If you’re building a new house, you have a lot to think about as far as what building materials to use – everything from siding to windows & doors to kitchen cabinets. And when it comes to roofing, most homeowners are thinking about shingles or tile, not necessarily what lies beneath. Well, let me add one more thing to your list – roof trusses, the structure beneath your tile or shingles that will add visual interest and withstand snow and wind no matter what you cover it with.
What is a Truss?
So, what is a truss, you ask? A truss is a mechanical structure that distributes a load through the members of the structure. They are made up of linear members arranged in triangular sections. Some of the members carry tensile loads, and others carry compressive loads. (A tensile load is a “pulling force”, the only type of load that can be taken by a rope, for example; whereas a compressive load is a “pushing force”, the load on top of the truss.)
A truss can be used to span an open area without requiring central support. Trusses can be made from a wide variety of materials, depending on the needs of the particular application, and can be found in buildings, bridges and other structures.
How Roof Trusses Work
Trusses are usually made from wood in residential design and from steel in commercial building design. They take the shape of a triangle because of that shape’s natural ability to disperse pressure through its entire structure, which distributes the weight of the roof away from the exterior walls of the building, making it extremely stable and rigid.
Triangles are naturally rigid geometric shapes that resist being distorted when pushed on. In the upright position, a truss is rigid for the same reason. Regardless of its overall shape, all its chords and webs form triangles, or triangulate. (The top beams in a truss are called top chords and are generally in compression, the bottom beams are called bottom chords and are generally in tension, the interior beams are called webs, and the areas inside the webs are called panels.)
Stick-built roofs operate on the same principle, with rafters, ceiling joists, and collar ties forming the triangles. Under the weight of sheathing and roofing, a roof truss as a whole is stressed in bending. Its chords and webs, however, are stressed principally in either tension or compression. Top chords, which are in compression, push out at the heel and down at the peak. The bottom chord, firmly fastened to the top chords, is stretched in tension to resist the outward thrust. The result is a stable, self-balancing structure.
The Difference between Stick-Built and Truss-Framed Roofs
Roof framing has evolved throughout the years. Most residential roofs today are installed using prefabricated trusses, which are modular triangular frames that serve the same purpose as traditional “stick-built” rafters and joists. Stick framing, or board by board, is still used in some cases, although you might have a hard time finding a contractor who can do this, as it has become somewhat of a lost art since pre-built trusses came on the scene.
One important difference between stick-built and truss-framed roofs is that with “stick-built” roofs, ceiling joists rarely span the width of the building. Instead, they bear on interior partitions, as well as on exterior walls. Roof trusses, however, are almost always designed to bear only on exterior walls, with the webs connecting the top and bottom chords providing intermediate support. That’s why webs, depending on their location, are stressed in either tension or compression.
Traditional stick framing is made up of:
- Rafters: These angle up to form the peak.
- Joists: These run horizontally below the rafters to tie the walls together and form the framework for attic floors
- Ceiling: This is the level below the roof.
In this method each board is cut and put in place individually, with the entire framework being held together with a single ridge board or spine running through each pair of rafters. Needless to say, this method is more time consuming, and because of this, usually more costly, as well.
Trusses, on the other hand, are typically built off-site and can be installed rapidly, so that an entire roof can be framed and decked in less than half the time needed for traditional stick framing. Also, trusses are considered stronger than stick roofs, although the continuous roof beam does add some strength to a stick frame.
Roof Trusses: A Brief History
Pre-built roof trusses were introduced to the construction market in the 1960’s. They revolutionized the homebuilding industry over traditional rafter framing. Pre-built roof trusses are the predominant method to build a roof today because they are time-saving to install, convenient, readily available, and cost-effective.
Some say that since the invention of the 2×4 in the 1830’s, there has been no greater force for creating change and improvement in American construction than the building component manufacturing industry. The invention of the first metal truss connector plate in Florida in 1952 marked the beginning of the industry that in just over 5 decades has vastly changed home, apartment and commercial building construction. These changes benefit all who are involved in the construction chain, from the building designer, to the builder, to the residential or commercial building owner.
Assembling a Roof Truss
Here at the ProBuild Truss Plant on County Rd M off of Highway 145, for example, you wouldn’t believe the technology that goes into it – we use a computer program to create and test each truss design to make sure it meets building codes and can stand up to snow load and wind specifications, etc.
And that’s just the planning and design process! Then we take huge, industrial-size saws to cut timber at speeds that would make old-school lumberjacks and sawyers green with envy. Again, the saws can even be computer programmed to cut at certain angles, lengths, etc.
After that, a crew of about half a dozen are guided by overhead lasers to place everything on a steel bed that has a machine that comes and presses all the connector plates into the joints and splices of the truss at a consistency and pressure much greater than one man with a hammer could achieve.
It’s an impressive sight and I wish I could take you on a tour of our truss plant, but safety policies don’t allow it – I guess because of all the big saws that can chop you in half and machines that can flatten you like a pancake, it’s probably a good idea not to allow just anybody in there, don’t you think?
Advantages of Roof Truss Framing
Approximately 4 out of 5 newly built homes in the United States use roof truss framing. This is because there are several major advantages to using truss framing.
Here are a few reasons to use pre-built truss frames for your building project:
- The trusses eliminate the requirements of inside load bearing walls.
- They can span a lot longer distances than stick built roofs.
- Truss framing is less expensive compared to stick roof framing, due to the fact that they are usually made of shorter lengths of lumber and require less time to install on a building.
- They can be erected in one single day, which further reduces the amount of time the home is exposed to the weather.
- The trusses are created and certified by engineers in order to meet the building code and roof load requirements.
- Truss framing can be designed for almost any roof or ceiling combination in modern homes.
- Through the usage of roof truss framing, the general contractor is able to construct and build the home in such a way as to have more complex and sophisticated ceiling designs. This also adds a greater amount of accuracy and speed to the whole building process.
Although I can’t give you a tour of the truss plant, I can connect you with our talented truss designers and give you a price on your trusses. Feel free to come down to the ProBuild on County Road M and Highway 145 and ask for Derek, or give me a call at my number listed below.
Derek Alvarez sells pre-built roof trusses and building materials at ProBuild here in Cortez, Colorado. If you have any questions for Derek, you can contact him at 970-739-9911. *The views and opinions expressed are those of Derek Alvarez alone and do not necessarily represent the views of ProBuild.