Energy efficient rooflights in Brighton & Hove

Start at the roof, because a very good pane of glass sitting on a cold, leaky kerb still wastes heat. The kerb is the raised upstand that lifts a rooflight or lantern clear of a flat roof. On an older extension it is often a simple timber box with little or no insulation, and the cold travels straight through it into the ceiling reveal. Energy efficient rooflights in Brighton are normally fitted on a kerb that is insulated and sealed to the roof deck, so there is no thermal gap between the warm room and the outside air.

The kerb also has to be airtight. Warm, damp air from a kitchen or bathroom finds any gap at the base of the upstand and condenses inside the build-up. Over time that rots the timber and stains the reveal. Good detailing does three things.

Kerbs, upstands and weatherproofing the roof

The kerb is only as good as the roof membrane that climbs it. On a flat roof the covering turns up the upstand and is finished under the unit's own flashing, so rain that runs off the glass has nowhere to go but away. If the existing membrane is tired where it meets the new kerb, that is raised in the survey and priced in the written quote, so you are not surprised halfway through the job. Our guide to flat roof rooflights goes through the roof build-ups we meet most often.

A kerb is also set to the fall of the roof. Flat roofs drain to a gutter or outlet, so the roof is never perfectly level, and the kerb has to be built so the glass above it sits true. That is one reason we measure the roof itself, not just the old opening.

Parapets, butterfly roofs and seafront exposure

Many Brighton and Hove terraces have a parapet wall around a shallow roof, and the older Regency and Victorian houses often have a butterfly roof, where two slopes tip inwards to a valley gutter in the middle. A rooflight on either type has to respect the drainage line, and the kerb needs enough height to keep clear of standing water in the valley. Near the seafront, wind and salt are a fact of life. Wind uplift on a large lantern is real, so the fixings and kerb connection are specified for exposure, and exposed aluminium parts carry a powder coat specified for coastal exposure rather than being left to the weather.

Modern energy efficient rooflights use sealed glazing units: two or three panes held apart by a spacer, with the gap between them filled with gas. The filling is usually argon, which conducts less heat than air. One face of the glass carries a low emissivity coating, a microscopically thin layer that reflects heat back into the room while letting daylight through. Together these are what bring a unit down to a good thermal figure.

Glazing specification, U-values and heat loss

A U-value measures how fast heat passes through a building element. The lower the number, the better. Part L of the Building Regulations sets two limits for existing dwellings. A new or replacement flat-roof rooflight or lantern has to achieve 2.2 W/m²K, and a pitched-roof window has to achieve 1.4 W/m²K or Window Energy Rating band B. Those are the minimum standards, not the target. Our page on rooflight U-values explained shows how to read the figure on a data sheet, and what U-value a rooflight needs deals with the rule for your particular roof.

Double or triple glazing

Whether the gain is worth it depends on the room, the orientation and how much of the ceiling the glass takes up. For a very large or very cold glazed area triple earns its place. We lay out the argument in double or triple glazed rooflights and the more direct question of whether triple glazing is worth it for a rooflight.

Safety, security and fire performance

The outer pane of a rooflight is usually toughened glass, and the inner pane is laminated, so that if anything breaks the pieces stay held together rather than falling into the room. This matters on a roof where people can fall or objects can land on the glass. Walk-on units use much thicker laminated glass and are a different product, covered on our walk-on rooflights page. Where a rooflight sits close to a boundary, Building Control looks at fire spread, and the choice of glass and frame can matter. Some stairwell rooflights are also fitted as smoke vents, which is a separate specification agreed at design stage.

The spacer is the thin strip that holds the panes apart around the edge of the sealed unit. It is easy to forget, and it is where a lot of heat escapes.

Frame materials, colours and finishes

Frame materials compared

Frame	Strengths	Trade-off
Aluminium	Slim, strong, suits long spans	Conducts heat, so it needs a thermal break
Timber	Made for rooflights too	Trades slimness against insulation and upkeep
PVC	Made for rooflights too	Trades slimness against insulation and upkeep

Frames for energy efficient rooflights in Brighton are normally aluminium. A proper frame has a thermal break: a section of insulating material between the inner and outer parts of the profile, so the cold outside never meets the warm inside. A powder coated aluminium frame needs little attention, and the finish can be chosen to match your windows. Dark greys and blacks are common on contemporary extensions, while a softer colour often suits an older house better.

Where a roof lantern is involved, the frame does more of the work. Its glazing bars carry the weight of the glass, so the section has to be slim without losing strength or thermal performance. Our page on roof lanterns deals with how bars, pitch and glass interact.

Energy efficiency is a property of how a unit is made, not of its shape, so every type below can be specified to meet or beat Part L. The real choice is which shape fits the roof and the room.

Types of energy efficient rooflights and which suits your roof

Rooflights for loft conversions and extensions

A loft conversion needs roof windows in the slope, and a rear extension usually needs a flat rooflight or lantern. The requirements differ. In a loft, the head height, the sleeping use and the escape route decide the window. An escape window helps only on a storey no more than about 4.5 m up, so a two-storey house needs a protected stair, while a bungalow or chalet bungalow can rely on a roof window. In an extension, the main issue is how much glass the room can take before it overheats or loses too much heat.

