As with any profession, one must learn the language. Despite the similarities between architecture and construction, building vernacular is much more expansive; not only do you need to know what to call the finished product, for example, “footers,” but you also need to know the parts required to make that product: batter boards, alligator clips, string lines, builders level, lime, sister-boards, “burning one,” chairs, wire twister, stakes, trench… I could go on. I don’t want to bore you with every definition, but most important in this phase of the project are batter boards, not to be confused with “board & batten,” this I know from experience.
Batter boards are located via the “Big Rectangle.” After picking a corner from the Big Rectangle the “building lines” are measured out, in two directions, and the batter boards are located. They are made out of scrap 2×4’s and metal stakes, and are critical for getting the building square. They are also used for setting the height of the slab, but that is a conversation for another day.
Below is another simplified diagram, (not this project) which shows the batter boards in perspective.
The grey areas in both diagrams are where the trenches are located, although they will be wider, approximately the width of a 16” bobcat bucket. While digging the trenches, the “building line” string is rolled up, to accommodate the bobcat, and later unrolled to double check that the trench is straight. It’s not fool proof, and we had a good deal of hand digging that day to get the trenches linear. I am still sore. Because the string lines are rolled up, the bobcat operator uses the lime line (white powder), to guide his excavation.
It has been expressed to me, on many occasions and by many people, the large number of corners in this project – sixteen to be exact. They are particularly difficult to dig out with a bobcat, so I definitely made Dan sweat that day. At one point he even dug himself into a corner.
After the trenches were dug, we laid the rebar. This sits permanently in the bottom half of the concrete footer and acts as a unifying strengthener. A few things one should know about rebar:
- It should not touch the earth, which is why the horizontal rebar sits on plastic “chairs”. Water from the earth will corrode it, and it will not pass inspection.
- Every 4’ there is a vertical grade pin, which sets the height of the footer. This is the only piece that can touch the ground, because if it rusts it will not the sacrifice the integrity of the structure. It also can’t touch any other piece of rebar because rust transmits through contact.
- Every 4’ there is a spreader, to keep the width consistent between the long runs of rebar.
- Rule of thumb: to find the amount of rebar length to overlap, multiply the diameter of the rebar by 40. For example ½” diameter rebar x 40 = 20 inches (of overlap).
- Rebar has to be 3” away from the edge of the concrete, in any direction.
- The tool used to tie the rebar together with wire is called a “wire twister.” Go figure.
- A piece of rebar is set into the concrete footer and travels up into the framed wall to act as a lightening ground. This is in most houses.
We passed the trenching and rebar inspection on Thursday, so concrete footers are in our near future. P.S. correction to well drilling process: The client was kind enough to inform me of my misunderstanding of the well-drilling process, so I have drawn this diagram to better illustrate the steps of reaching the water table; critical for habitation out on the dry mesa!