Great Frame-Up

An engineer living on a remote mining claim in a beautiful yet at times brutal environment at 9,000 ft. in the Rockies aimed to build affordable, energy-efficient,

An engineer living on a remote mining claim in a beautiful yet at times brutal environment at 9,000 ft. in the Rockies aimed to build affordable, energy-efficient, and durable housing. An ongoing process of trial, error, and revision over 25 years led to a solution in the form of Cavity Wall, a building system comprising lightweight concrete panels joined by expanded steel to create stay-in-place formwork.

The inventor emphasizes that the evolution of his building technology was a response to the environmental conditions in which it arose, primarily extreme cold, fire hazards, and especially, prolonged frigid winter winds. The solution, applicable to any environment, he notes, became obvious: Moderate the extremes.

To that end, the engineer devised a sturdy, yet lightweight, insulating frame that forms a cavity enclosing significant mass accomplished with native bulk material Û even contained water Û or ready mixed concrete for load-bearing elements. Thus, the system developer offers what he describes as a simple means to efficiently combine lightweight and conventional concrete for optimum structural performance and sustainability.

A chief ingredient of the Cavity Wall solution is lightweight (82-88 lb. per cu. ft.) concrete cast in molds to produce 2-in.-thick panels weighing 14-15 lb. per sq. ft. Their geometry is geared to standard building material dimensions, i.e., one, two, and three feet in length and 16 inches high. Using the system, walls are designed in 1-ft.-long increments and one foot thick. Convenient manual handling, the inventor affirms, is facilitated by panel size as well as their composition of 41 percent lighter concrete. Further, he adds, 1-, 2-, and 3-ft. lengths provide a pleasing symmetrical appearance and design versatility.

After concrete placement, expanded steel is positioned in the panel back on 12-in. centers, six inches from the ends, to preserve uniform spacing regardless of length combinations used in erection. A ?-in.-deep, 1/10-in.-wide slot is centered on the plane of each edge around panel perimeters to accept a Ê-in.-wide polycarbonate strip that aligns and reinforces adjacent units. Bolting together the overlapping expanded steel to join two panels completes the assembly for a stable, 12-in.-wide wall footprint.

Electric boxes can be cast into the panel and are accessible from the cavity for simple wiring. Moreover, incorporating window and door frames assures a 100 percent fireproof enclosure, the system designer contends; and, cast-in-place concrete can readily be used for structural elements, e.g., columns and beams within the wall cavity. Accordingly, the building solution features durable, glass-smooth, lightweight concrete wall surfaces, as it provides a stay-in-place form for a column, spandrel beam, and post-tensioned elevated slab structural system that satisfies ACI 318-05. That frame can be minimal or massive, the inventor observes, to suit application demands.

Cavity Wall technology demonstrates its versatility in adapting to various functions. For exterior walls, a rigid 2-in., foil-faced polyisocyanurate insulation board [R-7.5 per inch] is embedded in cement paste during casting to achieve bonding to the back of outer and inner panels. Narrow 4- _ ?-in. slots in the board accommodate expanded steel couplers, which are coated with nanotech pipe-insulating paint to prevent thermal bridging.

The remaining 4-in.-wide cavity allows sufficient space for installation by pneumatic ratchet of a bolt, washer, and nut assembly at the couplers to connect opposite wall panels. Wires and tubing then are routed, and the cavity is filled with lightweight cinders to prevent air infiltration, increase insulation, and provide forming support for the top spandrel bond beam.

Where columns and beams are cast, the insulation board on the interior panel is omitted, permitting a 6-in. thickness; or, a quarter-inch bubble/foil/bubble insulation can be used on the interior face, reducing column beam thickness to 5Ê inches. Vertical sides of cast-in-place columns are formed by attaching oriented strand board to the expanded steel couplers; and, the top level of cinders fill serves as the beam’s bottom support. Extending the base of the beam two inches into the next panel optimizes joint stability.

A high-performance exterior wall is thus produced, the engineer asserts, which combines the insulating properties of two lightweight concrete panels and, predominantly, two layers of polyiso board with a central fill of cinders to achieve a fire-resistant, air-infiltration-proof barrier. Additionally, the wall is immune to ultraviolet degradation and the elements, assuring minimal maintenance over time.

For interior walls, diminished insulating requirements make a full 8-in.-wide cavity available for load-bearing supports, allowing greater beam and column widths to enhance strength. Beyond interior columns and beams, the cavity may be filled with water in containers, e.g., recycled milk jugs or custom-made vessels, as water volume reportedly increases thermal storage capacity by a factor of three. Encasing the water containers by filling spaces between them with flowable, lightweight cinders eliminates splitting forces due to accumulated weight.

Overall, energy efficiency is maximized by means of a high thermal mass system that entails economical use of resources. A simple design enables four inches of lightweight concrete to produce a 12-in.-wide wall footprint and provides 30,000- to 60,000-lb./ft. load-bearing capacity per side. The lightweight concrete exterior and cavity wall construction optimize use of portland cement and cinders aggregate to achieve flood, earthquake, and wind resistance, plus R-30 and four-hour fire ratings. Further, the column, spandrel beam, post-tensioned elevated slab structural system requires no erection equipment. Û or (for licensing terms)