Put a standard roof window into a Victorian slate roof and you will see the problem from the street. The frame stands above the covering, the surround is thick and the plastic or wide aluminium trim looks like what it is, a modern unit added to a roof that never had one. A conservation rooflight sets out to avoid that. The glass sits almost level with the slates or tiles around it, the frame is slender, and a single central glazing bar echoes the cast-iron skylights that older buildings sometimes carry.
The look is only half of the subject. Period roofs tend to sit in the places where the rules are tightest: conservation areas, the South Downs National Park, streets covered by an Article 4 direction and, of course, listed buildings. Whether you may fit a rooflight at all, and which one, depends on which of those apply to your address.
This guide explains what makes a unit low-profile, how it is fitted into slate and clay tile, what the planning position is in general and in the Adur and Worthing directions that reach roofs, how listed buildings differ, and what to check on performance before you choose. It is written for owners of older houses in Worthing, Shoreham, Steyning, Arundel and the villages around them.
What makes a rooflight low-profile
A conservation rooflight is defined by how it sits, not by a label. Three features do the work. The first is a flush fit: the glazing lies in the same plane as the surrounding covering, with a slim frame that stands only a little above it, so from the street it reads as a thin line in the roof. The second is the frame itself, made from steel or slim aluminium finished to look like old metalwork, with fine glazing bars where the pane would otherwise look empty. The third is the flashing, the metal skirt that seals the unit to the covering, which is shaped to follow the courses of slate or tile and so does not show as a coloured collar.
In-plane units are roof windows, in the rules
Approved Document L describes a roof window as one installed in the same orientation as, and in plane with, the surrounding roof. A flush conservation unit therefore counts as a roof window for thermal purposes, even though it is sold as a rooflight. That matters for the numbers later in this guide.
Fixed units are the neatest, and they suit stairwells, landings and bathrooms where opening is not needed. Opening versions exist, usually top-hung with a hidden hinge, and they are the better choice in a loft room that needs ventilation. A larger unit may be built with two bars, and the spacing is worth checking against the rhythm of the roof, since a rooflight that cuts across the line of the battens looks more intrusive than one that follows it.
If you are weighing a conservation unit against an ordinary one, our skylights and roof windows section sets out the range.
Fitting one into slate, clay and stone roofs
The fitting on a period roof is more careful than on a modern one, because the covering around the opening has to be lifted and put back so that the repair does not show.
On a slate roof, the slates around the position are stripped, the opening is framed between the rafters with a trimmer above and below, and the unit is bedded onto the frame. Flashing is lapped with the slates above and below and dressed with lead at the sides. Old Welsh slates are brittle once they have been nailed for a century, and some will break on lifting, so a few spares from elsewhere on the roof, or from a reclaimed source, are part of the plan. We assess how sound the slates are at survey.
On a clay tile roof, peg tiles are small and numerous, so the opening works out to a whole number of courses, and the flashing is stepped to match them. For a stone-slate roof such as Horsham slab, the work needs a specialist and a conversation with the conservation officer first, since the Stone Roofing Association wants original slabs kept in service first.
Position and number
Where the rooflight goes matters as much as which one is chosen. Rear slopes, which are hidden from the road, are the easiest to justify. A pair of units set in line with the windows below look better than a single one placed at random, and a row of three or four regularly spaced reads as part of the design. Front slopes face the tightest scrutiny in a conservation area, and in an Article 4 area the street-facing slope is exactly where rights may have been taken away.
Sound rafters at the right spacing make a clean opening, so a timber check goes with the survey.
Conservation areas and the National Park: what Class C allows
Many owners assume that a conservation area bans roof windows. It does not. Class C of Part 1 of the General Permitted Development Order, which covers other alterations to the roof of a dwellinghouse, has no exclusion for article 2(3) land, the term that includes conservation areas and National Parks. Class C can therefore apply in both, unless an Article 4 direction or a planning condition has removed it, or the building is listed.
Within Class C, the limits that matter are physical. The alteration may stand no more than 0.15 metres proud of the original slope, a limit a flush conservation unit is designed to meet, and its highest point may not exceed that of the original roof. Chimneys, flues, soil pipes and solar equipment fall outside the class.
The side-slope condition
Class C also attaches two conditions to a window in a pitch facing the side of the house. Obscure glass is required without exception. The window must also stay shut, with one allowance: if the opening part sits higher than 1.7 metres off the floor, it may open. That height eases the keep-shut condition and nothing else. Clear glass in a side slope therefore needs a planning application.
