Energy-efficient concrete tilt-up homes are making news in Pueblo, Colo., where Castle Construction Co. is using insulated concrete sandwich panels to build two different home designs. Tilt-up panels can be made of either solid concrete or two layers of concrete, with an insulating layer sandwiched in between. Instead of using steel connectors, Castle Construction uses sandwich panels tied together with patented connecting rods made of a composite material combining a plastic resin with glass fiber for strength and durability. The connectors penetrate an expanded polystyrene core to join the two outer layers of concrete. Using the composite connectors significantly reduces heat loss that would otherwise occur with the use of conventional steel connectors. This optimizes energy efficiency; panel values range from 28 to 42 in the houses Castle Construction is building. With their high tensile strength, low weight, and low thermal conductivity, glass-fiber composites offer many advantages. Castle Construction is now developing a system of home construction that uses tilt-up panels made of lightweight cellular concrete. Cellular concrete flows more readily around forms for openings, integral hardware, and utility systems. This means minimal vibration is required for concrete compaction. With an estimated maximum unit weight of 70 pounds per cubic foot, the new panels require only a 35-ton crane for lifting.