Can a roof window be an escape window?

What is required

An escape window must give an unobstructed clear opening of at least 0.33 square metres, with a minimum of 450mm in both height and width, and the bottom of the opening must be between about 800mm and 1100mm above the floor.

Those figures are the clear opening, not the frame size, so an escape window is a larger unit than the numbers first suggest.

Why top hung

The whole sash has to swing clear so a person can get through. A centre pivot window has the sash across the middle of the opening when open, which blocks it.

Escape units are top hung and open to a wide angle, typically 45 degrees or more, which is more than a standard top hung window.

It cannot be retrofitted by adjustment

This is the point people get wrong. An escape window is a different unit, not a setting. Changing the handle, the restrictor or the hinge on a standard window does not create one.

If the conversion needs an escape window and a standard unit was fitted, the remedy is a new window, usually a larger one, which frequently means altering the opening as well.

When it applies

Generally for habitable rooms in a loft conversion, and for inner rooms where escape depends on the window. It is part of the Building Regulations approval for the conversion, so it is settled at design stage.

Where a conversion is being done by others, we ask whether escape is required before quoting, because it changes the unit.

Yes, and frequently it has to be

In a habitable room in a loft, Building Regulations require a means of escape, and in most conversions that duty falls on a roof window. It is not optional and it is not something to settle after the unit has been ordered.

What the requirement asks

Three things, and a window can fail on any of them.

A minimum clear openable area, measured as the actual unobstructed opening rather than the size of the window.

Minimum opening dimensions, so the aperture is not a long thin slot that meets the area figure but nobody can climb through.

A maximum height of the bottom of the opening above the finished floor, so a person can reach it. There is also a practical expectation that it can be reached from within the room without climbing over furniture.

Why the opening type decides it

A centre pivot window rotates about its middle, so when it is open the sash sits in the middle of the aperture. That obstruction frequently takes the clear openable area below the requirement, however large the window is.

A top hung window swings clear from a hinge at the head, giving the full opening. That is why top hung units are what get specified for escape duty.

Some models have a special escape hinge that allows the sash to swing fully clear, which is worth asking about specifically rather than assuming.

Where it is easy to get wrong

Setting the window high in the slope for a better view of the sky, which can put the bottom of the opening out of reach for escape purposes.

Choosing on appearance and then discovering at Building Control inspection that the unit does not comply, at which point the window is in and the covering is back on.

Assuming the largest window automatically complies. Area alone is not the test.

When it does not apply

Where an alternative escape route exists, or where the conversion has a protected stairway meeting the relevant standard, the duty may be satisfied elsewhere and the roof window is free to be chosen purely for daylight.

Which situation you are in is established at design stage with whoever is handling Building Control, and it changes what you should buy.

The practical advice

Settle the escape question before you settle anything else about the window, and get the specific model confirmed against the requirement in writing. Reversing it after the unit has arrived is expensive, and reversing it after the roof is closed up is worse.

What has to be satisfied

An escape window has to give an unobstructed clear opening of sufficient area and sufficient minimum dimension in both directions, and the bottom of that opening has to be within a workable height above the floor.

The clear opening is what matters, not the size of the window. On a centre pivot roof window the sash rotates into the opening, and half of it ends up inside the room, so the clear opening is substantially smaller than the glass area.

That is why a centre pivot window that looks generous can fail, and why escape windows on roofs are usually top hung or specific escape models that swing clear.

The height above floor

The sill has to be low enough to climb through and high enough not to be a fall hazard. On a raked roof that is a real constraint, because the sill height above the floor depends on both the pitch and where the window sits on the slope.

A window set high on a shallow roof can have a sill well above the workable range even though it is a large window.

Where the requirement comes from

Usually a loft conversion. Whether an escape window is required at all depends on the escape strategy for the whole house, which may instead rely on a protected stairway. That is a building control question and it is settled at design stage, not chosen afterwards.

Practical advice

Have the escape route confirmed before selecting the window, because it constrains the model, the operation, the size and the position simultaneously. Choosing the window first and then trying to make it comply is the expensive order.