Sills or Mud Sills

The next step is the installation of Mud Sills or Sills

The first consideration is how to keep the sills and rim joists from rotting.  There is a foam insulation that can be purchased to place between the concrete and the sills that excludes moisture from traveling up the concrete into the wood.   Also, sills provide a way of attaching the house to the foundation.

Make sure that you plan well for the overlap of the outermost trim board that will finish off the bottom of the wall.  The concrete should not show at all from outside.  In other words, it should not protrude beyond the trim.  You do not want a horizontal surface exposed to the weather that may catch water or snow, and allow it to wick under the sill.  Likewise, the insulation or membrane should not protrude beyond the wood sill, it should not collect water on top of it either as it will wick water toward the wood and that just defeats your efforts. 

So, now I am going to assume that you are not the perfect carpenter.  I know that I am not, and that most everyone makes little mistakes even if they have done this a million times.  Your bolts will not be perfectly aligned.  You just cannot be sure that you are going to be able to drill holes in the sills and have the sills just drop into place. 

It is easier if you have a poured foundation.  You have a reference point in the edge of the concrete to measure from.  Here, we do not.  I am going to have you do something that I hope will make you a success the first time, despite having to carry and jockey a heavy and awkward load into place.

Cut each sill to 11 feet 6.5 inches long.
Lay the four sills on a flat spot on the ground, on a slab of concrete or what have you.  Your new neighbor may have a deck or garage floor to do this on. 
Cut four triangles of scrap plywood, about three feet long on the hypotenuse.  Be absolutely sure that the corner opposite the hypotenuse is square(90 degrees).  Now, measure from corner to opposite corner of your four boards lying on the ground.  Adjust them until the two diagonal measurements are identical, and the ends of the boards, laid out as in the illustration, butt snugly against their neighbors. 
Fit the triangles onto the top of each corner, making sure that the edges are flush.  Using a drill fitted with a Phillips scewdriver bit, screw 2 1/2 inch sheet rock screws through the plywood into the boards below.  Use at least three screws for the short board end and five on the longer. 
Check to make sure the diagonal measurements remain the same after each corner is done.
When all four corners are done, nail two scrap 2x4s or boards on a diagonal across the square.  One or two nails in each end will do.  See the illustration.
With the help of a couple of really strong and stupid friends, carry the square to your foundation. 
Rest the square on top of your bolts,(Plywood triangles up) shimming with scraps of lumber(from the concrete to the sill, not under the bolts) till it is reasonably level, and the square is directly over the correct location of your future walls.  A plumb bob, or a washer tied to a piece of thread held suspended against the edge of the square will show you if you are over the correct spot.  
Now, with your friends holding it steady, just walk around the square, and give the top of the boards a quick rap with a hammer above each bolt, if the sill is resting on top of it.  If it is not touching, just look underneath and draw a circle directly above the ends of the bolts.
Flip the square upside down, and look for the little indentations on the boards and the pencil marks.  Drill through the boards with a spade bit about 1/4 inch larger than the diameter of your bolts.  Place the moisture barrier onto each bolt.
Flip the whole thing back over, and slide the sills down onto the bolts and onto your foundation. If a bolt is not quite in the correct place, just lift the sill up,  reinsert the drill and wiggle the moving drill around as you push it through to enlarge the hole a bit.  Remember that you will be using washers on each bolt, so a perfect fit will not be necessary as long as everything is still square and the ends are butted tightly together.  If the hole is slightly off center for the bolt, insert a round wood rasp into the hole and file open the hole in the direction needed.
Once the sills are in place, check for level, and for gaps between the board and the foundation.  Shim as necessary.  Use a shim that will not collapse with weight or time. Old asbestos shingles (Beware of asbestos dust if cutting and drilling...Wear a mask over mouth and eyes, and wear protective disposable Tyvek suits, keep people and pets away, and clean up carefully afterward.  Do not vacuum up, as this might spread the fibers around. ) or slate pieces will not collapse.  Remember not to allow the shims to extend beyond the outer rim of the proposed building walls.
Remove the temporary plywood triangles and the diagonal boards.  The diagonal boards and triangles will keep the construction square while you move it around, and will not be necessary once the sills are bolted down.

Top left:  The arrangement of the sills and approximate diagonal measurement.
Lower right:  The temporary plywood triangles and diagonal braces



When all is level, put washers and nuts on each of the the bolts and screw them down.  Do not over tighten.  They should not cut into the sills.

An alternative is to construct the Sills, Rim Joists and Floor Joists on a flat surface and lift the whole thing onto the foundation.  This is an extremely effective way to get it right, but you need a football team to lift the thing.  Pressure treated wood is very heavy.  It is not a good idea to breathe in sawdust from pressure treated wood.  Most of the dangerous chemicals have been removed from pressure treated wood lately, but still...lets just be safe and wear a mask anyway.  This might be a good idea whenever you are creating dust.