Spray foam insulation delivers outstanding thermal performance in commercial and industrial buildings — but like any organic insulation material, it must meet strict fire safety standards before it can be used in occupied structures. In the UK, this means complying with Building Regulations Approved Document B.
This guide explains the fire ratings that apply to spray foam insulation, how intumescent coatings provide the required level of fire protection, and what specifiers and building owners need to know to achieve full compliance.
Why Does Spray Foam Insulation Need Fire Protection?
Spray polyurethane foam (SPF) — whether open cell or closed cell — is a plastic-based material. In its raw, uncoated state, it will burn if exposed to a direct flame. UK Building Regulations do not ban spray foam or any other polyurethane insulation. Instead, they require the installed system to achieve specific fire performance classifications.
Without an appropriate fire protection coating, spray foam insulation cannot legally be left exposed in occupied commercial buildings. The coating is not optional — it is a regulatory requirement.
UK Fire Rating Classifications for Spray Foam Insulation
British Standard Classifications (BS 476)
- Class 1 Surface Spread of Flame (BS 476 Part 7) — the surface resists flame spread across it.
- Class O — a composite requirement under Building Regulations. Class 1 for surface spread of flame AND either non-combustible or has a fire propagation index (I) of no more than 12.
European Classification (EN 13501-1)
- Euroclass B-s2,d0 — very limited contribution to fire, limited smoke production, no flaming droplets. Broadly equivalent to Class O/Class 1.
- Euroclass C — limited contribution to fire. Acceptable in some lower-risk applications.
- Euroclass E — the base rating for uncoated closed-cell spray foam. Not sufficient for exposed use in most commercial settings.
For commercial buildings, the target is typically Euroclass B-s2,d0 or Class O.
How Intumescent Coatings Protect Spray Foam From Fire
An intumescent coating is a reactive fire protection material that swells when exposed to heat. At temperatures above approximately 200°C, the coating expands to many times its original thickness, forming a carbonaceous char layer that acts as a barrier between the flame and the spray foam underneath.
- Rapid activation — begins to intumesce within seconds of flame exposure
- High expansion ratio — creates a substantial insulating char
- Low smoke generation — limits smoke production during a fire event
- No flaming droplets — prevents burning material from falling and spreading fire
- Adhesion to foam — bonds directly to the spray foam surface
DC315 Intumescent Coating: The Industry Standard
DC315 is the most widely used intumescent thermal barrier coating for spray polyurethane foam insulation globally.
DC315 Technical Specifications
- Type: Water-based intumescent thermal barrier coating
- Application: Airless spray or roller
- Coverage rate: 0.5–0.75 litres per m²
- Coats required: Typically 2 coats
- Colours: White, Ice Grey, Black
- Fire rating: Euroclass B-s2,d0 when applied over closed-cell spray foam
- Elongation: Greater than 200%
When applied over Nexseal LE closed-cell spray foam, DC315 upgrades the system from Euroclass E to Euroclass B-s2,d0.
Where DC315 Is Required
- Left exposed (not covered by plasterboard)
- Installed in occupied commercial or public buildings
- Applied to soffits, car park ceilings or undercrofts
- Used in buildings where Class O or Euroclass B is specified
- Installed in escape routes, corridors or stairwells
Application Process
- Surface preparation — substrate cleaned and loose material removed
- Spray foam application — foam sprayed to required thickness
- Foam trimming — excess foam trimmed flush if required
- First coat of DC315 — applied by airless spray
- Drying time — minimum 4–6 hours between coats
- Second coat of DC315 — to achieve total required dry film thickness
- Inspection — wet film thickness checks and visual inspection
Choosing a Fire-Compliant Spray Foam Installer
Duratite Projects Limited manages commercial spray foam insulation projects nationwide. Every project where fire protection is required includes DC315 intumescent coating as standard.
Frequently Asked Questions
Does spray foam insulation need fire protection in the UK?
Yes. Under UK Building Regulations Approved Document B, spray foam insulation left exposed in occupied commercial buildings must achieve a minimum fire rating — typically Class O or Euroclass B-s2,d0. This is achieved by applying an intumescent coating such as DC315.
What fire rating does spray foam achieve with DC315?
When DC315 is applied over closed-cell spray foam at the recommended coverage rate in two coats, the system achieves Euroclass B-s2,d0, broadly equivalent to Class O.
What is the difference between Class O and Euroclass B?
Class O is a UK Building Regulations composite requirement. Euroclass B-s2,d0 is the European equivalent under EN 13501-1. Both are accepted by UK building control for commercial buildings.
Can spray foam be left exposed without an intumescent coating?
In most commercial applications, no. Uncoated spray foam typically achieves Euroclass E, which does not meet requirements for exposed use in occupied buildings.
How much does intumescent coating add to the cost?
DC315 typically adds between £5 and £12 per square metre to the total installed cost of spray foam insulation.
How long does DC315 intumescent coating last?
DC315 is designed for the lifetime of the building. Once applied and cured, it does not degrade under normal interior conditions and does not require reapplication.
Book a Free Fire Protection Survey
Call us on 01208 832602 to book a free site survey, or visit our DC315 intumescent coating page for full product details.
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