Conventionally, first floor framing is nailed to a pressure treated sill plate, which is attached to a concrete foundation with anchor bolts. From here your standard framing details will apply – where there are rim joists, joists, and blocking.
Items needed for this project:
· Tape Measure
· Circular or chop saw
· Chalk Box
· Air Nailer (optional)
· Speed Square
· Hammer Drill or Ratchet
· Nuts and Washers
Your typical floor framing begins by attaching pressure treated (p.t.) sill plates to the foundation by way of anchor bolts. The anchor bolts should have been set with your foundation pour and be 36″ on center and starting approximately 12″ from each corner. 36″ spacing is a maximum that I will go due to flexing of the p.t. 2×6 at anything further. I know of some contractors that will go up to 48″, but really gain nothing other than a wavy sill plate. Remember to put a layer of insulation or sill sealer under your sill plate to seal it to the concrete. This will lessen the amount of air infiltration and bugs that can enter the home.
Before starting, you will need “layout” to know where to put the plate. The easiest way I’ve found to do this is with a stringline, chalkbox, and a tape measure. Begin by going to two adjacent corners of the foundation and measure from the outside of the wall to the inside a distance of 5 1/2″ and marking it. Pull the stringline as tightly as possible between these two points. Make sure the stringline is unobstructed – you may need a 2x block to raise it up. We’ll call this the “reference” line. Put another mark 5 1/2″ from the outside of the wall along the reference line. We’re going to use what is known as “3-4-5 Triangle”.
Geometry shows us that a triangle with sides of length 3 (ft, inches, yards, whatever), 4′, and 5′, and all multiples, will always be a right triangle. Pull along your reference line 8′ from the mark you just put down. Mark the stringline and the top of the concrete wall at this location. Perpendicular to this line you will want to measure 6′ and mark an arc. Between the two marks should be 5′. Pull your tape measure from the first mark at a diagonal to the arc. Somewhere along that arc will be the perfect right angle.
Once you get your right angle you will need to pull another stringline through the two points (the mark at the arc crossing and the reference line. Make sure that the layout does not push the 2×6 out too far from the concrete wall. If it does begin to overhang the concrete too much readjust your reference line and begin again. Once you are satisfied with the layout snap the lines using a chalk-box. I recommend using red chalk for permanent layout lines and blue where you’re not too concerned with it staying there. Be warned, red chalk will permanently stain just about anything, so do not use where you have finish materials. Be sure that you are as close to perfect on your layout as possible – this will affect how square the home is once wall framing begins.
Now that you have your layout perfect you are ready to install the sill plates. First thing to do is lay down the sill sealer. Typically this is 1/8″-1/4″ foam in 4″ or 6″ widths (blue or green in color). Lay it close to the snaplines put down earlier but not over them, if possible; you will need to see the lines later. The next step is laying out the sill plates.
Lay the sill plates with the ends in the right direction approximately 1/4″ from the anchor bolts. Have them on the outside of wall and not on the inside or you will not be able to see your snaplines. You probably will be unsuccessful in keeping it at 1/4″ which is fine; just keep it close. Line the end of your first board up 5 1/2″ past the corner marks of your layout. This should put it right at the outside corner of the concrete. Using your speed square put a line on the p.t. 2×6 at the center of each anchor bolt, making sure that the line extends from the inside stemwall face to just past the center of the board. After you’ve transferred the anchor bolts to the sill plates you will measure for distance.
The distance will most likely be different for each anchor bolt, unless you were very anal when you installed the anchor bolts. The distance from the snapline to the center of the anchor bolt is the measurement you want. This dimension transfers from the inside edge of the sill plate (next to the anchor bolts) towards the outside face of the stemwall. This is a hard thing to explain on paper so the idea behind the layout technique used is that when you drill the hole you only need to lift it and place it over the anchor bolts. I’m assuming that you have used 1/2″ anchor bolts and that you will drill a 5/8″ hole to allow for some movement and play for ease of installation.
Now you need to install the sill plates by laying them over the anchor bolts and tightening them down with a 1″ washer and correct size nut that corresponds to your anchor bolt size. As you tighten each one you will want to check for layout by pushing or pulling the sill plate to line up with the snapline, as well as lining up the end.
One thing to make note of is to check the top of the foundation wall for level before proceeding. If it’s out of tolerance by more than 1/2″ you may need to grout and/or shim the sill plates up to match. I’ve also seen where contractors will tapcon (concrete screw) or Hilti anchor sill plates down between anchor bolts. In my opinion this is overkill – the weight of the structure will level the sill plate between the anchor bolts more accurately than I can. The Hilti anchor may not hold or the sill plate may be swollen when I installed it. Where you have plates butting up to each other without an anchor bolt nearby you should screw or somehow attach the ends to each other as well as tapcon them to the concrete. With proper anchor bolt placement this can be minimized. Lay this out before you install the anchor bolts.
So, if the top of the foundation has a difference of 1/2″ or more, grout it or shim the plate and don’t worry about anchoring the plates between bolts.
We now have the plates secured all the way around the foundation and everything is as level as possible. Before we get into framing the floor lets talk a little about types of joists and the selection process.
Read also Floor Framing – Part 2, Floor Framing – Part 3