Spray-applied insulation can solve two problems at once: it reduces heat loss and it closes the small cracks and junctions where buildings typically leak air. The difficulty is that not all spray products behave the same way in fire, and the language used in specifications can be misleading. A product described as fire rated may only achieve that performance in a particular tested build-up, at a stated thickness, with a defined coating or lining, and with specific installation controls.
This guide explains fire retardant spray insulation in practical terms: the main system types, what fire performance claims really mean, where each option is appropriate, and the checks that keep the solution compliant over its service life.
What is fire retardant spray insulation
On UK projects, the phrase fire retardant spray insulation is used to describe a few distinct systems. Understanding the category is the first step to specifying correctly.
1) Spray polyurethane foam used for thermal insulation
Spray foam is applied as a liquid and expands to fill voids. It is popular for roofs, lofts, and difficult-to-access cavities because it forms a continuous layer and reduces draught paths. Some formulations include fire-retardant additives, but many still require a protective lining or a tested coating system to meet fire safety objectives.
2) Spray-applied fire-resistive materials on structure
Spray-applied fire-resistive materials (often called SFRM) are typically cementitious or mineral fibre-based products sprayed onto steel or concrete to delay heat transfer in a fire. This is closer to structural fire protection than everyday thermal insulation, but it is often discussed alongside fire retardant spray insulation because it is sprayed and it provides an insulating barrier. In structural applications, fire proofing insulation extends beyond sprays to include integrated systems for comprehensive fire resistance.
3) Fire rated expanding foams used as firestopping
Fire rated expanding foams are commonly used to seal linear gaps and service penetrations, or around frames, to help maintain compartmentation. They are not a substitute for a full thermal insulation strategy, but they are a critical supporting element in passive fire protection. This is where you will most often see the term fireproof foam insulation used correctly: as a gap-sealing and smoke-resisting component within a tested detail.
In other words, Fire retardant spray insulation is not one product. It is a family of systems, and you need to match the system type to the risk you are managing.
Reaction to fire vs fire resistance: the difference that drives compliance
A frequent source of confusion is the difference between reaction to fire and fire resistance.
- Reaction to fire describes how a product contributes to fire growth: flame spread, heat release, smoke, and droplets. In the UK, guidance in Approved Document B uses the European reaction-to-fire classification framework (Euroclasses), which is based on BS EN 13501-1.
- Fire resistance describes how long an element or system maintains performance under fire exposure, typically expressed as minutes such as 60 or 120. Fire resistance is assessed through test standards and evidence for complete systems and details, not isolated ingredients.
For sprayed systems, this distinction matters because an insulation layer might achieve a particular reaction-to-fire classification, while the surrounding construction still requires fire resistance performance at compartment lines, floors, walls, and penetrations. Fire resistance testing for penetration seals and linear joints often references the BS EN 1366 series, which includes parts for penetration seals and joint seals.
A practical takeaway: do not accept a single headline claim as proof of compliance. Fire retardant spray insulation must be assessed as part of the whole build-up and the fire strategy.
Where fire retardant spray insulation is typically used
When specified correctly, fire retardant spray insulation can be a strong option in several building zones.
Roofs, lofts, and warm roof upgrades
Spray foam is often chosen to reduce thermal bridging and to seal air leakage at rafters, junctions, and irregular geometry. In these locations, the critical questions are ventilation strategy, moisture control, and what protects the foam from fire exposure on the occupied side.
Basements and soffits
Sprayed insulation is sometimes used on concrete soffits and underside areas to reduce heat loss and condensation risk. Here, coatings and linings are frequently used to improve fire performance and durability.
Structural steel and concealed service zones
SFRM systems are common in concealed structural zones, plant areas, and buildings where steel protection must achieve a defined fire resistance period. Specialist contractors treat sprayed protection as a thickness-controlled system, not an aesthetic finish.
Around openings, frames, and service penetrations
This is the domain of fireproof foam insulation used as firestopping: sealing gaps around doorsets, windows, and services to maintain the integrity of fire-resisting walls and floors. It is also where the most avoidable defects occur, because installers assume generic expanding foam is acceptable. Firestopping systems should align with test evidence and the relevant EN 1366 test regime for the detail in question.
What to look for when specifying spray foam insulation in the UK
For polyurethane spray foam used as thermal insulation, UK best practice revolves around certification, installer competence, and documented system limitations.
Third-party certification and trained installation
IMA guidance and UK consumer and compliance sources emphasise that spray foam products should hold independent certification such as BBA or Kiwa, and that installation should be carried out by trained, approved installers working to defined procedures.
This matters because the performance of fire retardant spray insulation is highly sensitive to mix ratio, substrate moisture, temperature, pass thickness, curing, and surface preparation.
The role of coatings and barriers
Many projects rely on a barrier strategy to manage fire risk when using spray foam. One approach is a spray-applied intumescent coating system designed specifically for spray polyurethane foam, used to improve the foam’s fire performance as part of a tested configuration. Product literature for commonly referenced systems describes them as thermal or ignition barrier alternatives and as fire protection coatings for spray foam.
This is the point where Fire retardant spray insulation becomes a system decision rather than a material decision: foam plus coating plus substrate plus thickness plus detailing.
