What fire safety is needed for a loft conversion?

A loft conversion creating a new storey requires: a protected stairway from loft to final exit with 30-minute fire-resistant construction, FD30 fire doors to all rooms opening onto the stairway, an interlinked mains-powered fire alarm to LD2 standard, and an escape window in each new loft room meeting the minimum 0.33m² clear opening.

Do existing doors need upgrading for a loft conversion?

Yes. When adding a loft storey, all existing doors opening onto the stairway (which becomes a protected escape route) need to be upgraded to at least FD20 fire doors. This typically means all bedroom, bathroom and living room doors on the first and ground floors. New loft room doors need FD30.

What fire alarm is needed for a loft conversion?

Approved Document B requires a Grade D LD2 fire alarm system for loft conversions. This means interlinked, mains-powered smoke detectors with battery backup in all circulation spaces (hallways, landings) plus all habitable rooms. Heat detectors are used in kitchens.

When are sprinklers needed for a loft conversion?

Sprinklers (or a mist system) are required if the loft conversion creates a new storey and the stairway cannot be enclosed as a protected route — for example, where the ground floor is open-plan without a hallway separating the living room from the front door.

How much does loft conversion fire safety cost?

Fire safety for a typical 2-storey to 3-storey loft conversion costs £3,000-£6,000. This includes 8-12 fire doors (£300-450 each), LD2 alarm system (£400-800), fire-resistant stairway lining (£500-1,500) and escape windows (£400 each). Add £2,000-4,000 for sprinklers if needed.

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Loft Fire Safety Calculator

Calculate fire safety requirements and costs for loft conversions per Approved Document B. Covers protected routes, fire doors, alarms, escape windows and sprinklers.

Conversion Type

Loft Floor Area

Usable loft area

New Loft Rooms

Bedrooms / rooms in loft

Existing Storeys

Before loft conversion

Stair Enclosure

Enclosed is the standard solution

Price per Fire Door

FD30 doorset supply and install

How We Calculate This

This calculator estimates the fire safety upgrades needed for a loft conversion per Approved Document B.

Requirements

Protected stairway + Fire doors + LD2 alarm + Escape windows

All doors onto stairway: FD20 (existing) or FD30 (new)
30-minute fire-resistant lining to stairway walls and ceiling
Interlinked mains smoke detectors (LD2)
Escape window in each loft room (≥0.33m², min 450mm)
Sprinklers if open-plan ground floor

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.