Guide to Conversion of Traditional Buildings

2.5 Internal linings

Standard 2.5

Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the development of fire and smoke from the surfaces of walls and ceilings within the area of origin is inhibited.

2.5.1 Type of standard

Mandatory Standard

In the case of conversions, as specified in regulation 4, the building as converted shall meet the requirement of this standard (regulation 12, schedule 6).

2.5.2 Commentary

This standard can have a significant impact on the conversion of traditionally constructed and culturally significant buildings because it is concerned with the ability of surfaces to restrict the spread of fire and smoke. The materials used to cover walls and ceilings can greatly increase the danger to people who are escaping from a building that is on fire, and they do so in two ways:

• they may ignite very easily, producing smoke and spreading the fire rapidly to ceiling level where it spreads and heat is radiated down to warm other combustibles to their auto-ignition temperature.
• they may give off toxic and flammable fumes when heated.

Many of the important surfaces found in historic buildings and which are desirable to preserve in a conversion can affect the spread of fire and its rate of growth.

Fire spread on wall and ceiling linings in escape routes are particularly important in this respect. Some will be classified into high or very high-risk categories, for example, historic timber panelling more than 18mm thick has a rating of D-s2,d0. Where necessary it may be improved by impregnation or finishing with mineral paint.

The Commission Delegated Regulations (EU) 2024/1399 on the conditions for classification, without testing, of solid wood panelling and cladding with regard to their reaction to fire and amending Decision 2006/213/EC, details the surface spread of flame rating of untreated timber.

a) Timber linings

Timber wall and ceiling linings are likely to be the most frequently encountered historic surface that will contribute to the spread of fire. They may burn readily and the presence of shakes, splits and shrinkage cracks will also contribute further to the fire risk. In addition, such linings may have been treated with waxes, polishes and paints, which tend to increase flammability of the surface.

b) Decorative treatments

The Technical Handbook guidance excludes any decorative treatments, such as paints and wallpapers. However, while some paints, polishes and varnishes may themselves be liable to ignition, it is the heavy build-up of layers of paint over many years that make them potentially vulnerable to fire and the production of smoke and gases. To counter this effect, multiple layers are not recommended in the Technical Handbook guidance. However, the stripping back of multiple layers may destroy important historical information. Where paint removal from surfaces is being considered in listed buildings, listed building consent may be required if they are part of a historic decorative scheme that is important to an understanding of the building.

For all historic linings and decorative finishes, a fire risk assessment is required. For the build-up of multiple layers of paint and wall coverings, a fire risk assessment will normally include an exploration of the layers, perhaps involving paint scrapes or sampling of a discreet segment of wall covering for analysis. This analysis may also include a chemical analysis of paint layers to determine the composition of the paint and its fire risk potential. Where an important decorative scheme survives, this type of investigation will help to identify the historic significance of hidden layers and assist in the development of a conservation strategy.

c) Plaster surfaces

The majority of wall and ceiling surfaces are likely to be plaster on timber laths. These traditional plasters, whether lime or gypsum, are inherently resistant to spread of fire. However, the strength of such finishes is determined by the quality of the key between plaster and laths (or other substrate). When this is damaged through movement of the substrate, decay of the timber laths, or rusting through of the fixings the capacity of the finish to withstand fire is reduced. In a fire situation, there is a risk that unstable plaster will collapse suddenly, exposing combustible material to fire. Thus, in the fire risk assessment of linings, the condition of the plaster and its substrate should be assessed.

2.5.3 Issues to be considered

Issue - Risks to historic / traditional buildings

1. Internal linings The removal or treatment of historic wall and ceiling linings to improve the surface spread of flame rating can result in loss of historic character and fabric. Multiple layers of paint or other coverings may present a fire risk, but their indiscriminate removal may destroy a layer of historic importance.

2.5.4 Recommendations to meet the standard

It is recommended that specialist advice for design and construction should be sought from those with appropriate heritage and fire expertise.

It may be appropriate to install an automatic fire suppression system (see guidance to standard 2.15) and an enhanced automatic fire detection and alarm system, for example a Category L1 to BS 5839- 1 2017, to ensure the earliest possible warning in the event of an outbreak of fire.

a) Mineral paints or intumescent paints and varnishes are widely available in a variety of forms for the treatment of timber and there are many examples of these products being successfully used in historic buildings. Also, other treatments are available for materials such as wallpaper, fabrics and drapes. Expert advice should be sought to ensure fire protection coatings are third party certified, robust and do not damage base materials needing preservation.

b) Following a full and detailed fire risk assessment, it may be possible to reduce or eliminate fire hazards to the extent that the possibility of internal linings contributing to a fire or consequently posing a hazard to persons in the building, is very limited. Should this be the case, it may be possible that, subject to the approval of authorities having jurisdiction, the linings in question may be left as they are. However, such a strategy will require good ongoing management in accordance with BS 9999 Section 9 and confidence that standards will be maintained. Furthermore, such an arrangement should be communicated to the relevant fire and rescue service as it could affect safe access for fire-fighting and may need recording on the fire strategy and any operational/tactical risk plan for the building.

c) Automatic fire suppression, particularly fire sprinklers with sidewall sprinkler heads, can provide sufficient wall wetting to modify flame spread across many combustible surfaces. For further information see Section 2.15 Automatic fire suppression systems.