A note on language
Terms like fireproof foam insulation and fire rated spray foam are widely used in the market, but they can be technically imprecise. In professional specifications, focus on:
- The required reaction-to-fire class where relevant
- The required fire resistance period for the element or detail
- The tested system build-up that achieves it
- Installation tolerances and inspection requirements
1 hour and 2 hour ratings: how to interpret the claim correctly
Clients often request a simple label such as 1 hour fire rated spray foam insulation or 2 hour fire rated spray foam insulation. These phrases can be useful, but only if everyone understands what is being rated.
1 hour fire rated spray foam insulation
In many real projects, a 60-minute requirement relates to a wall, floor, or protected opening detail, and the spray product plays a supporting role in maintaining the integrity of that detail. For example, a fire rated foam used around a frame or within a tested gap detail may contribute to a 60-minute performance where the system evidence supports it. It is reasonable to discuss 1 hour fire rated spray foam insulation in this context, provided it is tied to the tested joint configuration or penetration system, not assumed as a standalone property.
2 hour fire rated spray foam insulation
Similarly, 2 hour fire rated spray foam insulation is typically achieved in specific system configurations. Many fire rated expanding foams are advertised with up to two hours fire resistance depending on joint design, substrate, and installation. Manufacturer literature routinely makes this conditional on configuration.
A safe way to use these terms in documentation is to anchor them to the exact tested application, such as:
- Linear gap sealing up to a given width
- Penetration sealing for defined services
- Frame perimeter sealing in a tested wall type
- Foam plus coating build-up over a particular substrate at a specified thickness
Done properly, both 1 hour fire rated spray foam insulation and 2 hour fire rated spray foam insulation become meaningful, auditable statements rather than marketing shorthand.
Installation factors that make or break fire retardant spray insulation
A strong fire retardant spray insulation specification should include installation controls. The following are the most common performance drivers.
Substrate preparation and adhesion
Dusty concrete, damp timber, rusted steel, and contaminated substrates all reduce adhesion. With SFRM, poor adhesion can result in delamination under impact or vibration. With spray foam, it can create voids and inconsistent thickness.
Thickness control and continuity
Sprayed systems only perform as intended when thickness is consistent and junctions are continuous. This is particularly true for structural fire sprays where thickness correlates to fire resistance time, and for coated foam systems where the coating must form an uninterrupted protective layer.
Detailing at penetrations and junctions
This is where fireproof foam insulation often appears on snag lists. Common issues include over-trimming cured foam, leaving unsealed voids behind services, or substituting a non-rated foam where a tested firestopping system is required. Fire resistance testing for penetration seals and related service installation details is covered under the BS EN 1366 family, which exists precisely because these junctions are predictable failure points.
Documentation at handover
Approved Document B highlights the importance of fire safety information at completion, and the collated guidance includes provisions related to Regulation 38 information.
For fire retardant spray insulation, handover information should include product certificates, installer details, photographs of key details, and maintenance guidance.
Common mistakes to avoid
Most project issues come from repeating a small set of assumptions:
- Treating fire retardant spray insulation as inherently fireproof, rather than conditionally compliant as a tested system
- Using fireproof foam insulation as a general filler instead of a firestopping component supported by evidence
- Assuming 1 hour fire rated spray foam insulation or 2 hour fire rated spray foam insulation is a universal property, instead of a configuration-dependent performance claim
- Omitting third-party certification evidence, such as BBA or Kiwa documentation, for spray foam products and their intended application
- Failing to protect spray foam with a suitable barrier or tested coating system where the design requires it
How to choose the right system for your building
A practical selection process looks like this:
- Confirm whether the driver is reaction to fire, fire resistance, or both.
- Identify the location: structural steel, roof void, cavity, soffit, frame perimeter, or penetrations.
- Select the appropriate category:
- SFRM for structural fire protection
- Spray foam for thermal performance, with appropriate protection strategy
- Fire rated foams and sealants for firestopping and perimeter sealing
- SFRM for structural fire protection
- Verify evidence: certification, test data, and system limitations.
- Build installation and inspection controls into the programme.
This approach prevents the most expensive outcome: rework after inspection, when sprayed systems are already hidden behind finishes.
Conclusion
Fire retardant spray insulation can deliver real value when it is specified as a system, installed under controlled conditions, and documented properly at handover. The key is avoiding vague labels and anchoring performance to tested build-ups: the right product category, the right location, and the right evidence.
If you are reviewing an existing installation or planning a new one, treat fireproof foam insulation as a firestopping tool, treat spray foam as a thermal product that may need protective measures, and treat fire resistance durations such as 1 hour fire rated spray foam insulation or 2 hour fire rated spray foam insulation as configuration-specific claims that must be evidenced.
Frequently Asked Questions
1. Is fire retardant spray insulation the same as spray foam insulation?
Not always. Fire retardant spray insulation can refer to spray foam, but it can also refer to structural spray-applied fire protection or to fire rated foams used for sealing. The system type should match the risk and the location.
2. Can spray foam be left exposed?
In many designs, exposed foam is not acceptable without a suitable barrier or a tested coating system. Always follow the specific product certification and the building fire strategy.
3. What does fireproof foam insulation mean in practice?
Most commonly it refers to fire rated expanding foam used for gap sealing and firestopping, not full building insulation. Its performance is typically conditional on the joint design and tested configuration.
4. Is 2 hour fire rated spray foam insulation always better than 1 hour?
Not automatically. The right rating depends on the building design, compartment strategy, and the element being protected. A 2 hour fire rated spray foam insulation claim must still be backed by evidence for the specific application.
5. What standards relate to firestopping around penetrations?
Fire resistance testing for penetration seals and joint seals commonly references the BS EN 1366 series.