Retrofitting Your House for Hurricanes: Walls and Structural Concerns
Walls must withstand a lot of pressure from a hurricane, not only from the sheer sideways forces of the wind, but also the uplift pressure put on them from the roof.
There are many considerations when you’re examining and reinforcing your walls:
Types of Walls
Concrete (masonry) walls are very strong against compressing forces, but crack under tension. Steel can help concrete hold up under tension forces. The process of retrofitting a concrete home is not discussed here, because the process is extremely involved and not cost-effective for homeowners. Almost all newer concrete homes in hurricane areas are built up to code reinforced with steel, but if you are unsure, you can research your home’s construction.
Wooden frame walls are more common, and when built correctly, can be very effective structurally.
The key to a strong home is a continuous load path. So what is a load path?
The ability of a wall to stand up to pressure is called a load. You can measure a wall’s (or an area’s) load by how many pounds per square foot (psf) of force it can hold. The upward pull of forces on the roof, if properly connected to the house, can be offset by the weight and strength of the rest of the structure.
It’s helpful to work on retrofitting the walls from the top of the home downward. The roof’s uplift pull begins at the roof connecting point, and each lower area that is reinforced adds to the total strength of that starting point’s power. (Skipping down leaves a gap, meaning the upper and lower parts are separated instead of working together.)
The first point to consider in reinforcing the structure is the connection to the walls to the roof. Losing the roof is the number one way your walls can be left vulnerable, because being firmly attached to the roof keeps them from bending or falling over.
You can upgrade your wall-to-roof connections easily. Special hurricane straps and clips are designed to help strengthen the connecting point between the roof and the walls. The most important areas to reinforce are the corners of the home and gable ends.
Evaluating: You can usually visually examine the connection points yourself to see if there are straps or clips already installed. Older homes only use nails, or clips on every other rafter or truss. You’ll want to check and be sure every rafter is strapped or clipped down.
Installation: To install straps and clips, you may only need to go outside to remove the soffits (if you have any), which are the flat surface below your roof’s overhang, so you can reach the roof’s connecting points. They can be made from many materials, so removal will depend on the type of soffit you have, but it helps to number them so you can keep them in order when you replace them.
You will also want to remove any protective layers (if you have any) on the top exterior of the wall, so you can fasten the straps directly to the wall frame. Even some materials that seem sturdy, like bricks, are usually not attached firmly to the home. So if wall coverings are like that, you’ll want to remove a strip of them to expose the wall frame along the top. (Sometimes, they are not installed all the way to the top, anyway.)
You may also need to expose the top of the wall, which can be done by removing the sheathing on the rooftop around the perimeter so you access the connection from above.
The actual strength of a normal wall is pretty minimal, even though they are large and take up a lot of surface area. They can be reinforced with plywood or OSB panels, but it’s an intensive process, usually most conveniently done when you are re-siding a home.
It is also difficult to tell if your walls are built to withstand a hurricane or not without begin able to inspect its construction. If other elements in your home have not been hurricane-proofed, that might be a good indicator. You can also drill a hole to inspect the wall.
Connections Across Floors
In a 2-story home, you have to consider the floor connections between the roof and foundation. Taller homes endure stronger winds and more force during a hurricane, so maintaining your load path is more crucial.
But, it is very difficult to check the floor security without performing major construction on the home. If you aren’t sure about your floors in a multi-story home, it becomes even more important to secure your roof connections.
If you are questioning your home’s floor connections, and if you don’t have the time or money to undertake the major retrofitting project, put more importance on evacuating in case of an emergency. Strengthening your roof connection will hopefully provide sufficient reinforcement, however, it’s much better to take the extra caution to be safe in case it’s not enough.
A home firmly attached to its foundation will transfer the load of the roof’s uplift forces through the foundation, adding the stability of the foundation to the home’s overall strength.
It is difficult to check in any home, and nearly impossible to check when there are concrete walls. In a wood-frame home, you are looking for the sill plate, which sits directly atop the foundation wall. The wall studs of your home should be attached to the sill plate with special metal clips, which you can buy. To know how to space your clips, you’ll need an engineer to assess the potential force on your home.
If you need to (and can) install clips, you must drill a hole through the sill plate, as close to the center as you can possibly get it. Clean the hole, then use an epoxy anchor to install the clip. An epoxy anchor is an adhesive system that uses a filler liquid in the hole. Then, you slide in a bar, and the epoxy dries around a bar to hold it in place.
When in doubt, call a contractor to assess your home’s ability to withstand a hurricane.
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