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Roof construction with wood sheathing and framing
Structural Sheathing & IRC R908 Building Codes • Updated October 2026

Roof Rot & Structural Decking Cost Calculator

Accurately calculate replacement costs for soft, waterlogged CDX plywood and OSB sheathing. Itemizes rafter tail sistering, sub-fascia repairs, and Florida Senate Bill 4-D 25% threshold rules.

Estimate Decking Rot ↓ Structural Carpenter: (888) 555-0199
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Structural Rot Stepper

Step 1: Decking Material & Context

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Decking Material & Repair Context

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Rotted Sheets & 25% Building Code Rule

Rotted Sheets: 3 (96 sq ft)Roof Decayed: 4.8%
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Rafter Tails & Sub-Fascia Structural Decay

Rafters: 0 sisteredSub-Fascia: 0 LF
Structural Decking

3 Sheets (96 sq ft)

1/2"

4.8% of Roof

Estimated Structural Repair Cost

$915 - $1,695

Includes 8d ring-shank fasteners, cutting, blocking, and carpentry labor.

Decking Panels (3 sheets)$585 - $1125
Shingle Tear-Off & Weave-In$330 - $570

Carpentry Repair Methodology

Cut away shingle tabs around rotted zone, use circular saw set to exact decking depth to slice decayed wood along center of rafter flanges, nail 2x4 blocking where needed, screw down new exterior-rated sheathing with 8d ring-shank nails at 6" perimeter spacing, and install ice-and-water shield beneath replacement shingles.

Decking Decay Isolated: Underlying rafters appear intact based on initial inspection.

Call Structural Roofing Carpenter: (888) 555-0199

Licensed framing contractors for rotted decking, trusses & rafter tails.

3 Sheets Decking

$915 - $1695

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Roof Sheathing & Structural Wood Repair Benchmarks

Comparing standalone emergency spot repair rates versus contractor add-on pricing during full re-roofing projects.

Wood Member / Material Standalone Spot Cost Re-Roof Add-On Cost Moisture Tolerance Structural Fastening Spec
1/2" CDX Exterior Plywood (4x8 ft) $195 - $375/sheet $65 - $105/sheet High (Returns to dimension) Superior (APA Rated Sheathing)
7/16" OSB Strand Board (4x8 ft) $165 - $320/sheet $45 - $80/sheet Moderate (Edges swell when wet) Standard
Rafter Tail Sistering (2x6/2x8 PT) $180 - $380/rafter $140 - $260/rafter Pressure-Treated Structural Structural GRK screws / 16d nails
Sub-Fascia Board Replacement $16 - $28/LF $12 - $20/LF Moderate (Spruce/Pine lumber) End-nailed to rafter tails

Understanding Florida's 25% Rule & Senate Bill 4-D

How recent legislative updates protect homeowners from unnecessary mandatory roof replacements.

The Historic 25% Rule

Under Florida Building Code Section 706.1.1, if a storm damaged or rotted more than 25% of any contiguous roof section, municipal inspectors legally mandated that the entire roof be stripped and brought up to modern building code standards, resulting in surprise $25,000+ bills for homeowners.

The Senate Bill 4-D Exemption

Enacted in May 2022, Florida Senate Bill 4-D created a critical statutory exception: If an existing roof was permitted or installed in compliance with the 2007 Florida Building Code or any newer edition (roughly roofs permitted after March 2009), the 25% full replacement mandate is eliminated. Homeowners can now repair only the damaged decking.

Frequently Asked Questions

Essential insights on rotted plywood decking, rafter sistering, and structural codes.

How much does it cost to replace rotted roof decking in 2026? +
During a full re-roofing project when shingles are already stripped, replacing rotted 4x8 roof decking sheets typically costs $45 to $80 per sheet for 7/16-inch OSB and $65 to $105 per sheet for 1/2-inch CDX plywood. However, for a standalone emergency spot repair on an intact roof, the cost rises to $195 to $375 per sheet because contractors must remove existing shingles, cut out damaged sheathing along rafter centers, install 2x4 blocking, and re-shingle the patch.
What is the 25% Rule in roof replacement, and how did Florida Senate Bill 4-D change it? +
Historically, Florida Building Code Section 706.1.1 mandated that if more than 25% of a roof was repaired within a 12-month period, the entire roof had to be replaced to current code. In May 2022, Florida enacted Senate Bill 4-D (codified in Florida Statute 553.844). Under current law, if an existing roof was permitted or installed in compliance with the 2007 Florida Building Code or newer (roughly post-March 2009), the 25% full replacement mandate is eliminated, and homeowners are legally permitted to repair only the damaged portion.
How much does it cost to sister a rotted rafter tail? +
Sistering a rotted rafter tail typically costs between $180 and $380 per rafter. A carpenter attaches a matching piece of pressure-treated 2x6 or 2x8 dimensional lumber alongside the damaged rafter, extending at least 24 inches past the rotted zone, fastened with structural screws or staggered 16d nails to restore structural load-bearing capacity.
Which is better for roof decking: CDX plywood or OSB? +
CDX plywood is superior for moisture resilience. While OSB is cheaper and widely used in tract home construction, it swells irreversibly along its edges when exposed to roof leaks and takes weeks to dry out. CDX plywood expands slightly when wet but returns to its original dimension upon drying and maintains higher fastener withdrawal resistance over decades.
How do you know if roof decking is rotted without tearing off shingles? +
Warning signs include: (1) Visible sagging, dipping, or dished rooflines between rafters; (2) Soft, spongy sensations when walked on by an inspector; (3) Water staining, dark mold, or daylight visible from inside the unconditioned attic; and (4) Shingle nails backing out and pushing up through shingle tabs because the rotted wood beneath has lost its grip.