Misted & failed rooflights in Brighton & Hove

Most modern skylights and rooflights are double glazed. Two sheets of glass are held apart by a spacer bar around the edge, and a seal bonds the whole sandwich together. The cavity between the sheets is meant to stay dry and closed for good. That closed cavity is what gives the glazing its insulation value, and it is what keeps the view clear.

A failed unit is one where that seal has given up. You see it as a milky haze, a ring of droplets near the edge, or a lime-scale looking film that appears on warm mornings and never quite clears. It happens in order.

Our page on why rooflights mist up between the panes goes through the causes in detail.

Misting between the panes is not condensation

Sometimes the two things happen together. A badly ventilated bathroom with a rooflight above the bath will throw condensation on the inner face, and a failed unit above it will look worse because the two layers of moisture combine. Clean and dry the inside face first. If the cloudiness is still there, it is in the cavity.

Where failed units show up on a Brighton & Hove roof

Sea air is hard on edge seals, and so is the swing between a cold clear night and a bright south-facing morning. Rooflights on the seaward slopes of a terrace take the salt and the wind. Units in a flat roof that holds standing water around the kerb sit wet for long stretches, and a seal that sits in water is a seal on borrowed time. A roof window above a loft bedroom takes sun all afternoon and cools fast at dusk, which is exactly the thermal cycling that works on a spacer bond.

None of that means your rooflight was badly made. It means the unit did what sealed units do at the end of their working life.

Once the seal has failed, there is no way to dry out and re-seal the cavity in a way that lasts. A replacement is a new sealed unit, or, where the frame is also past it, a whole new rooflight or roof window. Which of the two you need is a judgement made on the roof, and our page on replacing the glass or the whole rooflight sets out how that call is made.

A new glazing unit in a sound frame

Where the frame, the opening gear and the flashing are all in good order and the only fault is the glazing, the unit can be taken out and a new one made to size can go in. The old frame stays. It is the quicker and cheaper route, and it only makes sense when the frame is genuinely sound: no rot in a timber frame, no corrosion pitting in an aluminium one, no sagging or twist.

A whole new rooflight or roof window

If the frame has moved, the kerb is out of square, or the unit is an old single-skin plastic dome, we recommend replacing the entire rooflight. A new unit comes with modern glazing, a thermally broken frame and an upstand that fits the roof as it is now, not as it was when the original was fitted. If your failed unit is an old dome, see replacing an old plastic dome rooflight.

On a pitched roof, the equivalent is a new roof window, often a VELUX window where one is already fitted. We keep the same size where the rafters allow it, which keeps the work to a swap rather than a structural change. Our roof windows and VELUX windows pages cover the new-unit side in more depth.

A rooflight is only as good as the thing it sits on. On a flat roof that is the kerb: a raised timber or insulated upstand, covered with the roof membrane, that lifts the glazing above the water line and carries the weight. Kerbs, upstands and the weatherproofing of the roof around them decide whether a new rooflight stays dry or starts a different problem.

What we check before the old unit comes off

Flat roofs are usually finished in felt, GRP fibreglass or EPDM rubber membrane. Whichever you have, three things get checked.

Weatherproofing a replacement

When the new rooflight is lifted into place, the flashing and the membrane are re-dressed so water has a clear route off and over the roof, not behind the frame. Where the existing membrane is sound, it is cut back neatly and tied into the new upstand. Where it is not, the affected area is re-laid so the kerb is not sitting on tired material. Our flat roof rooflights page shows what a finished kerb looks like.

Pitched roofs and flashing

On a pitched roof the equivalent job is the flashing kit around a roof window. Slate and tile need different flashing, and an old frame removed from a roof covered in slate often reveals lead soakers that are worth keeping and ones that are not. The new unit is flashed to match the roof covering in front of us, not the covering that was there when the original was fitted.

Misting turns up on every kind of glazed roof opening, and the replacement depends on what you have now. Here is how the common types break down across the roofs we see in the city and the towns around it.

Opening, walk-on, conservation and sun tunnel units

Flat roof rooflights and lanterns

These take the hardest weather. A rooflight on a kitchen extension, a rear addition on a Victorian terrace or a flat-roofed garden room is exposed on all sides, and the glass often reaches the end of its life together with the membrane around it. A flat roof rooflight is replaced like for like, or upgraded to a better specified unit.

A roof lantern is built up from several panes of glazing, a ridge and a perimeter frame, and when it mists it is usually one or two panes that go first. A lantern can sometimes be re-glazed pane by pane when the frame is sound. A frame that has weathered badly is replaced as a whole.

Roof windows and VELUX

In a pitched roof, the usual failure is the sealed unit in a roof window, including VELUX windows fitted when a loft was converted. A VELUX window can be replaced with a like for like unit when the size and type still suit your needs. Size codes confuse people: in a code such as MK04, the letter is the width and the digits are the height, so a quick read of the code on the old frame tells us what the replacement needs to match.

A replacement installation is not complicated, but it has a sequence, and the order matters most when the roof is open. We keep the sequence the same on every job so that nothing is decided on the roof for the first time. The full account is on the page what replacing a failed rooflight involves. This is the short version.

What happens inside the house

Where a lantern or large rooflight is coming out, we make sure nothing is stored under the opening. Blinds and any motorised fittings are disconnected carefully and tested afterwards.

Weather and timing

No one fits a rooflight into a downpour. If the forecast turns, the roof is made watertight and the job resumes when it clears. We would rather lose a morning than leave you with a wet ceiling.

Replacing a misted unit is the sort of job people assume needs no paperwork. Sometimes it does not, and sometimes it does. The difference is whether you are changing only the glass, or replacing the whole unit.

