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Cladding & Facades · For Architects
Exposed timber interior specification combines structural performance with architectural quality — every blemish is visible, every fixing is a design detail. This template covers visible glulam beams, CLT soffits, and timber feature walls in commercial settings, including biophilic design intentions.
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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
Architectural / Visible / Sichtqualität — knot-free outer face, sanded surface.
European Spruce (white), Larch (warm), Oak (premium). Affects appearance and cost significantly.
Sanded smooth, brushed, sandblasted. Affects tactile and visual character.
Clear matt UV-protective coating, hardwax oil, or untreated. Specify VOC content.
Charring rate calculation per EN 1995-1-2 if required. Class B-s2,d0 reaction class for compartments.
Exposed timber surfaces are reflective. Specify supplementary acoustic absorbers if required.
Concealed steel plates, recessed bolts, or expressed connection design — all carefully detailed.
Plan for re-coating intervals (typically 5–10 years for high-traffic interiors).
Example Clause (NBS Format)
EXPOSED TIMBER INTERIOR Glulam beams (exposed): - Strength class: GL28h to EN 14080 - Appearance class: Architectural (Sichtqualität) per EN 14080 - Species: European Spruce (Picea abies) - Surface: Sanded P120 smooth, ready for clear coating - Adhesive: Type I per EN 301 - Moisture content: 12% ±2% at delivery CLT soffit (exposed underside): - Visual grade: Industrial visible (concealed face: industrial) - Surface: Sanded P150 smooth on visible face - Edge finish: Square edge, clean machined Coating: - Type: Clear matt UV-protective wood lacquer, water-based - VOC content: ≤ 80 g/L per EU Decopaint - Application: Two coats sprayed in factory or controlled site environment - Specification: Sample panel approved by architect before bulk application Fire performance: - Charring rate: 0.65 mm/min per EN 1995-1-2 - Reaction to fire: Class B-s2,d0 with intumescent coating where required - Visible structural reduction: Per fire engineer's calculation Acoustic: - Supplementary absorption: Acoustic ceiling baffles or wall panels per acoustic engineer - Reverberation time target: T < 1.5 seconds (office) / T < 1.0 seconds (meeting room) Connections: - Concealed steel plates: All connection plates fully concealed within members - Bolts: If visible, recessed and plugged with matching timber dowels - Expressed connections (where designed): Stainless steel A2, brushed finish Site protection: - All exposed timber wrapped in breathable protective sheet from delivery to commissioning - Floor protection: Hardboard over membrane during finishing trades
Copy and paste this clause into your tender. Adjust dimensions, grades, and project-specific requirements.
Common Errors
Industrial grade glulam exposed
Correction: Industrial class has visible knots, fillers, and rough surface. Always Architectural for visible work.
No acoustic strategy
Correction: Exposed timber is acoustically reflective. Without supplementary absorbers, spaces become noisy.
No protection during finishing trades
Correction: Plaster, paint, and dust permanently damage finished timber surfaces. Wrap from delivery to commissioning.
Site application of coating
Correction: Site-applied coatings are inconsistent in appearance. Factory coating gives uniform high-quality finish.
Reference Standards
Frequently Asked
Glulam for linear elements (beams, columns). CLT for planar elements (soffits, walls). Both have Architectural grade options. Choice depends on architectural intent and structural strategy.
High-traffic commercial interiors: 5–7 years. Lower traffic / domestic: 10–15 years. Factor maintenance access into design (cherry pickers, scaffolding).
Not necessarily — timber chars predictably and can be designed to maintain structural performance during a fire. The design must include charring calculations per EN 1995-1-2 and verified by a fire engineer.
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