Viga (architecture)


Vigas are wooden beams used in the traditional adobe architecture of the American Southwest, especially New Mexico. In this type of construction, the vigas are the main structural members carrying the weight of the roof to the load-bearing exterior walls. The exposed beam ends projecting from the outside of the wall are a defining characteristic of Pueblo architecture and Spanish Colonial architecture in New Mexico and often replicated in modern Pueblo Revival architecture. Usually the vigas are simply peeled logs with a minimum of woodworking. In traditional buildings, the vigas support latillas which are placed crosswise and upon which the adobe roof is laid, often with intermediate layers of brush or soil. The latillas may be hewn boards, or in more rustic buildings, simply peeled branches. These building techniques date back to the Ancestral Puebloan peoples, and vigas are visible in many of their surviving buildings.
Since the modern Pueblo Revival style was popularized in the 1920s and 1930s, vigas are typically used for ornamental rather than structural purposes. Noted architect John Gaw Meem incorporated ornamental vigas into many of his designs. Contemporary construction in Santa Fe, New Mexico, which is controlled by stringent building codes, typically incorporates ornamental vigas, although the latest revision of the residential building code gives credit for structural vigas. Older structures that have been reconstructed may contain both structural and ornamental vigas.

Composition

Vigas are typically about 6 to 10 inches in diameter and average 15 feet long and are commonly used in interior spaces. Pinyon and Ponderosa Pine were the most common wood species used in Viga construction during the 17th century. Engelmann spruce is the preferred wood "for the wood character and lack of cracking," but Ponderosa pine is more commonly used. Wood characteristics, availability of trees, and transportation issues defined room depths that were mostly no longer than 15 feet. A layer of smaller branches or saplings known as latillas or Latias covers the top of the Vigas with Adobe for insulation and water repeal.
Although in prehistoric times Vigas were reused from old constructions to new buildings, this practice depended on the history of some sites since some Spanish settlement reused them such as the Walpi. In the 19th century, the traditional craftsmanship of Vigas changed with the arrival of the railroad in the 1880s and immigrants from the east coast. New dimensioned 2" X 4" lumber was introduced in the area.

Materials

Cutting trees for Vigas was usually done in Winter because of the good temperatures. “Dead and down” trees were the preferred source for Vigas in the adjacent forests. Traditional Vigas were usually cut to length with metal axes. Latillas were also collected, along with other construction materials at the same time. To make transportation easier wood preparation usually was done before shipment. Large labor crews were involved and Vigas were transported by teams of Oxen from the mountains. Some construction historians have mentioned the use of latillas under the vigas for carrying poles.
Wood cutting was an important aspect of material production. If cutting was done shorter than needed, the builders had to wait until one year later to get the same material thus representing a problem. These issues led to some structural and designing decisions in constructions like the building of second walls inside the proposed building so shorter materials can be used.
Large diameter Vigas were cut first so they can dry or cury for a longer period. As lighter elements for transportation, Latillas or Latias were cut last of various types of wood. In buildings, these were also laid in different patterns to the Vigas and painted in a different colors. The 1846 American immigration brought notions of New England architecture. New technologies substituted the use of Vigas for Machine-sewed beams, among other construction technologies that followed to the 20th century. This practice did not interfere with the use of Vigas mostly for decorative purposes in the Pueblo Revival Style architecture between the 1920s and 1930s.

Structural assembly

Traditional Vigas were mostly used for structural purposes in buildings. Vigas were spaced among other 3 feet apart, although irregular or unequal spaced was characteristic of Spanish colonial architecture. Forms of Vigas varies from large institutional buildings to small ones. The amount of Vigas used in rooms vary, but six was the standard. Some rooms like in Acoma, are roofed with five to nine Vigas. Also, other structural practices were added to later buildings such as placing horizontal bond beams to transfer structural loads to the adobe roof.
The extension of Vigas some feet outside of the Wall as a standard practice. This was used for the creation of Portals or covered porches. An Umbral or lintel was added for support of the Viga along with vertical posts in these spaces. The portal’s roof treatment was the same as interiors and the space provided for different uses.
Vigas were usually installed with the smaller ends to one side of the roof to facilitate good drainage. Also, Vigas usually sat directly on the adobe or stone walls and strapped. Decorative Corbels were used in Portales and in the interiors.
New technologies, especially in the Pueblo Revival Architecture were integrated. The practice of anchoring Vigas with rebar through pre-drilled holes at opposing angles and the designing of parapets for anchoring, was ideal for Vigas in low flat roofs. This was used to prevent roof uplift.
The vaulted Viga roof is another type of structural system using vigas, using parapets on the two side and eaves on the ends. The roof is left exposed on the interior and latillas are placed parallel with others in a diagonal pattern.

Examples

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