Wood Wool Cement Board (WWCB) Calculator: Complete Guide
What is Wood Wool Cement Board (WWCB)?
Wood Wool Cement Board (WWCB), also known as cement excelsior board or Heraklith board, is a building panel manufactured from long-strand wood excelsior (wood wool) mineralised and bound with Portland cement. The resulting board combines the acoustic absorption of fibrous materials with the fire resistance and durability of cement.
WWCB is widely used for ceilings, wall linings, soffits, and facades in sports halls, industrial buildings, schools, and commercial spaces where sound absorption, fire resistance, and vapour permeability are required simultaneously.
Acoustic Properties & NRC Classification
WWCB sound absorption coefficient (αw) ranges from 0.35 (25mm board, no cavity) to 0.90 (100mm board with 100mm cavity). NRC Class A (αw ≥ 0.70) is achievable with 75mm+ boards and an air cavity.
Air cavities behind the board shift peak absorption to lower frequencies (125–500 Hz), critical for controlling reverberation in large spaces.
Thermal Performance
WWCB thermal conductivity: λ ≈ 0.09–0.12 W/m·K. A 50mm board provides R ≈ 0.45 m²K/W — useful as a thermal bridge break but typically requires backing insulation to meet energy code U-values. WWCB also raises surface temperature, reducing condensation risk at cold thermal bridges.
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Installation & Fixing
- Wall mounting: Screw fix at 300mm centres with 60mm corrosion-resistant screws into studs or batten framework
- Ceiling suspended: Use proprietary ceiling clips or wire hangers rated for board weight + dynamic load factor 1.5×
- Cutting: Circular saw with carbide blade. Pre-drill fixing positions near edges to avoid splitting
- Finishing: Leave board surface exposed or apply breathable render/plaster coat. Do not cover with vapour barrier
FAQs
What is the fire rating of WWCB?
Most WWCB products achieve Class B-s1,d0 (EN 13501-1) for boards ≥50mm. This makes them suitable for use in buildings where Class B reaction-to-fire is required without additional fire treatment. Always verify the specific product's declared classification.
Can WWCB be used outdoors?
Standard WWCB is not suitable for continuous outdoor exposure. However, some manufacturers produce weatherproof grades with improved cement and treated wood wool for external soffit and canopy applications. Check product data sheets for exposure class.
What is the difference between WWCB and Heraklith?
Heraklith is a specific proprietary brand of WWCB manufactured by Knauf Insulation. It has become a generic term for WWCB in many European markets. Other brands include Celenit, Isotex and Eltomation. All conform to EN 13168 (wood wool insulation products) or similar standards.