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A1 non-combustible, MgO board

RCM Extremegreen MgO board is a high density structurally reinforced magnesium oxide-based sheathing board consisting of a proprietary composition of magnesium oxide that is reinforced with 2 layers of glass fibre mesh. Magnesium oxide is a mineral-based raw material.

The sheets are made in various lengths, widths and thicknesses providing a huge range of building options.

As an A1 non-combustible sheathing board Extremegreen is an excellent choice for structural timber applications.


  • Fire rated to EN 13501-1 class A1
  • Can be scribed and snapped up to 12mm
  • Water resistant
  • Environmentally friendly
  • Mould resistant
  • Contractor friendly
  • Gypsum and crystalline silica free
  • Easy to work with
  • Integrates with other RCM products

Standard board sizes

2400 x 1200mm (6mm, 9mm and 12mm)
2397 x 1198mm (9mm)
2697 x 1198mm (9mm)

Other board sizes are available.


If you would like a sample please click on the ‘add sample to basket’ button at the bottom right of this page and select your samples. Once selected you can add other products also, but please make sure you click on the sample basket at the top of the website to complete your request.


RCM Extremegreen can be cut, drilled and nailed using conventional hand tools; offering many of the properties of timber.

For cutting the product in any volume, we recommend the use of a hand held circular saw with a 60+ tooth finish blade. Alternatively, RCM offer a complete fabrication service, please contact our technical department for details.

Key applications

  • Sheathing board
  • Ceilings and roofing
  • Internal wall lining
  • Tile backer board
  • Buildings above 18m
  • Flooring and sub-flooring

Suitable for the following construction types

  • Timber Frame
  • Modular / Offsite

Technical Data

  • 931 kg/m3
    • Parallel
      16.15 N/mm2
    • Perpendicular
      22.77 N/mm2
    • Parallel
      6496 N/mm2
    • Perpendicular
      6827 N/mm2
  • R2 per inch
  • 11.36%
  • BS EN 13501-1 Class A1 Non-Combustible
  • Highly Resistant
  • Front Face - Smooth
  • Back Face - Textured
  • 25 years
  • 2400 x 1200mm
  • 2697 x 1198mm
  • 6 9 12
  • 7.16 10.09 13.45
    • Length
    • Width
    • Thickness
    • Fire Reaction Tests
      BS EN 13501-1 Class A1 Non-Combustible
    • BS EN ISO 1716:2010
    • BS EN ISO 1182:2010
    • Physical Properties
      BS EN ISO 12467
    • BS EN 594
    • BS EN 717-3:1996
    • Timber Frame
      4.2mm x 42mm Climaseal self drilling fixing


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