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Sauna & Wellness · For Architects
Sauna interior specification covers heat-resistant bench boards, ventilated wall cladding, and stainless fixings — every element must withstand 80–110°C operating temperatures and 100% humidity cycles. This template covers a complete dry sauna interior to industry best practice.
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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
Abachi (Triplochiton scleroxylon) is industry standard — knot-free, low thermal conductivity, no resin.
Class A (untreated, lightest colour) or Thermo-modified (caramel colour, +20% thermal stability).
22×95mm typical for benches. 28×145mm for backrests and surrounds.
Aspen, Alder, or Thermo-spruce common. Avoid resinous softwoods (Pine drops resin in heat).
Tongue and groove, 14×95mm typical. Soft Line profile for tactile finish.
Stainless steel A2 only. Pre-drilled, countersunk, plugged. Never standard galvanised.
Inlet vent below stove (60% of exhaust). Exhaust at high level opposite.
Aluminium foil on warm side, behind cladding. Continuous, taped joints.
Example Clause (NBS Format)
SAUNA INTERIOR Bench boards: - Species: Abachi (Triplochiton scleroxylon), Class A grade, knot-free - Dimensions: 22×95mm (seating), 28×145mm (backrest) - Lengths: Single-piece across bench width preferred - Surface: Sanded smooth, splinter-free, no resin - Spacing: 8mm gap between boards for air circulation and drainage Cladding: - Species: Aspen (Populus tremula) or Thermo-modified Spruce - Profile: Soft Line tongue and groove, 14×95mm covering width - Moisture content: 8–12% at delivery - Acclimatisation: Minimum 48 hours in sauna before fixing Fixings: - Type: Stainless steel A2 brad nails, 25mm length, predrilled - Pattern: Two per board per batten, in groove (concealed) - Never: Standard galvanised steel, brass, or copper (toxic at sauna temperatures) Substrate: - Vapour barrier: Aluminium foil, continuous, all joints taped with foil tape - Battens: 25×38mm pressure-treated softwood, vertical, at 600mm centres - Cavity: Minimum 25mm between vapour barrier and back of cladding Ventilation: - Inlet: Below stove, sized at 60% of exhaust area - Exhaust: High level opposite stove, sized at minimum 5% of floor area
Copy and paste this clause into your tender. Adjust dimensions, grades, and project-specific requirements.
Common Errors
Pine cladding in sauna
Correction: Pine drops resin at 80°C+ which burns and stains. Use Aspen, Alder, or Thermo-modified species only.
Standard galvanised fixings
Correction: Zinc coating breaks down at sauna temperatures, releasing toxic vapours. Stainless steel A2 minimum.
No vapour barrier
Correction: Without continuous aluminium foil vapour barrier, structure becomes saturated. Always specify continuous foil with taped joints.
Inadequate ventilation
Correction: Insufficient airflow leads to mould and rot. Inlet 60% of exhaust, sized correctly per cabin volume.
Reference Standards
Frequently Asked
Abachi (Triplochiton scleroxylon) is the international standard for sauna benches. It has the lowest thermal conductivity of any commercial timber, is knot-free, splinter-free, contains no resin, and remains comfortable to skin contact at 90–110°C.
Class A is lighter colour, slightly cooler thermal feel, and lower cost. Thermo-modified abachi has 20% better thermal stability, deeper caramel colour, and better resistance to discolouration over time. Specify Thermo for premium installations.
Pine and Spruce contain resin pockets that liquefy and seep at sauna operating temperatures. This stains the cladding, smells unpleasant when burnt, and creates uncomfortable hot spots on bench surfaces. Use Aspen, Alder, Abachi, or Thermo-modified species only.
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