A basement or a lower ground floor room has one thing wrong with it that nothing else fixes: it has no sky. A glass floor over a light well is the intervention that changes that, and it is the situation where walk-on glass earns its cost most clearly.
What a light well is
An open shaft against the outside of a building, dropping from ground level down to a window or a door serving a below ground room. On the Victorian and Regency terraces here they are common at the front, between the pavement and the house, frequently with steps down to a basement door.
The well brings daylight to a room that would otherwise have none, and it is a collection of compromises: it takes garden or forecourt space, it collects leaves and rubbish, it needs draining, and it is a hole somebody could fall into.
Covering it in structural glass keeps the daylight, recovers the space above, and removes the hazard.
Why the daylight matters more here
In an ordinary room a rooflight adds to daylight that already exists. Over a light well it frequently is the daylight.
Which changes every specification decision on the unit. Light transmission stops being a preference and becomes the point, and every choice that costs light has to be justified rather than adopted.
That runs directly against the anti-slip requirement, since every anti-slip treatment costs some light. Balancing those two properly is most of the specification on this kind of unit.
What it does to the room below
The change is larger than people expect, and it is qualitative as well as quantitative.
A basement room lit by a window at the bottom of an open well gets light that has bounced down a shaft, so it is dim, directional and comes from one side. Glazing the top of the well and treating the whole shaft as a light box changes it into overhead light, which is what makes a room feel like a room rather than a cellar.
Painting the walls of the well white or a very pale colour makes a substantial difference to how much of that light arrives, and it costs almost nothing.
Pavement lights, the historic version
Worth knowing about because they are all over Brighton, Hove and the older parts of Worthing, and because they are the ancestor of this whole product.
A pavement light is a cast iron grid set into a pavement or a forecourt, holding small thick glass lenses, over a vault or a basement below. They were how Victorian builders lit a cellar under a street, and a great many survive.
They are frequently listed along with the building, they are repairable, and they are not usually up to modern loads. Where one exists, the conservation question comes before the engineering one.
Repairing rather than replacing a pavement light
The conservation position, and it is frequently achievable.
Cast iron frames survive extremely well. What has usually failed is the lenses, the bedding and the surrounding concrete, all of which can be renewed. Replacement lenses are available and specialist firms do this work.
Where a pavement light is part of a listed building, or contributes to a conservation area, repair is the expected approach and a modern glass panel in its place is a considerable alteration. That is a listed building consent question and it starts before anything else.
Where the well is, and who owns it
A question that catches people out on a terrace.
A light well at the front of a Victorian terrace may sit within the property boundary, or it may extend under the public footway, in which case it is a vault and the highway authority has an interest in anything done to it.
Where the building is in flats, the well and the forecourt are frequently common parts rather than belonging to the basement flat that benefits from them. Establishing ownership and consents comes before design, and on a terrace it takes longer than the work.
Drainage, which is the whole engineering problem
An open light well drains because it is open. Cover it and you have created a sealed box below ground level, and that changes things fundamentally.
| Before | After | Consequence |
|---|---|---|
| Rain falls into the well | Rain runs off the glass | Where does it go instead? |
| The well drain takes it | The well drain takes almost nothing | It silts up unused, and matters when it is needed |
| The well is ventilated | The well is enclosed | Condensation and stale air |
| Leaves fall in and are cleared | Leaves sit on the glass | Light lost, and a slip hazard |
| Somebody can climb down | Access is through the glass or not at all | Maintenance has to be designed in |
The drain stays, and it matters more
The instinct on covering a well is that the drain is now redundant. It is the opposite.
The existing drain is the only route out for anything that does get in: a failed perimeter seal, condensation running down the walls, a burst pipe, water coming through the covering during storm conditions. A well with no working drain is a tank under a habitable room.
So the drain is retained, cleared, tested and kept accessible, and the fact that it now runs dry most of the time is precisely why it needs checking rather than forgetting.
Ventilation of the covered well
The second consequence, and the one that produces complaints.
An enclosed shaft below ground, with a cold glass lid and damp masonry walls, is a condensation machine. Warm moist air from the room migrates into it, meets the cold underside of the glass, and runs.
The answer is to keep the well ventilated rather than sealing it: a ventilated perimeter detail, a purpose made vent, or a design that maintains air movement through the shaft. Where a well has a door or a window into the room, that route needs thinking about too.
A well that was ventilated for a hundred and fifty years and is now sealed will tell you about it within one winter.
Damp, and what a covered well hides
Below ground masonry in an old building is frequently damp, and the well was where it dried out.
