Health & Safety Technical Update

The importance of roof voids inspections

It is a well-known principle that suitable fire compartmentation in a building will contain the spread of fire and smoke, thus protecting the occupiers and the property.

Nowhere is this more important than where evacuation is delayed or phased (such as care homes and healthcare) or where evacuation beyond the area of fire origin is not normally required (such as in most blocks of flats.

Whilst the necessity to ensure walls, floors, and doors are of a suitable standard, it has been often overlooked in less accessible, but equally important, areas such as roof voids.

Fires can spread very quickly through roof voids if they are not appropriately compartmentalised. This can cause a fire to spread quickly between different compartments of a block, undermining the fire strategy.

The lines of compartmentation between flats located on the top floor of a building should, where there is a common roof void above, extend through the roof void in a continuous vertical plane to the underside of the roof (see Figure 1).

This will ensure that the fire-resisting ‘box’ principle extends into the common roof voids to prevent fire spread between flats and fire spread from a flat into other areas of the building via the common roof void (see Figure 2).

It is not appropriate to complete the line of compartmentation within roof voids by installing cavity barriers above the compartment walls that separate flats, nor to treat the roof void simply as a concealed space within which cavity barriers are installed at regular intervals (other than, for example, where the void has been created by roofing over an original concrete flat roof).

The result of inadequate roof void separation is of rapid, unseen, fire and smoke spread that can and has led to fatality and multi fatality fire incidents (see Figure 3)

The provision of fire-resisting ceilings within top floor flats (see Figure 4) would not normally provide an alternative means of achieving an equivalent standard of safety, as it would fail, for example, to address the possibility of a fire that starts within the roof void (see Figure 5) or that enters the roof void externally (e.g. as a result of flames projecting from a top storey window – see Figure 6).

A fire-resisting ceiling will afford protection against the spread of fire from a flat into the roof void (see Figure 4), but not normally vice versa.

In certain situations, in existing blocks where 60 minutes’ fire resistance is not met or cannot readily be achieved by upgrading walls or floors, compensatory fire protection measures may need to be considered. These measures might include one or more of the following:

• provision of enhanced automatic fire detection; or
• provision of an automatic water fire suppression system, such as a sprinkler or watermist system.

However, in all situations, it should be remembered that, fundamentally, any ‘stay put’ strategy relies upon there being adequate compartmentation to restrict fire spread, to the extent that only the occupants of the flat of fire origin would need to evacuate, while the occupants of flats unaffected by a fire should be safe to remain in their flats unless directed to evacuate by the fire and rescue service.

Access into roof voids is therefore necessary as part of a fire risk assessment – if not possible due to lack of access provision, this would be raised as an action point as it cannot be assumed to be satisfactory.

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