Copyright Goodheart-Willcox Co., Inc. 282 Section 4 Construction Details wythe. A minimum of 1″ should be left between the cavity face of the external wythe and the insulation board. The 1″ space between the outer wythe and the insulation board facilitates the wall construction and allows for drainage of the cavity. During installation, ensure that all boards are abutted and installed between ties, and fit flush against the inner wythe. An adhesive should be used to hold the insulation in place. Two types of granular fill insulation are recom- mended—water repellent vermiculite masonry fill and silicone-treated perlite loose fill insulation. Granular fill insulation is usually poured directly into the cavity from the bag or from a hopper placed on top of the wall. Pours can be made at any conve- nient interval, but the height of any pour should be kept below 20′. Rodding or tamping is not necessary, and could possibly reduce the thermal resistance of the material. The insulation in the wall should be protected from weather during construction. Bonding The facing and backing (adjacent wythes) of cavity walls should be tied together with corrosion- resistant 3/16″ diameter steel ties, or metal tie wire of equivalent stiffness, embedded in the horizontal mortar joints. There should be at least one metal tie for each 4 1/2 sq ft of wall area. Individual ties in alternate courses should be staggered—the maximum vertical distance between ties should not exceed 24″, and the maximum horizontal distance should not exceed 36″. The ends of the ties should be bent to 90° angles to provide hooks not less than 2″ long, or ties bent to a rectangular shape should be used. Additional ties should be provided at all openings spaced not more than 3′ apart around the perimeter and within 12″ of the opening. Where the cavity width exceeds 3 1/2″ but is less than 4 1/2″, there should be at least one metal tie for each 3 sq ft of wall area. Flashing and Weep Holes Flashing details are important in cavity wall construction. In order to divert moisture out of the cavity through the weep holes, continuous flashing should be installed at the bottom of the cavity, and wherever the cavity is interrupted by elements such as shelf angles or lintels. Flashing should be placed over all wall open- ings not protected by projecting hoods and eaves. It should also be properly placed at all window sills, parapet walls, and spandrels. (In a multistory building, the spandrel is the space between the top of a window of one story to the sill of the window on the second story.) Since the purpose of the flashing is to collect moisture so it can be diverted to the outside, weep holes must be provided wherever flashing is used. Weep holes are located in the joints of the outer wythe immediately above the flashing. Spacing of weep holes should be approximately 2′ O.C. maximum, except for those using a wick material that should be 16″ O.C. maximum. Expansion Joints The movement of an outer brick wythe due to thermal and moisture expansion can be greater than the movement in solid or composite walls exposed to the same environment. This is due to the greater robcocquyt/Shutterstock.com Figure 14-10. Rigid insulation in the cavity between masonry walls. The insulation seam between sheets is sealed with special tape to reduce air infiltration. Wall ties protrude through rigid insulation to tie both walls together.