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Architectural Specification Note

System: Half-timber wall with light straw clay infill and lime plaster finish

Structural Frame

Material: Oak or softwood, sustainably sourced, squared section.

Function: Primary load-bearing skeleton; defines infill panels.

Typical dimensions: Posts and beams 120–200 mm.

Joints: Traditional mortise and tenon with pegged connections or equivalent engineered joints.

Infill

Material: Light straw clay (LSC) mixture.

Straw: Locally sourced, cut length 5–20 cm.

Binder: Clay slip (approx. 1:2 clay to water by volume).

Mix ratio: Approx. 100–120 kg clay slip per 1 m³ of loose straw.

Function: Thermal insulation (λ ≈ 0.08–0.12 W/m·K depending on density).

Density: 250–350 kg/m³ (light infill, non-structural).

Installation: Hand-packed or mechanically tamped into shuttering between timbers.

Drying: 4–8 weeks depending on climate; requires cross-ventilation.

Exterior Finish

Lime plaster: NHL 2 or NHL 3.5, applied in 2–3 coats.

Thickness: 20–30 mm total.

Properties: Breathable (μ ≈ 5–10), water-shedding, capillary-active.

Function: Protects infill from weather, ensures moisture regulation.

Interior Finish

Clay plaster or lime plaster, 10–15 mm.

Optional: Limewash finish for breathability.

Performance

Thermal resistance: R ≈ 3.0 m²K/W for 350 mm wall thickness.

Hygrothermal: Capillary-active assembly regulating indoor humidity.

Fire resistance: Euroclass B–s1, d0 (lime plaster surface).

Durability: >75 years with maintained plaster coat.