Can a roof window be used as a fire escape?

What Approved Document B actually allows

Approved Document B is the part of the Building Regulations for England that deals with fire safety. When someone sleeps in a room, there has to be a way out if the usual route is blocked by fire. In most rooms the way out is a door, and on an upper floor it can be a window that opens wide enough for a person to climb through.

The limit is height. An escape window is only accepted where the room sits within 4.5m of the ground outside, because above that a person cannot reasonably drop or be reached by a ladder. So the question is not really about the roof window at all. It is about how far off the ground the floor of the room is, and that is a measurement taken on your house.

A roof window is treated like any other window in this respect. It can be an escape window if it is in the right place, opens far enough and can be reached from the floor. If the room fails the height test, no choice of window changes the outcome.

Bungalows and rooms in the roof

A bungalow is where a roof window most often does this job. The floor of a room in the roof is not far above ground level, so the 4.5m limit is met and a window that is large enough and opens properly can serve as the way out. A dormer bungalow, a chalet bungalow and a single-storey house with a converted loft all fall into this group.

The details still count. The window needs to open to a clear size that a person can pass through, and the bottom of the opening cannot be set so high that nobody can climb out of it. Roof windows come in different sizes and in different opening types, so a window chosen only for the view or the light may not suit. The guide to top hung and centre pivot roof windows explains how the two opening types behave, which is useful when the window has to double as an exit.

Why a two-storey house needs a stair

On a two-storey house the loft floor is a third level, well beyond 4.5m from the ground. A roof window in that room does not count as an escape, however large it is. The regulations ask instead for a protected route: a stair that leads down to the ground floor and out through the front door, separated from the rooms it passes by fire-resisting construction.

In practice that means the existing first-floor landing and stair become part of the escape. Doors on the rooms opening onto them are usually replaced with fire doors, and the enclosure around the stair is checked. This is design work for your architect, designer or builder, and Building Control signs it off. It is the reason many loft conversions on two-storey houses are planned around the staircase first and the windows second.

A roof window in that loft is still useful. It brings in light, gives ventilation and lets someone look out. It simply is not the escape. Our guide to roof windows for a loft conversion covers how the windows are placed once the stair question is settled.

What the window itself has to do

Where a roof window is meant to be the escape, check these points with your designer before ordering.

• Clear opening. The usable gap when the sash is open, not the size of the frame. Approved Document B sets a minimum, and the window has to give at least that.
• Height of the opening. The lower edge has to be reachable from the floor of the room, so a window set high in the slope may need a different position.
• Which way it opens. A top hung sash and a centre pivot sash leave different gaps at the same angle, and some can be set to a wider position.
• What is outside. A person leaving by the window needs somewhere safe to arrive, such as a roof that can be crossed to the ground or a place a ladder can reach.

We do not quote the exact minimum dimensions here because they are set by the current edition of the document and your Building Control body applies them to your plans. Ask the person checking your drawings for the figures that apply, and give us the size they confirm.

Who checks it and when

Loft conversions and new rooms in the roof are notifiable building work. Your local authority Building Control team, or a registered building control approver if you use a private one, looks at the escape arrangement on the drawings and again on site. Having the window sizes agreed before the roof is opened keeps the inspection simple.

Our part is the window. We work from the opening size on the approved plan, order the unit against the build programme and fit it once the roofer has the opening weathered. If your plans change the window, tell us before the unit goes on order, because a different size means a different unit.

The wider rules for the work are in our Building Regulations guide, and the full list of roof window work is on the roof windows page.

Questions to settle before you order

Four questions will tell you where you stand. How high is the floor of the room above the ground outside? Is there already a stair that could serve as a protected route? Who is drawing the plans and has Building Control seen them? And is the roof window you have in mind able to open to the size the plans show?

Related questions

Does the window need to be a particular type to count as an escape?

No single type is named. What matters is the clear opening when it is open, the height of its lower edge from the floor and the room being within 4.5m of the ground. Several roof window types can meet that, so the plans and your Building Control body decide which one.

Can I add a roof window to an existing loft room and call it an escape?

Only if the room qualifies by height. If it does, the new window must give the clear opening the regulations ask for. If it does not, a protected stair is the route, and the window is for light and air.