A conservation rooflight is a roof window designed to copy the cast iron rooflights fitted to Victorian and Edwardian buildings. It sits flush or near flush with the tile or slate surface rather than standing proud, has a slim frame in black or very dark grey, carries a single vertical glazing bar down the centre, and is weathered with dressed lead instead of a visible aluminium flashing kit. Those four things define it.
Everything else about it, the glazing, the hinge, the thermal performance, can be identical to a standard modern roof window. The difference is what it looks like from forty metres away in the street, and that is the only thing a conservation officer is assessing.
The four defining features, in detail
1. It sits flush with the roof plane
This is the one that does the most work visually. A standard modern roof window stands 40mm or more above the surrounding covering, because the frame sits on top of the battens and the flashing is dressed down over the tiles. From ground level you see a raised box with a shadow line under it.
A conservation unit is set lower into the roof structure, so the outer face of the glass finishes close to level with the tile or slate face. Typical proud dimensions on conservation patterns run from flush to about 15mm. The unit itself is not usually thinner, the difference is in how deep it is recessed into the roof, which is why fitting one is more work rather than simply a different product off the shelf.
2. The frame is slim and dark
Original cast iron rooflights had very fine sections because iron is strong in thin members. A modern unit in white or natural pine reads as a bright border around the glass and draws the eye. A conservation pattern uses a narrow external frame finished in black or a near black grey, so from the ground it disappears into the shadow of its own recess. Sightlines are the term the manufacturers use, and slim sightlines are the point of the whole thing.
3. There is a central glazing bar
Most conservation patterns split the glass into two panes with a single vertical bar down the middle. That bar is the most recognisable feature of the original ironwork, because the cast frames could not span a full opening in one pane of glass. It is a decorative honesty about how the original was made. Some officers will accept a conservation pattern without the bar on a less sensitive elevation. Others will not, and it is worth knowing which you are dealing with before you order.
4. The flashing is dressed lead
Code 4 lead or heavier, formed to the roof covering by hand, rather than the pressed aluminium sections that come boxed with a standard unit. Visible aluminium on a listed roof is one of the fastest ways to get an enforcement letter. Dressed lead also copes better with the irregular handmade tiles and slates that these buildings tend to have, so it is a technical answer as well as an aesthetic one.
Conservation pattern versus standard, side by side
| Feature | Standard unit | Conservation pattern |
|---|---|---|
| Height above roof plane | 40mm or more | Flush to about 15mm |
| Frame colour | White, grey or natural timber | Black or very dark grey |
| External sightline | Wide, clearly framed | Slim, reads as shadow |
| Glazing bar | None | Single vertical bar, most patterns |
| Proportion | Squarer, often close to 3:4 | Tall and narrow, closer to 1:2 |
| Flashing | Pressed aluminium kit, visible | Dressed lead, code 4 minimum |
| Fitting depth in the roof | On the battens, standard detail | Recessed, deeper trimming required |
Proportions vary by manufacturer. The recessed fitting depth is what turns a conservation unit into a longer job on site.
The proportion point catches people out. A conservation rooflight is generally taller than it is wide by a wide margin, because that is what the original iron units looked like. If your loft room wants a broad landscape window, a conservation pattern may not give you the shape you had in mind, and you may need two narrow units rather than one wide one.
Where a conservation unit is required rather than preferred
This is the useful distinction. Plenty of people fit a conservation rooflight because they like it on a period house with no designation at all, and that is a straightforward taste decision. There are three situations where it stops being taste.
- Listed buildings. Listed building consent is required for a rooflight anywhere on the building, including a rear slope nobody can see. Officers will almost always specify a conservation pattern, and often a specific one. Carrying out work to a listed building without consent is a criminal offence, not a planning technicality.
- Visible slopes in a conservation area. Lavenham, Aldeburgh, Southwold, Dedham, Coggeshall, Clare, Kersey and a good part of central Ipswich are all designated. A rooflight on a front or otherwise publicly visible slope in one of those will usually be conditioned to a conservation pattern if it is permitted at all. The reasoning behind that is covered on why conservation areas restrict rooflights.
- Article 4 areas. An Article 4 direction withdraws permitted development rights that would otherwise apply, which can pull a rear slope into the consent process too. Whether you need consent at all is a separate question, dealt with on planning permission for a pitched roof rooflight.
We are installers, not planning consultants. Speak to the conservation officer at Ipswich Borough, East Suffolk, Mid Suffolk, Babergh, Colchester City or Tendring before you order anything. They will usually tell you what pattern they expect. We can supply the specification detail, sections and finishes for your application once you know what you are applying for.
What it means on a Suffolk roof
The stock these units go into is rarely regular. Handmade clay pantiles vary in thickness across a single slope. Rafters on a timber framed roof are irregularly sized and irregularly spaced, sometimes spliced, sometimes replaced in a different century to their neighbours. Recessing a frame lower into that structure means the trimming has to be surveyed rather than assumed, and the lead has to be formed to whatever the covering actually does rather than what a catalogue says it should do.
That is the honest reason a conservation rooflight costs more to fit than a standard one, and the figures are set out on how much a conservation rooflight costs fitted. The installation detail itself, recess depth, lead dressing and trimming, is covered on our conservation rooflight installation page, and the closely related question of flush fitting a non conservation unit is on flush fit rooflights for pitched roofs.
One more thing worth saying plainly. A conservation rooflight is not automatically the better window. On an unconstrained 1970s roof at Kesgrave or Chantry, a standard unit is the right answer and a conservation pattern is money spent on nothing. That choice is set out on conservation or standard rooflight.
Get a fixed price
Tell us the building, the roof covering, whether it is listed or in a conservation area, and what the officer has said if you have already spoken to them. We will survey the actual rafters and the covering, confirm what pattern and recess depth will work, and give you one written price with the unit, the lead and the trimming itemised. Every installation carries a 10-year workmanship guarantee. Request a fixed quote, or start at our pitched roof skylight installation page for the wider picture.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.