Enhancing Deck Stability with a Rolling Deck Girder
Today, we are looking at a structural failure in process st the deck of a contemporary row home, in a tract home development. More often, we’re working in the historic areas of Washington DC and/or the more original urban areas of the city, but this particular tract home happens to be similar to a few of the more modern developments within and in all of the areas surrounding the city.
Here, it’s an example of many residential single family home buildings, This particular row home has a deck built on the back of the house that leads from the kitchen on the inside of the house to an elevated outside space at the deck on the rear of the home.
If you look closely and the picture below, you can see that the deck is not built with very far from the adjacent building facade. The projection from the building, to the rearmost part of the deck is very limited, only about 6.5 foott in total. The projecting part of the deck is supported with a structural girder that runs perpendicular to the majority of the joist system.
A more common and typically proper method of framing this type of structural support system is to set a double joist, sistered together, into a nominal 6×6 post. The building code itself doesn’t specifically say that all similar types of installation have to have girder set into a shouldered position where they connect to the wooden support post. There are some specific requirements though that may make that a more optimal and effective type of installation. There are several problems with this particular installation, one of those very big problems is that there is not sufficient reinforcement to prevent this girder from rolling.
When a joist or girder has lateral force applied against it and that force destabilizes it from a vertical position and makes it start to tilt, that is referred to as rolling.
If you look closely, as shown in the picture below, you can see that this girder assembly is made with four individuals wooden joists. Those joists have been toenailed through the rim joist, down into the tops of the individual wooden members of the girder assembly, you can see these nails at the edge of the rim joist. This is not a sufficient method of attachment.
The next picture shows a different view from underneath of the deck and you can see here that they have not used hurricane clips or any other type of significant structural connection ties to connect each of the individual joists to the girder itself. In most cases, particularly in an application like this, that type of hardware is a minimum requirement.
The International Residential Building Code section 507.9 in several other sections and requirements of the code set out constraints for mechanical connections in lumber built building assemblies such as decks of this type, at the edge without cross blocking and without steel connecting hardware and additional fasteners is not sufficient.
Metal connectors and clips are specially made for this type of connection between the joists on top of the girder, As well though additional types of connectors you should be used for the connection between the post and the girder. Normally when shouldering, through bolt or other approved types of fastener should be used to connect these two types of elements because they both provide structural support in different or opposing directions. Proper structural supports are intended to stabilize and keep the deck together, even with seismic types of movement, high winds, and even uplift type forces.
When wind blows and moves over a structure, such as a deck, the wind flow creates lower pressure above the deck compared to underneath. This pressure differential can generate an upward force, effectively “pulling” the structure of the deck upward. The building code outline several requirements for structural ties and fasteners such as the ones described here to connect the girder to the underside of the joist to be used to prevent decks and specifically deck components from being pulled apart and lifted up into the air where they become a significant danger.
Use a contractor who understands and cares about doing things right. Always, feel free to reach out to us here at Dupont Decks and Patios. We are happy to help with almost all steps of the deck building and design process. A backyard and outdoor space should make a significant, positive impact on both quality of life and home value. We can help with more than just decks, we also build patios, pergolas, ramadas, awnings, gazebos, arbors, and privacy fences.
Let us know about your ideas and talk to us if you have questions about possibilities. We are happy to participate in improving your outdoor space and quality of life! You can call us at (202) 774-9128. You can find us online at https://dupontdeckspatiosdc.com and you can email us there as well at https://dupontdeckspatiosdc.com/contact-us
