Table of Contents

In modern Swiss timber engineering, constructing multi-story mass timber developments, vertical rooftop extensions, and complex roof structures requires a direct link between structural calculations, automated CNC joinery fabrication, and commercial pre- and post-costing. Volatile lumber prices, mandatory Swiss wood origin declarations, and demanding acoustic, fire, and thermal envelope standards require carpentry firms to track components with millimeter precision. An integrated timber ERP platform ensures that wood volumes, steel connectors, and assembly labor hours are estimated and invoiced accurately.

1. Legal Framework & Lignum Rules: SIA 265, Wood Declaration Duty, and Origin Tracking

Processing and distributing structural timber within the Swiss construction sector is governed by rigorous federal regulations:

  • Swiss Wood Declaration Ordinance (SR 944.021): When supplying roundwood, sawn timber, or engineered wood products to clients, contractors must state the exact botanical and commercial species name alongside its geographical harvest origin.
  • Lignum Quality Standards: The umbrella organization of the Swiss forest and timber industry (Lignum) defines mandatory grading rules for solid timber, finger-jointed structural timber (KVH), glued laminated timber (Glulam/BSH), and cross-laminated timber (CLT).
  • Fire Safety Regulations (VKF/AEAI): Timber structures up to high-rise thresholds (30 m) and special structures are fully permissible in Switzerland provided fire resistance (e.g., REI 30 to REI 90) is verified using charring rates calculated under SIA 265.
Mandatory Proof of Origin in Public Procurement

Under Swiss public procurement laws (BöB/IVÖ), public entities frequently mandate the label «Swiss Wood» (Certificate of Origin Swiss Wood HSH). Failing to document wood origin in the initial bid results in immediate disqualification.

2. Structural Sizing & Joinery: Strength Classes C24/GL24, BKP 214, and NPK 331

Structural design is governed by Standard SIA 265 (Timber Structures) based on service classes (NKL 1 interior, NKL 2 sheltered exterior, NKL 3 fully exposed) and load-duration classes (KLED):

  • Material Classifications: Sizing structural softwood (C24 per EN 338), glued laminated timber (GL24h/GL28c per EN 14080), and laminated beech veneer lumber (BauBuche).
  • Building Cost Plan BKP 214 (Timber Structures): Work structure from primary frames (BKP 214.1) and floor/roof cassettes (BKP 214.2) to ventilated facade sub-structures (BKP 214.5).
  • Standard Position Catalog NPK 331 (Carpentry & Joinery Works): Standardized tendering positions for sole plates, purlins, rafters, hips, valleys, and structural sheathing boards.

3. Building Physics & Moisture Protection: SIA 180, Airtightness, and Vapor Permeability

Timber components are vulnerable to interstitial condensation and air leakage convection. Standard SIA 180 (Thermal Insulation, Moisture Protection and Indoor Climate in Buildings) dictates critical parameters:

  1. Airtightness Layer (Blower-Door Testing per SIA 180): Continuous taped sealing of variable vapor control membranes with sd-values validated via hygrothermal simulations.
  2. Moisture Content Verification Before Erection: Installation wood moisture must not exceed 12 ± 3 % for protected indoor framing and 18 % for exterior elements.
  3. Acoustic Isolation in Timber (SIA 181): Elastic decoupling of timber-concrete composite (TCC) floors and double-stud acoustic walls to suppress low-frequency impact sound transmission.

4. Work Contracts, SIA 118 Standards, and Warranty in Structural Timber Works

Contract execution relies on the Swiss Code of Obligations (CO, SR 220) and standard SIA 118:

  • Statutory Limitation Period for Defects (Art. 371 CO): 5-year defect limitation period applies to structural timber components permanently fixed to immovable properties.
  • Dimensional Tolerances under SIA 414/1: Adherence to permissible tolerances for lengths, plumb, and squareness on prefabricated wall and roof panels.
  • Duty of Prior Inspection (Art. 92 SIA 118): The timber contractor must inspect concrete foundations and slab levels prior to assembly and immediately issue written notifications regarding any deviations.

5. System Comparison: Manual Timber Cutting Lists vs. ACCSoft Timber ERP

Workflow Manual Spreadsheets / Isolated Tools ACCSoft Timber & Joinery Module
Timber Takeoff & Sizing Manual extraction from paper drawings Direct import of BTL/BVX fabrication files from Cadwork, Dietrich's, Sema
Linear Nesting Optimization Lump-sum scrap allowances (10–15% waste) Automated bar nesting algorithms minimizing offcut waste
NPK 331 & BKP 214 Manual data entry into billing software Automated CRB-compliant BoQ generation and quantity takeoffs
Wood Declaration (SR 944.021) Frequently omitted on commercial quotations Automated printing of species, origin, and FSC/PEFC chain of custody
Jobsite Assembly Tracking Labor overruns only realized after completion Real-time planned vs. actual labor variance via mobile time tracking

6. Normative References and Swiss Statutory Sources