The current best-practice method for securing guardrail posts to the deck frame is to use tension-tie hardware that locks the posts to the deck joists. Alternatively, in late July 2015, Simpson Strong-Tie published an engineering letter showing four guard post blocking and screwing details that pass the 500-lb. concentrated load test called out in the ICC-ES AC273 criteria. The guardrail posts are attached to the deck frame using Simpson Strong-Tie's SDWS timber screws along with double joist blocks and 4x4 reinforcing blocks.

If you decide to use this detail, you'll need to follow the drawings closely - they depict the SDWS screw length at each location as well as the dimension off the top or bottom edges of the joist rim. The screw positions through one edge of a post are offset by 1/2-inch from those on the 90 degree edge, with the idea being they'll pass by each other without conflict. To ensure the screws don't drive into each other, you'll need to make sure that the screws are oriented so that they are perfectly level.

Table 1 in the letter lists the number and length of each SDWS Timber screw needed for each post to frame configuration. This will make it easy to tally up your screw order for a deck without referring back to the drawings. Only two screw lengths are needed to complete the details - 5 inches and 8 inches.

For many deck builders who are already using blocks and screws to secure their deck posts, the Simpson Strong-Tie details won't be a big change to their regular configurations, but ones they can feel confident that there's some testing behind. Still, if you're planning on using this detail, you should run the engineering letter by the local building official to make sure he will accept the system.