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Cladding & Facades · For Architects
Solid timber flooring specification covers species, grade, dimensions, moisture content, fixing method, and finish. Most flooring failures (cupping, gapping, squeaking) come from incorrect moisture content at installation rather than wrong species. This template addresses both timber and substrate conditions.
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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
European Oak, Walnut, Maple, Ash. Specify single species (no mixed batches).
Prime / Select / Natural / Rustic. Defines knot frequency and colour variation.
Typical 21×180mm or 21×220mm (T&G). Wider boards = more dramatic, but more movement risk.
8–10% at delivery for heated buildings. CRITICAL: do not deliver early to wet site.
Minimum 14 days on site at operating conditions before fixing.
Secret nailed, glued, or floating. Affects acoustic performance and ease of repair.
Plywood underlay (15mm) or concrete with DPM. Specify substrate moisture maximum (typically 75% RH).
Pre-oiled, pre-lacquered, raw (site finish). Pre-finished saves time but limits future refinishing.
If present, specify maximum surface temperature (28°C typical) and species suitability.
Example Clause (NBS Format)
SOLID TIMBER FLOORING Boards: - Species: European Oak (Quercus robur or Q. petraea), single batch - Grade: Natural — small tight knots and colour variation acceptable - Profile: Tongue and groove all four edges - Dimensions: 21mm thick × 180mm covering width × random lengths 600–2400mm - Moisture content: 9% ±2% at delivery - Certification: FSC or PEFC chain of custody required Substrate: - Type: 15mm WBP plywood on resilient acoustic underlay - Plywood moisture: ≤14% - Concrete substrate (where applicable): DPM in place, surface RH ≤75% Acclimatisation: Boards stored on flat surface in installation room minimum 14 days before fixing. Heating system operational throughout. Fixing: - Method: Secret nailed through tongue with ring-shank nails - Nails: Stainless steel A2, 50mm length, at 250mm centres - Adhesive: Bead of MS Polymer adhesive on each board (acoustic and stability) Expansion: - Perimeter gap: 12mm minimum at all walls and fixed elements - Intermediate expansion: Continuous expansion break every 8m Finish: - Type: Pre-oiled with two coats of natural hardwax oil - Maintenance kit supplied at handover Underfloor heating compatibility: Boards rated for UFH use, maximum surface temperature 27°C.
Copy and paste this clause into your tender. Adjust dimensions, grades, and project-specific requirements.
Common Errors
Delivering boards to wet site
Correction: Wet substrate causes immediate moisture absorption and subsequent cupping. Always confirm substrate moisture before delivery.
No acclimatisation period
Correction: 14 days minimum, with heating active. Skipping this step is the most common cause of flooring failures.
No expansion gaps
Correction: 12mm minimum at all perimeter and fixed elements. Without it, boards buckle when moisture changes.
Wide boards on UFH without verification
Correction: Wide boards (>180mm) have higher movement risk. Verify species suitability for UFH or specify narrower boards.
Reference Standards
Frequently Asked
8–10% for heated indoor environments, 11–13% for unheated spaces. Critical: substrate must also be dry (RH ≤75% for concrete, MC ≤14% for plywood).
Yes, with restrictions: maximum surface temperature 27–28°C, narrower boards (≤140mm typically), and species with lower thermal expansion (Oak, Walnut, Cherry). Avoid Beech and Maple.
Engineered is more dimensionally stable (better for UFH and humidity changes) but cannot be sanded as many times. Solid wood lasts longer with maintenance but requires stable conditions. For most modern projects, engineered is recommended.
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