Anyone who has walked up through Painswick, Uley or Nailsworth knows what an old roof is meant to look like from the lane: an unbroken sweep of stone or slate, with chimneys and gables as its only interruptions. A modern roof window with a chunky frame and a raised surround breaks that line. A conservation rooflight is designed not to. The glass sits almost level with the covering, the frame is thin and dark, and the whole unit reads as a line of metal, like the glazing of a Victorian mill or a Georgian outbuilding.
This guide is about the product: what it is, how it differs from an ordinary roof window, how to size it for a stone or slate roof, how it is flashed in, and what the energy standard asks of it. The permission side, whether you may add one at all in a conservation area, has its own answer in our guide to adding a roof window in a Stroud conservation area. The wider range of work is on our roof windows and skylights page.
What makes a rooflight a conservation rooflight
The name describes a look more than a regulation. There is no official definition, but the products sold under it share four features.
Flush glazing
The glass sits close to the roof covering, with little or no raised surround. On a slate or stone roof this means the pane catches the light much as the stone does, and from the lane the unit looks like a thin sheet of glass laid on the roof.
Slim frames
The frame is narrow, often a thin steel section, finished in a dark colour that sits quietly against slate. Steel-look is the term for a frame with the profile of an old cast or wrought iron rooflight, even where the material is aluminium or a coated steel. The slim frame also means more glass for the width of the opening.
Glazing bars
Many have a single central bar dividing the pane into two, echoing the older pattern of small panes. It is a styling choice and can often be left off for a plain pane.
Fixed or opening
Most are fixed. Opening versions exist, with a hinge and a restrictor, and suit a loft room or stair that needs ventilation. Compared with an ordinary roof window, which is made to open and close many times a year, the conservation type is built for appearance first.
Because the unit lies in the slope and is not a kerb-mounted rooflight on a flat roof, it is a different product from those in our guide to flat roof rooflights, even if the word rooflight is used for both.
Where planning officers look hardest
The council decides what is acceptable, and the products only help. Stroud District has 41 conservation areas, and Stroud District Council's list includes Painswick, Uley, Nailsworth, Minchinhampton, Chalford Hill, Chalford Vale, Dursley and the mill complexes of the valleys. Five of them carry Article 4 Directions, Bisley and Frampton on Severn being two of them. Whether those directions touch roof alterations is not spelled out publicly, so ask the planners directly before assuming either way.
Which elevations matter most
In a conservation area the planning question is usually how the unit looks from public places. A rooflight on the rear slope, out of sight of the road, is a lighter matter than one on the front slope facing the lane. On a terraced hillside house in Stroud, where one roof is seen from the street below and another from the hill above, the slope you cannot see from the front may still be seen from across the valley.
What the planning team is likely to ask for
Expect to be asked for the make and model, the dimensions, the frame colour and a drawing that shows the unit lying flush with the covering. A drawing that places the rooflight in line with existing features, such as aligned with the windows below, or evenly spaced across the slope, helps. A pair of identical small units usually reads more calmly than one large one.
Listed buildings
On a listed building the position is different. Cutting into a listed roof alters it, whatever the grade of the house, and that route runs through the council's conservation team. A slim flush unit makes the case easier to put but does not remove the need to apply. Churches still in worship follow a different route, a faculty from the diocese. The Cotswolds National Landscape takes in just over half of Stroud District, mostly the eastern side. Roof windows under Class C face no extra restriction there.
Sizing a rooflight for a stone or slate roof
Size is where a conservation rooflight succeeds or fails. The aim is a unit small enough to look like a feature of the roof and large enough to light the room beneath.
Working with the courses
On Cotswold stone roofs the slates get smaller as the roof rises, laid in diminishing courses, and the openings between rafters rarely line up with a neat dimension. Cotswold District Council's 2000 guidance records stone slates at around 600 mm long at the eaves and as short as 150 mm near the top. A rooflight cut into such a slope leaves an irregular edge, which has to be dressed in small stone or lead. Choosing a unit whose height spans a convenient number of courses, and whose edges fall on the rafters, reduces the cutting and keeps the covering looking right.
Between the rafters
Most conservation rooflights are made to fit between rafters. An opening wider than the gap between two rafters means cutting one and framing round it, covered in our guide to trimming rafters. On older roofs the rafters are not always evenly spaced, so the survey measures them on site.
