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Sealing Your Roof Deck: The Critical Step Many Roofers Skip
A roof is designed to shed water but can leak when protection is needed the most. Severe thunderstorms, hurricanes, and tornadoes can tear off or damage portions of your roof cover, and wind can drive rain beneath an unsealed or compromised roof cover—leaving your home vulnerable to costly interior water damage.
The solution? Sealing your roof deck can reduce water intrusion by up to 95% – but not every roofer includes this critical step!
Why Most Roofs Leak with Typical Construction
A typical roof is built with multiple layers, starting with the roof’s supporting frame of rafters or trusses, followed by sheets of plywood or oriented strand board (OSB) that form the roof deck. Small gaps in the roof deck allow for natural expansion and contraction due to temperature changes. A layer of underlayment is then installed over the wood deck, followed by the outer most layer, the roof cover material.
If shingles or other roof coverings are damaged or deteriorated with age, the underlayment should act as a secondary barrier against water entering through gaps in the wood deck. However, in high winds, standard underlayment alone may not be enough, especially if it’s thin, stapled on, not properly installed, or unable to withstand the elements.
While most building codes require these standard components, a roof without an IBHS research-based solution (sealed roof deck) remains susceptible to significant water damage if the roof cover fails.
Note: The 2020 Florida Building Code (7th edition) and newer editions for underlayment requirements include a sealed roof deck.
Components of a Typical Pitched Roof System: (Constructed from Bottom to Top)
Framing:
Rafters or trusses (e.g., wood or metal beams) form the roof’s frame structure, supporting its weight and defining its pitch.
Roof Deck (Sheathing):
The flat surface [typically Oriented Strand Board (OSB) or plywood] nailed to the roof frame, providing structural support for the roof cover.
Underlayment:
A protective layer (e.g. asphalt-saturated felt, self-adhered, synthetic) installed over the roof deck to help prevent water infiltration.
Flashing:
Sheet metal pieces are placed at critical areas (e.g., valleys, chimneys, wall intersections) to direct water away and prevent leaks.
Roof Cover:
The outermost material (e.g., asphalt shingles, metal panels, clay/concrete tiles, or slate) installed for weather resistance, fire classification, or aesthetic appearance.
- Note: When installing a new roof, most local building codes require removing all shingles and underlayment down to the roof deck. This prevents water damage, mold, and mildew that can develop if old underlayment is left in place. Removing the old layers also ensures a smooth surface, avoids adding unnecessary weight, and makes inspections easier.
What is a Sealed Roof Deck and How Does It Help Prevent Leaks?
IBHS field studies show that up to 90% of catastrophe-related insurance claims involve roof damage, which worsens with water intrusion. In lab tests simulating winds up to 130 mph and rainfall rates of 8 inches per hour, IBHS found that a properly sealed roof deck can prevent up to 95% of water intrusion, even in extreme conditions.
Your roof cover is your first line of defense against the elements—but what happens when it fails? High winds from severe thunderstorms, hurricanes, and tornadoes can tear off or damage portions of your roof cover, leaving your home vulnerable.
The solution? A sealed roof deck– based on research to help keep water out and protect your home.
A roof’s wooden deck is constructed with small gaps between each sheet of plywood or oriented strand board (OSB) to allow for natural expansion and contraction. A sealed roof deck covers these gaps, creating a continuous secondary water barrier that helps keep rain out if the primary roof cover is damaged or deteriorates over time.
When properly installed, a sealed roof deck can reduce water intrusion by up to 95%, protecting your home from costly interior damage and minimizing the risk of family displacement.
Sealing your roof deck is one of the most effective ways to prevent rain from infiltrating your home.
Research shows that there are several ways wind can cause your garage door to fail:
- High winds can cause weak garage door tracks to buckle.
- Flying debris can pierce your garage door.
- Inadequate attachment of the doors to the building can cause the door to detach and fail inward.
