Site Built Truss Engineering
PSE Consulting Engineers, Inc. offers structural analysis and design of site built lumber trusses. If you are looking for an alternative to utilizing a truss manufacturer, or you are needing a custom design that a truss manufacturer cannot design. Our experienced structural engineers can design lumber trusses of all types with efficiency and safety in mind.
Wood | Lumber Site-Built Trusses
Types of Trusses
There are many difference shapes, styles and sizes of lumber trusses. Each truss design is specific to the type of loading that it will encounter. Besides a regular shaped truss, some of the most popular truss styles include:
- Scissors Truss
- Sloped bottom chord allows for more ceiling height on the floor below sometimes used for vaulted ceilings.
- Polynesian Truss
- This dual pitched roof truss usually has two significantly different roof pitches from heel to peak.
- Cathedral Truss
- Mostly used to provide a partially vaulted ceiling.
- Gambrel Truss
- Usually used when designing barns and other like structures. Sometimes used when building an attic space.
- Attic Truss
- Used to provide storage space in attic. The important defining feature of this truss is that it uses a larger/heavier timber bottom cord to carry the applied loading.
Loads applied to Trusses
- Dead loads for:
- The roof.
- Bottom chord or attic
- Live load for:
- Roof live load per code.
- Attic load must include any load for:
- Mechanical and electrical loads.
- For Attic with any storage space, minimum 20 psf
- For livable space, minimum live load is 40 PSF
- For If the truss is a floor truss, live load is 40 PSF for residential, 50 psf for office space and 100 psf for commercial.
- Wind load per code
- Load combination using allowable Stress design per IBC
Gusset Plates and diagonal tension strapping components are used in conjunction with X-bracing in load-bearing shear wall assemblies to resist racking under wind and seismic loads. They are normally installed on both sides of the wall directly over the framing members and are easily covered with facing materials.
- Provides racking restraint
- Used in shear wall assemblies
- Resist uplift and shear forces
Steel Gusset Plates:
Roll On Plates:
Most steel gusset plates will be rolled on by the manufacturer to ensure proper installation. The only issue with this from a structural analysis side, is that we do not have values for how strong these plates are.
Simpson Strong-Tie Steel Plates:
These plates are similar to the size and shape of the roll on plates, but allow to be installed via nails. An engineer can look up the values for this plate and calculate a safe truss design.
Oriented Strand Board (OSB) or Plywood Gusset Plates:
OSB/Plywood Gusset plates are much more common when it comes to site built trusses. Sizing and calculating the OSB/Plywood gusset plate becomes easier as the values for OSB and Plywood can be found in the National Design Specification for Wood Construction. This type of site built truss design is our specialty here at PSE Consulting Engineers, Inc./Precision Structural Engineering. Our engineers will be sure to work with you and your needs to analyze and design the safest and most efficient lumber truss design possible.
Site Built Light Gauge Steel | Cold Formed Steel Trusses
PSE Consulting Engineers, Inc. offers structural analysis and design of site built light gauge steel/cold formed steel trusses. Similar to site built lumber trusses, your structure may require you to look into building your trusses on site with light gauge steel. Whether you are building your walls out of light gauge steel/cold formed steel and want to continue this with the roof structure, or the loads applied to the roof require a light gauge steel/cold formed steel design, our professionals can help.
Light Gauge Steel/cold formed steel Trusses provide structural sound options that can span up to 70’ depending on the depth of the steel, all while still considered economical. Similar to the configuration of trusses when using timber, all truss styles will be available when utilizing light gauge steel as well. Most light gauge steel/cold formed steel trusses are welded or screwed together depending on the type of connection needed.
Steel Trusses Vs Wood Trusses
Wood and Steel trusses alike are strong and very quick to install compared to rafters. It is important to choose the right material solution for your truss, specific to your project. There are many pros and cons to using steel trusses when compared to wood trusses.
- Longer Lasting
- Require less maintenance
- No need for chemical treatments
- More expensive
- More skill required to install