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Passive Fire Protection Calculator
Calculate quantities and costs for passive fire protection systems including intumescent paint, fire boards, cementitious spray and concrete encasement for steel and timber.
Heated perimeter of section (Hp)
Length of each member
Coating/board material cost only (~£4–£15/m²) — labour and primer added separately below
Coats applied — adds 15% labour per extra coat
Safety notice
Fire safety measures must satisfy Approved Document B and often need building control approval. Confirm the final specification with building control or a fire engineer before relying on it.
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How We Calculate This
This calculator gives an indicative budget cost for passive fire protection of structural members. It is an estimating tool, not a fire-engineering specification.
The formula
Total = (Surface area × material rate × rating multiplier) + Labour + Primer
- Surface area = section perimeter (Hp) × member length × number of members
- The material rate you enter is supply only; a rating multiplier scales it up for longer fire periods (more build)
- Labour is a per-m² rate by protection type, plus 15% for each coat beyond the first
- The all-in £/m² (supply & apply) is the total divided by the protected area
About the DFT figure
The dry film thickness shown for intumescent paint is a mid-range guide tied only to the fire rating. The real required DFT also depends on the section factor Hp/A and the limiting steel temperature, and must come from the manufacturer's loading tables assessed to BS EN 13381-8 (intumescent) or BS EN 13381-4 (boards and cementitious sprays). Cost rates here are indicative and unsourced — there is no published UK £/m² index, so confirm with a fire-protection contractor.
Frequently Asked Questions
Passive fire protection (PFP) refers to materials and systems that protect structural elements from fire without requiring activation. It includes intumescent coatings (which swell in heat), fire protection boards, cementitious sprays and concrete encasement. PFP maintains structural integrity during a fire.
As a budgeting guide, a typical all-in (supply and apply) rate for 60-minute protection is around £25-£40/m², rising to roughly £40-£65/m² for 90 minutes and £55-£90/m² for 120 minutes. The coating material on its own is usually only about £4-£15/m² — labour, primer, certification and access make up the rest. There is no published UK price index, so quotes vary widely with job size, section factor and access; this calculator asks for the material rate (supply only) and adds labour and primer separately to estimate the all-in figure.
DFT (Dry Film Thickness) is the thickness of the intumescent coating after drying, usually quoted in microns (µm) or mm. The required DFT depends on three things together: the fire-resistance period, the section factor Hp/A of the steel member (heated perimeter ÷ cross-sectional area, in m⁻¹) and the limiting/critical steel temperature. Higher ratings and lighter, higher-Hp/A sections need thicker coatings. The figure must be read from the manufacturer’s certified loading tables, assessed to BS EN 13381-8. Hp/A values for standard sections are published in the SCI “Blue Book”. The indicative DFT this calculator shows is a mid-range guide only and is not a substitute for that assessment.
Fire protection boards are preferred when the steelwork will be concealed (ceilings, risers), when a box profile is acceptable aesthetically, or when higher fire ratings (90-120 minutes) are needed cost-effectively. Boards can also be removed and replaced for inspection, unlike spray systems.
Not always. Single-storey buildings, portal frames in some industrial buildings, and external steelwork may not need fire protection depending on the fire engineering analysis. Also, concrete-filled hollow sections can achieve fire resistance without additional protection.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.