Fire Retardant OSB
Nobody wants to rip boards off a wall because the specification failed inspection. That gets expensive very quickly. Fire rated OSB helps avoid that problem before the first sheet is even fixed into place. These boards are designed for projects with increased fire protection requirements while still handling like standard OSB3 during cutting, fixing, and installation.
What is fire retardant OSB?
Fire Retardant OSB is a structural OSB3 board. It is commonly chosen where fire rated materials are specified as part of the build. At the same time, it still keeps the normal strength and rigidity expected from a standard OSB3 board. During installation, it handles much like a regular OSB panel. The difference becomes noticeable when the board is exposed to fire.
The board we stock is EGGER OSB Flammex. It is one of the leading fire rated OSB products available in the UK. It is CE marked to EN 13986:2015 and classified as Euroclass B under EN 13501-1. Euroclass B-s1,d0 rating means the board makes a very limited contribution to fire, produces minimal smoke and does not generate burning droplets during a fire.
Sheets come in 2440 x 1220mm, in 12mm and 18mm thicknesses. Both work in dry and damp conditions. OSB/3 are class 1 and 2 covered. The core is bonded formaldehyde-free (NAF), meets E1 emission class, and carries CE2+ certification to BS EN300. Manufactured by EGGER in Romania to consistent European quality standards.
What the fire classification actually means?
The board carries a B-s1,d0 fire classification. Each part of that rating describes a different aspect of fire performance.
- B means the panel has a very limited contribution to fire growth.
- s1 refers to low smoke production during fire exposure.
- d0 means the board does not produce flaming droplets during the first 600 seconds of testing.
What happens when the board is exposed to fire?
The surface coating is designed to react when temperatures become extremely high. At around 250°C, the coating begins a three-stage reaction: first it resists heat, then the surface carbonises, and finally that carbonised layer expands into a thick carbon foam over the board.
That layer helps slow heat from reaching the OSB core underneath. The board is not intended to stop fire completely. It helps the board resist heat and fire for longer. That delay can help improve evacuation time and support overall fire safety within the building.
What is fire retardant OSB used for?
Fire retardant OSB replaces standard OSB in any application where the build needs to meet a fire performance requirement. It installs the same way, takes the same fixings, and works with the same tools. The only difference is the rating it carries.
Walls and wall partitions
The most common use. Wall sheathing in timber frame construction often needs to meet fire performance requirements, especially in multi-occupancy residential, commercial, and public buildings. Egger Flammex OSB is designed specifically for wall sheathing applications, with guidance from Egger covering fixing patterns, joint spacing, and installation on timber or metal substructures.
Note that when Flammex is installed on timber or metal substructure, EGGER specifies that Euroclass A1 insulation with a melting point above 1000°C and minimum density of 35 kg/m³ must be fitted directly behind the panels. Mineral wool or rockwool products typically meet this requirement. The Euroclass B classification applies to the full system, not the sheet alone.
Roofs
Used as sarking board or structural deck in roofs where fire rated materials are specified. The 18mm thickness is typically required for roof applications with standard rafter spacing.
Ceilings
Fire retardant OSB can be used as ceiling lining in spaces where fire performance is required by the spec or the regulations. It provides the same structural contribution as standard OSB, with the added fire classification.
Site hoardings
Temporary hoardings around construction sites often need to meet fire performance requirements, particularly in urban environments or where the hoarding is close to occupied buildings. Fire OSB is a practical and compliant choice.
Lofts
Loft boarding in residential properties sometimes requires fire rated materials depending on the build type. Fire retardant OSB gives you a board that meets the fire spec where loft lining or boarding is required.
Furniture and joinery with fire requirements
Less common but relevant for commercial interiors. Where fitted elements need to meet a fire class but also need the structural strength of FR OSB rather than a board like FR MDF, fire rated OSB is the answer.
Where it is not suitable?
Do not use fire retardant OSB as floor decking laid flat. It is designed for wall and ceiling applications. It also needs to be protected from direct weathering and standing water. The Flammex coating is not designed for outdoor exposure.
Benefits of fire rated osb
- Improved fire performance compared with standard OSB.
- Typically classified as Euroclass B-s1,d0.
- Helps projects meet specification and compliance targets.
- Structural OSB3 core suitable for load bearing applications.
- Familiar installation process with normal woodworking tools.
- Low smoke development, certified s1 under EN 13501-1.
- Strong dimensional stability and rigidity.
- Faster than applying separate fire treatment systems on site.
- Suitable for many commercial and public building projects.
- E1 low formaldehyde classification available.
Why choose our fire rated osb3?
At Sheet Materials Wholesale, the range focuses on practical site ready products rather than endless variations that confuse buyers.
That means:
- Trusted brands like EGGER Flammex OSB.
- Structural OSB3 boards, not decorative substitutes.
- Euroclass B rated options.
- 12mm and 18mm thicknesses available.
- Standard 2440 × 1220mm sheet sizes for easier planning.
- Bulk pricing for larger commercial orders.
- UK wide delivery.
- Stock suitable for both trade and private buyers.
