Two units made for two kinds of roof
A standard roof window, of which VELUX is the best-known make, is designed to be fitted quickly into a wide range of ordinary roofs. It comes with a flashing kit made for the roof covering, a frame that is usually painted wood, white polyurethane or coated aluminium, and a sash that opens by pivoting or by top-hung action. It is a well-resolved product, and it sits proud of the roof by the depth of the frame and the flashing around it.
A conservation rooflight is designed to look as if it belongs to an older roof. The frame is slim and usually metal, the glass sits close to the plane of the slope, and a single vertical glazing bar splits the pane the way old cast iron rooflights did. The aim is a unit that a passer-by reads as part of the roof and not as a window added to it. The sizes and finishes on offer are laid out in our conservation rooflight specification guide.
Neither is better in every case. A standard unit is the sensible choice on a roof with no sensitivity, and a conservation unit is the sensible choice where the council expects care. This guide helps you work out which side of that line your roof sits on, and what to do when it falls in between.
Profile, frame and bar compared
Profile means how far the unit stands above the roof surface. A conservation rooflight is designed to sit very close to the slates or tiles, with the glazing running almost level with the covering. A standard roof window sits higher, because the sash, the frame and the flashing all add depth. On a quiet rear slope that difference barely registers. On a front slope, seen against a line of identical roofs, it can be what a conservation officer notices first.
Frame is the second difference. A conservation unit usually has a slender steel or aluminium frame in a dark finish that echoes cast iron. The frame is narrow so that more of what you see from outside is glass. A standard roof window has a deeper frame and a wider visible border, often in a light colour, and the sash has hardware and seals that add to the width.
The bar is the third. Old rooflights were small panes of glass held by a central bar. A conservation rooflight carries a single bar as a detail that links the new unit to that tradition. Some makers of standard roof windows now offer a conservation version with a bar and a lower profile, which narrows the gap. Our explainer on the glazing bar shows how it changes the look from the street.
| Feature | Conservation rooflight | Standard roof window |
|---|---|---|
| Profile | Flush or almost flush with the slope | Stands proud by frame and flashing depth |
| Frame | Slim, usually dark metal | Deeper, often white or wood |
| Glazing bar | Single central bar as standard | Not usual unless a conservation version is chosen |
| Opening | Fixed, or opening on some designs | Pivot or top-hung opening is common |
| Flashing | Fitted to the roof covering by the installer | Kit supplied for the roof covering |
| Typical aim | Sensitive roofs and older houses | Ordinary roofs and loft conversions |
Is a VELUX allowed in a conservation area?
A conservation area does not ban standard roof windows. A house in one usually keeps its permitted development right for rooflights, unless an Article 4 direction removes it, and the planning permission guide shows who keeps that right and how to check. So the answer to whether a VELUX is allowed in a conservation area is often yes, and the real question is whether it is a good idea on that particular street.
Councils write their own guidance, and many favour flush conservation-style units, particularly on slopes facing the road. Where the planning right is intact, the guidance is advice and not a legal bar, but it shows what an officer would want to see if an application were needed. Where an Article 4 direction applies, as it does in the Railway Village conservation area in Swindon, an application is required and the guidance becomes the test. Always confirm the direction currently in force with the council.
A listed building is a different case, because permitted development does not reach it and consent is needed first. Our guide to rooflights on listed buildings sets out that process. If your house is both listed and in a conservation area, the listed rules lead.
When a recessed standard window may be accepted
Between a full conservation rooflight and a plain standard window lies a middle option. Standard roof windows can be fitted recessed, with the frame sunk into the depth of the rafters and the flashing set lower so that the glass sits closer to the roof surface. Fitted this way, the unit stands much less proud than the usual installation, and the shadow line around it shrinks.
Add a glazing bar and a dark finish, and some conservation officers will accept the result on a less sensitive slope. It is a judgement call and nobody can promise the outcome, because it turns on the street, the age of the building and the council's own approach. What can be said is that the officer is more receptive when the proposal shows thought: the unit is small, the position is on the rear slope, the profile is low and the bar is there.
