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Engineered Timber · For Architects
CLT (Cross-Laminated Timber) specification requires panel-specific parameters — layup, strength grade per layer, fire resistance, and acoustic performance. This template covers a complete CLT specification clause for multi-storey timber buildings and modular construction.
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NBS-format clause, common errors checklist, and standards reference. Editable PDF format ready for your tender documents.
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Specification Checklist
3, 5, 7, or more layers. More layers = higher load capacity but more material.
Typically 20–45mm per layer. Common configurations: 3-layer 100mm, 5-layer 140–200mm, 7-layer 240mm+.
C24 standard. C30 for premium structural performance.
Polyurethane (PUR), MUF, or EPI. PUR is most common, allows formaldehyde-free option.
Industrial (concealed) / Visible / Selection (premium). Affects cost.
Tongue & groove, stepped, or square edge. Affects panel-to-panel joint detailing.
Specify required REI rating (e.g., REI 60, REI 90). CLT charring rate per EN 1995-1-2.
Specify Rw rating if separating element. Add resilient floor build-up if required.
Example Clause (NBS Format)
CROSS-LAMINATED TIMBER (CLT) PANELS Specification: - Layup: 5-layer, 200mm total thickness (40mm per layer) - Strength grade: C24 throughout per EN 338 - Adhesive: Polyurethane (PUR), formaldehyde-free - Visual grade: Visible (Sichtqualität) — knot-free outer face - Edge finish: Stepped lap joint for panel-to-panel connection - Service class: 1 per EN 1995-1-1 - Moisture content: 12% ±2% - Fire resistance: REI 90 minimum, verified by EN 1995-1-2 calculation - Acoustic: Rw ≥ 55dB (with floor build-up) - Marking: CE marked with Declaration of Performance - Certification: FSC or PEFC chain of custody required - Manufacturer: PEFC-certified European producer (Austria, Germany, or Sweden) Tolerances: Per ETA / EN 16351 Maximum panel size: As per project shipping constraints (typically 3.5m × 16m max) Cutting: CNC pre-cut to drawings, including all openings, services penetrations, and connection details.
Copy and paste this clause into your tender. Adjust dimensions, grades, and project-specific requirements.
Common Errors
Specifying "CLT" without layup
Correction: Always state number of layers and total thickness (e.g., 5-layer 200mm). This determines structural capacity and cost.
No fire performance verification method
Correction: Specify required REI rating AND require designer to verify by EN 1995-1-2 charring calculation.
Ignoring panel size limitations
Correction: Maximum panel transport is typically 3.5m wide × 16m long. Verify before specifying large single panels.
No CNC pre-cut specification
Correction: Always specify CNC pre-cut from approved drawings — site cutting CLT is impractical and wasteful.
Reference Standards
Frequently Asked
For residential floor spans of 5–7m at typical loads, a 5-layer CLT panel of 140–200mm is usually sufficient. The exact thickness depends on span, loading, acoustic requirements, and fire rating.
CLT can achieve REI 60–120+ depending on panel thickness and detailing. The charring rate per EN 1995-1-2 is approximately 0.65 mm/min for softwood CLT. A 200mm 5-layer panel can typically achieve REI 90 without additional protection.
Yes. CLT has been used in buildings up to 18 storeys (e.g., Mjøstårnet in Norway). For tall buildings, CLT is often combined with glulam columns and cores. Engineering and fire strategy must be validated by qualified structural and fire engineers.
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