Roof lantern, lightwell or flat rooflight

Start with plain definitions, because the words get used loosely and that is where most of the confusion begins.

A roof lantern is a raised, framed glazed structure that stands proud of the roof line. It has vertical or near-vertical sides and a hipped or pyramid top, so several panes of glass meet at a ridge or an apex above the plane of the roof. It sits on a builder’s kerb, the upstand, and lifts the glass anywhere from a few hundred millimetres to over a metre above the flat roof around it. From inside, you are looking up into a shaped glass ceiling with real depth to it. It is the option people mean when they picture a Victorian orangery roof, and modern aluminium versions carry that same shape with slimmer bars.

A flat rooflight is a single glazed unit that sits close to the plane of a flat or shallow roof, either flush or on a low upstand with a modest slope built in to shed water. There is no raised structure and no internal apex. You get one pane, or occasionally two, held in a slim frame. From below it reads as a bright rectangle set into the ceiling. It is the quiet option, the one that draws light without announcing itself, and on a contemporary flat roof it is often exactly the right answer.

A lightwell is not really a window at all. It is the shaft that carries daylight from a rooflight down to a room that does not sit directly under the roof. When there is a loft floor, a deep roof build-up, or a void between the glass and the room you want to light, the light has to travel through that depth. A lightwell is the lined, usually splayed, throat that guides it. At the small end sits a rigid light tube, sometimes called a sun pipe, with a mirrored shaft no wider than a dinner plate. At the large end sits a plastered, splayed shaft big enough to stand in, opening out as it drops so it spreads the light into the room rather than dumping it in a narrow column.

The roof usually makes the decision before taste gets a look in.

A roof lantern needs a flat or very shallow roof to stand on. The kerb has to be built level and square, and the flat deck around it has to be wide enough to carry the structure and let water run off past it. So the natural home for a lantern is a single-storey rear extension with a flat roof, the sort that covers a knocked-through kitchen and dining space. It does not belong on a steep tiled slope, and it is heavier and taller than the alternatives, so the structure below has to be sized for it.

A flat rooflight lives on the same kind of flat roof but asks far less of it. It is lighter, lower and simpler to weather, so it suits everything from a small utility roof to a run of several units marching across a wide extension. It is also the right call where headroom is tight or where the look is meant to be calm and modern rather than ornate. Our flat-roof skylight work is mostly these: single panels and runs of them over extensions where the ceiling is the feature and the glass is not supposed to compete with it.

A lightwell comes into play the moment the glass cannot sit directly over the room. Put a rooflight on a pitched roof above a loft that you have not converted, and the light lands in the loft, not the bedroom below. Form a lightwell down through the loft floor and you deliver it to the room. The same trick lights a windowless bathroom, a landing, a deep-plan hallway or an internal stair core that has no external wall to take a window. On a pitched roof the rooflight at the top of a lightwell is usually an in-plane unit sitting flush with the tiles, which is a job for pitched-roof glazing rather than a flat-roof product.

All three bring in overhead daylight, which is worth two or three times a wall window of the same area because it faces the open sky rather than a fence or a neighbour. But the quality of that light differs.

A roof lantern gives the most generous light and the most theatre. Because the glass is raised and multi-faceted, light enters from several directions through the day, and the internal reveals of the kerb bounce it around, so the room brightens early and stays bright late. The apex draws the eye up and makes a room feel taller than it is. If the effect you are after is a space that feels like it has had the lid lifted off, the lantern delivers it and nothing flush will match it.

A flat rooflight gives light that is even and undramatic. A single flush pane pours a clean rectangle of sky onto the floor and moves it across the room as the day turns. It is the honest, quiet daylight that suits a modern kitchen or a study. Gang several together and you get a bright, calm ceiling without any of the height a lantern adds. What you lose is the sense of volume; what you gain is simplicity and a lower, tidier roof line.

