Fig. 219. The Pergola
The stakes are three feet from the centre of the columns in each case, and angle a c d should be made square at the beginning. Measure distance a b equal to c d. From a measure along a line stretched from a to b three feet, and then three spaces of twelve feet each. Measure the same distance from c along c d, and place stakes at each point. A line stretched from e to f should pass over the centre of the stakes marking the centre of each column, as these latter stakes will be dug out in the process of excavating for the foundation, while stakes e and f are necessary for the proper location of the holes.
After digging the first two holes, test their accuracy by again stretching a cord or masons' line from e to f. Proceed with the next set of holes in the same way, placing new stakes three feet out from centres to correspond with e and f. When the eight holes have been dug, the arrangement will appear as shown at g, twelve stakes being left in the ground. Should the pergola be longer or narrower, the same method would be used, the dimensions only being altered. The size of the holes will depend on the following considerations:
Fig. 220. The pergola
Assuming that we are building the large pergola with eight-inch columns, the base will be about twelve inches square. Measure the base and add two inches to it, making, say, a fourteen-inch square, the size of the foundation. A box in the form shown at a, 14 inches square inside, must be made. No nails are used on the box. It is held together by cleats c c. They must be made to fit snugly, and are to be knocked off when the cement has hardened—i. e., about four days after making.
These boxes may be full depth of the hole, three feet, or, as is sometimes done, the hole is made just the right size and the box, about eighteen inches in length, wedged into the top as shown at i. This method calls for considerable care in levelling the top of the box and securing the proper projection above ground, as well as in pouring in the cement without dislodging it, but the box is removed more easily than is the case with a full-length one. The decision about this point determines the size of the hole. In case the short box is used, the hole must be fifteen inches square and just enough shaved from the sides at top to receive the box.
If the full length box is used, the hole should be about twenty inches square, to allow the cleats to be knocked off and boards withdrawn.