Proportion on the slope
As a rule of thumb, a rooflight reads best when it is narrow and taller than it is wide, in the same upright proportion as the windows below. It also looks better set a little way up from the eaves, not in the lowest courses, which are the heaviest and most visible.
Daylight in the room
The glass also needs enough area to light the space. A narrow unit placed over the middle of a room will light it better than a wide one pushed to the edge, and a pair of units on either side of a central chimney breast can light a long loft evenly.
Flashing a flush unit into stone and slate
A flush rooflight has no raised frame to shed water, so the flashing carries more of the load. The details differ from a standard roof window kit, and a kit made for a profiled concrete tile is not suitable for a thick, uneven stone slate. Our guide to roof window flashings explains the pieces for the ordinary case.
Lead and stone together
On a Cotswold roof the usual solution is lead, dressed to the edge of the unit and tucked under the slates at the sides and top, with a lead apron laid over the courses below. The lead has to follow the uneven surface of the stone without trapping water. Lead flashing, if properly installed, can last more than 80 years according to MyJobQuote, and higher codes can last more than 100. Leadworx names Code 4 as the standard for general flashing; the code chosen for a rooflight depends on the exposure and the stone.
Slate roofs
On a natural slate roof the covering is thinner and more regular, and the flashing is closer to a standard soaker and apron arrangement, with lead soakers worked into the slate courses at each side. The headlap of the slates above must not be reduced to fit the unit.
Underlay and the insulation
Under the covering, the underlay is lapped and dressed round the frame so stray water is carried clear. The gap around the unit needs insulation as well, as the thin frame leaves little thickness for a cold bridge to hide in. Both are hidden once the job is done, so we photograph them before the covering goes back.
The slates or stone are returned in their own courses, reusing the original stone in the same order. Like for like means a matching stone, not a cheaper substitute.
Energy limits for a slim steel-look unit
The thin frame and flush glass make the product look traditional, but the performance has to meet current rules. Approved Document L (2021 edition) gives different limits for different products, and the question is which one applies. A rooflight, standing above a flat or low roof, has to achieve 2.2 W/m²K. A roof window, lying in a pitched slope, has to achieve 1.4 or Window Energy Rating Band B.
Which row does a conservation rooflight fall under
That depends on the product and how it is described and tested. A flush-fitting unit lying in a pitched slope is, in function, a roof window, and its maker may declare it to either standard. We ask for the manufacturer's declared U-value for the exact model and check it against the table before we order. A listed building is a special case, because the building regulations recognise that historic fabric and special character can justify a different approach. Check with building control before relying on that.
Glass options
Slim frames give less room for multi-pane glazing, so the double or triple glazed unit is thin. Better coatings and gas fills, rather than extra panes, then carry the performance. Laminated glass is common because it holds together if broken and cuts noise.
Condensation and cold bridges
Thin steel frames conduct heat, so a frame that is poorly broken can mist on a cold morning. A thermal break in the frame and a good insulation collar reduce this. Our answer on windows for a loft conversion covers the related questions about daylight, escape and ventilation in a converted roof space.
Ask for the declared U-value of the exact model before you order. A slim frame that does not reach the limit is a slim frame that building control will not accept.
Fitting, cost and when a conservation rooflight is the wrong choice
Fitting follows the same sequence as any roof window. The covering is lifted round the opening, the frame fixed to the rafters, the flashing formed, the underlay dressed and the covering returned. On stone, slower sorting and re-laying add time compared with a modern tile, and scaffold makes up more of the total.
Cost
Conservation rooflights vary by frame, glazing and size, so we price the unit once the survey has settled which one suits. For ordinary units, MyBuilder's roof window guide (updated 21 August 2026) puts fitting of a standard roof window at £350 to £600 and scaffold at about £500, figures that apply to ordinary units. After the survey, our written quote covers the unit by model, the flashing, any rafter work, access, labour, waste and making good.
When it is the wrong product
A conservation rooflight is not the best choice for every house. If the room needs a window that opens wide, forms an escape route or is cleaned from inside, an ordinary roof window may serve better. The escape rules count a window only within 4.5 metres of the ground, which a second-storey loft room exceeds, so ask building control what that room needs.
Maintaining the finish
The finish on a steel-look frame needs a gentle wash, and the seals should be checked each year. Lichen and moss on a stone roof can creep over the edge of the glass, so a soft brush from time to time keeps the line crisp.
Our installation carries a written 10-year workmanship guarantee, the manufacturer covers the unit itself, and when the job ends the waste is cleared away.