Double Wall Precast -Concrete Sandwich Panels

The double wall process has been in use in Europe for many years. The walls consist of two wythes of concrete separated by an insulated void. The most commonly specified thickness of the wall panels is 8 inches. The walls can also be built to 10 and 12 inches thick if desired. A typical 8-inch wall panel consists of two wythes (layers) of reinforced concrete (each wythe is 2-3/8 inches thick) sandwiched around 3-1/4 inches of high R-value insulating foam. 

The two wythes of the interior and exterior concrete layers are held together with steel trusses. Concrete sandwich panels held together with steel trusses are inferior to those held together with composite fibreglass connectors. This is because the steel creates a thermal bridge in the wall, significantly reducing the insulative performance and reducing the ability of the building to utilise its thermal mass for energy efficiency. 

There is also the risk that because steel does not have the same expansion coefficient as that of concrete, as the wall heats and cools, the steel will expand and contract at a different rate to the concrete, which can cause cracking and spalling (concrete "cancer"). Fibreglass connectors that are specially developed to be compatible with concrete significantly reduce this problem.[12] The insulation is continuous throughout the wall section. The composite sandwich wall section has an R-value exceeding R-22. The wall panels can be made to any height desired, up to a limit of 12 feet. Many owners prefer a 9-foot clear height for the quality of look and feel it affords a building.

A single-family detached home being built up from precast concrete parts

The walls can be produced with smooth surfaces on both sides because of the unique manufacturing process, which form finishes both sides. The walls are simply painted or stained on the exterior surface to achieve the desired color or textured surface. When desired, the exterior surface can be manufactured to have a wide variety of brick, stone, wood, or other formed and patterned appearances through the use of reusable, removable formliners. Interior surfaces of the double-wall panels are drywall quality in appearance right out of the plant, requiring only the same prime and paint procedure as is common when completing conventional interior walls made of drywall and studs.

Window and door openings are cast into the walls at the manufacturing plant as part of the fabrication process. Electrical and telecommunications conduit and boxes are flush-mounted and cast directly in the panels in the specified locations. The carpenters, electricians, and plumbers do need to make some slight adjustments when first becoming familiar with some of the unique aspects of the wall panels. However, they still perform most of their job duties in the manner to which they are accustomed.

Double-wall precast concrete sandwich panels can be used on most every type of building including but not limited to: multi-family, townhouses, condominiums, apartments, hotels and motels, dormitories and schools, and single-family homes. Depending upon building function and layout, the double-wall panels can be easily designed to handle both the structural requirements for strength and safety, as well as the aesthetic and sound attenuation qualities the owner desires. Speed of construction, durability of finished structure, and energy-efficiency are all hallmarks of a building that utilizes the double-wall system.