For the team at the Landa-Ochandiano workshop in Spain, American ash was the natural choice for a building which stands as a testament to one of Spain's oldest industries - salt production.
Opened in October 2008, the simple design of the Visitors' Centre at the Añana Salt Valley, in the province of Álava, combines old and new elements and the aesthetical appeal and flexibility of American ash made this species the perfect choice.
Mikel Landa, one of the architects responsible for the project, says: "The light tone and marked grain of American ash provides a great visual effect and the wood is easy to cut into small strips which allow for the bending we needed to take on the shape of the building's skin. In some ways the building resembles an upside down ship's hull so wood is the natural choice."
HISTORY AND RESTORATION OF THE AÑANA SALT VALLEY
Añana Saltworks are inland saltworks that exist because of a geological phenomenon called a diapir which creates hyper-saline springs.
Saltmaking activity has been continuous from 822 until the end of the twentieth century, although it is thought to have started even earlier than the ninth century. In the Middle Ages its salt was sold throughout the Iberian peninsula. A series of circumstances during the last years of the 20th century, drove the saltmakers to other industries and with no maintenance, the buildings fell into disrepair.
A Master Plan restoration plan begun in 2003, including the refurbishment of some buildings between the town and the saltworks. Work began in 2004 to restore the old salt store which was to become a visitor's centre.
Only the perimeter walls of the salt store remained and the idea was initially to turn it into a visitors' centre with exhibitions, displays and guided tours on what had been an important industry for the area for hundreds of years. Later on, the idea is that this building could be used as a sales centre where visitors could buy salt made by the traditional method.
The base still existed on which to develop the new elements which would create a mix of old and new.
The project was based around a simple design for the visitors' centre. The exterior shape is elliptical, fulfilling all the requirements for a practical display and meeting area and creating an interesting interior space with subdued lighting to create atmosphere. This geometric shape is formed by the roof of the building, linked to the masonry walls on both sides and the floor. It has an oblique cut on the east side that creates access to the building, with two other side openings.
The inspiration for the design, material and structure came from the architect's experience of building his own kayak, using wood to create its unique curved shape. So the design resembles an upside down boat's hull.
There are seventeen vertical arches made of 12mm thick layers of laminated larch wood. The straight and curved elements were glued at the factory, so the frames were built into halves and assembled at the construction site. Joints were made using epoxy resins and stainless steel threaded bolts. Support steel shoes were made of stainless steel because the building is situated in a hyper-saline environment which causes corrosion.
The frames are connected to each other by American ash strips placed in two layers, one of them directly fixed to the upper face of the arch members and the other one fixed to the lower face. Waterproof sealant has been applied to the external face of the upper layer. The lower side of American ash wood is visible from the interior.
American ash was selected for aesthetical and mechanical reasons. On one hand, this wood has a great visual quality with a marked grain that makes you feel as if you are inside a ship's hull. Also this species is easy to machine into small strips, allowing the bending needed to take on the shape of the building's skin.
To obtain the two layers of American ash, boards 8mm thick and 25mm wide were used, with a curved dovetail so that the fit of one board with the next allows a turning between boards. The surface is sanded, to give its final appearance, and to be fitted in place, the strips of American ash are glued on the edge of the dovetails.
The exterior is completed with a third layer of wood placed on the outside to create the external visible surface. Ipe wood was chosen for this function for its natural weathering properties and good durability.
This Ipe wood layer is fixed in rectangular strips 8mm thick and 25mm wide, placed with an 8mm space between them. The arrangement allows water to flow through onto the waterproof sealed layer below, above the outer layer of ash. An elastic one-component waterproof sealing has been used for this. To allow the boards to take the shape of the ellipsoid, the space between the boards varies from 8mm to 12mm depending on the radius from the transverse curvature which differs along the shape.
The building's roof has a horizontal section built with a glulam wooden framework of Larch wood and a board of phenolic-plywood. On the exterior, the waterproof seal is visible, placed right on top of the plywood board. The rain water from the flat roof and from the ellipsis runs through two stainless steel gutters that take the shape of the wall and of the ellipsoid. The gutter section has three sheets, the first one is flat, the second sheet is cylindrical and the third one has an ellipsoidal shape. All three are welded together.
Between the two layers of American ash there is a thick layer of insulation of rockwool. The masonry perimeter walls are visible from the interior in the intersections in the ellipsoidal skin. The heating system for the building is an electric radiant floor.
Architect Mikel Landa says: "The environmental conditions of high salinity, the requirements for the structure and the ellipsoid idea led us to select wood as the main material. Wood has been used for the structure, interior and exterior sheathing, joinery and some flooring. The use of different species, in line with their individual mechanical, technological and aesthetic characteristics, has produced a unique building which testifies to the adaptability of this naturally sustainable material."