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Inspecting Floor Trusses

Home inspectors are seeing more floor truss systems because they are replacing manufactured “I” joist flooring systems. I think that this is happening because of the poor fire rating of manufactured I joists. Although we know that installing fire rated drywall significantly increases the rating. Floor trusses offer some unique benefits that conventional joists and manufactured I joists do not. Floor trusses also offer long unsupported spans and can be used for cantilevering. Most floor joists are built with a 2X3 or 2X4 chord.  Spaces in the web of the truss allow room for electric runs, HVAC and plumbing pipes.  If you refer to the detail above, you will see the areas on a floor truss that should not be notched, cut, or drilled. This is very important, as doing so will not only reduce the strength of the member, it may also cause complete failure.

So what should a home inspector be looking for when inspecting floor trusses?

  • Floor trusses should be within ½” of plumb
  • Solid rim joists should be used and properly attached to the floor truss to avoid rollover
  • Heavy loads should not be concentrated from the bottom flange.
  • Light loads (ceiling fans, light fixtures, etc) could be suspended from the bottom flange
  • Floor trusses should be protected from the elements including pre – installation
  • Floor trusses can be moved up to 3” to allow plumbing piping. Joist spacing should not exceed 19” OC
  • End bearing length must be at least 1 ½”
  • Floor trusses should not be in direct contact with concrete
  • Nails installed perpendicular to the wide face of the flange shall be spaced not closer than 3 inches OC, using 8d nails
  • Adhesives used should comply with ASTM D3498-03 specification
  •  Joist hangers can be used
  • Strong backs or solid blocking should be installed at the mid-span.
  • Floor trusses can be reinforced for concentrated top load by adding plywood (glued and nailed using 3” nails, 5” o.c)

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