Compartmentation in Heritage Buildings: What's Required?
Anyone responsible for a heritage building comes up against the same difficult question sooner or later. The fire risk assessment, or the insurer, or the fire and rescue service, calls for better compartmentation, and the honest worry that follows is whether it is realistically possible to build effective fire separation into a structure that was put up long before fire compartmentation was ever conceived of, and to rely on it the way you could rely on it in a modern building. It is a fair question, and it deserves a fuller answer than a simple yes or no, because the way you arrive at the answer is what makes the difference between protection that works and money spent on protection that does not.
What compartmentation is, and what it is for
Compartmentation is the division of a building into separate fire-resisting cells, using walls, floors, ceilings and doors that will hold back fire and smoke for a defined period, commonly thirty, sixty or one hundred and twenty minutes. Vertical compartmentation, the walls and partitions, stops fire travelling sideways through the building, while horizontal compartmentation, the floors and ceilings, stops it climbing from one storey to the next. The purpose is to contain a fire close to where it starts, which buys time for people to escape, limits the damage to a single area, and gives the fire and rescue service a smaller and more manageable fire to deal with. In a modern building this is designed in from the outset as a coordinated network of sealed boxes, but a heritage building has to have it introduced into fabric that was never arranged with this in mind.
What is actually "required"
There is no single prescriptive list of compartments that the law imposes on an existing historic building. The duty under the Regulatory Reform (Fire Safety) Order 2005 is to provide general fire precautions that are appropriate to the premises, flowing from a suitable and sufficient fire risk assessment carried out by a competent person. What compartmentation is required is therefore a judgement specific to the building, its use, its occupants and its risks, informed by the recognised guidance rather than dictated by a fixed code. For heritage premises that guidance includes the London Fire Brigade's heritage guidance note, the advice published by Historic England, and the standards that sit behind them, including BS 9999 and the conservation guidance in BS 7913, all of which point towards a building-specific fire strategy rather than a one-size-fits-all answer.
A principle runs through all of it, which is that almost every old building already has natural lines of compartmentation, the thick masonry walls, the stair enclosures, the substantial cross-walls, that can be identified and reinforced to provide separation, and that working with these existing divisions is very much easier and more sympathetic than imposing new ones where none ever existed.
Why heritage buildings resist compartmentation
The difficulty is real, and it is worth being clear about, because the honest answer to the reliability question depends on understanding it. Heritage buildings work against compartmentation in several ways at once. They contain large undivided spaces, the great halls, galleries, worship spaces and stairwells that give them their character but offer a fire room to grow. Their structure is frequently combustible, with timber floors, roofs and panelling, and full height panelling or tapestry can carry flame from floor to ceiling with alarming speed. Most seriously of all, they are riddled with concealed voids, the cavities behind lath and plaster, redundant flues, ventilation stacks, old dumbwaiter and bell-pull shafts, and floor and roof voids, which interconnect and let a fire smoulder unseen for hours before breaking out somewhere far from where it began.
Two particular weaknesses recur. Compartment walls in old buildings very often stop at ceiling level and do not continue up through the roof void, leaving an open path above the line of separation, and the historic doors, however beautiful and however solid, are almost never fire rated to a modern standard, which makes them the most common gap in the protection.
The hidden killer: service penetrationsEven where good compartmentation exists, it is routinely undone by later work. Every time a pipe, cable or duct is run through a compartment wall or floor and the hole is not properly fire-stopped, the line of separation is breached. Unsealed service penetrations through compartment walls were cited as a factor in the rapid fire spread that destroyed Clandon Park in 2015, and they are the single most common reason that compartmentation fails to perform when it is needed.
How effective compartmentation is retrofitted
None of this means the task is impossible, and the toolkit for doing it well, sensitively and to a recognised standard is now well established. Historic doors can usually be upgraded rather than replaced, by adding intumescent strips and cold smoke seals, lining the reverse with a discreet thin fire-resisting board, and improving the fit to close the gaps, so that a door of real historic value is brought up to a notional or rated standard while keeping its appearance. A periodic fire door inspection then confirms those doors continue to perform. Concealed voids are sealed with intumescent products, fire-stopping mortars and cavity barriers, work that is highly effective and very often completely invisible once finished. Floors and ceilings can be upgraded, frequently by adding a fire-resisting layer to the ceiling from below, to provide the horizontal separation that limits vertical spread.
