Roof lanterns in Brighton & Hove

Start at the bottom, because that is where a lantern succeeds or fails. The kerb, also called the upstand, is the raised box that lifts the lantern clear of the flat roof. It does three jobs. It carries the weight of the glass down into the roof structure. It gives the roof membrane something to climb, so standing water never reaches the joint between lantern and roof. And it sets the lantern level, even though the roof below it is laid to a fall.

That last point catches people out. A flat roof is never truly flat. It is built with a gentle slope so rain runs to a gutter or an outlet, and on a rear extension that slope usually runs away from the house. A lantern has to sit dead level or its glazing bars rack, the glass loads unevenly and the seals start to work. So the kerb is taller on the low side than on the high side, and the top edge is set with a spirit level, not by eye against the roof.

Kerbs, upstands and flat roof weatherproofing

There are two ways to build the kerb, and both work. Which suits your roof depends on the opening, the membrane and how much of the old roof is staying.

Whatever the kerb is made of, the membrane must turn up its face and finish under the lantern's base frame, with enough height above the finished roof that a heavy downpour or a blocked outlet cannot push water over the top.

How the membrane meets the kerb

Covering	Detail at the upstand
EPDM rubber	A bonded upstand detail with a termination bar
GRP fibreglass	The laminate carried up and over the kerb as one piece
Torch-on felt	The cap sheet dressed up, with a flashing trim over the edge

If the existing roof covering is near the end of its life, the honest advice is to recover it at the same time, because cutting a new lantern into an old roof only moves the next leak a few feet sideways.

The kerb is also where heat escapes if it is built carelessly. An uninsulated timber upstand is a cold bridge between the warm room and the outside, and on a winter morning its inside face will run with condensation that people mistake for a leak. We line the kerb with insulation on the inside, carry the room's plasterboard up to meet the lantern, and keep the vapour control layer continuous. Our longer guide to roof lantern upstands and kerbs walks through each detail with drawings.

Trimming the opening

A new lantern on an existing flat roof needs an opening cut through the deck and the joists. The cut joists are carried on trimmers, doubled timbers running across the opening that take the load back to the joists either side. On a wide opening the trimmers may need to be sized by a structural engineer, and the opening becomes part of the Building Control application. Where the lantern goes into a new extension, the opening is framed in at the build stage, which is cheaper and neater, so it is worth bringing us in before the roof is decked.

Above the kerb sits the frame: a base or eaves beam running round the top of the upstand, and glazing bars rising from it to the ridge. The bars are what you see from the room below, so they decide much of how the lantern looks. Slim bars make the glass read as one surface. Heavy bars break the sky into strips. Between them sit the sealed glass units, held by gaskets on the inside and capped on the outside.

Aluminium, timber or PVC frames, colours and finishes

An aluminium roof lantern is the usual modern choice, and for sound reasons. Inside and outside can be different colours: a dark grey outside to suit a slate or zinc roofline, white inside to match the ceiling, or any RAL shade you choose.

Lantern frame materials

Frame	Strengths	Worth knowing
Aluminium	Carries large glass units on slender bars, does not rot or swell, thermal break between outer and inner sections, powder-coated finish needs only an occasional wash	The usual modern choice
Timber	Suits older houses, listed buildings and garden rooms where the joinery is already painted wood; good hardwood or engineered timber looks right in a Victorian back addition	Needs repainting, and the bars are thicker for the same span
PVC	Costs less at the outset and is thermally efficient	Bulkier bars and a narrower colour range

We compare the first two in detail in aluminium or timber roof lanterns.

Glazing specification and thermal performance

Overhead glass is treated differently from a wall window. Each unit is double glazed or triple glazed, with a toughened outer pane to take hail, wind-blown grit and a dropped tool, and a laminated inner pane. Laminated glass holds together if it breaks, so nothing falls into the kitchen. The cavity is filled with argon and the inner pane carries a low emissivity coating that reflects heat back into the room.

The thermal performance of the whole lantern, frame and glass together, has to meet Part L of the Building Regulations. For a lantern or any rooflight on a flat roof in an existing house, the limit is 2.2 W/m²K. A good double glazed aluminium lantern meets that, and triple glazing goes further where the room is used all day in winter. Energy efficiency is not only about winter, though. A south-facing lantern over a kitchen can overheat a room in July, so we look at solar control coatings, which cut the heat coming through while letting the daylight in, and at how the lantern will be ventilated.

At the top, the glazing bars meet at a ridge beam or, on a square lantern, at a single point. This is the part that decides the lantern's shape and how it sheds water. Rain lands on the glass, runs down the slope between the bar caps, reaches the eaves beam and drips clear of the kerb onto the membrane, which carries it to the gutter. Nothing should ever stand on the glass, and nothing should collect against the upstand.