A lightwell gives the least light of the three, and how much depends entirely on the shaft. A rigid light tube can transform a windowless internal bathroom from a room that needs the switch on at noon to one that does not, but it will not flood the space. A large plastered lightwell, splayed wide and painted a flat white, can throw a surprising amount of daylight into a room below a loft, but every metre the light travels down the shaft costs you brightness. The rule is simple: keep the shaft short, keep it wide, splay the sides outwards and paint them the palest you can. A tall narrow lightwell painted a warm colour is a good way to waste a rooflight.

This is where the three options stop being a matter of taste and become a matter of physics, and it is the part most quotes leave off the page.

Southend faces south across the Thames Estuary, which is unusual for an English seaside settlement and changes what a good overhead specification looks like. A south aspect with an open horizon and a large reflective body of water in front of it means the roofs along this coast collect more solar energy than roofs further inland, for more hours of the year. Overhead glass faces the sky more squarely than any wall window, so it gathers the sun’s heat efficiently in exactly the months you do not want it. A roof lantern, with the largest glass area of the three and several planes catching the sun through the day, is the strongest solar collector you can put on a house. Over a south-facing kitchen it will bake the room between early afternoon and evening unless the glass is specified for it.

This is the whole reason we survey orientation before we talk about product. The number that governs summer heat is the G-value, the fraction of the sun’s energy that passes through the glass and becomes heat in the room. Clear double glazing sits around 0.6, so more than half the incident energy comes through. A solar-control unit drops that to roughly 0.3 without turning the room dark, because a good coating rejects the invisible near-infrared that carries the heat while letting the visible light through. On a south-facing lantern or a run of south-facing flat rooflights, that difference is the difference between a room you use all summer and one you shut the blinds on by two o’clock. Glare matters too: a low sun through a large overhead pane straight onto a screen or a hob is not just uncomfortable, it drives people out of the room. Choosing solar-control glazing for south and west planes is not an upsell, it is what the aspect requires.

A lightwell, oddly, is the gentlest of the three on this front. The shaft and the smaller aperture mean less direct beam reaches the room, and the walls of the well diffuse what does. That does not exempt the rooflight at the top from a sensible glass choice, but a lightwell into a south-facing loft is far less likely to overheat the room below than a lantern over the same aspect.

These are industry-typical ranges for domestic work, not a price list. Exact numbers move with size, glass specification, access and the state of the roof, so read them as the shape of the choice rather than a quote.

Read across the table and the pattern is clear. The lantern costs the most and gives the most, in light and in volume, but it asks the most of the roof and the budget and it needs the most careful glass choice on a sunny aspect. The flat rooflight is the efficient middle: less money, less building work, a lower profile, and a clean even light. The lightwell is the specialist, the only one of the three that can reach a room the sky cannot see directly, at the cost of the least light and a fair amount of internal building work to form and finish the shaft.

One thing the table cannot capture is that these are not always exclusive. A single-storey extension might take a lantern over the dining end and a couple of flat rooflights over the kitchen run. A pitched loft might take an in-plane rooflight for the converted room and a light tube down into the landing outside it. The right answer is often a combination, chosen plane by plane and room by room.

Each option makes a different demand on the building, and getting that wrong is where problems start.

A roof lantern needs a level, square kerb and a flat roof structure sized to carry both the weight of the glass and aluminium and the wind loads on a raised object. The upstand is not optional trim: it lifts the glass clear of standing water and gives the flashing something to turn up against. Bigger lanterns need proper structural thought about the opening in the roof, the trimming timbers or steel around it and how the load gets back to the walls. This is the sort of thing a bespoke rooflight design resolves before anything is ordered, because a lantern that arrives without the structure ready for it is a lantern that waits on the drive.

A flat rooflight is far more forgiving. It still wants an upstand, ideally at least 150mm, to keep the glass above the wet line of a flat roof, but the loads are lower and the opening in the deck is smaller. Where a roof is genuinely flat, a purpose-made upstand with a built-in fall matters more than most people expect, because a rooflight sitting in a puddle is a rooflight that will eventually show it.