Where there is simply no existing line on which to hang a wall or a doorset, more inventive solutions are used. At Chatsworth, for example, a major compartment line that could not take a new doorset was achieved instead with a fire-resisting fire curtain, and elsewhere new fire doors have been introduced into previously blank openings to sub-divide long corridors. Fire-resisting glazing, secondary glazing and improvements to how historic glass is held in its frame address the weakness that windows and glazed openings present in an otherwise sealed compartment. The common thread, and the part that determines whether the result can be trusted, is that the work should be specified after an accurate survey, carried out using certified products installed by certified and competent contractors, and recorded so that its performance can be demonstrated.
So can it be relied upon completely?
This is the heart of the matter, and the answer is a qualified yes. If an accurate survey is carried out, including intrusive investigation where it is needed to find the hidden voids, and if the remedial works are effective and done to the requirements of the relevant guidance, preferably using certified products fitted by certified contractors, then it can and should be assumed that the compartmentation will perform as it is intended to. That is the standard the heritage sector works to every day, and it is achievable.
The word to be careful with, though, is the idea of relying on it one hundred per cent. Compartmentation is never an absolute guarantee, in a heritage building or a modern one, because its fire resistance is rated for a period of time rather than forever, because that performance depends entirely on correct installation and continued maintenance, and because, as the Clandon Park lesson shows, it can be silently compromised by the next contractor who runs a cable through a wall. The right way to think about it is not as a single barrier that either holds or fails, but as one layer in a defence in depth. Compartmentation that has been properly surveyed, specified, installed, certified, maintained and protected from later breaches can be relied upon to do its job, and it becomes more reliable still when it sits alongside early detection, automatic suppression where it can be accommodated, and the active management that the building's fire strategy provides.
How the heritage sector handles thisHistoric England, the National Trust and the bodies that look after the royal palaces wrestle with exactly this balance, achieving modern fire performance while respecting listed fabric. After the 1986 fire at Hampton Court Palace, retrospective compartmentation was introduced throughout, with the building divided into separate fire-compartmented sections and the floors upgraded with fire-resisting materials to check vertical spread, an approach that shows what can be done even in a building of the first rank. Windsor Castle after 1992 tells a similar story of fire performance rebuilt into historic fabric.
Working with listed status, not against it
Listed building consent will often be needed, and the guiding principle is minimal, sympathetic and where possible reversible intervention, which is why so much of the modern toolkit, the discreet door upgrades, the invisible void sealing, the concealed suppression, has been developed precisely to deliver fire performance without sacrificing the fabric. Conservation and fire safety are not in opposition when the work is done by people who understand both, and the early involvement of the conservation officer, the insurer and a fire risk assessor experienced in historic buildings is what keeps the two aligned. Many of the buildings where this matters most are historic churches and places of worship, where the same principles of natural compartment lines, void sealing and door upgrading apply.
For anyone managing a heritage building, the practical route is therefore clear enough. Begin with a competent fire risk assessment and compartmentation survey carried out by someone experienced in historic buildings, use that to build a building-specific fire strategy rather than a generic checklist, have any works carried out with certified products by certified installers, and re-survey whenever services are altered so that a hard won line of separation is not quietly undone. Done that way, retrofitted compartmentation in a traditionally built structure can be genuinely relied upon to perform as intended.
An independent assessment, with nothing to sell youWe carry out fire risk assessments and advise on the compartmentation strategy a heritage building needs, but we do not sell or install fire doors, fire-stopping or suppression. That means our recommendations are driven by the building and the guidance alone, giving you an impartial basis for deciding what work is genuinely necessary and what is not.
As independent assessors covering the North West, North Wales and the West Midlands, with particular experience in historic and ecclesiastical buildings, we are glad to look at your building, identify where its real compartmentation weaknesses lie, and set out a proportionate, sympathetic strategy for addressing them.
Managing a heritage building?
We can survey your compartmentation, identify the hidden voids and weak points, and set out a clear, sympathetic fire strategy that respects the listed fabric. If you would like to discuss your building, please get in touch.
Get in touch Fire Risk AssessmentsThis article is provided for general guidance and does not constitute professional advice for any specific premises. It refers to the Regulatory Reform (Fire Safety) Order 2005 and to published heritage fire safety guidance, including that of the London Fire Brigade, Historic England, BS 9999 and BS 7913. Considerable care has been taken to ensure accuracy at the time of writing, but legislation and guidance change over time. Fletcher Risk Management Limited provides Fire Risk Assessments, Fire Door Inspections and Fire Safety Training across the North West, North Wales and the West Midlands.