Step 12: Framing - The Bottom Plate
The bottom plate is the base of all the walls you're about to build. It will be secured to the floor using Tapcon concrete screws, and the studs will be nailed and/or screwed onto it. Since it will be in contact with the concrete floor, it must be pressure treated in case of moisture issues.
When you select the lumber for the bottom plate, make sure it is straight, flat, and without any warps or twists. Before you load each piece onto your cart at Home Depot (or wherever you get your lumber), sight along the length to look for defects. If you spot anything, put it back. To reduce headaches later on in construction, the bottom plate (and the top plate) must be perfect.
*Note: Don't go lumber shopping with a spouse or child. They'll go nuts with boredom as you spend an hour or two sorting through a skid of wood looking for the best pieces. Trust me.
The bottom plate will determine where all of the walls are, so make sure you position the pieces carefully. Place the 2x4s close to the wall, with no more than a 1/4" gap between the wood and the wall/insulation. For long spans requiring more than one piece of wood, make sure that the pieces are parallel. At corners, double check your angles - 90, 45, etc. It pays to take your time here.
Nothing complicated here. Measure twice, cut once with the miter saw. Strive for an easy fit with no gaps between pieces.
DRILLING & SCREWING
Grab the hammer drill and install the masonry bit. The drill should have a gauge on the side, that you can use to control the depth of the hole. In this case, the hole will be the length of the screw plus a bit of margin (say, 1/2" extra). With the bottom plate in place where you want it to be, drill straight through the center of the wood and into the concrete, perpendicular to the floor. Drill the first hole near the end of the piece, about 6" from the end. It may be necessary to pull the drill out a few times, so the concrete dust can escape. It helps to stand on the wood as you're drilling to keep it from moving around.
With the first hole drilled, drive in a Tapcon screw using the power drill. I suggest using a socket head bit to do this, it slips a lot less. Don't drive it all the way in just yet. Again, it helps to stand on the wood so that it stays flat on the ground.
Now, go to the other end of the bottom plate, realign the wood if necessary, and drill a second hole. Drive in another Tapcon. Now the bottom plate won't move, and you can go ahead and drive in a few more screws along the length of the bottom plate. At the very least, place one every two feet or so.
Continue in this manner with the rest of the room. Take extra care when aligning interior dividing walls - they should be perpendicular to the outside walls (unless you have something avant garde planned). In places where a door will be, place the bottom plate right across the gap - that section will be cut out later when the door frame is finished.