Lintels are to earthen architecture what headers are to stud frame walls. A lintel is a sturdy beam that spans the space above a door or window opening that bears the weight of a roof or second story. Traditionally, they were made from large dimension lumber. These days, lintels are often built up from laminated small-dimensional lumber or constructed into a box beam. Pallets are an excellent resource for Velcro plates and for making laminated lintels. Whatever the design, our focus is on how to anchor a lintel to an earthbag wall (Fig. 8.1).
On average, lintels need to be at least three-quarters the width of the wall, and extend past the opening to rest on the wall a minimum of 12 inches (30 cm) on either side. Our approach is to attach Velcro plates to the underside of each end of the lintel to extend another eight inches (20 cm) beyond the lintel (Fig. 8.2). The Velcro plate provides a pad that protects the wall from the point of contact from the lintel, while distributing the weight over a
8.2: An example of a lintel pre-attached to Velcro plates that extend another eight inches beyond the ends of the lintel.
broader area. The Velcro plate also anchors the lintel during construction.
Structural dimensions for load bearing and shear-strength change with the length of the opening being spanned. The bigger the opening, the beefier the lintel must be. Check on structural requirements appro-
8.3 (above): In designs with multiple windows, they can share Velcro plates or the lintel can span across the top of all the windows.
priate for your design. When designing the dimensions of a lintel, consider rounding off the thickness (or height) so that, including the thickness of the Velcro plate, it is equal to the thickness of the bags being used. This will make it easier to maintain the level of the bag wall (Fig. 8.3).
For a narrow opening, of two to three feet (60-90 cm) maximum, a minimum five-inch (12.5 cm) thick lintel is needed. For wide spans, of three to four feet (90-120 cm), a ten-inch (25 cm) thick lintel is called for. According to New Mexico Adobe Codes, 12-inch (30 cm) tall lintels are advised for spans over five feet (1.5 m). Occasionally the lintel and the bag wall may end up at different levels. You can either over- or under-fill the bags, or, if the lintel is lower than the bags, shim it with wood or throw a layer of cob on top to bring it up to level. Wait until the cob sets up some before continuing the bag work. To further secure a lintel, we like to lay a minimum of two rows of bags over them. The extra anchorage is particularly advisable when preparing the walls for a conventional roof system without a conventional bond beam (see Chapter 9).
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