VERT / GREEN
Simple roof without a meaningful height step: use normal local design snow loads with the appropriate designer.
Snow drift at additions and roof steps
Check unbalanced snow loads when a new lower roof, addition, parapet or roof-height step creates a drift zone.
JAUNE / YELLOW
New lower roof beside a higher wall/roof: explicitly consider drifting, not just uniform snow load.
ROUGE / RED
Do not size addition beams/joists from average snow load when geometry creates drifting.
Project triage
What the professional checks
- Calculate balanced/unbalanced snow and drift loads
- Verify load transfer through new and existing structure
Official sources
Sources checked: 2026-08-22. Always confirm local rules and the applicable edition.
Related path
Continue with the right tools
These links connect this page to the next useful checks and decisions without repeating the full content.
Plan a complete construction projectConnect feasibility, design, permits, concealed work, commissioning and closeout.Open →Check permit triggersPrepare the questions and documents to confirm with the local authority.Open →Check a contractorDocument licence, insurance, scope, payments, changes and warranties.Open →Update a construction costEscalate a historical cost using comparable index values.Open →Prepare pre-delivery reviewRecord documents, enclosure, systems, finishes and deficiencies before closeout.Open →
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