Q: I’ve never worked with metal joist hangers. When I hold one in my hand, I question whether it’s actually strong enough to support all the weight that will be resting on it. Are they safe? Are there any best practices when it comes to using them, both indoors and outdoors on decks? What about the beams that joist hangers are attached to, or the support posts?
A: Joist hangers are safe, if they’re installed correctly. You typically need to hang a joist if the top of the joist needs to be on the same plane as the beam that supports it. There are all sorts of reasons and conditions where this is necessary.
To start, I recommend finding the actual installation instructions from the manufacturer of your joist hanger, and installing it by the book. You can also get general information about joist hangers and other metal structural connectors from manufacturers such as Simpson Strong-Tie.
The best way to attach your joist hangers to the beam is by using structural screws or bolts. You can buy structural nails that are rated for the weight, but trust me, structural screws or bolts are far better. If you’re using an impact driver tool, be careful not to overdrive the fastener, which will strip out the wood.
It’s extremely important that you use the correct joist hangers or other metal connectors, along with fasteners that are rated for outdoor use. Modern treated lumber has a higher copper content, and when copper gets wet and comes into contact with the galvanized metal connectors and fasteners, it can corrode the metal.
Beam sizing should only be done by a registered structural engineer. Sizing is complex because there can be concentrated loads on beams. The type of material used for the beam makes a huge difference.
The posts and columns that support beams are just as important. Once again, an engineer can specify exactly what to do and what to use. The material used for the post or column is a key consideration. I recently walked through a new home being built near my home and saw a massive beam in a garage supported by regular lumber. I’d be more inclined to install treated lumber to support a beam in a garage, where water and insects have a better chance of coming in contact with lumber.
Keep in mind that hollow steel round or square columns used to support beams can fail in a residential fire. Steel can’t easily burn, but once it gets hot it can bend and twist. Most engineers specify that hollow steel columns or posts be filled with dry sand to prevent failure in a fire. It takes a bit of work to do this, but it’s worth it.
Tim Carter has worked as a home-improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.