Which shape suits your roof

Pitch, ridge caps and water at the eaves

The pitch of the glass, set by the lantern's design, has to be steep enough that rain runs off rather than sitting in films that leave dirt behind. The ridge itself is capped and sealed so water running from both sides cannot find a way in at the top. At the bottom, the eaves beam has an internal channel that catches any condensation forming on the inside of the glass and drains it to the outside, so cold mornings do not drip onto the worktop.

The weak point on a poorly specified lantern is the corner, where the hip bar meets the eaves beam and water from two faces converges. A well-made lantern handles this with a moulded corner cap and a continuous gasket. Cheaper ones rely on site-applied sealant, which is why so many old lanterns start to drip at the corners first.

Gulls, salt and the coast

Close to the seafront, gulls treat flat roofs as their own, and a lantern ridge makes a good perch. Their droppings are acidic and their nesting material blocks outlets. A self-cleaning coating helps the glass, but the gutters and outlets around the lantern still need clearing, especially after the nesting season. Salt in the air dulls a powder-coated frame over time, and a wash with clean water a couple of times a year keeps the finish as it should be. That is the whole of the maintenance on a good aluminium lantern: clean glass, a clear roof and clear outlets.

Roof lanterns are made in standard sizes and to measure. Standard sizes come off the manufacturer's range in common widths and lengths, and they are quicker to supply. A bespoke roof lantern is made to the exact opening, and on a Brighton and Hove roof that often matters, because older extensions rarely have square openings or tidy dimensions.

Standard sizes or bespoke made-to-measure

Getting the proportion right

A useful starting point is to look at the ceiling, not the roof. The lantern should sit centrally over the part of the room that is used most, usually the kitchen island or the dining table, with enough plain ceiling round it for downlights, extractor ducting and any steel beam. On a narrow terrace extension the width is set by the joists and the party walls either side, so the lantern grows in length rather than width. Our guide to roof lantern sizes and proportions has the rules of thumb we use.

A roof lantern needs a flat roof above the room, so it belongs on single-storey parts of the house.

Where a lantern can go

Roof	Suits a lantern?
Rear and side extensions, back additions	Yes
Garden rooms and orangeries	Yes
Flat roof over a ground-floor shop or studio	Yes
Flat crown of a mansard, flat top of a stair	A small lantern, where the roof is accessible and the structure allows
A pitched roof	No: the right product is a roof window, set in the slope

Why natural light from above matters

A window in a wall lights the first few metres of a room. A skylight overhead lights the middle. In a deep kitchen extension behind a terraced house, where the only windows are the bifold doors at the garden end, the back of the room near the old house wall can be dim all day. A lantern placed over that back half evens the light out, so the room feels like one space rather than a bright end and a dark end. Light from above also changes through the day in a way a side window does not, and it is the change you notice first once it is fitted.

There is no Building Regulations requirement for daylight in a house, so the choice is yours. But a lantern does more for a dim room than another downlight, and it costs nothing to run. Whether that is worth the outlay depends on the room. Our page are roof lanterns worth it? sets out the questions to ask yourself.

Kitchen extensions on terraced houses

A classic place for a lantern is over a kitchen in a single-storey extension on a terrace. We cover this room in depth in roof lanterns for kitchen extensions in terraced houses.

Opening vents and electric controls

For a fully opening unit over a stair or a roof terrace, our electric and opening rooflights are the better fit.

Lantern or a flat rooflight

A flat rooflight is a single sheet of glass, slightly angled, sitting on a kerb. It is lower, less visible from neighbouring windows and simpler to weather. A lantern gives more height to the ceiling, a sense of volume and light from several angles. On a roof overlooked from upper windows next door, or where the planners want something low, a flat roof rooflight can be the better answer. Our page roof lantern or flat rooflight compares them side by side.

Two separate systems apply to a lantern, and people often confuse them. Planning is about whether you are allowed to change how the building looks. Building Control is about whether the work is built safely and to the energy standards. You may need one, both or, in a few cases, neither.

Planning permission

On a house, rooflights can be fitted under permitted development, the national rules that let some work go ahead without an application. For rooflights those rules say the unit must not protrude more than 150 mm beyond the roof plane and must not be higher than the highest part of the roof, among other conditions.

Our planning guide for rooflights in Brighton & Hove covers each case, and the short answer page do you need planning permission for a roof lantern? starts from the lantern itself.

Building Regulations

Cutting a new opening in a roof is building work. Building Control looks at the structure, meaning the trimmed joists and the load from the lantern, the weathering of the kerb, fire where the roof is close to a boundary, and the energy performance of the unit. Replacing a whole lantern, even like for like, is also notifiable and the new unit has to meet Part L. Changing only the glass in a sound frame is not treated as a controlled fitting.

