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® three-connector system for stick-frame roofing.
There are two common ways of framing the roof of a house: with premanufactured trusses, or with rafters and ceiling joists, commonly called stick framing. While truss roofs are the most popular construction style today — by some estimates, truss roofs outnumber stick-frame roofs two to one— there are regions of the country where builders still prefer stick-frame roofing. There are several reasons for this. One of the most common is that with a site-built roof, it’s easier to customize the roofline. Builders sometimes also prefer this construction method when they want to provide a large attic space or high, vaulted ceilings (often called cathedral ceilings).
However, constructing a stick-framed roof is not always easy. For example, in Texas where stick framing is common, there are entire crews specializing only in framing roofs. Whether it’s because of the growing size of houses, or because roofs are getting more complicated, the code requirements for stick framing roofs have become more complex over the years, too. Meeting current IRC roof framing requirements means builders are really constructing very simple triangles using the rafters and ceiling joists, because triangles are known to be the most stable shape. In order to maintain the triangle shape, there are specific requirements for how to fasten the corners of the triangle together. Most importantly, the bottom of each triangle (the ceiling joists), must be fastened securely to the rafters on each end and must continue across the entire width of the ceiling so they keep the ends of the rafters from spreading out when loaded. (See illustration.)
Also because of this triangle shape, the connection of rafters to the ridge board is easy because all the weight of the roof is assumed to transfer down to the bearing at the top plate. That’s why the ridge board is nonstructural and can consist of 1x lumber.
However, there are a couple of cases where the bottom leg of the triangles (the ceiling joists) might not be present or might not connect rafters together. The first case is when the ceiling joists are oriented perpendicular to the rafters. The other common case is the cathedral or vaulted ceiling.
The load-resisting concepts of the vaulted ceiling are completely different. Without the tie at the bottom, the rafters must be supported at their upper end to prevent the rafter thrust at the lower end. Since half the load is now supported at the ridge, the ridge member becomes a ridge beam that is a load-carrying element, and must be designed to bridge the span between the supports, which carry the vertical load to the ground. This requires a secure connection of the rafters to the ridge beam at the top.
Furthermore, if the vaulted roof is constructed as a hip roof, things get even more complicated. Not only must the ridge beam be supported, but the top ends of the hips must also be supported. And the rafters must have a secure connection to the hips.
Simpson Strong-Tie recently developed three products that can greatly simplify the construction of these types of roofs. They’re designed to provide strong, simple connections at three points of the roof that often don’t get the structural reinforcement they deserve.
Rafter-to-Hip or Rafter-to-Valley Connections
The LSSJ field-adjustable jack hanger is the ideal hanger for connecting jack rafters to hip or valley members. The LSSJ is designed with a versatile, hinged seat allowing for easy field adjustment to typical rafter slopes, from 0:12 of 12:12. It’s manufactured with a 45° skew, making it ready to place for the most typical rafter conditions, but it can be field-adjusted for lesser skews. Best of all, it can be installed after the jack rafter is temporarily fastened in place. Note that the LSSJ is available in both right and left skews to cover all the applications.
The LRUZ rafter hanger is an economical sloped hanger for rafter-to-ridge connections. Used with solid sawn rafters, the LRUZ’s design enables the hanger to be installed either before or after the rafter is in place. The field-adjustable seat helps improve job efficiency by eliminating mismatched angles in the field and lead times associated with special orders. The LRUZ offers a load capacity comparable to or better than other rafter hangers’ capacities at a reduced cost while requiring fewer fasteners.
The HHRC hip-ridge connector is a heavy, field-slopeable connector that attaches hip and other roof beams to the end of a ridge beam. It accommodates higher loads and uses Simpson Strong-Tie® Strong-Drive® SD Connector screws.
Used in combination, these new connectors make it astonishingly easy to build strong roofs without relying on premanufactured trusses.