How to Choose Roof Components for a Strong Roof

04/14/2023

Why do they matter?

In a high-wind event such as a hurricane or tornado, keeping the roof on your home is a top priority as is protecting it from wind-borne debris and hail. A resilient roof system will provide wind-resistance and impact-resistance when it counts the most.

What do I need to know?

The roof is the primary structural element of the house, transferring the loads that act on the walls facing the wind into the walls that are parallel to the wind. The roof structure includes framing and roof sheathing, which is covered by a roof covering that serves as a barrier to weather and keeps water from entering the structure.

Roof framing can be composed of either rafters cut from dimensional lumber, often called “conventional framing,” or engineered trusses. Either can provide a strong and secure means of framing a roof. Proper design and installation of roof framing is critical, including the connections of any roof elements by a mechanical means such as metal connectors.

The main structural components of the roof assembly include:

• Strong nailing of the roof deck to the framing, especially at the edges
• Connection of the roof to shear walls with blocking
• An unbroken double top plate on the shear walls that acts as a structural chord.

The connections between the roof and walls are crucial, including:

• Rafter at Ridge Board. Typical construction practices include cutting out a ridge vent in the roof decking to allow for air to flow freely from inside the attic. This free flow of air causes an unintended weakening of the roof diaphragm at a critical location because the ridge board serves at a boundary of the roof diaphragm. When the decking is cut away for the vent, the decking is no longer connected between the rafters. Installing a strap or straps will strengthen the connection between rafters allowing for roof venting at the ridge.
• Rafter at Top of Wall. Rafters attached to the top of a wall in a high-wind zone should be fastened to the top plates of the wall with more than just framing nails. Typically, metal connectors, straps, or clips, are specified to hold down the rafter. Eave blocking between the rafters in high winds does more than keep the birds out of the attic; it helps tie the roof diaphragm to the walls and keeps the rafters from rolling due to lateral loads.
• For Concrete Design, the top plate is anchored to solid concrete or grouted masonry.
• Truss at Top of Wall. When a truss attaches at the top of the wall, it is similar to a rafter in the hold-down connection. A metal strap or clip is specified to hold down the truss in the same way a rafter is held down, but the eave blocking detail is somewhat different. Most local building codes do not require full eave blocking when trusses are used for the roof structure; however, 2x4 blocks should be installed to help resist lateral loading.

Ensure the same strong roof design and connections are made throughout the house, including other areas such as porches, lanais, carports, and breezeways.

Where do I start?

• If you’re not ready to reroof, contact a home inspector or licensed roofer to evaluate your roof and identify any retrofit options such as installing additional metal connectors to secure the roof to the wall.
• If you’re ready to reroof, ask your roofer to include resilience upgrades such as installing a high-wind resistant roof covering, renailing the roof sheathing, and installing a secondary water barrier to seal the roof deck.

More Resources:

• FLASH. Resilient Design Guide: High Wind Wood Frame Construction Edition
• FLASH. Resilient Design Guide: Concrete Construction Edition