FBC 8th Edition (2023)Last checked Oct 21, 2026

Secondary Water Barrier & Re-Roof Mitigation Checklist

These mitigation rules apply when the roof covering is removed and replaced on an existing building with a sawn lumber, wood plank or wood structural panel deck.
FBC-EB 706.7; FBC-R R908.7 ↗
Buildings that were originally permitted under the Florida Building Code are exempt from Section 706.7 (deck renailing and secondary water barrier) and Section 706.8 (roof-to-wall).
FBC-EB 706.7 Exception; FBC-EB 706.8 Exception ↗
When the covering is replaced, install a secondary water barrier per FBC Building 1507.1.1 or 1518.2 (HVHZ) or FBC Residential R905.1.1.
FBC-EB 706.7.2; FBC-R R908.7.2 ↗
Option 1: cover the entire deck with ASTM D1970 self-adhered polymer-modified bitumen underlayment, installed per both the underlayment and roof-covering manufacturers (not permitted under wood shingles or shakes).
FBC-R R905.1.1.1 Item 1 ↗
Option 2: apply 3-3/4 inch minimum strips of ASTM D1970 membrane or AAMA 711 Level 3 flashing tape over all deck joints, then cover the whole roof with underlayment per Table R905.1.1.1.
FBC-R R905.1.1.1 Item 2 ↗
Option 3: install two layers of ASTM D226 Type II, D4869 Type III/IV or D8257 underlayment (half-sheet starter, then half-lap plus 1-2 inches), fastened with 1-inch cap nails on a 12-inch grid and 6 inches at laps.
FBC-R R905.1.1.1 Item 3 ↗
An existing self-adhered underlayment may stay if it and any required deck renailing can be verified, but a new approved underlayment must go over the entire roof on top of it.
FBC-R R905.1.1.1 Item 1 Exception 2; FBC-R R908.1 Exception 2; FBC 1518.2.1 ↗
Roofs with slopes under 2:12 that have a continuous roof system, and clay or concrete tile roofs installed to code, are deemed to already meet the secondary water barrier requirement.
FBC-EB 706.7.2 Exceptions 1–2; FBC-R R908.7.2 Exceptions ↗
Check deck nailing: an existing 8d nail must be at least 0.113 inch by 2-1/4 inches, and plank decking up to 12 inches wide needs two 8d nails at each framing member it crosses.
FBC-EB 706.7.1; FBC-EB 706.7.1.1 ↗
Panel decks held with staples or 6d nails, or 8d nails spaced more than 6 inches, need supplemental fasteners so spacing is 6 inches on center or less at panel edges and intermediate framing.
FBC-EB Table 706.7.1.2 ↗
Supplemental deck nails must be ASTM F1667 RSRS-01 ring-shank nails with a 0.113-inch shank and a 0.280-inch full round head (the Existing Building code says 2-3/8 inch minimum length; the Residential code says 2-1/4 inch).
FBC-EB 706.7.1.2; FBC-R R908.7.1.2 ↗
The $300,000 threshold applies to roof-to-wall connections, not to the water barrier: in the wind-borne debris region, buildings insured (or, if uninsured, tax-assessed) at $300,000 or more need roof-to-wall upgrades on reroof.
FBC-EB 706.8; FBC-R R908.8 ↗
Required roof-to-wall retrofits are capped at a 15 percent increase in reroofing cost, with gable ends and corners as the priority, and are not required where the connections were required when the house was built.
FBC-EB 706.8; FBC-EB 706.8.1 Exceptions; FBC-EB 706.8.1.7 ↗
No more than 25 percent of a roof or roof section may be repaired, replaced or recovered in 12 months unless the whole roof or section is brought to code, except roofs built to the 2007 FBC or later.
FBC-EB 706.1.1; FBC-R R908.1.1 ↗

Coming with the 2026 code:

The 9th Edition (2026) Florida Building Code takes effect December 31, 2026, per Miami-Dade County; the Florida Building Commission workplan lists the same date and notes the code takes effect 6 months after publication.
New FBC-EB 706.7.3.1, 706.7.3.2 and 706.7.3.3 cover which underlayments may go over an existing self-adhered underlayment when replacing shingle, metal, slate and wood roofs, tile roofs, and low-slope (under 2:12) continuous roofs.
FBC-EB 706.3 Exception 5 (roof coatings) is deleted and replaced with language on existing vapor barriers or self-adhering underlayments; in the Residential code, coating of asphalt shingles moves to a new R905.2.9.
FBC-R R905.1.1: underlayment must lap over hips and ridges at least 6 inches, except where ventilation openings are provided.
The Commission's change analyses did not show any change to Sections 706.7.1, 706.7.2, 706.8 or the $300,000 roof-to-wall threshold.

Official sources

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