Although truss-designed roofs are predominant throughout most of the residential construction industry, there are regions where building with stick-frame roofs is still common. In this post, Randy Shackelford discusses some design choices available to stick-frame builders, the challenges they pose, and the solutions offered by the Simpson Strong-Tie® connector system for stick-frame roofing. The post will also discuss some changes in the 2021 IRC that affect construction of stick-frame roofs.
When our company is considering a new or improved product, we like to start out by talking to our customers first. That’s what we did recently with a connector improvement project for attaching jack rafter hangers in roof framing – and we got lots of feedback!
We heard from installers that they really wanted a hanger that could be easily adjusted in the field for different slopes and skews. We were asked whether we could design a hanger that could be installed after the rafters were already tacked into place to support construction sequencing and retrofit applications. Also, having a hanger that could be installed from one side was a popular time-saving request.
Our Engineering innovation team took all this feedback and closely evaluated our current selection of hangers. After much consideration, the team decided that rather than adapt one of our existing hangers, they would try to come up with an all-new design that would satisfy our customers’ most pressing needs.
After months of designing and testing prototypes in the lab and in field trials, the answer was yes. The result is our new LSSJ field-adjustable jack hanger. It’s an innovative field-slopeable and field-skewable hanger that features a versatile hinged seat. This new design allows it to be adjusted to typical rafter slopes, with a max slope of 12:12 up or down.
What is a jack hanger and why does it provide a better connection than nails alone?
There are two basic types of wood roof construction: framed roof construction (stick framing) as shown above, and truss assembly. The main difference is that stick assembly takes place onsite, while trusses are prefabricated and ready to place. In the United States, the number of truss-built roofs versus stick-frame roofs is about two to one. The LSSJ jack hanger is used for stick-frame construction and provides a connection between the jack rafter to either the hip rafter or the valley rafter as shown below.
Connecting a 2X jack rafter to a hip is hardly new. The hardest thing is making a good compound miter cut – something an experienced framer can figure out (and most engineers marvel at). In many parts of the country, these are simply face-nailed into place. Often there isn’t a lot of engineering that goes into that connection. However, a closer look raises a couple of questions.
Random Nail Placement
Where exactly are those nails going? When there’s no seat support for the rafter, the allowable shear is reduced per the NDS depending on where the lowest nail on the rafter is. This is based on the split that develops at the lowest fastener. The LSSJ provides a partial seat which not only meets the bearing requirement of section R802.6 of the IRC but also delays the type of splitting found in a nailed-only connection.
Consistent Nail Placement
The LSSJ conforms to the bottom of the jack rafter slope and ensures consistent nail placement on both the rafter and the hip. Consistent nail placement promotes consistent performance based on testing (or as consistent as wood gets)! The highest nail on the hip is located near the neutral axis if the hip is one size deeper than the rafter. This assures that not all the load is focused at the bottom of the hip.
A Closer Look at the LSSJ Jack Hanger
Some of our customers may be familiar with our current product, the LSSU, which is used for the same connection. Here’s a closer look at the improvements that the LSSJ offers.
You can see the differences and improvements just by looking at these hangers, installations and load tables. Here’s a different way of showing the advances and benefits of the LSSJ:
One of the greatest improvements is the fact that there are fewer nails to install in the LSSJ, and the loads are very similar if not better.
In addition to the LSSJ, Simpson Strong-Tie offers a full line of connectors for wood-framed sloped roofs, including:
We look forward to hearing from you about our newest innovation. For more information about the LSSJ hanger, please see strongtie.com.