A1 non-combustible, BBA certified calcium silicate cement building board

RCM Y-wall is a high-quality flexible calcium silicate cement based building board, perfect for use as a fire rated sheathing board.  Offering excellent fire properties as well as high levels of dimensional stability, Y-wall is an exceptional board for use in multiple applications.

Y-wall is used primarily as a fire rated sheathing board or building board. Used extensively on both steel frame and timber frame structures, Y-wall is used behind all types of façade solutions, as well in ceilings offering a non-combustible classification.

  • Fire rated to EN 13501-1 class A1

  • 2400 x 1200mm (6mm, 9mm, 12mm and 15mm) Other board sizes are available

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Key Applications

  • Fire rated sheathing board
  • Ceilings
  • Partition walling
  • OEM applications for improved strength and density
  • Recommended for buildings above 18m
  • Ideal for Offsite Construction Regimes


  • Fire rated to EN 13501-1 class A1
  • BBA approved
  • Flexible and strong
  • Excellent water resistance
  • Easy to use
  • High levels of dimensional stability
  • Integrates with other RCM products


RCM Y-wall 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 an RCM poly crystalline diamond Dart Blade to avoid excessive wear on other blades. Alternatively, RCM offer a complete fabrication service, find out more.

Suitable for the Following Construction Types

  • Lightweight Steel Frame

  • Timber Frame

  • Modular / Offsite

Y-Wall as part of a system build-up

  • Steel Frame

Technical Data

  • Nominal Density

    1200 kg/m3

  • Bending Strength

    ((Modulus of Rupture))

    12 N/mm2

  • Modulus of Elasticity


    4000 N/mm2

  • Thermal Conductivity

    ≤0.23 W/mk

  • Moisture Content


  • Reaction to Fire

    BS EN 13501-1 Class A1 Non-Combustible

  • Biological Resistance

    Highly Resistant

  • Surface Condition

    Front Face - Smooth

    Back Face - Textured

  • Durability

    ((Life Expectancy - Minimum))

    30 years

  • Standard Board Sizes

    2400 x 1200mm

  • Thickness


    6, 9, 12, 15

  • Nominal Mass of Product


    7.3, 11.1, 14.6, 18.2

  • Dimensional Tolerance

    • Length


    • Width


    • Thickness


  • Product Testing and Certification

    • Fire Reaction Tests

      BS EN 13501-1 Class A1

      BS EN ISO 1716:2010

      BS EN ISO 1182:2010

      BS 476 Part 4

      BS 476 part 21 and BS 476 part 22 fire rated through wall solutions

    • Physical Properties

      BS EN ISO 12467

      BS EN 594 Category 1

      BS EN ISO 1015-11

      BS EN ISO 1062-1

  • Recommended Fixing

    • Steel Frame

      4.8mm x 38mm Wing tip self drilling fixing

    • Timber Frame

      4.2mm x 42mm Climaseal self drilling fixing

Y-Wall FAQs

RCM Y-wall can be used as an external sheathing board on all structure where a fire rating is required including those greater than 18m in height, where a structure is over 18m in height RCM Y-wall should be used from ground level all the way up the structure.

RCM Y-wall is rated as A1 non-combustible.

No, RCM Y-wall cannot be left permanently exposed.

RCM Y-wall has one smooth face and one textured face, the smooth face should be fixed outermost.

RCM Dafa tape should be applied to all board to board joints as soon as possible after fixing the boards, unless an airtight seal is required to the external face of the sheathing board, for an airtight seal then the RCM Joint Seal system should be used.

If the joints are taped using RCM Dafa tape as soon as the boards are fitted they can be left exposed during the construction phase for twelve months.

RCM Y-wall edge distance is 15mm except at the board corners where fixings should be moved up or down to achieve 50mm. Fixings should be fixed using a maximum 600mm x 300mm grid pattern.

  • 27 No. fixings per 2400mm x 1200mm sheet when fixed in a vertical orientation.
  • 25 No. fixings per 2400mm x 1200mm sheet when fixed in a horizontal orientation.
  • For fixing into SFS framing 4.8mm x 38mm self-drilling wingtip fixings suitably treated against corrosion should be used.
  • For fixing into Timber framing 4.2mm x 42mm self-drilling fixings suitably treated against corrosion should be used.

RCM Y-Wall should not be fixed to a radius but should be cut into vertical strips and fixed to form the curve from a series of flat panels.

RCM can supply Poly Crystalline Diamond (PCD) blades suitable for cutting RCM Y-Wall in a range of diameter and bore sizes, please contact RCM Technical department for further information.

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Download the Y-Wall Fact Sheet

Find out about Y-wall, a high-quality flexible calcium silicate based fibre cement building board, perfect for use as an A1 fire rated sheathing board.

Download Fact Sheet


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