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Install Blocking Between Joists

When the floor joists run parallel to the wall you’re building, you’ll need to install blocking for attaching the top wall plate. Screw or nail one side of the block through the joist, and secure the other side to the sill plate. Use treated lumber if the brace will come in direct contact with bare concrete. It may be easier to install the braces before you install the foam board on the walls and insulate your rim joist. It’s a smart idea to places blocks 2-ft. apart so they work as drywall backers down the line.

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Snap Lines on the Floor

Snap a line on the floor 4-in. away from the foam as a guide for the bottom plate. This will leave a 1/2-in. gap between the bottom of the new wall and the foam. That’ll allow a bit of wiggle room if the foundation walls aren’t perfectly plumb or straight.

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Assemble the Wall on the Ground

If you have the space for it, it’s much faster and easier to assemble a wall on the ground. Sight every stud for a “crown” (a slight curve on the narrow side of the board), and mark an “X” on the crown. Have all the crowns face the same direction. If you don’t, you’ll end up with a wavy wall.

It’s easier to assemble your wall with the crowns up; that way both ends of the studs are solidly on the ground when you attach the top and bottom plates, instead of acting like rockers on a rocking chair. Build the wall so it can be tipped right up; there’s usually not enough room to swing the whole wall around if you don’t.

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