It's been about two years since I first wrote about the lateral load anchor detail that was included in the 2009 International Residential Code (Structure, November 2009; deckmagazine.com). The relevant IRC section reads: The lateral load connection required by Section R502.2.2 shall be permitted to be in accordance with Figure R502.2.2.3. Hold-down tension devices shall be provided in not less than two locations per deck and each device shall have an allowable stress design capacity of not less than 1,500 lb.
In short, this means that decks attached to houses must be provided with a minimum of 3,000 pounds of lateral resistance to keep the deck from falling away from the house. The idea is to prevent the deck ledger from detaching from the band joist and also prevent the band joist from detaching from the house. The one detail shown in the code to achieve this - using two special tension anchors - isn't specifically required (Figure 1).
As a building inspector, I've worked under the 2009 IRC since it was adopted; however, no tension anchors have been installed in my jurisdiction during that time, and inspectors in other local jurisdictions say they haven't seen any either. Why aren't they being used? There are a few reasons, not the least of which is that the anchor detail isn't required - it's just one possible way to address lateral loads. Also, the 2009 IRC is a whopping huge book, with quite a few high-profile changes in it that have monopolized the attention of code professionals. (For example, residential fire sprinklers are now required for new construction, and the electrical codes call for tamper-resistant receptacles and arc fault protection.) And in truth, the mere addition of something to the code doesn't mean it'll be enforced; some things have been in the IRC for decades and still get no attention, such as treating the cut ends of pressure-treated lumber. Finally, deck failures that pull the band joist completely from a house aren't common enough in my area for regulators to push for enforcement of the lateral load requirement.
Regardless, the code is very clear that lateral load restraint must be provided.
Practicality of the Lateral Anchor Detail
Unfortunately, in all but new construction, the IRC's lateral anchor detail is often not feasible. For one, it requires access to floor framing inside. Also, the floor sheathing in the area of the anchor must be nailed 6 inches on-center. This creates an unreasonable situation when a deck is being added to an existing home, because the floor sheathing in most homes is nailed 12 inches on-center; in order for the code detail to be followed exactly as published, the floor covering will have to be removed for fasteners to be added. Assuming the deck is connected to a joist using tension anchors, would a deck failure really extract a floor joist lengthwise from a home if a few extra nails were not installed? I think not. That said, Simpson Strong-Tie (strongtie.com) does publish a detail of a way to attach an existing floor to the joists from below (Figure 2).