Intro: Emergency Hurricane Roof Reinforcement
If you face a hurricane approaching with little warning, here is a solution to hold your roof in place. The approach here is for houses that are have a sound wall structure but have a badly secured roof or one with overhangs that can catch the wind. Taking the steps outlined here can reduce the upward force on overhangs and the many forces on roof gables that can cause a roof to buckle or lift off.
Steps described here may not be needed for a category 1 storm, but may be important to keeping your roof intact in a storm that could peak with "strong Cat 2" or higher winds. The threshold for roof damage will depend on the construction of your home.
This guide does is unikely to help in the rare case that your home is directly exposed to high "Cat 4" or "Cat 5" winds. It also cannot help if a building is undermined by storm surge. So always evacuate to a stronger structure if one is available to you even after completing the steps in this guide.
1) This modification requires drilling in your home and the holes created must be filled after removal.
2) The concrete reinforcement suggested here is designed to be removable. Depending on the building codes in your neighborhood and country, you could choose to leave it on (if it does not cause water/ice dams). Weather conditions could determine whether you decide to remove before the concrete fully cures, or whether you leave it on until the end of hurricane season.
Step 1: Needed Tools and Materials (depends on Roof Size)
1. two to six sheets of plywood, 3/4" or greater, 4x8 feet, and a circular saw
2. 200 to 500 construction screws with special bit for drill, 2 1/2" in length
3. 20 to 50 lag bolts, 1/4" x 4", with 1/4 inch bit for predrilling, and ratchet
4. one extra sheet of 1" plywood or 3 16-foot pieces of 2x8 framing lumber
5. Access to sand (preferably) or dirt, no more than 1/2 yard for medium sized house
6. 20 forty-pound bags of concrete (for around 24 feet of roof, could be less or more)
7. Two 5-gallon buckets and one ladder
Approximate Cost: $200-500 (USD) excluding cost of tools.
Step 2: Cover Up/ Reinforce Gables and Their Overhangs
If your gables have an overhang that can catch the wind, cover it up so that wind will not catch it like a sail. Wind hits the gables at a 90 degree angle, so they see a lot of force. It will be necessary to put strips of 2x4 or 2x6 or behind these at the points where pieces of plywood must be nailed. Fasten with lots of screws (including some 1/4" lag bolts) for easy removal after the storm. This smooths out your gable from the wind. Important: leave around 9 inches of vertical overhang on top of the end of your roof, where the gutters would be if you have them.
In the interior of the house, diagonal bracing that is screwed down at each vertical attic support and at the attic floor can make a roof stronger. According to FEMA, "roof failures, especially in unbraced gable roofs, are a common cause of major damage to structures and their contents in high winds."
also see http://articles.extension.org/pages/13871/preventi...
Step 3: Add an Edge Strip Cover the End of Your Roof
This can be placed just above the gutters if you have them. It needs to be attached well enough to hold the weight of some sandbags (see next step). Cut it at 90 degrees so that it butts against the plywood overhang described at the end of step 1. The goal is to place it seven to nine inches elevation above your existing roof to later add significant ballast material to the edge of your roof. Make a decision based on time you have available, and the ability of your walls to support the ballast (concrete walls should support this weight with no problem).
Use 2x10 lumber or cut a long strip of plywood (up to 1" thick is best) to be around seven to nine inches tall.
Step 4: Fill Part of the New Gutter You Created With Sand Bags.
At this point your roof is still unstable. The gap (gutter) created by the new end board must be filled with ballast.
To preserve your roof for future maintenance or replacement, a layer of plastic must be placed into this gutter. To do this fill a few dozen grocery bags 20 to 25% full with sand. This will cover up the air gaps at the bottom and protect any shingles if you have them (however few shingles can stand actual cat4 winds). Kids can add sand to the bags with sand and tie them. Then they can be layered into the bottom of the new gutter, to make a level surface about 3 inches below the lip of the board you added at the end of your roof. These bags then have to be covered so they are not ripped up by wind.
Step 5: Pour Concrete on Top of the Sand Bags.
Concrete will add weight to your house. (Disclaimer: this instructable will not protect your house if the walls are weak.) Starting on the side of the house expected to get the most wind, mix concrete in 5 gallon buckets, about 3-4 buckets per bag to the consistency of thick pancake mix. As it starts to harden pour on top of your sandbags. (For added strength place pieces of chicken wire fence or scrap metal on top of the sandbags.) Cover the thin plastic sandbags completely and fill just above the lip of the end board. Make a tiny slope above your overhang so the water can still run off of your roof, about 15 minutes after pouring each batch while it is still workable.
Step 6: Cover Up Other Vulnerable Spots
The other thing that can be done to reduce roof liftoff is to place a heavy housewrap style material over the overhangs around the entire building and staple it securely so that when wind travels up to the overhang, it is guided away from the inside corner of the overhang.
The photo above shows such a building wrap, partially installed. Material used could be whatever is at hand; housewrap folded over twice, a pool liner, etc. The picture above shows how plastic (i.e. 20mil or 3 sheets of 6 mil glued together) can be stapled and drawn taut in order to allow air to flow more easily past your house in extreme winds. If a stapler is not able to penetrate the siding it may be better to nail strapping or plywood strips to the bottom or top edge of the wrap material. Try to maintain a slope greater than 45% to reduce the lift on the house.
Other methods that have been used to keep a house standing in a hurricane are "hurricane straps", i.e. large straps that go over the roof and are bolted to the ground on opposite sides of the house, and guy wires (more difficult) which can be installed as they would be put in place to hold up a telephone poll. (These may be difficult to come by on short notice if you don't already have them.)
Step 7: When the Storm Is Over...
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The concrete can be left in place but if you do that, give it a little more than 2 days to cure before unscrewing the wooden forms.
Keep in mind that this instructable applies in only certain situations. It is designed to limit roof tear off but will not help you if your structure cannot withstand strong winds. If you know people whose basic building structure can can benefit from this, please share on social media. If you have access to a shelter with good roof that is out of storm surge danger, always go there rather than remain in your home, even if you reinforced your roof.