The Sightline Sketch: How We Plan the View Through Your Skylight

A sightline sketch is a line drawing of the view up through the glass from one fixed point in the room: the pillow, the sofa cushion, the sink edge or the desk chair. It shows where the frame edge crosses the sky, where a glazing bar falls if the rooflight has one, how the reveal opens or narrows the opening, and roughly how much clear sky sits above all of that. It is not a brochure image or a computer render. It is a drawing made for one room, from one seat or one pillow, before anyone cuts into the roof.

Most rooflights are sold on a size and a U-value, and both matter, but neither tells you what you will actually see lying in bed or standing at the sink. Two rooflights of the same size, in the same roof, can give completely different views depending on where the frame sits, how wide the bar is and how the reveal is lined. The sketch exists to answer the one question a spec sheet cannot: from where you actually sit, stand or lie, what is between you and the sky.

A rooflight does not have one view. It has as many views as there are places in the room to look up from, and each one changes with height and angle. Lying flat with your head on a pillow, you look almost straight up through a narrow cone; the frame edge nearest your feet can vanish from sight while the one behind your head fills half the glass. Sitting upright on a sofa, the cone widens and shifts forward, so a bar that was invisible from the bed sits squarely in the middle of the glass. Standing at a sink or a worktop, you are further back and often further off to one side, so the same rooflight can show you a corner of sky rather than the centre of it.

The sketch always starts by fixing that point. On a bedroom job, it is drawn from where the pillow actually sits against the headboard, not from the middle of the room. On a kitchen extension it is drawn from the sink, the hob or wherever the client says they stand or sit most, since that is the seat that has to earn the glass above it. Move the rooflight fifteen centimetres along the ridge, or move the bed six inches from the wall, and the drawing changes again, which is exactly why it gets drawn for the room as built rather than assumed from a catalogue image.

A frame has to hold glass in place, carry its weight and seal the opening, so it can never disappear entirely from the view. What varies hugely between products is how much of the sky that frame takes with it, and the sketch is where that gets tested against the actual eye position rather than argued about in the showroom.

A slim aluminium frame on a modern flat rooflight can sit only a few centimetres wide on the inside face, so from most seated positions it reads as a thin line at the edge of an otherwise open rectangle of sky. An older timber-framed roof window, or a rooflight with a glazing bar splitting the pane in two, puts a much thicker element into the same sightline, and if that bar happens to land at head height from the bed, it stays in view every time you look up. Electric and opening rooflights carry a little more hardware again, a vent mechanism or a hinge along one edge, and the sketch is where that extra depth gets weighed against the room rather than discovered afterwards.

None of this makes a bar or a slightly heavier frame wrong. A large lantern roof over a kitchen extension often needs its ridge beam and hips for structural reasons, and the sketch simply shows where those land against the ceiling height and the table below, so the choice of size and layout is made with that in mind rather than against a surprise. Our roof lantern installation and electric and opening rooflight installation pages set out where that extra structure tends to sit on each product.

The reveal is the lined opening between the ceiling plane and the glass itself, and its shape decides how much of the sky the frame actually lets through into the room, quite separately from the size of the glass unit above it. A square reveal, cut straight down through the depth of the roof structure, frames the sky tightly and can make even a generous rooflight feel like looking through a tube from some seated positions. A splayed reveal, angled outward as it drops from the glass to the ceiling, opens the view wider from below, so more sky reaches the eye from a seat further back in the room, at the cost of a little extra plastering and lining work.

On a flat roof with a deep insulated build-up, the upstand and kerb add real depth between the glass and the ceiling below, and a reveal left square through that depth can turn a perfectly good rooflight into a letterbox by the time the view reaches a sofa across the room. Splaying that same reveal, even by a modest amount, widens what reaches the eye without changing the glass itself. The sketch is where that trade-off gets drawn and agreed before the plasterer is on site, rather than found out once the scaffolding has gone. Our flat roof rooflight installation page covers how the kerb and upstand are built on a typical extension roof.

The sketch is only as honest as the measurements behind it, so a home visit gathers a specific set of information before a line is drawn:

• the exact seat, bed position or worktop the room is drawn from, measured on site rather than guessed from a plan;
• the roof pitch, or the depth of the flat roof build-up where the rooflight sits on an extension;
• which way the roof faces, since a south-facing opening reads differently in the sketch to a north-facing one even at the same size;
• the structure already in the roof: rafters, purlins or a lantern's own ridge and hips, which set where a bar or beam has to fall;
• and the finished ceiling height and reveal depth, worked out from the existing roof rather than assumed.

Skip any one of those and the drawing turns back into a guess. On an older Fletton brick terrace with a loft conversion already in place, the rafter spacing and existing roof line often set real limits on where a roof window can go, which is exactly the kind of constraint the sketch has to work around rather than around it separately at a later stage.

