After a hurricane, hailstorm or fallen tree, a tarp is what stands between an open roof and the inside of the house until it's repaired. Done well, it buys weeks or months. Done badly, it blows off in the next storm and takes shingles with it.
What the government does
After major disasters, FEMA funds Operation Blue Roof, run by the U.S. Army Corps of Engineers, which installs temporary covers on eligible homes for free. Their crews use reinforced plastic sheeting fastened to the roof with wood strips nailed or screwed through the sheeting, rather than relying on grommets alone. The program has covered tens of thousands of roofs; the Corps installed its 30,000th blue roof after Hurricane Ida. FEMA has also said that homeowners who put up their own tarp can still qualify for the program and for other assistance. Check the current FEMA and Corps guidance for your disaster, since eligibility rules change.
How to tarp a roof
- Stay safe first. Wet roofs are slick, damaged decking can give way, and power lines may be down. If you're not comfortable on a roof, wait for help.
- Size it generously. Cover the damaged area plus at least 2 ft on every side, and run the tarp over the ridge if you can, so water can't run under the top edge.
- Use battens. Roll the tarp edge around a 2x4 or furring strip and fasten the strip to the roof. Wood spreads the load; nails or screws through grommets alone tear out in wind.
- Keep it tight. A loose tarp flaps, and flapping is what destroys tarps and the shingles under them.
- Check it after every storm.
Vinyl or poly?
A 12 mil poly tarp is fine if the roofer is coming in days or a few weeks. If the wait is longer, or it's the middle of storm season, use heavy-duty vinyl. Sunlight breaks poly down, and a tarp that fails in the second storm costs more than doing it right once. See vinyl, poly or canvas for the details.
Watch for scams
Operation Blue Roof is free. FEMA warns that anyone asking for money to sign you up for it is not part of the program.
What storm wind does to a tarp
Hurricanes are rated on the Saffir-Simpson scale, which starts at Category 1 with sustained winds of 74 mph. The pressure moving air can exert grows with the square of its speed, q = ½ρv², so 74 mph wind carries about four times the pressure of a 37 mph wind: roughly 14 pounds per square foot. On a roof the worst load is often suction, not push. Wind flowing over the ridge and around the edges lowers the pressure on top of the roof, and the tarp is pulled up and away from it.
That's why battens work. A grommet concentrates the pull of a whole section of tarp onto a ring a little over an inch across. A batten spreads the same pull along several feet of wood and fabric, so the fabric doesn't tear and the fasteners don't pull through. It's also why a tarp has to be tight: every flap and ripple gives the wind a pocket to pull on.
Fasteners and the roof. Nails or screws through the batten go into the roof deck, so they leave holes. Space them along the batten, not just at the ends, and seal or patch the holes when the permanent repair is made. A roofer can tell you what's best for your roof type.
Sources
- FEMA, Operation Blue Roof fact sheet
- U.S. Army, "USACE installs 30,000th blue roof after Hurricane Ida"
- Florida Division of Emergency Management, Operation Blue Roof
- FEMA photo library: installing a blue roof after Hurricane Gustav (Wikimedia Commons)
- NOAA National Hurricane Center, Saffir-Simpson hurricane wind scale
- NASA Glenn Research Center, Beginner's Guide to Aeronautics: dynamic pressure
Written by the TrueTarps team. Questions about your job? Contact us or request a custom tarp.