Keeping Your Roof Sealed During Flash Floods

As the most common and widespread of all weather-related natural disasters, floods affect more homeowners than any other disaster. In the U.S., floods kill more people each year than tornadoes, hurricanes, or lightning.

Flash floods are the most dangerous because they combine the destructive power of a flood with little warning and a lot of unpredictability. They can last for days or weeks and cover a house to the rooftop.

Flash floods can happen anywhere at any time, even in areas that are not prone to floods. It’s important to know the facts about flash floods to protect your home, and to keep your roof sealed during unpredictable weather. According to the National Flood Insurance Program, just an inch of water can cause costly damage to your property, and the average residential flood claim is about $30,000. Taking precautions to keep your roof sealed can minimize your chance of devastating damage to your home in the event of a flood.

The Best Options for Keeping Your Roof Sealed

If you are building a home and installing a new roof, or re-roofing your current home, there are ways that you can plan to have the best protection against flash floods. Installing an underlayment to your roof can keep your roof sealed from water leaks that may occur during flash floods.

When installing or re-roofing, you can work with your residential roofing contractor to determine the best method to seal your roof. Here are six common options for sealing your roof:

Option 1: Two Layers of Underlayment

With this option, the roofing contractor installs two layers of underlayment in a shingle fashion. The underlayment is fastened at approximately 12 inches on center and secured.

Option 2: Self-Adhering Polymer-Modified Bitumen Flashing Tape

This flashing tape is applied directly to the roof deck to all horizontal and vertical joints. Then, install felt or synthetic underlayment over the entire roof deck and secured.

Option 3: Self-Adhering Flexible Flashing Tape

Apply a flexible flashing tape directly to the roof deck to all horizontal and vertical joints. Then a felt or reinforced synthetic underlayment is installed over the entire roof deck and secured.

Option 4: A Full Layer of Self-Adhering Polymer-Modified Bitumen Membrane

A full layer of self-adhering polymer-modified bitumen membrane (peel-and-stick) is installed over the entire roof deck.

Note: Some local building departments (e.g., Miami-Dade and Broward counties in Florida) prohibit the use of a self-adhered membrane applied directly to the roof sheathing. Check with the local building department for any restrictions in your area.

Option 5: Reinforced Synthetic Underlayment

Reinforced synthetic underlayment or felt paper is installed and secured. Horizontal and vertical underlayment laps are sealed/taped.

Option 6: Closed Cell Polyurethane Spray Foam (Existing Roof)

A closed cell polyurethane spray foam is applied to the underside of the roof sheathing at the joints, between the sheathing panels and along all intersections between roof sheathing and all roof framing members.

Each of these methods should be installed by a professional roofing contractor. A professional roofing company will be able to guide you in choosing the best method for your home and budget.

 Additional Measures for Protecting Your Roof from Flash Floods

Even after you keep your roof sealed with an underlayment, regular maintenance is important to keep your roof in the best possible condition to withstand flash flood conditions.

• Cut back tree limbs that hang down onto the roof or eaves. When these tree limbs make contact with the roof during windy conditions, they can damage the roof. Cut back vines that touch the roof surface because these can grow under the roof surface and cause a leak.
• Debris lodged in areas that water would drain through can cause a damming affect that may result in a leak. Removing debris and leaves is important maintenance to your roof. Sweep debris out of low spots behind chimneys and especially away from drains on any flat roof. Check the roof every three to four weeks during the winter or after a major storm for further accumulation.
• Clean gutters and downspouts of all leaves and debris during the fall. Remember to recheck them several times during the winter to make sure they have not become clogged.
• Inspect gutters and downspouts for leaks by running a hose into them and watching for proper runoff. Patch any small holes found by cleaning the inside area with a wire brush and sealing with gutter cement, available at most hardware stores and home centers.
• If you have a flat roof with drain holes, install quarter-inch “hardware cloth” mesh (available from building suppliers) over the drains to keep debris from clogging them. Form a dome with the material over the drain opening and wedge it into place.
• Inspect the roof for cracks or openings of any kind. Pay close attention to areas where vents or flashings come through the roof surface or where joints exist. These are places where leaks are most likely to occur. Small cracks up to one-quarter-inch wide can be easily sealed using silicone sealant, available in cartridges for a caulking gun at most hardware or paint dealers. You can repair larger gaps with roofing cement. Follow the instructions on the containers.
• When inspecting the roof, check for missing or damaged shingles or tile. You can replace these by carefully sliding a new one into position, taking care not to tear the roof paper below in the process. Many building suppliers sell painted “tin” shingles designed for this purpose; they are often easier to work with than regular shingles. Seal cracks in tiles with clear silicone sealant or roofing cement to protect the waterproof membrane below them from weathering.
• Check for cracks or breaks in vertical wall surfaces or painted trim above the roof line (like a second-story wall above a first-story roof). Leaks from these areas are often mistaken for roof leaks. Repaint or seal any cracks with caulking material.

Properly sealing and maintaining your roof with these suggestions will ensure that you protect both the investment of your home and your family’s wellbeing during flood conditions.