How to Strengthen Floor Trusses


Floor trusses are installed in homes with an upper level floor or a crawl space. A typical floor truss is manufactured with metal and engineered wood in V shapes to allow for ductwork or plumbing. I joists, which are shaped like the letter I, perform a similar function in the building industry. The trusses and joists are set on the top of the downstairs wall frame and nailed to the floor above to strengthen the structure and avoid a bouncy, squeaky floor upstairs.

Things You'll Need

  • Floor trusses or I joist
  • Hammer
  • 3 1/2-inch galvanized 16-penny nails
  • Hurricane clips
  • Joist hangers

Correct installation

  • Install the floor truss every 16 inches "on center", instead of the minimum requirement of 24 inches on center. Start the first truss against the wall and measure 16 inches away for the "center" of the next truss. By keeping the trusses closer together, you will create a stronger floor with less deflection.

  • Reduce deflection by using stronger, engineered wood. Deflection is the amount of sag the truss running across the room will produce. In long rooms, old wood beams would "give" as people walked across them. Metal or engineered woods are much stronger. Sustainable wood also is better for the environment.

  • Use joist floor hangers to give your trusses extra strength. Attach the metal hanger to the wall and the truss using 3 1/2-inch galvanized 16-penny nails. The hanger will have nail holes already punched out. Nail the hanger to the rim of the wall and set the joist in the metal sling for extra support. Wood will dry and shrink as it ages; the floor joist hanger will prevent the wood from twisting.

Strengthening old floors with existing floor trusses

  • Nail new trusses right next to the old beams if your floor is weak. Older homes with weak, sagging floors will need new trusses installed for safety. This method will require the removal of the existing floor to access the joist below.

  • Metal truss hangers are attached flush to the top of the wall and wrapped around the truss or beam for extra support. Hangers should be purchased to fit the exact width of the the wood. For instance, 2-by-10-inch trusses should have 2-by-10-inch hangers.

  • Nail the hanger to the rim (or top) of the wall. It is nailed to the ledger (or back board) perpendicular to where the truss will set.

  • Installing specially made hurricane clips to the floor trusses provides even more support. These clips are purchased at home improvement centers or online and attach to the top of the wall above where the joist will be set and the other half to the truss itself. The hurricane clip was developed for high-risk wind- and hurricane-prone areas of the country.

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