Guide to Conversion of Traditional Buildings

Part 2: Application of the fire standards

2.1 Compartmentation

Standard 2.1

Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, fire and smoke are inhibited from spreading beyond the compartment of origin until any occupants have had the time to leave that compartment and any fire containment measures have been initiated.

Limitation:

This standard does not apply to domestic buildings.

2.1.1 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).

2.1.2 Commentary

One of the primary design considerations in converting or making alterations to a building is to prevent the spread of fire beyond its point of origin. This measure aims to reduce the chance of a large fire developing, ensuring the safety of both occupants and individuals in the vicinity of the building, and assisting fire and rescue service personnel with fire-fighting and rescue operations.

The creation of larger and more open plan structures is rare, as most conversions involve dividing traditional buildings into smaller units. This might be the creation of apartments, or sub-division into compartments with corridors for a hotel or residential care home. In any situation, while it is possible to consider the existing fire load, anticipating the proposed fire load arising from changes in use or layout may not always be feasible. Nevertheless, certain room uses such as kitchens, lounges, or storage areas will have a higher fire load compared to bathrooms or dining rooms, potentially influencing the fire strategy.

Traditional buildings may be vulnerable to the risk of fire spread because of how they have been built. In addition, most traditional buildings will have undergone changes since their original construction, which may increase the risk of fire spread if the original compartmentation is compromised. Classic examples of rapid fire spread through unprotected openings into hidden voids were the 2002 Cowgate fire in Edinburgh, the Glasgow School of Art building (2014), Clandon Park mansion house in Surrey (2015) and the Royal Clarence Hotel Exeter (2016).

Buildings proposed for conversion should be systematically inspected by a competent fire engineer to identify existing masonry walls which can provide fire separation of at least thirty minutes and often over an hour. The design should incorporate these natural fire compartments, as their removal or alteration could have a serious impact on the fire performance, the historic fabric and the economics of development.

Compartmentation is the simplest means of inhibiting the spread of fire, heat and smoke (comprising toxic and highly flammable gases) within the building. It will assist in protecting escape routes, helping occupants to evacuate the building and aid fire-fighters entering for the purposes of search and rescue and extinguishing the fire.

In assessing compartmentation, it is necessary to consider the boundaries to each compartment (normally the walls, ceilings and floors) for fire resistance and the function of the elements or components of construction in terms of load bearing capacity, integrity, and insulation. In many traditional buildings, the integrity of the boundaries will be compromised by openings such as doors, service ducts, electrical pattress boxes, ceiling roses and other weaknesses. In addition, most older buildings will have undergone alteration and repair, which may have further compromised the fire integrity of the construction and compartmentation. Nevertheless, it is still possible to improve the fire performance of existing construction while retaining or restoring historic finishes.

The purpose of this standard is to enable occupants to escape and to limit the severity and spread of fire and smoke. While efforts should be made to enhance the fire resistance of compartments, there may be a point where further improvement could result in the loss of significant historic fabric and features or impact on the appearance of architecturally interesting spaces.

In such circumstances, it may be possible to adopt a fire engineering approach which balances weaknesses in compartmentation with other fire safety measures that will protect escape routes or reduce the evacuation time and/or facilitate fire-fighting and rescue operations. Such measures may include the adoption of a fire engineering methodology along with improved fire safety management, fire alarm and detection systems or automatic fire suppression systems.

Smoke and heat exhaust ventilation systems (SHEVS) are rarely present in historic or traditional buildings but may be required in flats, hotels and large shops more than 5600 square metres or in the mall of an enclosed shopping centre or shops within an enclosed shopping centre with a storey area more than 1,300 square metres. Their introduction may result in significant levels of damage to historic fabric unless existing voids or shafts can be used.

To mitigate the risk of fire and smoke spreading through ventilation systems, it is essential to design a mechanical ventilation system that either shuts down automatically or operates in a fire-mode upon detecting a fire. This can be accomplished by integrating the MVHR system with the building's fire detection system.

This is covered further in LABSS Information Paper - INFOP24/2019 Version 1 DMEV/MEV Installation in a flat with a protected enclosure.

2.1.3 Issues to be considered

Issue - Risks to historic / traditional buildings

1. Maximum compartment areas vertical and horizontal fire breaks Large un-compartmented spaces, especially if used for high fire loads such as stacked goods or flammable stock allow fires to spread rapidly and may make escape difficult. Sub-dividing historic spaces to comply with maximum compartment areas can be destructive to the historic character of a space or building.

2. Standards of fire resistance (short, medium and long) Existing elements of a building’s structure may be inherently fire resistant while some may not; however, there may be additional difficulties faced in ensuring that barriers surrounding fire compartments provide the required standard of fire resistance.

