SALINAS "In the Midst of a Loneliness": The Architectural History of the Salinas Missions

THE SECOND CHURCH AND CONVENTO (continued)

The Clerestory Window

Constructing a clerestory window always taxed the skills of masons and carpenters, as well as the shear-legs crew. The beams forming the upper and lower edges of this window were among the largest in any church, and the upper beams were among the highest. The task of lifting these beams to heights of twenty-six to thirty-five feet was probably always a time of great tension, and to set them into place without accident or injury to workers or to the fabric of the church was cause for relief and rejoicing.

Figure 7. Hypothetical section down the nave of the church of San Gregorio de Abó as completed about 1652. The details shown in heavy outline are not conjectural. They are taken from standing walls, photographs, and drawings. The probable section of the church as it looked at the time of its completion is shown by fine lines. The tribunes and catwalk can be seen in the side chapel and transept areas, as well as the lower and upper clerestory beams, the beams supporting the roof in the transept, and the beams supporting the roof in the sanctuary and apse. The probable structure of the main altar, altar platform, and stairs are shown. Compare this section to the photograph of the altars at Hawikuh, shown in figure 5. (click on image for an enlargement in a new window)

In San Gregorio II, the four main vigas were each about forty-six feet long and twelve inches square. Each of them weighed about 1,700 pounds. Sixteen corbels of the same size as those beneath the vigas of the nave supported them, two at each end of each viga. The shear-legs crew lifted the lower vigas and the construction crews guided them as they were lowered into place. Then the masons built up the towers at the south corners of the side chapels, adding supporting beams to form the ceiling of the staircase through the southwest tower to the bell-platform. At the same time they built up the other walls of the side chapels, sanctuary, and apse.

When they had raised the walls to a height of thirty-four feet, the construction crews carefully levelled the wall tops. Using the nivel de albañil, the mason's level, Acevedo and the mayordomo checked to insure that the west walls were about twelve inches lower than the east walls, so that when the vigas were set into place the roof would slope down to the west for proper drainage.

Next, the shear-legs crew began lifting the timbers for the supporting structure of the high roof. The largest of these were the upper clerestory vigas and the other crossbeams that reached from the east to the west walls. The construction crews set the upper clerestory corbels in place and braced them against the scaffolding, placed the corbels for the crossbeams at the mouth of the sanctuary and the mouth of the apse in the same way, and then began laying beams along the wall tops.

Acevedo's plan for the high, relatively thin walls of his addition to San Gregorio demonstrated that he wanted to be sure the structure had more strength than stone walls alone would give him. He worked out a method that would tie together all the walls at their upper edges, giving them resistance to wind pressures and the strains introduced by foundation shifts and settlement. He used the same system as in the nave, with two 12-inch-square beams laid along the inner edges of the wall tops. Here in the side chapels and sanctuary, however, he did not use them as bearing plates, but as bond beams. The ends of the corbels and crossbeams interlocked with these bond beams in the upper corners of the side chapels and transepts, so that when the entire set of beams was in place it formed a series of box frames around the tops of the walls, bracing them against the effects of side pressures and shifting foundations. All the beams were either enclosed within stonework and plaster or beneath the roof of the church, protecting them from the decaying effects of the weather.

Once the lower network of corbels and bond-beams was in place, the shear-legs crew began lifting the upper layer of timbers. They lifted the upper clerestory viga and the construction crews guided it into place, while at the same time setting two upright posts between the upper and lower vigas, dividing the window opening into three equal sections. The clerestory window was not only a means of illuminating the sanctuary, but was also a critical part of the support structure for the transept roof. The beams over a transept ran lengthwise down a church, resting on the upper clerestory beams at one end. Therefore clerestory beams were required to support the weight of a number of corbels and vigas, as well as the latillas, matting, puddled adobe covering, and plastered surface of the transept roof. In order to support such a weight, the friars doubled the clerestory vigas, so that the lower set absorbed about half of the forces applied to the upper set. Without such an arrangement, it would have been impossible to construct a transept roof. The clerestory window itself was nothing more than a space between the upper and lower transept crossbeams, and may have been a later development after the invention of the transept crossbeams themselves. When and where this invention occurred is unknown.

The shear-legs crew began lifting the two vigas for the north end of the side-chapel crossing. These were the same size as the clerestory window vigas, but had to support almost twice as much weight. The vigas supporting the roof of both the side chapels and the sanctuary would rest on them. Acevedo, however, had thought of this. The massive pair of beams and corbels, acting as the south support of the catwalk at a height of twenty-two feet, also served as the lower set of supports for the sanctuary mouth beams. A series of square posts, 11 1/2 feet long, set vertically on the catwalk beams, probably transferred some of the forces from the upper beams to the lower set. Functionally, the arrangement was almost identical to that of a standard clerestory window. Acevedo's creative imagination took this common structure and modified it to produce both a unique combination of spaces within a seventeenth century New Mexico church, and the unheard-of catwalk at the same level to allowing movement from one side of the church to the other high above the floor.

Finally, the shear-legs lifted the last of the large vigas into place at the north end of the sanctuary across the mouth of the apse. These vigas were shorter than the large, forty-six foot beams that spanned the entire width of the side chapels. They were only about thirty-six feet long, and each weighed about 1,300 pounds. These three sets of upper beams, the top clerestory, the sanctuary mouth, and the apse mouth beams, were the main supports for the high roof of the church. Once they were in place, the lifting crews raised the upper set of bond beams and the construction crews set them onto the ends of the vigas along the tops of the walls, locking the crossbeams into position. The final roofing could now begin.