Flat Roof Replacement in South Florida

Flat and low-slope roofs sit on a lot of South Florida houses: older concrete-block homes, additions, Florida rooms and covered porches, and houses with parapet walls around the roof edge. If yours is worn out, the one thing that matters most is simple: the water has to leave. The Florida Building Code requires a design slope of at least 1/4 inch per foot for every common flat-roof membrane (built-up, modified bitumen, TPO and other single-ply, spray foam and liquid-applied roofing), with a 1/8-inch exception for coal-tar built-up roofs. A re-roof can keep a flatter slope only if the roof still drains.¹ A replacement is your chance to fix slope, drains and edge details, not just lay down a new sheet.

Replace or repair?

Look for these signs that a flat roof is at the end of its life, not just leaking in one spot:

• Soft or spongy areas underfoot, which usually mean wet insulation under the membrane.
• Water that stays in the same low spots days after a storm.
• Blisters, open seams or a cap sheet worn down to the felt.
• Leaks that keep coming back at parapet walls, drains or around AC stands after they have been patched.

The code also sets a hard line. No more than 25 percent of a roof or roof section may be repaired, replaced or recovered in any 12-month period unless the whole roof or section is brought up to the current code.² There is an exception: if your existing roof was built, repaired or replaced under the 2007 Florida Building Code or later, only the part being worked on has to meet today’s code, even at 25 percent or more, and local governments cannot change that.³ See flat roof repair if your roof still has life in it.

Tear-off or recover

A recover means installing the new roof over the old one. Outside Miami-Dade and Broward, the code requires a full tear-off to the deck when the existing roof is water-soaked or too deteriorated to be a base, when it already has two or more layers, or when blisters have not been cut open and secured.²

In the High-Velocity Hurricane Zone (HVHZ), which the code defines as Miami-Dade and Broward only, the bar is higher.⁴ One additional roofing system may go over the original, but only if the old roof passes these checks:⁵

• Moisture: no more than 5 percent moisture by weight in the old membrane and 8 percent in rigid board insulation, verified by a TAS 126 moisture survey (Section 1521.12).
• Uplift: if the new roof will be bonded to the old membrane, the old membrane is tested under TAS 124 and must resist the design wind pressures (1521.10). If it will be fastened through the old base sheet or insulation, the fasteners are field-tested under TAS 105 (1521.11).
• Deck: no new system goes over sheathing that is not fastened to code or is water-soaked or deteriorated; bad sheathing is removed and replaced (1521.5).

The test results go in with the permit application. On many older roofs, a tear-off is simpler than proving the old one is sound.

How the job works

In Miami-Dade and Broward (HVHZ)

• Permit. Every re-roof or recover uses the HVHZ Uniform Roofing Permit Application, signed by a licensed contractor, with the product approvals and the Owner’s Notification for Roofing Considerations attached.⁵ We pull the permit.
• Owner’s notification. We walk you through the form and you initial it. It covers renailing wood decks, nail points showing through exposed-beam ceilings, and overflow scuppers where parapet walls could trap water.⁵ Before starting, the contractor must also tell you if ponding is possible and recommend a structural review if it is (1521.13).
• Product approval for every layer. Each roofing component, system and assembly needs a valid approval, and the roof is installed exactly as the approval says, even where the manufacturer’s printed instructions differ.⁵ Insulation boards need their own approval and are attached following the assembly approval and RAS 117.⁵
• Deck preparation. Concrete decks are dried before primer goes on. Lightweight insulating concrete decks get a TAS 105 fastener pull test, and if results fall below 80 percent of the approval’s values, an engineer must write the attachment specification before a permit is issued (1521.6 to 1521.7.1).⁵ On wood decks, nails are 12-gauge ring-shank nails driven through tin caps.⁵
• Edges, parapets and equipment. Parapet details and edge metal follow RAS 111 (1519.10, 1519.13).⁵ Rooftop AC units must be secured to the structure with no wood sleepers, and conduit and piping run at least 8 inches above the finished roof. Condensate lines may not drain onto the roof (1522.2, 1522.3.4, 1522.3.5).⁵
• Surfacing. On slopes of 3:12 or less, a gravel-surfaced roof needs at least 400 pounds of gravel per square; mineral-surfaced cap sheets need nothing extra unless the fire rating requires it, and smooth surfaces get an approved aluminized or emulsion coating (1519.12).⁵
• Inspections. Miami-Dade schedules flat-roof work under codes 059 (Tin Cap / Dry In / Base Sheet / Anchor Sheet), 063 (Cap Sheet / In Progress) and 001 (Final).⁶

Everywhere else in Florida

• Permit. Florida law requires a building permit to repair or replace a roof unless a law exempts the work,⁷ and the statewide permit-exemption list in the code has no roofing item.⁸
• Florida Product Approval. The membrane and components must carry state product approval (an FL number), which you can look up at floridabuilding.org.⁹
• Wind uplift. Modified bitumen and TPO roofs must have an approved uplift resistance at least equal to what the code requires for your house (FBC Residential R905.11.3 and R905.13.3).¹
• Drainage. Unless the roof drains over its edges, drains go at each low point. Where water could back up behind a parapet and no other overflow exists, overflow scuppers go 2 to 4 inches above the finished roof.¹
• Slope on a re-roof. A re-roof does not have to meet the 1/4-inch minimum slope if the roof still provides positive drainage.¹

Some cities add their own flat-roof rules on top of the code. Miami Shores limits which flat-roof materials and where,¹⁰ and North Miami Beach requires an extra affidavit before a flat roof’s final inspection.¹¹

Materials and how long they last

• TPO (a white thermoplastic single-ply membrane): 10 to 25 years depending on quality and thickness, per HomeGuide; This Old House says 7 to 20.¹²¹³
• Modified bitumen (asphalt-based rolls, often with a mineral cap sheet): 20 years per This Old House, 30 per HomeAdvisor.¹³¹⁴
• Flat roofs in general: replacement within 15 to 20 years, up to 30 with ideal conditions and maintenance, per Forbes Home.¹⁵

These are national figures. We found no Florida-specific lifespan data for flat roofs.

What it costs

National cost guides put a flat roof replacement at $3,331 to $11,558 for a typical home ($4 to $35 per square foot), TPO at $4 to $14 per square foot and modified bitumen at $4 to $8 per square foot.¹⁴ Tear-off of the old roof adds $1 to $2 per square foot per HomeGuide, or $1 to $5 per HomeAdvisor, and HomeGuide puts insulation boards at $0.50 to $3.00 per square foot.¹²¹⁴ These are U.S. national averages, not Miami prices. Our own price comes after we measure.

Insurance

Florida counts roof age from the last date 100 percent of the roof surface was built or replaced.¹⁶ A full replacement resets that date; patching does not. Under Florida law, your roof contract must include the notices required by F.S. 489.147. It is illegal for a contractor to offer to waive your deductible.¹⁷ A new roof also changes what a wind mitigation form records. A roofing contractor can do the roof work, but the form insurers must accept has to be signed by an inspector on the F.S. 627.711(2) list, which does not include roofers.¹⁸