FBC Section 706.1.1: The 25% Rule and the Positive Drainage Exception

The Section That Replaced Two Old Citations

The 8th Edition Florida Building Code, effective in 2023, renumbered the reroofing rules. The 25% replacement trigger and the slope exception that used to live in FBC 1510.1 and FBC Existing Building 611.1 now sit in one place: 2023 FBC Existing Building Section 706.1.1.

This matters before you write a word of the estimate. A supplement that cites 1510.1 in 2026 tells the adjuster the contractor's documentation is two code cycles behind. The supplement that cites 706.1.1, Exception 1 tells the adjuster the file is current. Same argument. Different signal.

The current citations:

• 2023 FBC Existing Building §706.1.1 — the 25% Rule itself
• 2023 FBC Existing Building §706.1.1, Exception 1 — the slope exception
• 2023 FBC Building §202 — the positive drainage definition

These three sections, working together, decide most of the scope on most Florida reroofs. The two halves of the rule — the 25% replacement trigger and the positive drainage exception — answer different questions on different roofs. A file that handles one and ignores the other gives up recovery on every project where both apply.

Half One: The 25% Rule and the March 1, 2009 Threshold

Senate Bill 4-D (2022) carried the modern 25% Rule into the 2023 code. The rule now runs on a two-tier system divided by one date: March 1, 2009.

That date is when the 2007 Florida Building Code took effect. The legislature treats roofs permitted under that code or any subsequent edition as current enough that a partial-replacement scenario does not trigger a full-section mandate. Roofs permitted before that date are still subject to the original 25% Rule, with the entire damaged section pulled up to current standards if the threshold is crossed.

The measurement is the permit date on the existing roofing system, not the year the building was constructed. Most carrier workflows do not pull permit history. The adjuster reads the year built off the policy and applies a generic depreciation schedule. The actual permit record sits at the county building department waiting for someone to ask for it.

Pre-2009 Roofs: The Hard Trigger

If the existing roof was permitted before March 1, 2009, the 25% Rule applies in full.

Damage exceeding 25 percent of a roof section requires the entire section to be replaced to 2023 FBC standards. That replacement carries the current code's deck fastener requirements, current underlayment, current drip edge sequence, and current secondary water barrier provisions where applicable.

The fight on a pre-2009 roof is the damage percentage. Two carrier tactics show up most often: aggregating the entire roof as one section to dilute the percentage, and pricing visible damage at face value while ignoring the code-mandated upgrades that come with bringing a section to current code.

Both tactics fall apart against accurate section definition. The carrier does not get to define the section. The code does. A roof section is divided by parapet walls, elevation changes (excluding hips and ridges), changes in roofing material, and expansion joints. Hips and ridges do not divide sections.

One more rule on the math. Under Declaratory Statement DS 2021-007, the related work area — the tie-off needed to integrate a repair into surrounding undamaged roof — does not count toward the 25 percent calculation. The threshold runs on primary damage area only.

Post-2009 Roofs: The Pivot to Matching

If the existing roof was permitted on or after March 1, 2009, the 25% Rule does not apply. A 30, 50, or 80 percent loss does not force section replacement. The code is satisfied by a properly executed repair.

That sounds like bad news for the contractor. It is not. It changes the argument, not the outcome.

When the code does not force replacement, the argument moves to Florida Statute 626.9744, the matching statute. If the damaged shingles are discontinued, if the run, color, or granule blend cannot be matched, if the repair will produce a visibly inconsistent appearance, the matching statute requires the carrier to make the insured whole. In most post-2009 wind and hail losses, that still means a full replacement. The mechanism is just different.

The documentation pattern shifts: manufacturer, product line, color of existing shingles, evidence of discontinuation or unavailability, photographs of the visual contrast a partial repair would create.

A contractor who walks into a post-2009 loss still arguing the 25% Rule gets a denial that is technically correct. The post-2009 argument runs on matching.

Half Two: The Positive Drainage Exception on Commercial Reroofs

The same Section 706.1.1 contains Exception 1, which governs slope on commercial reroofing. This is where carriers run the flat-ISO play on tapered insulation supplements.

The new-construction rule (FBC 1507.12.1 — verify against current renumbering) requires single-ply membrane roofs to have a design slope of at least 1/4 unit vertical in 12 units horizontal. On reroofing projects, carriers cite that rule backwards: if the existing roof never had 1/4-in-12 slope, they argue the taper is a "betterment" they are not required to fund. Their estimate proposes 2-inch flat ISO at uniform thickness over the existing flat deck.

