The integrity of a home’s roof and its ability to withstand high winds is only as strong as the weakest link in its construction. Hurricane ties are one of the most commonly specified roof fasteners for new home construction, especially for homes in the coastal regions of the Southeastern United States. Hurricane ties play a critical role in the building’s resistance to both uplifting forces and lateral forces caused by hurricanes and severe storms. Hurricane ties play such a role by providing a path for uplifting and lateral loads to travel from the roof down to the foundation of a building. This allows strong forces to be distributed throughout the entire building’s structure, rather than just the roof. In this post, we dive deeper into hurricane ties, what they are, how they work, and important factors to consider to ensure you have all the information necessary for your project.
What Are Hurricane Ties?
Hurricane ties (also known as hurricane clips or straps, rafter ties, or truss ties) are metal fasteners used in construction that connect the rafters or beams of the roof structure to the wall structure of the building. Often made from stainless or galvanized steel, these specially designed fasteners help buildings resist strong upwards forces that result from hurricanes and severe storms – forces that could lift the roof off a building and cause catastrophic damage. However, hurricane ties are also used in regions with high seismic activity and can provide additional support to a building’s structure during an earthquake. By connecting the rafters to the wall structure, which itself is attached to the foundation, forces are distributed throughout the entire building’s structure rather than just the roof. This enables a far more robust structure capable of withstanding even the strongest storms or earthquakes.
How Do Hurricane Ties Work?
Oftentimes jointed connections are only as strong as the fasteners used to hold components together. During strong winds, many joints and connections at the roof of a structure will be subjected to exceptionally high shear forces. Screws are notoriously weak and break easily when excessively high shear forces are applied. This is due to stress concentrations that develop on the threads when shearing occurs. If you take a cross-section of a screw, the threads form a sawtooth pattern with several sharp corners. Shear stresses concentrate in these sharp corners and inevitably break the screw.
On the other hand, nails are much stronger in shear and preferred in framing due to having a smooth shank body that doesn’t concentrate stresses. Nails are also much more resistant to bending than screws for the same reason. This makes nails ideal for mounting hurricane ties over screws to secure members.
By fixing the roof trusses and the walls together, forces applied to one component will be distributed to the other components – depending on the location and direction of the load. Since wall components are fixed to the foundation of a building, using hurricane ties essentially fixes all components to the foundation.
How to Install Hurricane Ties?
Proper installation of hurricane ties is crucial to successfully protect a building against strong winds and earthquakes. In general, hurricane ties fasten together the angled trusses that form the roof and the horizontal wall plate of the wall structure. The angle and positioning of the trusses in relation to the wall plate, as well as the dimension of the beams, determine the type of hurricane tie that is used. Some hurricane ties join two components (the trusses and wall plate) while others join three (trusses, wall plate, and vertical wall beams).
In new construction, installation of hurricane ties is straightforward and can be completed before any drywall or shingles go up. However, installing hurricane ties on existing construction is more nuanced. Listed below are the 4 steps to installing hurricane ties on an existing structure:
- Examine your Roof – Climb into the attic and count each angled beam that forms the roof structure. Measure the cross-section dimensions and thicknesses of both the trusses and the horizontal beams to determine which size hurricane ties are needed. Purchase a sufficient amount of ties.
- Mark and Position the Hurricane Ties – Place your purchased ties in the locations where they will mate with the trusses and horizontal beams. Mark on the wooden components where nails will be driven through the holes of the hurricane tie. Orient the hurricane tie correctly based on the type of tie you are using. More on this is below.
- Secure the Hurricane Ties to the Structure – Secure the tie to the horizontal beams first, in the locations you marked previously, then to the trusses. Ensure you use nails that are sufficient length, as shorter nails will negatively affect the structural integrity of the beams. A length of at least 2.5” is generally recommended. Additionally, ensure the nails are the same material as the tie. Dissimilar material nails and ties will cause galvanic corrosion in the components and compromise structural integrity. Refer to a galvanic corrosion chart and check the compatibility of your nail and tie if they are dissimilar materials.
- Verify your work – Ensure all components are sturdy and not loose. Ascertain that all holes of the tie contain a nail. A single missing nail is enough to compromise a joint.
Important Factors to Consider Before Your Purchase
Purchasing hurricane ties is as easy as finding a tie that exceeds the uplift force rating of a roof’s trusses, right? Wrong. Picking the right hurricane tie requires careful consideration. Picking the wrong tie can be detrimental in the event of a storm. Aside from picking a properly sized tie, pay special attention to these points before your purchase:
Selecting a hurricane tie that is capable of withstanding a certain uplift force is simply not enough. There are several loads that are applied simultaneously to buildings during a storm. Often a tie’s ability to resist uplift is limited by the lateral forces that are simultaneously applied. Therefore it’s important to consider all loads, not just uplift. You must also factor in dead weight (the weight of the roof itself and associated components) and live weight (the weight of environmental factors such as snow, plant debris, etc.) If a single tie at a connection is not sufficient to handle the applied loads, use multiple ties if possible.
Roof and Wall Framing
While most roofs and walls are square and aligned with one another, some are not. If roofs and walls are indeed square, consider using the same type of hurricane tie, such as an H2 style tie. This will help simplify both load paths and the installation of hurricane ties. If roofs and walls are not aligned, you may be still be able to use multiple H2.5 style ties to simplify installation. Failing that, it may be necessary to use multiple types of hurricane ties.1
Hurricane ties are a true lifesaver for both homes and people in coastal regions susceptible to hurricanes and heavy storms. Contact an Albany County Fasteners sales representative today to discuss which hurricane tie is right for your project.