New Requirements to Resist Lateral Loads
Let’s say you own a house with a finished basement and no deck. Let’s say you’d like to add a deck by attaching it to your house using a ledger board. Well, depending on where you live, your job may have just gotten significantly more difficult.
Changes to International Residential Code for projects where decks are supported by an adjacent structure (your house), now require a “positive attachment” to resist lateral loads. That positive attachment is a new piece of hardware called a hold-down device “with an allowable stress design capacity of not less than 1,500 pounds”, which must be installed on at least two locations per deck (IRC 2012 Section R507.2.3).
These new hold-down devices must be attached to the joists of the deck, penetrate through the ledger board, the wall sheathing and band joist of the house, and then fasten to the floor framing inside the house.
So, if your home has finished walls, ceiling, cabinets, etc., blocking access to the home’s floor framing, then to satisfy the new code requirements you’ll need to deconstruct the interior to gain access. Naturally, this code change requires more labor, hardware and expense to building a new deck, and in some circumstances it may result in even further cost increases to the project, because the homeowner will need to repair the disturbed interior living space.
The change in code was spurred by deck failures caused by ledgers that pull away from the house structure, resulting in complete collapse. These problems are generally due to improper flashing and/or improper fastening that lead to water accumulation and rot at the ledger connection, weakening the structural integrity.
When properly protected with flashing, a bolted ledger-to-rim board connection—or a connection fastened with properly spaced and staggered wood structural screws—is a suitable connection to support the gravity load of a deck. However, the new hold-down devices are required to resist lateral loads, as required by your local building code. In such a case, the devices should be used to tie the deck joists directly to the house joists.
Whether or not the code change applies to your project depends on whether your muni-cipality has adopted the IRC’s code change. Deck construction must always conform to local building codes and may also require a building permit. In general, building codes are developed by industry associations “to provide minimum safety standards for a home’s occupants, the environment and the public at large.”The codes are adopted and enforced by local governments and vary based on local political issues, environmental regulations, etc. Check with your local building inspector to determine all local requirements.
If your local code requires installation of the hold-down devices, you have a couple of hardware options.
The lateral-load connection from Simpson Strong-Tie consists of two DTT2Z Deck Tension Ties—one screwed to the deck joist, the other to the house joist. Access is drilled through the ledger connection to allow passage of a rigid threaded rod that connects the two ties. This is a sturdy connection that meets the new code requirement and works well for deck joists that align with the house joists.
However, deck joists don’t always line up with the house joists, and the Deck Harness from GRK Fasteners has the advantage of flexibility. By utilizing a chain instead of a rigid rod, it’s much easier to adjust placement of the GRK anchors, enabling connection to offset joists, perpendicular joists or to wood blocking. The Deck Harness consists of a steel chain-linked assembly with a thermoplastic plug in the center that installs through the ledger connection. One end of the Deck Harness is attached to the house floor joist with a U-bolt and washer plate. The other end of the Deck Harness is attached to the deck joist with identical U-bolt and washer plate. The GRK Deck Harness is recognized in the ICC (International Code Council) Report ESR-3224.
The other advantage of GRK’s system is that the insulated plug prevents moisture and frost from building up on cold steel and causing a rot problem where the device enters the house. Rotting of the ledger is one of the problems with deck collapses, and the very reason for an additional support to hold the deck up.
In the event of deck failure and the deck separates from the house, these new lateral hold-down devices prevent it from completely collapsing.
Learn more about the deck ledger fastening options at www.grkfasteners.com and www.strongtie.com.