A rooflight in a sloping roof delivers noticeably more daylight than a vertical window of the same area, because it sees more of the sky. Dormer windows give headroom and a conventional view. At least one window must meet the escape requirements, and its opening and handle position decide whether the room is usable.
- Rooflights beat vertical windows for daylight, area for area. Use them where light matters most.
- One window has to meet the escape size and position rules. Fix that before choosing styles.
- Centre-pivot or top-hung changes whether you can stand at the window and whether it escapes.
- A Juliet balcony needs no floor, but it does usually need planning permission.
Why rooflights win on daylight
This is the point worth understanding before choosing anything, because it runs against intuition.
A window set into a sloping roof faces upwards towards the sky. A vertical window faces sideways towards the horizon, and much of what it sees is the ground, the house opposite, a fence or a hedge. Since daylight comes from the whole sky rather than from one direction, the rooflight sees far more of the source.
In practice a rooflight delivers substantially more daylight than a vertical window of the same glazed area, and the difference is most pronounced on dull British days when light is diffuse across the whole sky rather than coming from a sunny direction.
That has a few consequences for a loft:
Fewer or smaller rooflights can do the job, which matters where budget or roof area is limited.
A rooflight over the stair lights the whole stairwell and can also create the headroom that makes the stair compliant.
Rooflights on a north slope still work well, because they collect diffuse sky light rather than depending on direct sun.
Overheating is the trade-off. Facing the sky means facing the summer sun, and a south-facing rooflight with no blind can make a loft uncomfortable. External blinds or solar-control glass deal with it and are far cheaper specified at the start.
Where a loft has both a dormer and rooflights, the usual pattern that works is rooflights for daylight and the dormer for headroom and view. They are doing different jobs.
The four options compared
| Rooflight | Dormer window | Gable window | Juliet balcony | |
|---|---|---|---|---|
| Daylight per m² of glass | Highest | Moderate | Moderate | Moderate |
| Adds headroom | No | Yes, significantly | No | No |
| Adds floor area | No | Yes | No | No |
| View out, standing | Limited unless low-set | Yes | Yes | Yes |
| Relative cost | Lowest | Highest | Low if gable exists | Moderate |
| Planning | Often permitted at rear | Often permitted at rear | Usually permitted | Usually needs permission |
| Overheating risk | Higher | Lower | Lower | Lower |
| Escape window suitable | Often, if sized and positioned | Usually | Usually | Not on its own |
Front-facing alterations are treated differently throughout. A rooflight or dormer on the rear slope frequently falls within permitted development where the same thing on the principal elevation would need an application.
The escape window rule
At least one window in a loft bedroom normally has to serve as an emergency escape, and this is a specification rather than a preference. Get it settled before choosing window styles, because it constrains both the size and where it sits.
The requirements, in substance:
An unobstructed openable area of at least 0.33m², with a minimum of 450mm in both height and width. The 0.33m² is the clear opening you could actually climb through, not the size of the window.
The bottom of the openable area between 800mm and 1100mm above the floor, so it can be reached and climbed through without being so low as to be a falling hazard.
Opening wide enough to pass through, which affects the hinge type — a centre-pivot rooflight that only rotates partway may not give a clear 0.33m².
Somewhere safe to land, meaning it should give onto a place a person can wait for rescue or get down from.
In a rooflight conversion this usually means one rooflight specified as an escape unit, which opens to a much wider angle than a standard one. In a dormer, the window is normally large enough already, but the opening casement still has to meet the clear-opening figure.
Where the design cannot provide an escape window, a sprinkler system is sometimes used as an alternative route to compliance. That is a design decision with a cost, and it belongs in the budget early rather than appearing at inspection.
Opening type: the detail people regret
Centre-pivot
The sash rotates about its middle, so the top half swings inwards as the bottom swings out. Cheapest and most common, and it works well where the window is above head height. The drawback is that you cannot stand right at it when it is open, because the top of the sash comes into the room. In a low-set rooflight you position yourself to the side of it rather than in front of it.
