Do all loft rooms need a fire escape window?

Every habitable room in a loft conversion (bedrooms, studies) needs either a fire escape window or access to a protected stairway leading to a final exit. If the loft has a 30-minute fire-protected stairway down to an exit, escape windows may not be required. Building control will advise.

What size does a fire escape window need to be?

Part B requires a minimum clear openable area of 0.33m² with no dimension less than 450mm. The window must be openable from inside without a key. For roof windows (Velux type), the opening must be large enough for a firefighter wearing breathing apparatus to enter.

What is the maximum sill height for an escape window?

The sill of the escape window must be no more than 1100mm above the finished floor level. For roof windows, this is measured to the bottom of the opening light. The sill should also be at least 600mm above floor level for safety (guarding requirement).

Can I use a Velux window as a fire escape?

Yes, if it meets the minimum clear opening requirements (0.33m², no dimension less than 450mm) and the sill height is no more than 1100mm from the floor. Top-hung Velux windows are generally easier to escape from than centre-pivot types. Check the window's clear opening dimensions in the manufacturer's data.

What if my loft windows don't meet fire escape requirements?

If windows cannot meet the escape requirements, you may need to install a suppression system (sprinklers) or create a fully protected escape route with FD30 fire doors, fire-rated construction and a stairway leading to a final exit. A fire engineer can design an alternative solution.

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Fire Escape Window Calculator — Part B Loft Compliance Check

Check loft conversion windows against Building Regulations Part B: minimum 450×450mm clear opening, maximum 1100mm sill height, for each habitable room.

Habitable Rooms in Loft

Each needs an escape window

Clear Opening Width

Min 450mm required

Clear Opening Height

Min 450mm required

Sill Height Above Floor

Max 1100mm, min 600mm

Protected Stairway Available

FD30 doors on protected route

Price Per Window (optional)

Escape window installed cost

How We Calculate This

This calculator checks loft windows against Part B fire escape requirements for habitable rooms.

Part B requirements

Clear opening: minimum 0.33m², no dimension less than 450mm

Sill height: 600-1100mm from finished floor level

Compliance checks

Width: Clear openable width >= 450mm
Height: Clear openable height >= 450mm
Area: Width × Height >= 0.33m²
Sill: 600mm <= height <= 1100mm

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.