How much does it cost to repair a sagging roof?
By Best Roofing Answers · Published May 2026 · Updated July 2026
Repairing a sagging roof typically costs $1,500–$7,000 for localized decking replacement, $3,000–$12,000 for rafter sistering or reinforcement, and $10,000–$25,000 or more when structural trusses have failed and engineering is required; costs vary by span, cause, and whether load-bearing members are compromised.
Sag is a structural symptom
A visible sag between rafters or across a roof plane is a structural signal, not a cosmetic one. Per NRCA and IRC Chapter 8, common root causes are (1) rotted decking from a chronic leak, (2) under-sized rafters relative to snow or dead load, (3) failed truss webs or connectors, and (4) removed load-bearing walls below. Diagnosis dictates the fix.
Any roof with a truss-related sag should be evaluated by a licensed structural engineer before repair. Cosmetic patching over a structural sag is a code violation in most jurisdictions and typically voids homeowner's insurance if it later collapses.
Sources
- International Residential Code (IRC), Chapter 9 — Roof Assemblies — Chapter 8 — roof/ceiling construction loads
- NRCA (National Roofing Contractors Association)
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