Top-hung
The sash hinges at the top and the whole thing swings outwards, leaving the opening clear. You can stand at it, lean out and get a proper view, and it is the type that gives a clear escape opening. More expensive, and the handle is usually at the bottom, which means you need to be able to reach the bottom of the window.
Top-hung and centre-pivot combined
Some units do both: top-hung for everyday use and view, pivoting for cleaning the outer face from inside. The most practical option for a window you will use often, and worth the extra on an accessible one.
Handle position
Top-mounted handles suit windows out of reach, since you operate them without stretching across. Bottom-mounted handles suit windows you can reach and give a better seal at the head. This sounds trivial and it is the thing people are most irritated by afterwards — a window you cannot comfortably open gets left shut.
Juliet balconies and glazed gables
A Juliet balcony is a set of doors opening onto a balustrade with no platform beyond it. It gives a loft room a full-height opening, a proper view and a lot of light, without the structure, cost or planning difficulty of an actual balcony.
What to know:
It usually needs planning permission. Inserting doors and a balustrade into a roof slope or a dormer face is a more significant alteration than a window, and the overlooking argument is stronger because the opening is full height. Permitted development is less likely to cover it than a plain dormer window.
Overlooking is the usual objection. A full-height opening at second-floor level looking into neighbouring gardens is exactly what planning officers scrutinise, particularly on a terrace or a tight suburban plot.
The balustrade is a safety barrier and has to meet the loading and height requirements, with glazing toughened or laminated as appropriate.
It does not add floor area, so judge it on light, view and feel rather than space.
A glazed gable is the other option where a hip-to-gable has created a new vertical wall. A large window or glazed panel in that gable gives excellent light and a conventional view, and it is often simpler to achieve than a Juliet in the roof slope.
Both are worth considering at design stage rather than later, because both affect the planning route and neither is easy to add once the roof is finished.
What it costs
These are the loft conversion figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Velux / rooflight conversion | £25,000–£35,000 | Simplest type |
| Dormer conversion | £35,000–£50,000 | Adds head height & space |
| Hip-to-gable | £45,000–£65,000 | End-of-terrace / semi |
| Average loft conversion | ~£35,371 | Type & extras dependent |
Windows sit inside those conversion figures rather than alongside them, but the specification moves the total: escape units, top-hung mechanisms, solar-control glass and external blinds each cost more than the standard equivalent, and a Juliet balcony is a separate item with its own planning cost.
We settle the escape window first, because its size and position constrain everything else you might want.
Frequently asked questions
Do rooflights give more light than normal windows?
Yes, area for area. A rooflight faces upwards and sees much more of the sky, whereas a vertical window faces the horizon and sees ground, fences and buildings. The difference is most pronounced on dull days when light is diffuse across the whole sky.
What size does a loft escape window need to be?
An unobstructed openable area of at least 0.33m², with a minimum of 450mm in both height and width, and the bottom of that opening between 800mm and 1100mm above the floor. It is the clear opening you could climb through, not the overall size of the window.
Should I choose centre-pivot or top-hung rooflights?
Top-hung where you want to stand at the window, lean out or use it as the escape, because the sash swings clear. Centre-pivot is cheaper and fine above head height, but the top of the sash comes into the room when open so you cannot stand in front of it.
Does a Juliet balcony need planning permission?
Usually yes. Inserting full-height doors and a balustrade is a more significant alteration than a window, and the overlooking argument is stronger because the opening runs to floor level. Permitted development is less likely to cover it than a plain dormer window would be.
Will a rooflight make the loft too hot?
It can, facing south with no shading, because facing the sky also means facing the summer sun. External blinds work far better than internal ones since they stop the heat before it enters, and solar-control glass helps. Both are much cheaper specified at the start.
Can a rooflight be the escape window?
Often, if it is specified as an escape unit. Those open to a much wider angle than standard rooflights, giving the clear 0.33m² opening required. A standard centre-pivot that only rotates partway may not provide enough unobstructed area, so it has to be specified deliberately.
Escape window first, then the rest
Its size and height above the floor constrain the whole window layout, so we fix that before anything else is chosen.