How to attach a floor joist to a concrete block wall

Sometimes the design of a home's floor structure calls for attaching floor joists to a concrete block wall. The most common means of securing floor joists to a concrete wall is to install a ledger board that matches the joist size. The method used in typical 2 by 8 floor joist construction will insure proper support for the floor joists. The installation procedure can also be adapted to any floor joist size.

Determine the designated level of the top surface of the floor joists and mark that point on the vertical surface of the concrete block wall at both ends of the wall. Snap a chalk line between the marks to establish a guideline and check the line with a level. This guideline will define the top edge of the ledger board.

Measure the horizontal length of the concrete block wall and cut 2 by 8 pressure-treated lumber to the length measured. The cut boards will be used for the ledger board(s). If your construction plans call for a different joist dimension, cut the appropriate corresponding lumber size for the ledger board(s).

Lay out anchor bolt locations on the ledger board(s). Hook the end of a measuring tape on the end of the ledger board(s) and place marks over the full length spaced 30-inches apart. For ledgers with multiple pieces, repeat the marking procedure for each board. Extend each of the marks across the width of the board(s) using a framing square.

Place a mark 3 inches in from the edge at every other line marked on your ledger board. This will mark the centre points of the anchor holes along one edge of the ledger board(s).

Repeat Step 4 for the alternate marks at the opposite board edge to create a zigzagged pattern for the anchor bolt positions.

Add an additional anchor bolt location 3 inches from each end of each ledger board and centred in the board's width.

Drill a 9/16-inch hole at each anchor bolt centre point marked on the boards.

Position the ledger board(s) against the concrete block wall with the top edge aligned with the chalked guideline and mark each of the drilled anchor bolt holes on the wall. Insert a pencil into each hole to mark the wall surface, or you can insert a nail set and tap it with a hammer to place a mark in the concrete. When the anchor hole locations have been marked on the concrete wall, set the ledger board(s) aside.

Bore a horizontal hole in the concrete block wall at each anchor bolt location using a power drill mounted with a 5/8-inch masonry bit. Drill the hole depth to match the specific anchor length being used, typically about 2 1/2-inches deep. Blow or brush the concrete dust out of each hole as it is completed.

Insert a concrete anchor into each hole drilled in the concrete block wall.

Reposition the ledger board against the wall and align the top edge with the chalked guideline. Slide a flat washer onto a 1/2-inch by 4-inch steel bolt and insert a bolt into each anchor location. Tighten each bolt using an adjustable or socket wrench to secure the ledger to the concrete block wall.

Repeat Step 11 for additional ledger boards, if applicable.

Mark the floor joist layout along the installed ledger boards and extend the layout lines vertically using a framing square.

Install one joist hanger at each floor joist location and install the joists following standard framing practices.

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