What is the difference between a toe nail, clip, single wrap, and double wrap for the wind mitigation form?
Thursday, July 26, 2018
The reduction on the windstorm portion of your homeowner’s insurance that is allowed for a strong roof-to-wall attachment averages 35%, and is the largest discount for many homeowners. It is exceeded only by the discount for a hip roof (sloped on all sides), which averages 47%. As part of explaining each category of connector, we will show the actual text in the Florida wind mitigation form, outlined in yellow, and include an illustration of each one. If there are several different types of connectors, which would occur when an older house has had a more recent addition, the weakest connection is required to be used for the form.
“Toe Nails” is the way a roof structure was secured to the walls until around the 1960s, and it is nails driven diagonally through the side of the roof truss/rafter into the top plate of the wall. In an older masonry house, the truss/rafter may be toe nailed to a wood plate that is bolted to the tie beam at the top of wall.
There is only a tiny discount for toe nailing. The reason it has a low rating is that it is just nails, and they are approximately aligned with uplift force on the roof framing caused by a hurricane (in withdrawal). They offer little resistance, and the nails simply pull out under uplift. The higher-rated connectors are metal plates that are secured with nails that are are perpendicular to the uplift force (in shear).
Also, higher rated connectors that are not nailed to the truss/rafter with a minimum of three nails, or are offset so far as to reduce their structural effectiveness, are kicked back to the Toe Nails level. The nailing of the connector to the wall below is not required to be inspected because it is typically not visible when construction is completed.
The photo below shows a strap with only two nails securing it to the truss, so it will be dropped back to the toe nails level discount.
The first level that receives a worthwhile discount is “Clips,” and a photo of one is shown at the top of this page, and also an illustration below.
And here’s an example of an incorrectly installed clip that will also get kicked back to the toenail discount level because the nails connecting to the truss to the top plate of the wall are in withdrawal. The bottom of the clip should be positioned at the side of the top plate, so the nails are in shear.
Next is “Single Wraps,” a strap that goes over the top of the truss/rafter and down the other side, secured with a minimum of two nails in front and one more on the back of the wrap. A Single Wrap that is not nailed properly gets dropped back to Clips level if it has three nails on the front side.
The best tie-down discount is for “Double Wraps,” which is either one Single Wrap on each side of the truss/rafter or a single metal connector, like the one shown below, that is secured with a minimum of three nails on each side; however, we rarely see double wraps.
The inspector is required to include a photograph of the metal connector observed as part of the submission of the Wind Mitigation Form, which is formally known as “OIR-B1-1802.”
To learn more about how to make your home more hurricane resistant, click below to download a pdf of the booklet “Make Mitigation Happen,” by the Florida Division of Emergency Management.
Also, see our blog posts How do I get the hip roof discount for my homeowners windstorm insurance? and What are the different roof deck attachment discount categories for a wind mitigation inspection?
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