We handle the Building Control notification where the work is notifiable, either through the local authority or through a registered building control approver, and the route is written into the quote so you know who signs it off. Our guide to Building Regulations for skylights and rooflights explains each part of the regulations as it applies to a lantern.

Neighbours and the party wall

A large lantern arrives as a frame and a stack of heavy sealed units, and every piece has to reach the roof without going through a neighbour's garden uninvited or across a kitchen floor. In Brighton and Hove that is often the hardest part of the job. Rear extensions on terraces are reached through the house or over the back wall, streets are steep and narrow, parking is by permit, and the flat roof you want to glaze may belong to a building split into flats.

This is what the access plan is for. It is a written page in every quote that sets out how we will reach your roof, which permissions are needed, who applies for each and what it costs. We draw it up from the survey, not from a map, and you read it before you agree to anything. See the access plan for an example of what it covers.

Routes to the roof

We apply for the scaffold licence and any parking bay suspension ourselves, and our page on scaffold licences and parking suspensions explains the process.

Converted houses and freeholders

In a house split into flats, the roof, including the roof of a rear extension, usually belongs to the freeholder. A leaseholder who wants a lantern normally needs the freeholder's written consent under the lease, often called a licence for alterations, as well as planning permission. The freeholder's insurer may want to know. The neighbours in the flats below need notice of the work and the dates. None of this is legal advice, so check your lease first. We plan the timing around consents and write them into the access plan. Our guide to rooflights in flats and leasehold buildings goes further.

Why a local installer plans the access

The lantern itself comes from a factory and is the same wherever it is fitted. What changes from street to street is the route up, the consents and the roof it sits on. A local installer who has walked the street at the survey knows whether the lorry can stop outside, whether the garden has a side gate and whether the council will want a licence. That knowledge goes into a fixed written quote, so the price you agree is the price for your roof, reached your way.

Some of the lanterns we are asked about are already on the roof. Some are early polycarbonate or PVC units gone yellow and brittle. Some have misted glass, where the seal on a sealed unit has failed and moisture has got between the panes. Others drip at the corners or along the eaves every time it rains hard. In each case the fix is assessment first, then the right replacement.

Misted units and failed seals

A misted sealed unit cannot be repaired. Once the edge seal has gone, the cavity has lost its gas and taken on moisture, and the coating inside is degrading.

Our misted and failed rooflights page explains how we tell the two apart.

Leaks at the corners and the kerb

Water coming in around a lantern is rarely the glass. It is usually the kerb, the membrane where it turns up the upstand, or a corner cap that has opened. We trace where the water is getting in before recommending anything, and on an old lantern with a tired kerb the right answer is often a new kerb and a new lantern together. Our answer page do roof lanterns leak? sets out the usual causes in order.

A whole-lantern replacement is building work, notifiable and measured against Part L, so the new unit will be far warmer than the one it replaces. The kerb is checked and, where needed, rebuilt and insulated, and the membrane is renewed around it. If the old opening is a size no longer made, the new lantern is made to measure to fit it.

Every job starts with a free survey. We go up on the roof where it is safe to do so, measure the opening or the proposed opening, look at the joists, the membrane, the falls and the outlets, and walk the route from the street to the roof. Inside, we look at the ceiling and where the light will fall. From that we write a fixed quote with the access plan as one of its pages.

How the installation works, step by step

On a small lantern over an existing opening, roof and lantern can be done in a short visit. On a large new opening with a new roof covering, the work runs over several days, and weather sets the order. Lantern installation is never done in the rain, and an opening is never left without a temporary cover overnight.

What affects the cost

We do not publish prices for lanterns, because the unit is only part of the job and the rest depends on your roof. The main things that change the price are set out below.

What moves the price of a lantern

Factor	What changes
The lantern	Size and shape, frame material, the glass specification and any coatings, opening vents and blinds
The roof	Whether the opening is new or existing, whether the kerb is reused or rebuilt, how much of the roof covering is renewed
Access	Above all else: a bungalow extension reached from a driveway and a mansard top above a steep street with a permit-only bay outside are very different jobs, even with the same unit

Our page how much does a roof lantern cost? takes each factor in turn, and our costs page explains how quotes are put together across the range.

The quote is fixed and written. If the survey shows the joists or the roof need more work, that is in the quote before you agree it. The work is covered by our 10-year workmanship guarantee, and every unit is installed to current Building Regulations.

If you are weighing up roof lanterns in Brighton and Hove, the next step is the survey. Book a free survey and we will look at your roof, the room under it and the way up.