Exception 1 to Section 706.1.1 removes the 1/4-in-12 minimum on reroofs. It does not remove the drainage requirement. It replaces it with a performance standard.

The performance standard is positive drainage, defined in 2023 FBC Building §202 as:

The drainage condition in which consideration has been made for all loading deflections of the roof deck, and additional slope has been provided to ensure drainage of the roof within 48 hours of precipitation.

Three requirements, all mandatory: consideration of loading deflections, additional slope, and drainage within 48 hours.

A flat deck with flat ISO cannot meet this definition. Physics does not allow it. Water on a zero-slope surface does not drain in 48 hours unless something is moving it, and on a flat membrane roof the only thing that can move it is the slope built into the insulation system above the deck.

The carrier proposing flat ISO over a dead-flat deck is not proposing a cost-saving alternative. The carrier is specifying a finished roof system that cannot satisfy §706.1.1, Exception 1. The contractor who installs that scope inherits the code violation, signs the permit, and carries the warranty when the roof ponds in two years.

The Evidence Stack

For any commercial flat-roof reroof where tapered ISO is in scope:

Topographical mapping on a 20-foot grid. The dead-flat condition has to be documented at a resolution the carrier cannot rebut. A coarser grid lets the carrier argue intermediate high points exist between measurement points. A 20-foot grid produces enough data points to settle that question.

Forensic removal photographs of the existing drainage logic. This is where most files come up short. The existing tapered system, if there is one, was engineered. Removal photos document what direction the existing taper was carrying water and which drainage components were doing the actual work. On Case Study #5081, DCS documented a 12-year-old tapered system that had inverted the original drainage logic — moving water away from failed internal drains toward perimeter scuppers that had become the building's actual drainage path. Removing the taper would have destroyed the only functional drainage the building had. That argument exists only in the photos.

Endoscope documentation when the carrier proposes reverting to internal drainage. A high-definition endoscope down the existing drain lines documents the condition. Collapsed lines, structural failures, joint separations — whatever the endoscope finds, the file then carries documented evidence that the carrier's proposed alternative is physically impossible.

Code citations. §706.1.1 for the rule, Exception 1 for the slope waiver, §202 for the positive drainage definition.

Manufacturer specifications for the tapered ISO product line and panel layout.

Case Study #5081: Financial Verification

The supplement was not negotiated by argument. It was carried by evidence the carrier could not rebut. The topographical grid documented the dead-flat subsurface. The forensic photos documented the inverted drainage logic. The §706.1.1 Exception 1 citation framed the flat-ISO proposal as a documented code violation.

Why Carriers Run Plays the Code Already Lost

The carrier's interest is loss-cost containment. On a pre-2009 residential roof, repair-only pricing keeps the indemnity below replacement cost. On a commercial reroof, flat ISO saves five to six figures on a single file. Across a book of business, the savings on these defaults are large enough to be worth the denial-letter language even when the denial is wrong.

The contractor's interest is a code-compliant, weather-tight, manufacturer-warrantied installation that does not generate a callback in 18 months. Partial repairs on aged systems often void manufacturer warranties. Flat ISO on dead-flat decks generates the callback every time. The contractor's downside is uncapped.

Section 706.1.1 is the referee. The contractor's documented scope satisfies the code. The carrier's repair-only or flat-ISO proposal does not. When the file shows the permit history, the section definition, the topographical grid, and the forensic removal photos, the carrier's argument loses the ability to live in the realm of opinion.

Where DCS Fits

DCS writes the Xactimate scope and the supporting documentation. The estimate references the current §706.1.1 citation, the appropriate threshold (Pre-2009 or Post-2009), the matching statute where it applies, and the positive drainage exception with its three-part definition. Every line item ties to a specific piece of evidence in the file.

The contractor takes the document onto the job and uses it. The contractor handles the carrier conversation, the field inspection, and the installation. DCS does not contact the carrier, the adjuster, or the property owner. We write the document. You carry it.

If your next Florida reroof has a 25% Rule question or a flat-ISO denial on it, the documentation has to be in place before the conversation starts. The estimate that wins the argument is the one built on the evidence stack from day one.