Construction Class
Construction class categorises a building by the combustibility and fire resistance of its structural materials, and is queried in property proposal forms to gauge fire severity potential and set base rates.
- Category
- Building
- Data type
- Enumeration
- Risk drivers
- Severity, Accumulation
- Underwriting impact
- Premium, Deductible, Condition/Warranty
Typical proposal-form questions
- What is the predominant construction type of the building (e.g. non-combustible, fire-resistive, combustible)?
- Are the load-bearing structure, floors and roof deck built from the same construction class, or are they mixed?
- Has the construction class been confirmed by a building permit, architectural drawing or on-site survey?
Evidence
- Building permit or construction drawings
- Risk engineering survey report
- Architect's or structural engineer's specification
Why it matters for underwriting
Construction class is one of the oldest and most predictive rating variables in property insurance because it directly governs how a fire behaves once it starts. Non-combustible or fire-resistive structures confine and slow a fire, limiting structural collapse, whereas combustible or lightweight construction can allow rapid fire spread and early loss of structural integrity. Underwriters use the declared class to benchmark probable maximum loss, compare a risk against loss experience for similar building types, and decide whether engineering input is needed before quoting.
Capturing the attribute and evidence
Proposal forms typically ask for the construction class of the load-bearing frame, external walls, floors and roof deck, since these elements can differ within the same building. Underwriters verify self-declared answers against the building permit, structural drawings, and, for larger or older risks, an on-site survey that records actual materials rather than assumed ones. Discrepancies between declared and surveyed construction are a common source of coverage disputes at claim stage.
Effect on coverage, premium and conditions
Fire-resistive and non-combustible classes generally attract lower base rates, higher natural-catastrophe and fire sublimits, and fewer warranties. Combustible or mixed-construction risks, particularly where lightweight or engineered timber elements are present, commonly see rate loadings, deductible increases, sublimits on total insured value, or specific conditions requiring enhanced fire protection or compartmentation before full limits apply.
Mitigation measures
Where construction class increases severity potential, insurers typically look for compensating measures such as upgraded fire-resistant compartmentation, sprinkler protection matched to the occupancy hazard, and restrictions on storage or processes near combustible structural elements, often formalised as policy warranties or risk improvement recommendations.