Every block of flats needs a fire risk assessment of its common parts under the Regulatory Reform (Fire Safety) Order 2005. What the order does not say is how deep that assessment should go — whether the assessor stays in the corridors, samples inside flats, or opens up construction to see what is behind the surfaces. The sector guidance for purpose-built blocks of flats answers that with a typology that has become standard across residential fire safety: Types 1 to 4.
The typology is widely used and widely misunderstood. Responsible persons are sometimes sold a deeper, more expensive assessment than the building warrants; more often, a portfolio sits on a stack of Type 1 reports when the building's history says someone should have looked further. This article sets out what each type actually covers and how to decide — on evidence — which one a building needs.
What the four types cover
A Type 1 assessment covers the common parts of the building, non-destructively. The assessor inspects the corridors, stairways, plant rooms and other shared areas, examines what is visible of the construction and fire protection, and assesses the management arrangements. Flat entrance doors are examined from the common-parts side. This is the baseline assessment, and for most purpose-built blocks in normal circumstances it is sufficient.
A Type 2 assessment covers the same scope as Type 1, but with destructive sampling in the common parts — opening up wall, ceiling or floor construction in selected locations to establish what is actually there. A Type 2 is commissioned where a Type 1 has raised doubt about the construction that cannot be resolved from records or visual inspection.
A Type 3 assessment extends the non-destructive scope into a sample of the flats themselves: the means of escape within flats, the fire separation between flats and common parts as far as it can be seen, and flat entrance doors from both sides. It requires access, and therefore cooperation from residents or leaseholders, but no opening-up.
A Type 4 assessment is the fullest scope: common parts and a sample of flats, with destructive sampling in both. It is the right tool where there is serious reason to doubt the fire separation throughout the building — a known era of poor conversion work, evidence of unrecorded alterations, or findings from a fire or a previous survey that point to systemic deficiency.
How to choose — evidence, not habit
The default for a purpose-built block with no adverse history is a Type 1. The justification for going further should be specific and recordable: what doubt exists, what raised it, and what the deeper scope is expected to resolve. A Type 2 answers doubt about common-parts construction; a Type 3 answers doubt about conditions inside flats; a Type 4 answers doubt about both, where the stakes justify the intrusion and the reinstatement cost.
Two practical points follow. First, the types are not a quality ladder — a Type 4 is not a "better" assessment than a Type 1, it is a different scope for a different question, and commissioning one without a reason is spending money to answer a question nobody asked. Second, the choice belongs at the scoping stage, made openly between the assessor and the responsible person. An assessor who recommends deeper work should be able to say exactly what doubt the work will resolve — and an assessor with no stake in any remediation that follows has no reason to inflate the answer.
Where converted buildings change the picture
The typology was written for purpose-built blocks, and the assumptions that make a Type 1 sufficient — consistent construction, documented compartmentation, a predictable standard of fire separation — are weakest in converted buildings. A Victorian house converted to flats in the 1980s may have little in common with its neighbours behind the plasterboard. For conversions with no construction records, a sampling approach (Type 2 or 3, occasionally 4) is more often justified at the first assessment, precisely because the baseline is unknown.
The same logic applies to any building with a significant unrecorded alteration history, whatever its original form. The question is always the same: does the evidence available support a confident conclusion about the fire separation, or does someone need to look?
What good looks like
A well-scoped assessment programme records the type of each assessment, the reason that type was chosen, and the trigger that would prompt a deeper look — so the depth of investigation is itself a managed, defensible decision. That record is exactly what a regulator, a fire and rescue service audit or a building safety case will ask for.
Apex carries out Type 1 to Type 4 assessments under BS 9792:2025, the British Standard that now governs fire risk assessment of residential buildings, and agrees the type — with the reasoning — before any commission starts. Because we carry out no remediation work, the recommendation to go deeper is only ever made because the evidence warrants it.
Common questions
What is the difference between a Type 1 and a Type 4 fire risk assessment?
Scope and destructiveness. A Type 1 covers the common parts of a building non-destructively — it does not enter flats or open up construction. A Type 4 covers both common parts and a sample of flats, with destructive sampling in both. Types 2 and 3 sit between: Type 2 adds opening-up in the common parts; Type 3 adds a non-destructive look inside a sample of flats.
Does every block of flats need a Type 3 or Type 4 assessment eventually?
No. There is no schedule that escalates a building through the types over time. A purpose-built block with sound records, no adverse findings and a stable management regime can properly remain on Type 1 assessments indefinitely. Deeper types are justified by specific doubt — construction uncertainty, unrecorded alterations, findings from previous assessments — not by the passage of time.
Who decides which type of assessment is needed?
The responsible person commissions the assessment, but the type should be agreed with the assessor at the scoping stage, based on the building, its records and its history. A competent assessor will say which type the evidence supports and why. If a deeper type is recommended, the recommendation should identify the specific doubt the additional work will resolve.