Some of the most tragic deck accidents occur because of the failure of the deck-to-house connection.
This is one area of code that is changing quite literally as we speak, and they are getting serious. Lateral and various dynamic loads can easily cause a deck to want to “pull away” from the house. As we learned in the blog post about railings and band-joists, nails don’t to a whole heck of a lot in resisting those forces. Screws, of course, are somewhat better, (depending on your choice of screw, which I want to also cover soon in a future blog). However, the ability of a nail to resist pullout forces is limited, especially into endgrain as it is here with a bandjoist-to-floor-joist connection.
Of course, through bolting is pretty good usually, but in this case they are finding examples of ledgers through-bolted to the house band-joist, that fail because the band-joist actually pulls away from the floor joists, as though the sheathing wasn’t even there. This is a situation similar to the problem we discussed in our previous post about railing connections. Using a longer structural screw such as the Ledger-lok or Timber-lok screw into the floor joists could work better, but you risk splitting and damaging the end-grain of the joists if you miss or hit a knot.
Once again, as in our previous post, the DTT2Z Hold-down is a Horizontal application that will create a solid Deck-to-House Lateral Load Connection. Two of these hold-downs per length of band joist will ensure a solid connection that will effectively sandwich the band-joist and deck ledger, between the deck joist system and the house floor joist system.
These hold-downs are derived from the hardware used to hold houses to foundations in seismic zones, and are fairly painless to install.
Remember, these failures have the potential to do the most damage. In 1995, over 100 people were injured when a deck collapsed at a Grateful Dead after-party in Wisconsin.
Tom, in our office, tells of a professor he had who told him one time, (perhaps more than one time actually) that when a Doctor makes a mistake, usually there is one victim. When an engineer/designer/carpenter makes a mistake, there could be a hundred casualties, so it behooves us to be extra vigilant and to make Safety our #1 design parameter.
If you are considering building a deck soon, or are interested in making sure your existing deck is up to par, call us at Nolan Engineering. We offer inspection, design and engineering services that will let you rest assured your deck is safe.