Compartmentation
/ kəmˌpɑːtmɛnˈteɪʃ(ə)n /
Also known as: fire compartmentation, fire compartment, compartment wall, compartment floor, separating wall
Definition
Compartmentation divides a building into fire-tight sections using fire-resisting walls and floors, so a fire starting in one section is contained within it for a defined period. This protects occupants elsewhere in the building and limits total fire spread. It is the fundamental strategy of passive fire protection. In domestic houses: party walls must achieve 60 minutes; loft conversion floors and staircase enclosures require 30 minutes; integral garages require 30-minute separation. All service penetrations must be fire-stopped to maintain integrity.
In practice
The compartmentation of a building is only as good as its weakest point - a single unsealed pipe penetration through a 60-minute party wall can defeat the purpose of the entire fire-resisting construction. Compartmentation is compromised in practice by: unsealed service penetrations; fire doors propped open; ceiling tiles removed and not replaced (in suspended ceiling systems that form part of a compartment floor); holes cut through compartment walls for later pipes and not fire-stopped; and cavity barriers missing or poorly fitted in roof voids above party walls.
In loft conversions, the existing ceiling of the floor below becomes the compartment floor - it must achieve 30-minute fire resistance (REI 30). An existing plasterboard ceiling (12.5mm standard plasterboard) does not achieve this on its own. The solution is either to add a second layer of 12.5mm board below (to achieve 30 minutes), or to fix 15mm fire-rated plasterboard to the existing joists. All new or existing penetrations through this ceiling must be fire-stopped as part of the loft conversion work.
Building Regulations
Approved Document B (Section 8, Compartmentation) sets out compartmentation requirements for dwellings and other buildings. For houses, the key requirements are: separating walls and floors between dwellings must have REI 60; protected stairways (escape stairs) must be enclosed in 30-minute fire-resisting construction; and garage separations must have 30-minute resistance. The document requires that any element forming part of a compartment (wall, floor, ceiling) must also be fire-stopped at all junctions, edges, and penetrations. Building Control will inspect compartmentation at relevant stages before it is concealed.
Full Building Regulations guidance