Information we need to design and manufacture an order of trusses

  • Geometry
  • Location and size of all points of bearing
  • Center-to-center spacing of trusses
  • Design loads
  • Special conditions

Canadian Customers:
We can design trusses with British Columbia stamp approval as well!
We can work directly with you or through a broker for delivery

A Discussion Of Each Item Follows:

Furnish span (out-to-out of bearings, plus cantilevers, if any), slope, overhang conditions, etc., that form the profiles or external geometry of the trusses. Web configuration need not be furnished, as it is determined by the overall truss design. Also furnish any minimum lumber size requirements.

Specify all exterior and interior points of bearing, showing location by dimension and size. Reaction forces at point of bearing may affect the required size of bearing surface to prevent crushing.

Give center-to-center spacing of trusses. If trusses are spaced greater than 24 inches center-to-center, it is necessary to indicate the purlin spacing and method of attachment to the trusses.

Design (Specified) Loads
Truss design (specified) loads include both live and dead loads which may be uniformly distributed or may be concentrated at various locations.
1. Live loads: Live loads are non-permanent loads. Environmental loads produced by snow, wind, rain, or seismic forces are live loads. The weight of temporary construction materials and occupant floor loads are live loads. Live loads are usually uniform in their application and are set by building codes or building designer. Live loads will vary by location and use and should be furnished in pounds-per-square-foot, or other clearly defined format.
2. Dead loads: Dead loads are the weight of the materials in the structure and any items permanently placed on the structure.
3. Special loads: Special loads can be live or dead. Examples of special loads might include mechanical units, poultry cages, cranes, sprinkler systems, movable partition walls, etc. The weight, location and method of attachment must be provided to the truss designer. Multiple load cases may be required in truss design.

Special Conditions
Some of the special conditions that are important to truss design include:

l) Jobsite conditions that may cause rough handling of the trusses.

2) High moisture or temperature conditions.

3) Use of trusses to transfer wind loads.

4) Fire resistance requirements.

5) Higher adjacent roofs that may discharge snow onto lower roofs.

6) Location from coastline, exposure and height above ground for wind.

7) Parapets, signage or other obstructions that may cause snow drifting, or prevent the free run-off of water from the roof

8) Any other condition that affects the load carrying ability of the roof or floor framing.

9) Floor trusses, office loads or ceramic tiles require special considerations during the building and truss design process.

Lack of information about any of these conditions could adversely affect the performance of the trusses.