How to Put a Support Beam Under Long Rafters


Often, long rafters need a support beam to help them handle the weight they are required to support on a structure. These beams should be constructed according to individual needs for correct load levels and to maintain the structural integrity. Consult a structural engineer to determine the type of beam, where it must be located and if any further structural bracing may be needed under the floor in crawlspaces or basements. The engineer will also determine the type and number of supports for the beam needed to maintain the integrity of the structure. Beams are heavy, and you may require extra help to do the job correctly; this is not a task for the inexperienced.

Things You'll Need

  • Beam
  • Beam supports
  • Posts
  • Step ladders
  • Level
  • Heavy-duty framing nails
  • Hammer
  • Metal post-to-beam connectors
  • Support the floor as required with posts or cement blocks placed under the floor wherever a support post or column will be placed. These floor supports should fit tightly to prevent sagging of the floor when the beam is installed.

  • Place the beam into position under the rafters, where it will equalize the load it will support. Stand on the ladder if necessary to reach the rafters. Any crown on a beam should be placed on top when set against the rafters. Support the beam in position with well-placed supports. In most cases, strategically-placed two-by-fours can be wedged under the beam hold it in place flush against the rafters. Partially nail these temporary supports in place if needed.

  • Set the beam's permanent support posts or columns into place, wedged tightly between the bottom of the beam and the floor. Place these posts in the locations specified by the structural engineer. Level them so that the weight will be coming straight down the post and not at any type of angle that could weaken the structural integrity. Toenail the posts to the floor and to the beam, driving in the nails completely at slightly different angles and using the metal post to beam connectors to attach them securely.

  • Remove the temporary support posts one at a time, and inspect the beam and rafters to make sure the permanent posts are handling the load and the neither the beam or floor is sagging before removing them all. The beam is now installed and ready to be finished with drywall, paint, trim or anything else you may want.

Tips & Warnings

  • Make sure the beam is properly supported by the temporary posts before releasing it.
  • Beams can also be placed inside a ceiling so they do not hang down in the room, by cutting out each rafter and installing joist hangars to hold them in place against the beam.
  • Failure to follow the recommendations of the structural engineer in all manners could mean a support beam that does not have the proper structural integrity and could cause the structure to collapse.

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