Flats do not have these rights, because the order defines a dwellinghouse so as to exclude a flat or a building containing flats. Dormers are a separate matter: in a conservation area or the National Park they are not permitted development at all.
Inside the National Park, the Park authority, not the borough, takes planning decisions for the Adur and Worthing land lying within it. Outside the Park, ask the Adur & Worthing planning team. Our guide to planning permission for skylights goes through the rules in order.
Article 4 areas in Adur and Worthing
An Article 4 direction lets a council take named permitted development rights away within a mapped area, so you apply for the items the direction names before starting. The councils stress that a direction does not forbid the work. It only means asking first. In some conservation areas they have served directions that remove normal rights for alterations such as replacing roof tiles and windows.
We have read the notices for several roof-relevant directions, and what each removes is specific.
- Old Shoreham (in force 20 January 2023): on faces turned towards a road or public path, Class C alterations to the roof, including coverings and rooflights, and the installation or alteration of a chimney, flue or soil pipe anywhere.
- Kingston Buci (in force 10 February 2023): the same pattern, with Class C including roof coverings, and chimneys.
- Warwick Gardens, Worthing (made 2001): chimney alterations, and, where the house faces a road or open space, altering how a roof slope looks or what it is made of.
- Warwick Place, Worthing (made 1997): where fronting Warwick Place, Class C roof alterations.
- Western Row, Worthing (made 1978): annotated as removing all dwellinghouse permitted development rights.
Other directions exist, and not every direction touches roofs. Ambrose Place and Cowper Road, for example, deal only with outbuildings, hard surfaces and enclosures, and do not remove roof rights.
The first step is always to confirm the status of your own street with the Adur & Worthing planning team. Do not rely on a neighbour's experience, because a direction may cover one side of a road and not the other.
Listed buildings and places of worship
For a listed building, permitted development is not the starting point. Under the Planning (Listed Buildings and Conservation Areas) Act 1990, any work that changes a listed building in a way touching its special architectural or historic interest needs prior authorisation, and doing it unauthorised is a criminal matter. Cutting a new opening in a historic roof, and removing the old fabric around it, will normally be that kind of alteration.
The Adur & Worthing guide counts repairs made in non-matching materials among the works that need consent, and treats prudent maintenance and general repair as needing none. The South Downs National Park Authority draws the same line: keeping a roof in order with small matching repairs needs no listed building consent, but changing or fully replacing historic fabric, and so affecting the building's character, does. A rooflight in a roof that never had one replaces nothing.
What to prepare
An application for consent is easier to decide when it shows the existing roof, the exact position of each unit, the section through the frame and the finish. Keep the number of openings to the minimum, put them where the roof is already plain, and expect the conservation officer to ask why the light cannot come from elsewhere.
A church still used for worship may be exempt from listed building control: Anglican churches go through the faculty system, and four other named denominations run their own approval procedures. Other faiths, redundant churches and scheduled monuments follow different routes. If your roof belongs to a place of worship, ask the denomination or the planning team before anything else.
Do not order the unit until the consent is in hand.
Performance, condensation and choosing a unit
Historic character and modern thermal standards can sit together if the specification is right. For a roof window installed in an existing dwelling, Approved Document L Table 4.2 sets a ceiling of 1.4 W/(m²·K) for a roof window, with a Window Energy Rating of Band B accepted in its place. A true raised rooflight on a kerb is held to 2.2 instead. A flush conservation unit lies in plane with the roof, so the first figure is the one to put to the supplier. Part L also asks that a swapped element is not poorer than its predecessor, a test an old single-glazed skylight is easy to beat.
Slim frames are the usual trade-off. A narrow steel or aluminium section with a thermal break will not insulate as well as a deep modern frame, so choose the unit on its whole-window figure, not the glass alone. Double or triple glazing, an inner pane that is laminated and a low-emissivity coating all help. Ask for the data sheet and keep it with your building control or planning papers.
Condensation is the usual complaint after fitting. A cold frame in a warm bathroom will mist, and the cure is better ventilation rather than a different unit. If a unit has already misted between the panes, that is a failed seal and a separate fault, covered in our guide to a misted roof window.
When an old unit is simply worn out, replacing an old roof window is the right page, and for a loft room needing a proper escape window see roof windows for a loft conversion. For a dark landing with no suitable slope, a sun tunnel may avoid altering the visible roof at all.
We survey the roof, show you photographs of it and follow with a written quote, one total figure, that names the rooflight specification, the flashing and the finish.
