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About Us > Sustainable Systems > Structures & Finishes

The structure of a building consists of the foundation, floor, walls and roof. Finishes protect or hide the structural systems. At the monastery, most of the structural systems are hidden. The project team considered the following factors before deciding on specific materials:

  • The cost of materials. The initial cost must fit the budget. The cost of maintaining the buildings must be acceptable.
  • The site is remote. What is available nearby? Is delivery possible?
  • Energy efficiency. Which material is the most efficient for its purpose? Is it produced in an energy efficient manner?
  • The aesthetics of the materials. Does the material integrate with the existing buildings and lend itself to the character of the new buildings?

Straw bales as wall material addressed all of the criteria. Straw is the waste product of grain plants after threshing and as a waste product it is relatively inexpensive. Agricultural areas of southern Colorado, only 100 miles to the north of MCD, are a good resource. Straw bales are sound absorptive and have an R-value of 45, a good insulator. (A frame wall measuring 2' x 6' with fiberglass insulation has an R-value of 19.) The bales are 18" thick, similar to the wall thickness of the existing double adobe construction of the chapel. However, at present, New Mexico building codes allow straw bales to be used only in a non-load-bearing capacity. The load bearing walls must consist of a separate structural system with straw bales filling the spaces between the structural supports. The structural system was refined as the construction progressed.

The structure of the Cloister, the first phase of new construction, consists of wood columns supporting a steel channel beam. Columns were constructed of small framing lumber to equal the entire 18" depth of the straw bale wall. The steel channels support the roofing trusses. Steel bracing from the top of a column to the foot of the adjacent column provides lateral support. The columns were spaced at regular intervals along the exterior perimeter of the structure. Column spacing defined an individual cell width. Straw bales filled the space between the columns. At the interior, cells are separated by an adobe wall on one side and a wood frame wall that encloses a shared bathroom on the other.

The wood column system of the cloister proved to be cumbersome in several respects. Periodic diagonal steel bracing from column to column limited the placement of doors and windows. The bracing was a nuisance to the smooth movement of laying bales. Additionally, since the columns spanned the full depth of the wall and the columns were placed at regular intervals, many bales were cut in order to fill the spaces between the columns. This was not using the bales or labor force most efficiently. Finally, due to dissimilar heat coefficients, the steel bracing and the straw expanded and contracted at different rates. This translated to cracking in the finish material.

 

The corridor addition

The corridor addition

The corridor addition and convento structures benefited from a reevaluation of the structural system. Steel columns replaced the wood ones. Due to steel's greater strength, the column profiles were reduced to 31/2" x 31/2" and the columns were located at the outer face of the walls. The diagonal bracing was replaced with a top connecting plate to control lateral movement. Instead of cutting bales to fit between the columns, the bales were notched with a hand grinder. The notched bales slipped around the columns quickly. The walls retained their insulation qualities and provided material continuity at the interior surface. This eliminated factors responsible for the cracking of finish materials.

The roof/ceiling structure of the existing buildings is exposed timber and decking. Several structural systems are used for the roofs of the new construction. Vigas support a ceiling of wood decking and R50 rigid insulation in areas of shorter spans like the six foot wide corridor. Vigas are tree trunks and act like round beams. The side branches are cut off at the trunk and often, the bark is removed. Using vigas on short spans minimizes the size required to span the distance, eliminating the need to use large diameter old growth timber. The vigas were purchased from Forest Trust, a local, not-for-profit organization that promotes sustainable lumber production. The vigas and decking are exposed to the interior of the space, as in the existing Refectory and Abbey Church.

Areas with longer spans employ another structural system consisting of an I-beam constructed from composite wood, composite wood decking above and R50 batt insulation placed between beams. The I-beams use smaller lumber that is glued together to form a larger section. This method results in a very stiff, strong structural unit of compact dimensions. The beams are hidden above a painted gypsumboard ceiling.

The cloister roof is constructed of a different type of composite roofing member, the scissor truss. Trusses are able to span long distances using smaller framing members by engineering the transfer of loads. This means that the truss construction is a very efficient use of timber resources. The configuration of a scissor truss allows for abundant insulation space between ceiling and roofing.

The foundation system did not extend beyond the thickness of the walls above. Brick laid on a compacted sand bed over earth is the flooring throughout the new construction. Brick on sand is a traditional floor finish in the region. Also, the portals are constructed with a similar floor finish, so it serves to visually unify the complex. In another regard, brick and compacted sand combine to form an effective thermal mass, a good component for the solar heating aspects of the project.

Finally, the straw bale walls required a protective finish on the interior and exterior. The choices were a cementitious plaster like the existing construction or a mud plaster consisting of clay and sand. While the technique to apply both types is the same, the use of straw bales weighed the decision to mud plaster. Due to the irregularities in the bales, the first coat (scratch coat) uses more material to fill the voids. The monastery is located in an area of good plastering clays. Natural colors range from tan to deep red. Using local free materials would eliminate the cost of the additional materials. Aesthetically, the local plaster integrates the new construction to its surroundings and provides a quiet backdrop for the Abbey Church.