Why many contractors choose EGGER Flammex OSB?
EGGER Flammex is popular because it solves two problems at once.
First, it keeps the structural performance expected from OSB3. Second, it improves the fire classification without making installation complicated.
The factory applied intumescent coating system is one of the main advantages. It reacts under heat conditions and helps reduce flame spread across the surface.
Another reason contractors like it is consistency. The coating is factory controlled rather than applied manually on site. That removes a lot of variability from the process.
How to choose between 12mm and 18mm fire rated OSB?
12mm fire retardant OSB
Usually chosen for:
- Wall sheathing.
- Ceiling applications.
- Lighter partitions.
- Non heavy duty lining work.
- Projects where weight matters.
18mm fire retardant OSB
More commonly used for:
- Stronger structural applications.
- Heavier duty roof sections.
- Higher impact areas.
- Commercial fit out work.
- Areas needing improved rigidity.
The correct thickness always depends on the framing centres, loading requirements, and full system specification.
FAQ
What does Euroclass B OSB board actually mean for my project?
Think of it as the second-highest fire performance category for building materials in Europe. Class A covers non-combustible materials like concrete and steel. Class B sits just below that. It means the board contributes very little to fire, produces minimal smoke, and drops no burning debris. For most commercial, residential, and public projects in the UK, a Class B material is exactly what the spec is asking for. Fire rated OSB3 with a B-s1,d0 classification hits that mark.
Are there fastener requirements for Flammex OSB?
Yes. EGGER specifies minimum fastener length of 2.5 × board thickness (minimum 50mm). Nails should be flat-head ring groove, screw nails, or grooved nails. If using staples, minimum wire thickness is 1.53mm. All fixings must be corrosion-resistant.
The coating chipped slightly around my fixings. Is the board still rated?
Yes. EGGER confirms that coating defects up to 3mm around fasteners do not impair the fire performance of the panel.
Can I use fire retardant OSB outside?
Not as a permanent solution. The Flammex coating needs protection from rain and standing water. During construction, cover the panels straight after installation and keep them away from direct exposure to the elements. A bit of UV will cause surface discolouration but does not affect how the board performs. Water is the real issue. Once the build is weathertight, the board is fine in the conditions it is rated for.
Do I need to do anything special before installation?
One thing worth doing is leaving the panels on site for 48 hours before you fix them. This lets the boards settle into the moisture conditions of the space. Skip that step and you risk movement after installation. Keep them flat, off the ground, and away from water during that period. After that, installation follows the same process as standard OSB.
Can I cut and drill fire retardant OSB with standard tools?
Completely standard process. A carbide-tipped blade with a high tooth count gives the cleanest cut without tearing the coating. When using a circular saw, keep the coated face down. For drilling, any electric drill or hand machine suitable for timber will work. No special bits, no special settings. The board processes like OSB/3 because underneath the coating, that is exactly what it is.
Can I paint or decorate the surface?
This catches people out. The Euroclass B rating is for the Flammex coating exactly as it comes from the factory. Put standard emulsion paint over it, hang wallpaper, or apply a laminate and the classification may no longer apply. If your project needs the fire rating to stay intact after finishing, standard decorating products are off the table. Check with EGGER for coatings that have been tested and approved on the system. If appearance is critical to the project, raise this before you order.
Does the fire protection fade over time?
No degradation, no expiry date. The intumescent coating stays active for the full life of the panel. You do not need to treat it, re-coat it, or replace it on any schedule. For buildings where fire rated materials need to do their job ten, twenty, or thirty years from installation, that permanence matters.
Where can I buy fire retardant OSB in the UK?
Order online at sheetmaterialswholesale.co.uk. EGGER Flammex OSB in 12mm and 18mm is in stock and available now. Next day delivery runs across the UK. For project orders or trade pricing, get in touch and we will sort it before you need them on site.
Can I use fire rated OSB for site hoardings?
Yes, and it is a sensible choice for urban sites or anywhere close to occupied buildings. Fire retardant OSB meets the performance requirements that often come with hoarding specifications in those locations. Keep the panels protected from prolonged water contact and check the specific fire class required by your site permit or local authority. Most hoarding requirements sit comfortably within what Euroclass B covers.
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35-69 70+ £40.44£48.53 £39.61£47.53 
12mm EGGER Fire Retardant OSB 3 Flammex Board 2440 x 1220mm (8′ x 4′) FSC®
12mm Egger Fire Retardant Flammex OSB3 Board has flame-retardant intumescent coating and UV coating applied. It can be used for exterior/interior walls, floors and roofs.
£41.69£50.03 Ex VATInc VAT Add to cart -
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30-59 60+ £45.27£54.32 £44.34£53.21 
18mm EGGER Fire Retardant OSB 3 Flammex Board 2440 x 1220mm (8′ x 4′) FSC®
18mm Egger Fire Retardant Flammex OSB3 Board has flame-retardant intumescent coating and UV coating applied. It can be used for exterior/interior walls, floors and roofs.
£46.67£56.00 Ex VATInc VAT Add to cart