3. Smoke and heat exhaust ventilation system Heat exhaust ventilation systems (SHEVS) are rarely present in traditional buildings but may be required in flats, hotels and large shops with floor areas of more than 5600 square metres or malls larger than 1300 square metres. Their introduction may result in significant levels of damage to historic fabric and character unless existing voids or shafts can be used.

4. Buildings and change of use New uses that increase fuel loads, like hotels or retail spaces, can raise fire risks. Converting traditional buildings to offices, hotels, retail spaces, or cultural venues has been successful, but all potential impacts must be carefully considered. When converting to hotel or residential use, it is highly probable that a suppression system must be provided (Refer to The Building (Scotland) Amendment Regulations 2025).

5. Residential Buildings The requirement to make every floor a compartment floor in a conversion to a residential building may affect historic features or character. However, suitable fire performance can still be achieved by implementing solutions such as upgrading the fire resistance between the joists from above.

6. High rise buildings The requirement for every floor, at a height of more than 18 metres above the ground, to be a compartment floor may be difficult to achieve if historic finishes are to be retained (for example in the conversion of a large historic house to a hotel). The requirement to fit a suppression system, whilst being the minimum standard, may also be a compensating feature for variations to other standards.

7. Basements The ground floor and basement ceiling should form a fire compartment unless the building comprises one basement and not more than ground and first floors with no storey more than 280 m². In these cases, a compartment floor need not be provided. It may be relatively easy to make the compartment floor fire resisting if the basement does not contain significant historic fabric or features of interest. A building with separate entrances at street level and garden level should not automatically be considered to have a basement simply because one of the levels is referred to as a "lower ground floor".

8. Fire hazard rooms and services These should be enclosed in fire resisting construction and will include:

• Electrical intake rooms and switch rooms,
• Transformer substations,
• Boiler room and plant rooms,
• Lift motor rooms.
• Service duct or cupboard
• Waste storage room
• Communal lounge or laundry in a sheltered housing complex.

9. Fire resisting ceilings Careful consideration should be given when upgrading the fire resistance of historic ceilings and their junction with compartment walls may affect the historic fabric.

2.1.4 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.

Where an automatic fire suppression system is installed, compartment sizes may be larger, and there may be a case for the fire resistance periods to be reduced.

Where compartments are overly large, low levels of combustibles (such as may be found in a museum, church or gallery) may offer sufficient compensation provided that the fire risk is well managed in accordance with BS 9999: 2017 Section 4.1. In certain instances, a comprehensive fire engineering analysis is necessary to assess the fire growth potential in accordance with BS 7974.

Only in extreme cases would the installation of new fire rated floor over an existing historic floor be a practical solution because the doors, skirtings and fireplaces are all likely to need modification. If the new floor is removed in the future, the effect of the modifications on the original features will be evident.

The requirement to replace original doors with modern rated fire doors is one of the most contentious issues in the process of modifying historic buildings for new uses. Thin panels, door edge gaps and panel joints and cracks are the weak points. The fitting of smoke seals and intumescent strips to the door edges and intumescent veneers to protect the panels can provide a reasonable standard of fire resistance for timber panel doors.

Automatic self-closing devices will be required where a door is in regular use and protecting an escape route. Where the door is not in regular use, such as in a cupboard or duct, it may be kept locked shut. The choice or design of a self-closing device may depend on the historic significance of the door it will control.

• Overhead closers are face fitted and cause little damage (screw holes) so are reversible, though visible. They are difficult to use on doors with arched heads.
• Hidden overhead closers are recessed into the top rail or into the frame which causes more damage and may affect the door’s fire resistance.
• Concealed closers are fitted mid-rail and can be used on doors with arched heads.
• Controlled closers are preferable to those that have an uncontrolled action which causes doors to slam shut.
• Floor springs are suitable for heavier doors and those with arched heads, but those with a straight head may be fitted with an overhead closer.

The gap between the wall and the door frame may provide a route for fire spread around the door set. This should be infilled with lime mortar or a proprietary intumescent product that is suitable for the size of gap.

Protecting penetrations is a straightforward process given the available range of modern fire resisting compounds and traditional materials such as lime mortar, lime plaster and lime putty. Where a building is being rewired there will be an opportunity to fit fire resisting cable transit systems and carry out local fire stopping or even upgrading fire compartmentation.

The fire resistance of lath and plaster ceilings will vary according to their condition, thickness, strength of keying and fixings to the laths. It is possible to introduce modern fire-resistant materials in such areas, for example under-floor fire barriers, which might be installed with minimal disruption to historic fabric when floors are being removed for re-wiring. Exposed masonry walls forming fire compartments should be inspected and repaired or fire stopped as necessary to maintain their fire integrity.

Mansard roofs pose challenges in preventing fire spread, as the eaves form hidden voids that may also contain discreet lead gutters that run along the length of the building. The voids may also extend up into the roof space, with difficult or no access. The lines of fire resistance cannot cross the gutter, so the eaves will need protection from fire occurring on the floor below and the adjacent rooms.