Q: What is the best way to connect a deck railing to the posts? There are detailed instructions for how to connect railing posts to the rim joist to meet code. However, the attachment of the railing to the post can be the weakest link in the system. How should the railing be connected to the rail post to meet the code when force is applied to the railing? The post connection to the rim joist will meet code but the railing may break away from the connection to the railing post. Thanks, Larry
A: The building code and manufacturers of steel-connector are mainly concerned with the post-to-rim joist connection due to the leverage exerted over the length of the post, multiplying the force at that joint.
According to the International Residential Code (IRC), the railing assembly needs to resist the following loads:
- 125-pound uniform load applied horizontally or vertically to the railing
- 200-pound point load applied at the top of the post in any direction, or at mid-span along the railing
Engineers then apply a safety factor of 2.5 for testing, so these loads become 300 pounds and 500 pounds, respectively. It’s very hard to meet these load requirements without specialty hardware such as the Simpson DTT2Z (read more on steel connectors).
The connection of the top railing to the posts does not have the leverage effect, so it is mainly a shear connection resisted by the screws or nails into the tops of the posts.
The American Wood Council (AWC) publishes a prescriptive deck construction guide based on the IRC. The guide is accepted by many code officials as compliant with the code. A typical connection for the railing to post is shown in the diagram below. It uses a 2×6 or 5/4 top rail attached to each post top with three 3” screws or three 16d nails. Additional fasteners into the horizontal 2×4 would add additional strength.
Since these joints are rarely engineered, an authoritative prescriptive guide is often the most practical approach for a builder and likely to be accepted by the local inspector. Click here to download a copy of the most recent copy of Prescriptive Residential Wood Deck Construction Guide by the American Wood Council.
For the sturdiest railings, use the longest top rails you can find, with the fewest joints. One continuous railing is best, if possible. I typically reinforce all joints in the railing with galvanized steel strapping or angles. I typically use one or two straight straps at horizontal railing joints (on the edges or bottom of the 2×6 railing) and a corner angle on the outside edge of the railing at each corner. Where feasible, I also use a steel angle to tie the inside ends of the railing to the house wall framing. The steel straps add rigidity and help a lot over time when pressure-treated lumber starts to check and twist, which can loosen the railing connections.
Read more on Building Code-Compliant Deck Railings