How to Attach Floor Joists to a Concrete Block House

Written by j. cavan barry
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Floor joists are structural members used to support floors in the majority of homes built today. For homes built with concrete block, wood floor joists are almost always used to support main and additional floor levels. Effectively fastening floor joists to concrete block walls can be a labour intensive task that usually requires a general knowledge of structural framing. However, with the right tools and instructions, it can be a task that can usually be completed by almost anyone.

Skill level:
Moderate

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Things you need

  • Floor joists
  • Building plans (floor framing plan)
  • Pressure-treated wood ledgers (size depending on floor joist size)
  • Concrete anchor bolts (and nuts and washers)
  • Hammer-drill with concrete drill bit (size of drill bit depends on size of anchor bolts)
  • Concrete epoxy
  • Electric drill with wood bit (size of drill bit depends on size of anchor bolts)
  • Impact wrench and socket (size of socket depends on size of anchor bolts)
  • Circular chop saw with wood blade
  • 4-foot level
  • Tape measure
  • Chalk line
  • Lumber crayon
  • Joist hanger brackets (size depends on floor joist and ledger size)
  • Tico nails
  • Hammer or tico nailer (tico nailer is optional, and will require the use of an air compressor)
  • Duct tape (optional)
  • Framing square (optional)

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Instructions

    Ledgers

  1. 1

    Measure and mark the top of the floor joist and ledger on the concrete block wall and snap a reference line across the length of the wall using the chalk line. The top of the floor joist and ledger measurement will be noted on the floor framing plan.

  2. 2

    Snap a parallel line below the reference line made in step 1. This line should be offset half of the width of the ledger so the line will be centred on the ledger. Make sure the lines are level using the 4-foot level; adjust or correct the lines accordingly.

  3. 3

    Measure and mark the anchor bolt locations along the lower reference line using the tape measure and lumber crayon. Refer to the floor framing plan for anchor bolt spacing requirements.

  4. 4

    Drill the block wall at the marks made in step 3 using a hammer drill and a concrete drill bit that has a diameter 1/2-inch greater than the anchor bolt (unless otherwise noted in the floor framing plan). The gap will provide a space for concrete epoxy. The holes should only be drilled to a depth specified in the floor framing plan. You can wrap the drill bit with duct tape to mark the specific depth.

  5. 5

    Inject the concrete epoxy into the back of the anchor bolt holes, filling them about halfway.

  6. 6

    Insert the anchor bolts into the holes. You may need to add more epoxy if when the bolt is inserted, epoxy does not reach the edge of the hole. You can use a framing square to ensure that the bolts are square in the wall as they set in the epoxy. Allow the concrete epoxy to dry before moving on. Refer to epoxy packaging for curing information.

  7. 7

    Drill holes down the centre of the ledger boards to correspond with the anchor bolts set in the wall. These holes can be drilled using the electric drill and wood drill bit (size to match anchor bolt diameter).

  8. 8

    Mount the drilled ledger to the concrete block wall, guiding the anchor bolts through the ledger holes. Slide the anchor bolt washers over the anchor bolts and twist the nuts finger-tight to the ledger board. Tighten the anchor bolt nuts using the impact wrench.

  9. 9

    Repeat steps 1 through 8 on remaining walls before moving on.

    Floor Joists

  1. 1

    Measure and mark the floor joist locations (on centre) on the face of the ledger board using a tape measure and lumber crayon. Floor joist spacing will be noted on the floor framing plan.

  2. 2

    Cut the floor joists to length using a circular chop saw; the length should be the distance between opposite ledger boards.

  3. 3

    Hold a floor joist centred to a mark made in step 1 and slide the joist hanger bracket under the joist. The top of the floor joist should be flush with the top of the ledger board to ensure a level floor.

  4. 4

    Fasten the joist hanger bracket to both the ledger and joist (both sides) using tico nails and nailer. The joist hanger brackets have predetermined and drilled holes where the nails are to be driven. Repeat this on the other end of the joist and opposing ledger board.

  5. 5

    Repeat steps 2 through 4 on remaining floor joists.

Tips and warnings

  • Always follow the specifications noted on the floor framing plan, as failure to do so may result in costly or dangerous structural failure of the floor joists. When in doubt of the task at hand, consult with a framing professional.

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