A fixed rooflight is the most thermally efficient because it has no moving joint. But a room with a lot of glass above it will also trap heat in summer, and an opening rooflight is the simplest fix. Warm air rises, so a vent at the top of the room draws cooler air in lower down and lets the hot air out. Our electric and opening rooflights page covers the range, and the effect on summer heat is the subject of do rooflights overheat in summer.

An opening rooflight in a loft counts as the way out only if the floor sits no higher than about 4.5 m above the ground. Where a stairwell needs a smoke ventilation rooflight, the specification comes from the fire design, and Building Control signs it off. We note both at the survey so they are in the written quote.

Most roof windows come in standard sizes, which is why they are quick to order and easy to replace like for like. VELUX size codes are a good example: the letter shows the width and the digits show the height. Flat rooflights and lanterns are different. They are often made to measure, because the opening in a flat roof is rarely a stock dimension. A bespoke unit is cut to the opening, so there is no oversized frame hiding a gap.

Mansards, conservation areas and listed roofs

A mansard has a steep lower slope and a shallow upper one, and a rooflight there has to sit within the pitch without breaking the line of the roof. Dormers already in the slope limit where a new window can go, and the glass has to clear their cheeks and the rafters behind. In a conservation area, or on a listed house, the council often prefers a slim conservation style unit that sits flush with the slates or tiles, with a single central glazing bar. These can still be thermally efficient: the bar and frame are slim, but the glass behind is a modern sealed unit. Our conservation rooflights page covers the style, and the planning guide linked below covers when consent is needed.

Why natural daylight matters

Natural light changes how a room feels and how it is used. A rooflight lets in more light than a wall window of the same size, because it faces the sky, and a room lit from above feels taller and calmer. Houses in England have no legal daylight minimum to meet, so the amount of glass is your decision. The aim is to bring in enough light that you do not need the lamps on in the day, without so much glass that the room runs cold in winter and hot in summer. The glass specification helps with both.

A common worry is whether rooflights make a room cold, and the answer sits in the glass specification and the fit.

Two separate systems apply, and a rooflight job can touch both.

Planning permission and Building Regulations

For houses, rooflights are usually allowed under permitted development, Class C. Permitted development caps the projection at 150 mm from the roof plane and keeps the unit lower than the roof's highest point, and a side-facing unit needs obscured glass with a fixed or high-level opening. Flats have no such rights, so a flat needs planning permission. Those rights survive a conservation area boundary but not an Article 4 direction or a planning condition, and Article 4 directions cover many conservation areas in the city, so ask the council before you order the glass. A listed building needs listed building consent as well. Inside the South Downs National Park the park authority, not the district council, handles planning. Our full guide to planning permission for rooflights in Brighton and Hove sets this out.

Building Regulations are separate. Replacing a whole rooflight or roof window unit like for like is building work, so it is notifiable and must meet Part L. A new glazing unit in a frame that is still good is not a controlled fitting. A brand new opening in a roof is also building work, because the structure around it has to be trimmed and weathered correctly. Where an upgrade is notifiable, we file the Building Control notification ourselves, with a registered building control approver or the local council. Our Building Regulations guide for skylights and rooflights covers the detail.

Every job starts with a free survey and ends with a unit installed to current Building Regulations. In between is the part that is easy to overlook: how the work actually reaches the roof.

How the installation works, step by step

Our guide to scaffold licences and parking suspensions for roof work explains the process.

Why choose a local installer

A rooflight installed in the wrong place stays wrong for decades. A local installer knows the roofs, the streets and the councils, and plans the job around them. We back every job with a 10-year workmanship guarantee, described in our guarantee.

Where we work around Brighton and Hove

We install energy efficient rooflights in Brighton and Hove and in the towns and villages within 30 miles of the city by road. Contact us through the contact page or the quote form on this page, and we will arrange a visit.

We do not give price figures on a web page, because the price depends on things that only a survey shows. The survey produces a fixed written figure, and the main factors behind it are these.

Cost and what affects it

Large glass areas also move the price in steps, not smoothly. A lantern with several bars, a long run of opening vents or a very large single pane needs more crane time, more people on the roof and sometimes a reinforced kerb. These are the details a survey finds, and they are why a phone price from a stranger is unreliable.

Do not choose on the headline unit price alone. A cheap rooflight on a poor kerb or a bad fix costs more in the end. The quote lists the unit, the work to the roof, the access and the Building Control route, so you can compare like with like.

A well made rooflight needs little attention. Self-cleaning glass has a coating that helps rain wash off dirt, and it works best on a pitched or sloping unit. On a flat unit it is of less use, as dirt tends to sit. The routine is short.

Low maintenance is one of the strengths of aluminium frames with a powder coat. The seals and the gas fill are what age. When a sealed unit fails, you see moisture between the panes that will not clear. A failed sealed unit cannot be repaired, so it is assessed and replaced, and the cost depends on the glass and size. See misted and failed rooflights for what to look for.

A good rooflight should last for decades, and the roof beneath it often wears out first. That is a good reason to fit a new rooflight when the roof covering is being renewed, so the two are weathered together. If you see a problem, book a survey and we will assess it.