The short answer
A roof window balcony is a two part roof window. The top sash swings up and out on a pivot, and a lower section folds forward to stand as a small railed platform, so you can step up and look out from inside the loft. It needs a fairly steep pitch, a room with enough floor and headroom beneath it, and a proper check of planning and Building Regulations first.
Two sashes doing the work of a window and a doorway
Close it and it reads as one rooflight. Open it and the loft gets a small outdoor ledge it never had before.
The best known version is the VELUX Cabrio, though other makers have their own take on the idea. The upper sash is hinged near its middle, like a centre-pivot window, and it rotates outward and upward. The lower part, which looks like the bottom of the glass, is hinged along its base. It drops forward and locks into place, and it carries side rails that rise as it moves. What you end up with is a half-height opening at waist level, a glazed canopy above your head and a narrow railed shelf to lean on.
It is not a balcony in the sense of a platform you can sit out on with a chair. There is no floor to stand on outside the roof plane. You stand on your own loft floor, and the folded section gives you a rail and a surround so that your upper body is outdoors while your feet are still inside. Think of it as a French window scaled down to fit a roof slope, more than a terrace.
The appeal is easy to see in a loft room. A standard roof window lets the sky in, but the lower part of the opening sits low and is often hard to use. The balcony pattern turns the lower half of the glass into useful space, and it lifts the upper half clear of your head when it is open. A bedroom gets air on a warm night, a study gets a place to stand with a coffee, and a stair landing gets a proper sense of height.
What roof pitch and room depth it asks for
The mechanism only works within a band of angles. Below it the lower section will not unfold cleanly, and above it the opening is awkward to reach.
Makers publish a working range for each model, and for the well known two part windows it sits roughly between the mid thirties and low fifties in degrees of pitch. Always confirm the range against the current product sheet, because it changes between models and sizes. We measure the pitch on the survey with a digital level, rather than trusting the drawings, since an older roof can sit a little off its stated angle.
| Roof pitch | What it means for a balcony window |
|---|---|
| Below the range | The lower section cannot fold out safely. A standard top-hung or pivot window is the right choice. |
| Inside the range | The two parts open as designed. Room depth and sill height still need checking. |
| Above the range | The opening sits near vertical. A dormer or a gable window may suit better. |
Our wider guide to roof pitch and roof windows explains how angle affects every type of opening, and it is worth reading beside this one.
Room depth matters as much as angle. The lower section swings into the room as well as out, so the floor in front of the window has to be clear of furniture, and the sloping ceiling must leave standing room at the sill. A window set too high in a slope leaves you on tiptoes. One set too low puts the rail at your knees. The fitted height is worked out with the same thinking as our page on setting the height of a roof window in a sloping ceiling.
Checking whether your loft room suits one
Some lofts want a balcony window and plenty do not. A short walk through the room usually settles it.
- Standing room at the window. You should be able to stand upright a little back from the sill, with clear floor in front of it.
- A slope in the right range. Measure it on the rafters themselves, or along the roof slope outside.
- A position that works with the rafters. The frame is wide and tall, so it may need framing work. Our page on whether a roof window needs the rafters trimmed covers what that involves.
- A view worth standing at. Privacy from neighbours matters, since you will be visible at the rail.
A loft that has already been converted is usually the simplest candidate, because the floor, stairs and insulation are in place. An unconverted roof space needs the wider work in our guide to choosing roof windows for a loft conversion before a window of this size makes sense.
Rules, noise and the practical snags
A balcony window is still a roof window in the eyes of the regulations, but it sits nearer the edge of what is allowed.
Planning first. Fitting roof windows on a house is often permitted development, so long as they do not project more than 150 mm beyond the plane of the roof and sit below the highest point of it. A balcony window is different in one respect: when open, it forms a projecting railed platform, and permitted development rules for houses exclude balconies, verandas and raised platforms. Whether the open position counts is a question to put to the planning authority for your address, and homes in conservation areas and flats are treated differently again. The planning position is checked for the address before we quote, and nothing gets ordered on an assumption.
Building Regulations apply as they do for any roof window. The work has to meet Part L on thermal performance and Part F on ventilation, and where it serves a bedroom, Part B sets the size and height of an opening that you could escape through. Our answer on how big a roof window needs to be for a fire escape sets out the figures. Part K is the part that deals with falling and impact, and it is what makes the rails and the fixings matter here. We handle the Building Control notification where the work is notifiable.
With the window closed, sound passes through the glass, the seals and the frame. A two part window has more seals than a single sash, so the quality of those gaskets and how well the sashes seat when closed are worth asking about. A laminated acoustic inner pane is usually the sensible choice in a bedroom, and our guide to acoustic glazing options for roof windows in loft bedrooms explains the options. Rain is a question of its own, and our answer on whether roof windows are noisy in the rain looks at it.
When you are ready, get a quote and we will survey the room, measure the slope and write up what suits.
What people ask before choosing a balcony roof window
These are the points that come up once the idea has taken hold.
Can you sit out on a roof window balcony?
Not in the way you would on a terrace. The folded section gives a rail and a small shelf, so you can stand or lean with your head and shoulders outside. There is no floor outside the roof line for a chair.
Will it cost much more than a normal roof window?
Yes, because it is a larger, more complex unit with more framing around it. The exact difference depends on the size, the roof covering and the room below. Our costs page explains what moves the price of rooflight work, and a quote gives you the real figure for your roof.
Does the window need a roof with a particular covering?
No, it fits tiled and slate roofs with the right flashing, though the flashing kit has to match the covering. Read our note on flashings for tiles and slates for how it differs.
Is it a good fit if I only want more daylight?
Often it is more than you need. A plain roof window brings the same light for less work, and a balcony pattern earns its place when you want the opening itself as well.