A flat rooflight, a pitched roof window, a lantern and a sun tunnel each put the glass in a different relationship to the room, so the sketch is drawn differently for each even when the brief is the same: as much sky as possible from where you sit.

A flat rooflight over an extension roof usually sits directly above the room it serves, so the sketch is mostly about kerb height, reveal splay and where any glazing bar lands against the ceiling. A pitched roof window installation or VELUX window installation sits within the slope of the roof itself, so the sketch has to account for the pitch angle changing the apparent height of the sky as well as its width, and for how the lining steps down from the sloped glass to a level ceiling. A roof lantern spans a wider opening with its own ridge and hip bars, so the sketch usually needs more than one seated position, since a family kitchen table is looked up at from several places rather than one. A sun tunnel installation works differently again: there is no direct sightline to the sky at all, only a diffuser at ceiling level, so the drawing there shows the spread and evenness of the light it delivers rather than a view of open sky.

A walk-on rooflight, set into a terrace or a flat roof that people stand on, is looked up at from below in the room underneath in exactly the way any other flat rooflight is, so the same sketching approach applies, with the extra structural depth of a trafficable unit factored into the reveal.

The Fens run flat to the east and north of the city, which means a rooflight placed and lined correctly can frame open sky with nothing else in the frame at all: no roofline, no neighbouring gable, no rising ground to cut across the top of the view. That only holds if the frame and reveal are drawn tightly enough to take advantage of it, which is exactly what the sketch is for on a Fenland-facing roof.

Peterborough's new-town townships, Bretton, Orton, Werrington and Hampton, carry large numbers of flat-roofed extensions and loft conversions built from the 1970s onward, many with roof structures deep enough that reveal shape genuinely changes what a family sees from a kitchen table or a landing. Older Fletton brick terraces closer to the centre tend to have shallower rafters and tighter loft spaces, where frame width and bar position, rather than reveal depth, usually decide the view. Around Stamford and the limestone and Collyweston stone slate villages along the Nene valley, the roof covering itself is often the thing being protected, so the sketch there is drawn alongside a slimmer, flush conservation profile rather than a standard frame; our conservation rooflight installation page covers that setting in full.

The sketch shows the view on the day it is drawn, but the promise behind it is that the same view holds up over time rather than fading as the glass ages. That comes down to what the glass itself is doing, not just how it is framed.

An edge seal that fails lets moisture between the panes, and the first sign is usually a faint mist that never quite clears, right in the middle of the view the sketch promised. A self-cleaning outer coating, useful on a low-pitched rooflight that rain does not sheet across as readily as a steep one, keeps the outer pane clearer between cleans, so the sky stays the colour it should rather than dulling under a film of dirt. Where an existing rooflight has already misted or its seal has failed, our misted and failed rooflight replacement service swaps the unit without disturbing the surrounding roof, and a fresh sketch is drawn for the replacement glass just as it would be for a new opening. Our energy efficient rooflights page covers the coatings and spacer choices that keep the glass performing, and clear, well into the years after the sketch was first drawn.

The sketch is not a separate extra step tacked onto the quote. It is drawn during the same home visit that measures the roof, checks the structure and works out what the job actually involves, and it comes with every quote we give, at no separate charge. You see the view before you commit to the size, the product or the reveal shape, and if the first version does not give you the sky you wanted from that seat or that pillow, it gets adjusted before anything is ordered rather than after the roof is open.

Once the drawing is agreed, it sits alongside the rest of the specification: the frame and glass chosen, the reveal detail, and where the work is notifiable under Building Regulations, which we handle as part of the job so the paperwork is in place when you come to sell. Every finished installation carries our 10-year workmanship guarantee, and what the whole job costs, sketch included, depends on the product, the size and the roof it is going into, which our page on what affects the cost of a rooflight sets out in full.

Book a home visit and we measure the room, the roof and the seat, bed or worktop that matters to you, then draw the view before anything is ordered. You can read about the products we fit across Peterborough and 30 miles around on our page for skylight and rooflight installation in Peterborough, browse our full set of rooflight and skylight guides, or check rooflight and skylight questions answered for anything not covered here. When you are ready, book your home visit or message us on WhatsApp, and find out more about the firm on our about page or the towns we cover on areas we cover around Peterborough.

Does the sketch cost anything extra?

No. It is drawn during the same home visit as the rest of the survey and comes with every quote we give, whatever product or size you are considering.

Can the sketch change after it is first drawn?

Yes. If the first version does not give you the sky you were hoping for from that seat or pillow, we adjust the size, the frame choice or the reveal and redraw it before anything is ordered.

Do you draw more than one view for the same room?

Where a room is used from more than one spot, a kitchen table looked up at from several chairs, for instance, we draw from whichever position matters most, and can add a second view where it genuinely changes the answer.

Is the sketch to scale?

It is drawn to reflect the real measurements taken on the visit: the roof pitch or upstand height, the reveal depth and the frame and bar widths of the product being quoted, rather than a generic stock illustration.