Wood Framing
Question:
I am conducting an investigation on the costs associated with building a 15,000 sq. ft. addition to an existing school building. I need to determine if wood trusses, steel bar joists or light gauge steel trusses would be the most economical material for the building system. The truss spans range from 42 ft. to 56 ft.
Answer:
All other factors being equal, wood is usually the least expensive of the three building systems that you list. To get an accurate cost estimate for this project, we recommend that you contact a truss manufacturer in your local area (see our Members Section for truss manufacturer listings).
One potential issue that you may need to explore further is whether your building code permits wood as a construction material for that specific type of construction. Under some codes, there are restrictions for building heights and areas based on construction type (in this case, wood framing), occupancy and use (educational) and level of fire protection (whether fire-rated assemblies or sprinklers are specified).
For example: according to IBC 2012/2015, buildings for education through the 12th grade are typically Group E. IBC 2012/2015 chapter 6 defines types of construction. Wood frame construction is assigned to Type V, which includes A (protected wood with 1-hour-rated elements) and B (unprotected wood having no fire resistance). IBC 2012/2015 Table 503 specifies limits are for area and number of stories, and IBC 2012/2015 506 covers other area modifications.
To determine whether wood is an allowable construction material for a 15,000 sq. ft. school, you can analyze the governing building code. You may want to contact a local architect who is familiar with educational building construction in your code jurisdiction.