Timber Frame Construction — Compliance Reference
Condensed simulation corpus — 5 essential domains
Sources: BS EN 338, BS EN 1995-1-1 (EC5), Building Regs Part L / Part B, BS EN 13501-1

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§1 — GENERAL
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§1.1 — Scope
This document applies to timber-frame buildings up to 2 storeys (ground + first
floor), in wind zones 1 to 4 and climate zones A, B, C.
Main structural element types: load-bearing studs, non-load-bearing studs,
sole plates, top plates, rafters, joists, insulation, vapour control layers.

§1.2 — Contractor qualification
The contractor must hold a recognised timber frame construction qualification
(e.g. UKTFA member or equivalent) before commencing structural works.

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§2 — TIMBER MATERIALS — QUALIFICATION
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§2.1 — Strength classes (BS EN 338)
Sawn timber is classified by ascending strength: C14, C16, C18, C24, C30, C35, C40.
Minimum strength class required by element type:
  - Load-bearing stud, sole plate, top plate : C24 minimum
  - Non-load-bearing stud                    : C16 minimum
  - Rafter (roof structure)                  : C18 minimum
  - Joist (floor/roof)                       : C24 minimum
Any element whose strength class is below the required minimum is REJECTED
at qualification stage.

§2.2 — Moisture content (BS EN 1995-1-1 §2.3)
Timber moisture content at time of installation must be between 10% and 18%.
Below 10%: risk of excessive moisture uptake after installation.
Above 18%: risk of fungal development and differential shrinkage.
Any element with moisture content outside [10%, 18%] is REJECTED.

§2.3 — Allowable deflection (EC5 §7.2)
Instantaneous deflection under load must satisfy:
  - Allowable deflection = L / 300  (L = span in mm)
  - Minimum floor value: 5 mm over 2 m span
Any element whose measured deflection exceeds L/300 is REJECTED.

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§3 — FRAME GEOMETRY
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§3.1 — Stud spacing (BS EN 1995-1-1 §5.1)
Stud centre-to-centre spacing must be between 300 mm and 600 mm.
Standard values: 400 mm or 600 mm (± 5 mm tolerance).
Spacing exceeding 600 mm is non-compliant.

§3.2 — Minimum cross-sections for load-bearing studs (BS EN 1995-1-1 §5.2)
Minimum cross-sections depend on clear height and spacing:
  - Height ≤ 2700 mm, spacing ≤ 400 mm : 38 × 89 mm minimum
  - Height ≤ 2700 mm, spacing ≤ 600 mm : 38 × 140 mm minimum
  - Height ≤ 3000 mm, spacing ≤ 400 mm : 38 × 140 mm minimum
  - Height ≤ 3000 mm, spacing ≤ 600 mm : 44 × 140 mm minimum
  - Height > 3000 mm, any spacing       : 44 × 184 mm minimum
Cross-section is compliant if b ≥ b_min AND h ≥ h_min.

§3.3 — Minimum cross-sections for non-load-bearing studs
Non-load-bearing studs require a minimum cross-section of 38 × 63 mm,
regardless of clear height.

§3.4 — Continuity of load-bearing studs (BS EN 1995-1-1 §5.4)
A load-bearing stud must not contain a longitudinal splice (end-to-end joint
within the storey height). The presence of a longitudinal splice on a
load-bearing stud is a structural non-conformity.

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§4 — THERMAL PERFORMANCE AND VAPOUR CONTROL
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§4.1 — Minimum thermal resistance of insulation (Part L + BS EN ISO 6946)
Thermal resistance R is calculated as:
  R = thickness (mm) / (1000 × lambda)   [unit: m²·K/W]
  lambda = thermal conductivity in W/(m·K)

Minimum R required by climate zone:
  - Zone A (highland / severe cold)   : R_min = 6.5 m²·K/W
  - Zone B (temperate)                : R_min = 4.5 m²·K/W
  - Zone C (mild — coastal south)     : R_min = 3.5 m²·K/W

Typical conductivity values:
  - Mineral wool 035 : lambda = 0.035 W/(m·K)
  - Mineral wool 040 : lambda = 0.040 W/(m·K)
  - Rigid PIR 022    : lambda = 0.022 W/(m·K)

§4.2 — Vapour control layer: minimum Sd value (BS 5250 / BS EN ISO 13788)
The vapour control layer must provide sufficient resistance to vapour
diffusion (Sd value) according to the service class:
  - Service class 1 (dry interior)   : Sd ≥ 5 m
  - Service class 2 (humid interior) : Sd ≥ 18 m
  - Service class 3 (very humid)     : Sd ≥ 50 m
Any vapour control layer with Sd below the required minimum is NON-COMPLIANT.

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§5 — FIRE SAFETY
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§5.1 — Required fire resistance period (Building Regs Part B / BS EN 13501-2)
Structural elements must achieve a minimum fire resistance period:
  - Single occupancy dwelling (non-collective) : REI 30 minimum
  - Multi-occupancy building (collective = 1)  : REI 60 minimum

§5.2 — Reaction to fire of internal lining (BS EN 13501-1)
The internal wall lining (typically plasterboard) must satisfy:
  - Reaction to fire class: A1 or A2 minimum (Euroclasses)
  - Surface mass: ≥ 8 kg/m² (standard 12.5 mm or 15 mm plasterboard)
Any lining with a reaction class below A2 or insufficient mass is NON-COMPLIANT.

§5.3 — Plasterboard thickness (Building Regs Part B §B3)
To achieve the required fire resistance:
  - REI 30 (non-collective) : plasterboard thickness ≥ 12.5 mm
  - REI 60 (collective)     : plasterboard thickness ≥ 25 mm (two layers)

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§6 — GLOBAL COMPLIANCE
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§6.1 — Compliance conditions by element type
An element is declared COMPLIANT if and only if all applicable conditions
for its type are satisfied:

  For all elements     : qualified = 'YES'
  For structural elements (load-bearing studs, sole plates, top plates) :
    + frame_ok = 'YES'
  For insulation and vapour control layers :
    + thermal_ok = 'YES'
  For all elements if collective = 1 :
    + fire_ok = 'YES'
  For all elements if collective = 0 :
    fire_ok = 'YES' also required (REI 30 minimum applies)

§6.2 — Pipeline termination
The pipeline terminates (solved) when all elements carrying the slot
needs_compliance have received their compliance_status.
