above is a roof rather than a floor, a standard rooflight lights the room below just as well for a fraction of the money.

We are asked for walk-on units fairly often by people who do not need one, usually because the flush appearance appeals. A flush glazed standard rooflight looks very similar from below and costs far less.

The honest conversation

Ask yourself whether anybody will genuinely stand on it, and how often. If the answer is once a year to clean a window, that is not a walk-on case; that is a case for planning how the window gets cleaned.

Half measures

Where a terrace is large, a walk-on panel over the part that needs light and standard construction elsewhere is usually better than a large walk-on area. Light distribution does not improve much past a certain size and the cost keeps climbing.

One situation, really

A terrace, balcony or roof surface that people use, sitting over habitable space that has no other route for daylight. There, walk on glazing is the answer and it is worth what it costs.

Everywhere else, one of three cheaper products does the job better, and it is worth checking which situation you are in before pricing structural glass.

Where a non fragile rooflight is the right answer

A rooflight in a flat roof that is not a terrace, not a route and not regularly accessed.

Non fragile means a person falling onto it will not go through, which is a life safety requirement and a much lower specification than a designed foot traffic load. It costs a fraction as much, and it is what most flat roof rooflights should be.

Non fragile does not mean you can use it as a step. It means it will not kill you if you fall on it.

Where access planning is the right answer

A roof visited twice a year for gutter clearance does not need a floor. It needs a non fragile unit and a safe way to work around it, which is a matter of how the maintenance is done rather than what the glazing is rated for.

Where moving the glazing is the right answer

The one worth half an hour with the plan. A terrace rarely needs to be glazed across its whole width, and putting the daylight outside the walking route turns an expensive engineered installation into an ordinary rooflight.

Where the room below could be lit from a different part of the roof entirely, a standard fixed rooflight does the same job at a quarter of the cost.

Why it costs what it does

Not the fitting. The glass, which is a laminated stack of three or more toughened plies. The structure, because the opening has to carry the unit and the people on it, which on a retrofit means an engineer and frequently steel. And the access, because a large pane weighs several hundred kilograms and needs a crane or a glass robot.

What we will not do

Fit a standard rooflight where somebody intends to walk on it, or certify an existing unit as walk on because it looks robust. The specification is either there in writing from the manufacturer or it is not.

We would rather tell you which of the four situations you are in than sell you the expensive one by default.

The situations that justify the cost

A roof terrace over a habitable room. The same square metre is floor above and window below. On a site where outdoor space is scarce, that is a genuine gain rather than a luxury.

A basement or light well. The glass is frequently the only daylight the space will ever get, and putting it in the courtyard floor is the only place it can go.

A side return or courtyard where a rooflight at ground level would otherwise block the only route to the back of the plot.

A link between two parts of a building where a walk on strip lights the space below without interrupting circulation above.

Where it does not make sense

Where the only motivation is being able to stand on the rooflight to clean it. A water fed pole costs a tiny fraction of the difference and reaches most domestic rooflights from the ground.

Where the roof is not otherwise being used and never will be. A standard rooflight does the daylight job for far less.

Where the structure would need substantial work to carry it and the space below does not really need the light. The steel is frequently the largest line on the job.

What to weigh before committing

The engineering and steel come first and cost real money. The waterproofing and drainage detailing is demanding, particularly for a flush finish. Lead times are weeks because every unit is bespoke. And access for lifting large panes may be the constraint that decides the design.

Where the case is genuine, it is a superb piece of construction. Where it is aspirational, it is an expensive way to get light that a simpler unit would have delivered.