Table of Contents:

In commercial Swiss architectural sheet metal fabrication and building envelope engineering, precision metalworking forms the vital barrier against storm events, heavy rainfall, and alpine snowmelt. On standing seam roofs, rainscreen metal façades, or heritage copper dome restorations, uncalculated thermal movement, galvanic corrosion between dissimilar metals (e.g., copper run-off washing over zinc), or undersized box gutters under SN 592000 cause severe building fabric water damage. A dedicated tinsmith database links profile unfolding patterns, hydraulic gutter calculations, and Swiss NPK items in a unified project structure.

1. Statutory Framework: SIA Standard 232/2, suissetec Directives & Craftsmanship Rules

Fabricating and installing architectural sheet metal on roofs and façades is governed by SIA Standard 232/2 (Sheet Metal Work) , technical guidelines from suissetec , and the Swiss Code of Obligations (SR 220 CO ):

  • Roof Pitch & Upstand Minimums: Minimum pitch for double standing seam systems (≥ 3°\ or\ 5.2%) and mandatory perimeter upstand flashing heights (at least 150 mm above the water-carrying layer).
  • Lightning Protection Integration (SNR 464022): Utilizing sheet metal roof coverings as natural air-termination systems and down-conductors with compliant bonding terminals.
  • Building Cost Code (BKP) Segregation: Clear classification under BKP 225 (Tinsmith / Sheet Metal Works), BKP 224 (Roofing), and BKP 271 (Waterproofing).
Galvanic Corrosion Risk: Water draining from noble metals (such as copper) onto less noble metals (such as titanium zinc or galvanized steel) causes rapid pitting corrosion through galvanic action. The software automatically flags incompatible metal pairings during quotation.

2. Roof Drainage Hydraulic Sizing under Swiss Standard SN 592000

Sizing half-round eaves gutters, box gutters, and rainwater downpipes follows Swiss Standard SN 592000 (Building Drainage Systems) :

  1. Design Storm Flow Calculation (Q in l/s): Determining peak flow based on the local 100-year storm intensity (r15), plan catchment area (A in m2), and run-off coefficient (C = 1.0 for sheet metal):
Q = r × A × C × 110'000
  1. Gutter Cross-Section Selection: Automated calculation of gutter girths (e.g., 250, 330, or 400 mm developed width) and verified longitudinal gradient (≥ 0.5%).
  2. Emergency Overflow Sizing: Mandatory calculation of emergency overflow scuppers or weir outlets on parapet and internal valley gutters to prevent structural roof ponding.

3. Seaming Details, Thermal Expansion Joints & Galvanic Corrosion Prevention

Roofing metals undergo significant thermal expansion:

  • Linear Thermal Movement: Zinc expands approx. 1.8\ mm/m under a temperature differential Δ T = 80\ K; aluminum expands 1.9\ mm/m.
  • Fixed and Sliding Clips: Positioning fixed cleats in the upper third of tray runs and installing sliding clips to accommodate longitudinal travel.
  • Maximum Tray Lengths: Continuous standing seam pans are restricted to 10–14 m depending on the alloy; longer runs require expansion steps, transverse seams, or staggered laps.

4. BKP 225 Job Costing, NPK Measurement Positions & Workshop Coil Nesting

Pre-calculation and workshop fabrication follow Swiss NPK standards:

  • NPK 351/352 Measurement Rules: Invoicing eaves gutters and downpipes by linear metre (m); wall claddings and seam roofs by developed surface area (m2); separate billing for stop ends, mitres, expansion joints, and pipe outlets.
  • Coil Slitting & Folding Nesting: Automated cut-pattern generation for CNC folding machines and slitting lines to minimize scrap from master coils.
  • Daywork Variations under SIA 118: Mobile logging of custom chimney flashings, dormer trims, and interface adaptations with digital signatures from the site architect.

5. Comparative Overview: Manual Field Sketches vs. Integrated Tinsmith Database

| Operational Benchmark | Hand Sketches & Spreadsheets | Integrated ACCSoft Tinsmith Database | | :--- | :--- | :--- | | Gutter Hydraulic Sizing (SN 592000) | Rough manual table lookups | Automated storm flow calculations and profile sizing | | Sheet Unfolding for CNC Bending | Slow manual workshop geometry drafting | 1-click generation of bending profiles for CNC machines | | Galvanic Compatibility Check | Easily overlooked metal mixing errors | Automated warning system against incompatible pairings | | NPK Quantity Takeoff Structure | Tedious manual sorting of field measurements | Structured export compliant with BKP 225 and CRB rules | | Suva Jobsite Safety Records | Incomplete harness and scaffolding logs | Digital safety check protocols for roof work |

6. Statutory Framework and Official Resources