Part L and notification for the new unit

Replacing a whole rooflight or roof window, like for like, counts as building work. It is notifiable, and the new unit has to meet Part L of the Building Regulations. For an existing dwelling, a pitched-roof window has to reach 1.4 W/m²K or Window Energy Rating band B. The figure for a flat-roof rooflight or lantern is 2.2 W/m²K. Replacing only the glass in a frame that is sound is not treated as a controlled fitting under the guidance in Approved Document L, so the regulations do not bite in the same way.

We submit the notification ourselves for a notifiable replacement, whether the route is a registered building control approver or the council's own team. Our pages on Building Regulations for skylights and rooflights and whether replacing a rooflight needs Building Regulations approval set out the detail.

Planning permission

A like for like replacement in the same opening, at the same size, rarely raises a planning question for a house. Permitted development for house rooflights comes with conditions: the new unit may project no further than 150 mm from the roof plane, and its top has to stay below the roof's highest point. Flats do not have those rights, so anything beyond a straight swap in a flat needs a conversation with the council first.

Sitting in a conservation area is not enough on its own to take those rights away. Only a planning condition or an Article 4 direction does that, and the council has applied Article 4 to a number of conservation areas in the city, so confirm your address with it first. A listed building needs listed building consent in addition for anything that affects its character. Houses within the South Downs National Park come under the Park Authority for planning purposes. Our planning guide goes through each case.

Paperwork to ask for

Whoever you choose to do the installation, ask to see how the Building Control notification will be handled, and ask for the route in writing. We put it in the access plan, so it sits next to the price rather than behind it.

People search for a repair when a rooflight mists, which is understandable. The honest answer is that a failed sealed unit cannot be repaired. There is no way to re-open the cavity, dry it, refill it and bond the seal in a way that holds up on a roof. So the real question is not repair versus replace. It is which replacement is proportionate. The page on whether a misted rooflight can be cleared covers why the cheaper-sounding fixes do not last.

Signs that point to the glass only, or the whole unit

Cost and what moves it

The price depends on the size of the unit, the type of glass, the kerb or flashing condition, and above all the access to the roof. A rooflight on a ground floor extension that can be reached from a mobile platform costs less to reach than one on a fourth floor terrace behind a parapet. We do not quote figures here because a fixed written quote after a free survey is the only number worth trusting. Our replacement cost guide and the costs page explain the factors.

In Brighton & Hove, the glass is rarely the hard part. Getting to the roof is. The city is full of tall terraces, butterfly roofs behind parapets, mansards, converted flats and streets where nobody parks without a permit. A rooflight sits in the middle of all that, and a new unit is a pane of glass that has to be lifted to it.

Can a rooflight be replaced without scaffolding?

The access plan

That is why every quote carries a written access plan. For a misted unit it spells out the way up, be that garden scaffold, a tower from the street or a mobile platform. It says who applies for the council's scaffold licence and any parking bay suspension (we do). It says whether a freeholder's consent or a licence for alterations is needed, what notice neighbours receive, the Building Control route, and the price. Pavement scaffold and bay suspensions are covered in our scaffold licence guide.

Butterfly roofs, parapets and mansards

A butterfly roof falls to a central valley, with a parapet at the front and back. A rooflight in or near that valley is exposed to every leaf and every gull. Access over a parapet means lifting glass over a wall, and the scaffold has to be built to carry it. On a mansard, the steep lower slope and the shallow upper slope each have their own detail, and a roof window in the steep part sits at a very different angle to one in the flat deck above.

Flats and shared roofs

In a converted house, the roof is usually the freeholder's. Before a misted rooflight in a flat is swapped, the leaseholder normally has to obtain a licence for alterations, meaning the freeholder's consent in writing. Check your lease. The usual position is set out in our leasehold rooflight guide. We list the consent step in the access plan when the building needs it.

A misted rooflight does not only look poor. A hazy unit lets less daylight into the room and flattens the view of the sky. The room below feels darker than it should, and the lights go on earlier. Replacing the unit restores the natural light the opening was put in to deliver.

Light, warmth and ventilation

Loft rooms

In a loft conversion, a roof window is often the only daylight a room has. The Building Regulations set no daylight standard for houses in England, but a bedroom with a clouded window feels it. Means of escape matters here too. A window can be the escape route only on a storey about 4.5 m or less above the ground. A loft on a two-storey house needs a protected stair, not an escape roof window. A roof window can serve as an escape in a bungalow or chalet bungalow within that height, and any replacement has to keep that function.

Blinds, security and noise

Some roof windows have integrated blinds, which can be motorised. If yours does, the replacement needs to match the blind system or be matched with a new one. Laminated glazing is worth asking about on ground level roofs and rooflights above a flat roof extension, for security and for rain noise. We cover the options on the survey.

A local installer knows how the roofs behave. Brighton & Hove is one city, but the roofs change street by street, from the Regency terraces and their parapets to the semi-detached houses of the outer estates, and from the seafront blocks to the downland villages. A person who has been on those roofs will find the problem faster and will plan the access to suit.

What local means in practice

In practice it comes down to three things. There are no public premises, so every visit is booked and every visit is to your roof.

The work carries a 10 year workmanship guarantee, and you can read the terms on our guarantee page.

Where we work around Brighton & Hove

We cover the city and the area up to 30 miles around by road, which takes in the coast east and west, the towns inland and the villages on and below the Downs. Planning and Building Control differ slightly from one authority to the next, and we know the routes in each. For a visit, contact us, or send photographs through the quote form.

If the rooflight is not yet failing but you want to know what you have, the page on whether a misted rooflight is urgent helps you judge how long you can wait.