Secondary Water Barrier for Florida Metal Roof Systems
MRM Tornado Underlayment — a self-adhered secondary water barrier under every roof we build.
A roof is a system, not a single layer. Above the deck, under the panel, MRM Tornado Underlayment is built to help keep water off the deck if the panel above it is damaged in a storm.
What Makes a Florida Roof System Different
Not every underlayment is engineered to double as a secondary water barrier. Ours is self-adhesive, seals around fasteners, and is built to sit between a corrosion-resistant panel and a Florida roof deck.
The Layer That Keeps Working on the Roof's Worst Day
Self-adhered to the plywood deck, sealed tight around every fastener, before the panel goes on. If wind or debris damages the panel above it, this layer helps keep water off the deck until the roof can be repaired. It is a backup, not a replacement for the panel.
Secondary Water Barrier
Helps keep water off the deck if the panel above is damaged in a storm, until repairs are made.
Self-Adhered Leak Barrier
Built for Florida's wind-driven rain rather than ice. Bonds to the deck and helps seal around fasteners; seams, edges and penetrations are detailed during install.
Class A Fire Rated
Class A fire resistance as part of a tested roof assembly, alongside the storm protection.
Radiant Energy Barrier
Still reflects heat on the 350 days a year there isn't a storm.
Sound Barrier
Dampens the noise of hail and driving rain hitting the panel above.
How Water Moves Through a Storm
What happens when wind-driven rain gets past a metal panel, step by step.
Wind pushes rain sideways
Storm winds can drive rain uphill, under panel laps, ridge caps and edge trim.
Water finds a weak point
Usually a fastener, a seam, or the flashing around a vent, skylight or wall.
The underlayment meets it
Bonded to the deck and sealed around fasteners, the membrane keeps that water on top of itself.
Water drains to the eave
Each course overlaps the one below, so water runs downslope and out at the drip edge instead of into the deck.
Where Roof Leaks Usually Start
Penetrations
Plumbing vents, exhaust fans and skylights need their own flashing or boots, with the membrane detailed around them before the panel goes on.
Walls and chimneys
Where a roof meets a vertical surface, step and counter flashing carry water away. The underlayment turns up the wall behind it as a backup.
Valleys and eaves
Valleys concentrate water and eaves are where it leaves the roof, so laps and the drip edge have to go in the right order.
What a Secondary Barrier Can and Can't Do
- Can: limit how much water reaches the deck when a panel, seam or fastener lets water through.
- Can't: hold the roof down. Wind resistance comes from the panels and how they're attached.
- Can't: stay exposed indefinitely. After storm damage, have the roof inspected and repaired promptly.
- Can't: make up for missing or failed flashing at walls, valleys and penetrations.
- Warranty: coverage is set by the manufacturer's written warranty. Ask for a copy with your quote.
Storm-Season Certifications Worth Knowing
- Miami-Dade County Approved
- Meets or exceeds ASTM D1970
- Class A Fire Resistance
- Standard 20-Year Limited Warranty
- Manufactured in the USA
- Paired system approval with MRM Tornado Steel & Aluminum Roof Panels (FL-approved)
Four Products, One Job: Back Up the Panel
Each of these installs as a self-adhered secondary barrier under the panel.
MRM Tornado Radiant Barrier SWR 5000 FR
Reflective face, self-adhered as a backup barrier under the panel.
MRM Tornado Radiant Barrier SWR 2000 FR
A lighter version of the same reflective backup layer.
MRM Tornado Duo Barrier 1500 HT
A duo-layer, high-temperature backup barrier for the deck.
MRM Tornado White SBS Cap Sheet 4000 FR
Mineral-coated cap sheet with the same secondary-barrier role.
Building a Roof System, Not Just a Panel
Assess the roof
We look at deck condition and prior storm exposure.
Quote the full system
Panel and underlayment priced together.
Install the backup layer first
Self-adhered directly to the deck.
Close it in with the panel
Completing a system built for storm season.
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