Conservation rooflight installation in Birmingham

A conservation rooflight is a slim, flush-fitting roof opening designed to sit in the plane of the slope instead of standing up from it. The glass lies close to the slates or tiles, and the frame is narrow, usually steel or aluminium, with a single glazing bar running from top to bottom.

The shape is borrowed from the cast iron skylights of Victorian outbuildings and workshops, which is why it looks at home on a slate roof, a clay tile roof or a stone-flagged barn. Some owners call it a heritage skylight, and trade catalogues call it a conservation rooflight. They mean the same unit.

We look at the covering, the pitch and the way the roof is seen from the street before we suggest one.

What flush means in practice

A flush unit has a low upstand and a shallow flashing that follows the roof covering. Slates or tiles are cut and laid tight to the frame, so the rain runs over it and off. A standard roof window sits higher and relies on a wider flashing kit to bridge the gap.

From the street, the difference is a thin dark line against the slate, compared with a deeper box with a visible surround.

How we decide which to quote

We start with the room. A landing, a stair or a bathroom that is already ventilated usually needs light and nothing else, so a fixed unit costs less and has nothing to wear. A bedroom or a studio under the slope may want a sash that opens.

Then we look at the roof. A heritage unit is the first choice on slate, clay and stone slabs. On a modern concrete tile roof with a plain house below, both a heritage unit and a standard roof window go on the quote, and you can see what the extra detail buys.

Why every quote carries more than one unit

A quote with only one option cannot be weighed against anything. So we show the heritage units next to a standard window wherever the roof can take either, with the difference in looks, ventilation, upkeep and price in plain words.

Our comparison page, a conservation rooflight or a standard roof window, lines the two up on glazing bar, flashing, thermal figure, lead time and price, and you can read it before the survey.

Steel is the traditional material for a cast iron style skylight and it makes the thinnest frame. It is strong enough that the bars can be very fine, which is the main reason it appears on listed and high-profile buildings. It needs a good coating to keep rust away, and the makers specify the coating for the life of the unit.

Aluminium makes a frame that is a little wider but still slim, and it is easier to ship and to handle on a roof. It is powder coated in a range of colours, and the finish is durable. On many roofs the eye cannot tell steel from aluminium once the unit is in, unless it is looked at from close range.

Where both fit the opening, each appears on the quote with its sightline, finish and price stated so the difference is plain.

The Part L figure

Part L 2021 caps the heat that new glazing in an existing home may let escape: 2.2 W/m²K applies to a rooflight, and a roof window is judged against 1.4 W/m²K, or against WER Band B. Which limit applies to a given unit depends on how the maker classes it, and the data sheet says so. Where a unit could fall either side, we ask Building Control before the order goes in, because the answer changes which figure the quote has to meet.

Each unit quoted carries the maker's own figure, which shows how it sits against the limit and against the other units it is priced alongside. Our guide to rooflight U-values explains what the numbers mean.

Heritage frames are slim, so there is less room for glass and spacers than in a standard window. Makers have worked on this for a long time, and slim double glazed units with warm-edge spacers and gas fills are now common in conservation ranges. Triple glazing is possible in some, though it needs a deeper unit and so a slightly thicker look.

On a listed building or inside a conservation area, Building Control may weigh the character of the building when it considers the energy limits for a particular opening. We raise that at the start and put the question to Building Control before the unit is ordered.

The glazing bar is a separate matter. On some units it is a real bar that holds the glass, and on others it is applied on the surface. Our answer on why conservation rooflights have a glazing bar shows how the two look and why the bar is there.

A tall narrow unit between two rafters often leaves the roof structure untouched.

Planning and consent

On an ordinary house, a rooflight is often covered by permitted development, and the conditions that go with it are set out in our rooflight planning guide. Before this work starts on a listed property, consent for listed building work has to be in place, however permitted development might otherwise read, and the right itself can be lost through a condition on an earlier permission, or through a direction under Article 4. Your address gets checked during the survey visit, and what we find is passed on to you. The council decides.

Listed building consent is required both for a new rooflight and for altering one already in the roof of a listed property. Our answer on whether a listed building needs rooflight consent covers the drawings and details the council expects. We can supply the unit drawings and product details for an application.

What goes into the price

A conservation rooflight price is built from the unit itself, its frame material, its glass, the work to the roof covering around it, any trimming of rafters and battens, and the finish inside. Each line is shown for each option on the quote.

Heritage units usually cost more than standard roof windows of a similar size, because they are made to a finer profile in smaller runs. Our answer on how much a conservation rooflight costs explains each part, and our page on skylight replacement costs sets them in context.

On a typical fitting the slates or tiles are lifted around the opening, the rafters are trimmed and doubled where needed, and the unit is fixed and flashed. The covering is relaid tight to the frame, and the roof is made watertight before we leave each day.

Inside, the reveals are lined and finished so the opening looks like part of the room. If you want a plaster splay, a timber lining or a painted return, say so at the survey so it is priced and planned.

After it is fitted

We tidy up before leaving, demonstrate how any opening sash works, and pass you the maker's paperwork and, for notifiable work, the Building Control certificate, going through both with you.

Each installation comes with our 10-year workmanship guarantee, while the maker separately warrants the unit itself. The details of what each covers are on our guarantee page.

A heritage unit asks very little of you: rinse the glass now and then and clear leaves and moss from the roof around the frame.