Covering the well removes the drying route as well as the water. Where the walls of the shaft were previously wetted by rain and dried by air, they are now neither, which is usually an improvement and occasionally is not.
Where there is existing damp in the basement, covering the light well should be part of a considered approach to it rather than something done in isolation and hoped about.
The glass over a well is doing less structural work
One respect in which this is easier than a terrace unit.
A light well is usually narrow, so the span is short, and short spans need considerably less glass than long ones. A well a metre wide is a much simpler structural proposition than a terrace panel spanning two and a half metres.
Where a well is long and narrow, it is frequently divided into several panels on intermediate supports rather than spanned in one piece, which keeps the build-up sensible and makes the panels handleable.
The load category is frequently the higher one
Against that, the loads may be higher rather than lower.
A light well at the front of a terrace, between the building and the public footway, may have public access or be treated as though it does. A forecourt that people cross to reach a front door is not a private terrace.
Which means a small panel over a well can require a heavier specification than a larger one on a private roof terrace, and the span working in your favour is partly offset by the category working against you.
What to establish before designing anything
- Whether the well is within the boundary, or extends under a public footway as a vault.
- Whether the building is listed, and whether an existing pavement light is historic fabric.
- Who owns the well and the forecourt, which on a building in flats is rarely the basement flat.
- Whether the room below is habitable, and whether its escape route passes through the well.
- Where the existing drain runs and whether it works.
- Whether there is public access across the space above, which sets the load category.
Six questions, none of them technical, and between them they decide whether this is a straightforward job or a project.
Getting into the well afterwards
Designed in, or it does not happen.
Somebody has to be able to clear the drain, clean the underside of the glass, and deal with anything that goes wrong down there. A well covered in fixed panels with no access is a maintenance problem waiting.
The usual answers are one removable panel, a hinged section, or panels light enough to be lifted out with the right equipment. Whichever it is, it is decided at design and the means of lifting is left with the building.
Cleaning the underside
The surface nobody plans for and everybody notices.
The underside of a glass floor over a light well is visible from the room below, at close range, lit from above. Dust, condensation marks and cobwebs on it are conspicuous in a way they never are on a rooflight three metres up.
Which is another reason access into the well matters, and a reason to keep the shaft as clean and as sealed against dust as the ventilation requirement allows.
Basement conversions
The common project this arises within, and the glass is one element of a larger job.
A basement conversion has its own considerations: waterproofing to a defined grade, ventilation, escape, headroom, and structural work to the building above. The light well glazing sits inside that and has to be coordinated with the waterproofing design rather than added to it.
In particular, the junction between the glass perimeter and the waterproofing system is a detail the waterproofing designer needs to have seen, because a below ground waterproofing system with an unconsidered penetration in it is not a system.
Escape, and the window at the bottom
A light well frequently contains the escape route from the room it serves, and covering it changes that.
Where a basement room is habitable and its means of escape is a window or a door opening into the well, with steps up to ground level, then glazing over the top of the well encloses that route. Whether it remains acceptable is a question for the fire strategy rather than an assumption.
Solutions exist: an openable panel in the glazing, a route out at the other end of the well, or a different escape strategy for the room. What is not acceptable is discovering the question after the glass is in, which is why it belongs at the first conversation on any habitable basement.
Security
Worth naming, because a covered well changes it in both directions.
An open light well at the front of a terrace is a place somebody can climb down into, out of sight from the street, next to a door and a window. Covering it removes that entirely, which on a basement flat is a genuine improvement.
Against that, laminated structural glass in a floor is extremely difficult to get through, which is exactly what you want until the day somebody needs to get out or in. Which loops back to the escape question and to designing an access panel rather than a sealed lid.
What it is worth
Being straight about the value, because it is a substantial cost.
Covering a light well in structural glass costs a great deal more than leaving it open. What it buys is the space above recovered for use, a hazard removed, a room below that is genuinely lit rather than dim, and on a terrace an outdoor space that gains a usable area.
Where the space above is doing nothing and the room below is habitable, it is one of the better value interventions available in a building of that type. Where the well is out of the way and the room below is storage, it is an expensive way to cover a hole.
What we establish first on walk on glass
We establish ownership and consents first on any terrace, and whether an existing pavement light is historic fabric before proposing anything. We keep the drain, keep the well ventilated, and design the access for cleaning and maintenance in rather than leaving it. And we specify the light transmission as the priority it is on this kind of unit, taking the minimum anti-slip coverage the situation genuinely needs.
Covering a light well turns a hole into a floor and a shaft into a lightwell. The drainage and the ventilation are what decide whether it stays that way.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.