A lightwell is mostly internal building work. The rooflight at the top follows the rules for whatever roof it sits in. Below it, the shaft has to be framed, insulated where it passes through cold roof space, boarded, plastered and decorated. Splaying the sides so the well opens outwards as it drops is what turns a dim column into a room that feels naturally lit, and it is worth insisting on even though it takes a little more work than a straight vertical shaft. Insulation around the shaft matters too, because an uninsulated lightwell through a cold loft is a cold bridge that will show up as a stripe on the ceiling in winter.

All three are building work, and two of them change the outside of the roof, so the rules apply.

New or enlarged rooflights are notifiable under Building Regulations. Part L governs the thermal performance, which is why the glass has to meet a maximum U-value, and Part K governs safety glazing and guarding, which is why anything overhead needs laminated glass on the inner pane so it cannot fall as shards if it ever breaks. We make the Building Control notification to Southend-on-Sea City Council, or to the relevant local authority for your address, as part of the installation, so that side is handled.

Planning is usually more relaxed, with important exceptions. As general guidance, rooflights on a house are permitted development where they project no more than 150mm beyond the roof plane and do not sit above the highest part of the roof. A flush flat rooflight and a modest in-plane unit at the top of a lightwell normally fall inside that. A roof lantern, by definition, stands well proud of the roof, so on some elevations it will need a planning application even where a flush unit would not. The rules tighten again for flats and maisonettes, listed buildings, and conservation areas. Leigh and Leigh Cliff carry an Article 4 Direction that removes permitted-development rights for changes to roofing and windows, so a lantern, and often a rooflight too, needs a planning application there where it would not elsewhere. Clifftown and Leigh Old Town are conservation areas as well. None of this is a reason to avoid overhead glass, only a reason to check with the local authority before ordering, and we will tell you which category your address falls into.

Match the option to the roof, the room and the aspect, in that order.

The very large 1930s semi belt across south Essex, with its rear extension over a knocked-through kitchen, is lantern and flat-rooflight territory. If the roof is flat and the room wants drama and height, a lantern earns its cost. If the ceiling is lower, the budget tighter, or the look meant to be calm, a run of flat rooflights does the job with less fuss and less roof. Either way, if that extension faces the estuary, the glass on the south planes has to be solar-control, or the room becomes unusable on the afternoons you most wanted to sit in it. The roof lantern installation service starts from that orientation survey rather than from a catalogue.

The Victorian and Edwardian terraces and villas along the cliff, and the newer estates at Shoeburyness and Basildon, are where lightwells earn their keep. A loft you have not converted, a windowless internal bathroom, a dark central landing: these are rooms no lantern or flat rooflight can reach directly, and a well-formed lightwell or a light tube is the only clean way to get daylight into them.

Whatever you are leaning towards, four questions settle it with whoever is quoting:

1. Which way does this roof plane face? Orientation drives the glass choice, and on a south or west plane it drives it hard. A quote that does not mention aspect has skipped the step that matters most on this coast.
2. What is the G-value of the glass, and is the U-value whole-unit or centre-pane? The G-value tells you how the room behaves in summer; the whole-unit U-value is the honest thermal figure and the one Building Control cares about. Centre-pane numbers always flatter.
3. How tall is the upstand, and does it have a fall built in? On a flat roof this is what keeps the glass out of standing water. On a lantern it is also structure.
4. If it is a lightwell, how deep is the shaft and how wide does it splay? A short, wide, splayed, brilliant-white well delivers usable light; a tall narrow one delivers disappointment.

We have been installing skylights, rooflights and roof lanterns across south Essex for over fifteen years, every job backed by a ten-year workmanship guarantee and notified to Building Control on your behalf. If you are weighing a lantern against a flat rooflight against a lightwell for a particular room, the fastest way to settle it is to have the roof surveyed and the aspect worked out. Ask us for a specification and we will tell you which of the three that roof is asking for, with the G-value and the U-value written down for each plane.