Recessing needs space. The rafters have to be deep enough to take the frame lower, and the lining inside has to be built to suit. A shallow roof build-up may rule it out, which is why the survey measures the rafter depth. The result goes into the plan, so recessing is a known quantity before you approach the council. Our roof window installation page describes how standard units are fitted.
- Recessed fitting needs enough rafter depth to take the frame lower
- Keep the unit small and on the less visible slope
- Choose a dark finish and a single glazing bar where the maker offers one
- Ask the council before ordering, as the view varies by street
Thermal trade-offs with a flush profile
Cutting a fresh opening for either unit is building work, and Part L sets thermal limits for it. For existing dwellings the table holds roof windows to 1.4 W/m²K or Window Energy Rating Band B. Rooflights are held to 2.2 W/m²K. Which limit applies depends on how the product is classified, so the first thing to ask any supplier is the declared figure for the whole unit, frame and glass together.
A flush conservation unit trades a little thermal ease for its looks. The slim frame means less framing in the opening, which can help, but the frame still needs a proper thermal break, and the narrow sightlines leave less room for deep insulation around the edge. The glazing itself can be double or triple sealed units with a warm-edge spacer, as in any modern rooflight. Reading the declared figure for the finished unit tells you more than any description of the frame.
A standard roof window is designed around the same limits and generally has its figures declared for the complete window. The trade-off there runs the other way: the deeper frame and sash are good for insulation, but they add to the visual weight on the roof. What the figures mean, and how to read a data sheet, is explained in our U-value guide.
Do conservation rooflights meet Part L? A well-made one can, and the declared figure is the evidence. The job plan lists the figure for the unit we propose, and the Building Control route that goes with it, so the compliance question is answered in writing before anything is ordered. We also take care of notifying Building Control when the fitting needs it.
| Point | What to ask for |
|---|---|
| Declared figure | The U-value for the whole unit, frame and glass |
| Classification | Whether the product is a roof window or a rooflight under Part L |
| Glazing | Sealed unit type and spacer, from the maker's data sheet |
| Frame | Whether the metal frame carries a thermal break |
| Edge detail | How the insulation sits around the opening |
Comparing the two for a real roof
A worked comparison helps. Take a stone cottage in a village conservation area with a rear slope of old tiles, and a loft bedroom that needs daylight. The front is visible to the whole street, and the rear is visible only from a neighbour's garden. On the front, a conservation rooflight is the safer proposal. On the rear, a recessed standard window with a bar could be tried first, with a conservation unit as the fallback if the officer prefers it.
Now take a 1930s semi on an estate with no conservation area and no condition removing rights. Here the standard roof window usually makes more sense: it opens, it is easy to order, and its flashing kit matches the tiles. A conservation unit would be a style choice and not a requirement, and the extra cost of metal framing buys nothing the planning position asks for.
In between lie the Victorian terraces. A brick terrace with slate roofs in a street the council cares about may point to a conservation unit on the front and a standard one at the back. The decision follows from the facts of the address, and the facts are what the survey and the council check collect.
How the choice is checked with the council
We do not choose between the two units on taste. At the survey we measure the roof, record the rafter depth and spacing, and note the slope, covering and aspect. Next the address goes through the council's conservation area pages, then its planning register, then the national list, and the result is written into the plan. Our part is to look and advise. The decision belongs to the council.
If the position is clear, the plan names the unit and says why. If it is borderline, the plan suggests a short email or a pre-application enquiry to the conservation officer with a sketch of the proposed profile, so that the view is on file before the order is placed. You can also ask the council directly, as every authority has a planning or conservation contact. In Swindon that is Swindon Borough Council, and outside the borough it is whichever authority covers the house, such as Wiltshire Council.
Costs follow the choice, and they are not guessed at here. The quote is written after the survey, when the unit, size and permission position are settled. Our guide to conservation rooflight costs explains the factors that move the figure.
Whichever unit wins, the rest of the job plan looks the same: lead time, fitting day, the Building Control route, and the sign-off. Workmanship carries our 10-year guarantee. For the full service, see our conservation rooflight installation page.