After analyzing damage from Hurricane Ike (2008), the Joplin, Missouri tornado (2011), and the Moore, Oklahoma tornado (2013), IBHS found garage door damage was more likely to lead to structural damage in other parts of the home.
How To Get a Sealed Roof Deck and Prevent Costly Roof Leaks!
When installing a new roof, don’t just focus on the look – protect what’s underneath. No matter what roof cover material you choose, preventing leaks starts with a better underlayment installation by sealing roof deck. However, most local building codes don’t require this step or may not be enforced, leaving many homes at risk. Without a sealed roof deck, water can seep in, damaging ceilings, walls, floors, and belongings, leading to mold, structural issues, and costly repairs.
To properly protect your home, ask your roofer to include this critical step before installing the roof cover. When requesting a roofing quote, confirm that a better underlayment by sealing the roof deck is part of the plan to ensure long-lasting protection against leaks.
For both new roofs and re-roofing projects, IBHS research recommends one of these three proven methods for sealing a roof deck:
1. Roof Flashing Tape: A 4-inch-wide self-adhering roof tape applied over all deck seams followed by #30 felt or a reinforced synthetic underlayment over the entire roof deck.
2. Fully Adhered Membrane: A fully adhered membrane covering the entire roof deck.
3. Two Layers of Underlayment: Two layers of #30 felt or synthetic felt with a 50% overlap, secured with 1-inch button cap nails.
Don’t need a new roof yet but want to seal your roof deck?
A professional who is certified can apply a closed-cell polyurethane spray foam to the underside of your roof’s sheathing can seal all cracks and penetrations, adding an extra layer of protection from water intrusion. As a bonus, this method also strengthens the bond between the roof deck and the trusses, helping to keep your roof intact.
4. Interior Attic Spray Foam: Apply closed-cell polyurethane spray foam along all interior seams — at the joints between sheathing panels and where the roof sheathing meets framing members — to create a watertight seal.
Building Stronger: Can I Do More Than Just Seal My Roof Deck?
Yes! A FORTIFIED Roof™ is a system developed by the Insurance Institute for Business & Home Safety (IBHS), a non-profit dedicated to preventing avoidable family displacement and financial loss caused by severe weather.
Your roof is your home’s first line of defense. A FORTIFIED Roof not only requires a sealed roof deck but includes additional reinforcements, like ring-shank nails that secure the wooden deck to the roof trusses, doubling the roof’s resistance to wind uplift.
Extra attention is also given to the roof’s edges, where damage often begins as wind gets underneath tearing it away from the home. To help protect this vulnerable area, FORTIFIED requires specific materials and installation methods, including a wider drip edge and a fully adhered starter strip. Together, these components create a stronger, more resilient roof system.
Benefits of Installing a FORTIFIED Roof
With over 20 years of building science research, IBHS has developed FORTIFIED Roof as a science-based designation program to help keep your roof intact and water out during severe weather. Benefits of a FORTIFIED Roof:
- Stronger Protection – Your roof is the first line of defense against extreme weather. FORTIFIED standards go beyond building codes to provide greater protection and peace of mind.
- Insurance & Financial Incentives – A FORTIFIED designation may qualify you for insurance discounts, tax credits, or deductions.
- Increased Home Value – In some areas, a FORTIFIED designation can increase a home’s value by nearly 7%.
- Affordable & Accessible – Sealing a roof deck is cost-effective, and the materials are widely available.
- Better Leak Protection – A properly installed sealed roof deck can reduce water entry up to 95%, minimizing interior damage and speeding up recovery after a storm.
- Protection Beyond the Coast – While common in hurricane-prone regions, a FORTIFIED Roof also benefits inland homes, helping to protect against tornadoes, severe thunderstorms, and hail.
- Easy for Roofers to Implement – Professional roofers can quickly learn and get certified online to apply FORTIFIED Roof installation techniques.
Learn more about how to get started with a FORTIFIED Roof to better protect your home or find a professional to get started.