Tie type A for masonry cavity walls

Connect the leaves of a cavity masonry wall only where necessary by wire type (butterfly) ties as described in BS EN 845-1 and spaced as required for structural purposes, see BS 5628-3 which limits this tie type and spacing to cavity widths of 50 mm to 75 mm with a minimum masonry leaf thickness of 90 mm. Alternatively, use wall ties with an appropriate measured dynamic stiffness for the cavity width. The specification for wall ties of dynamic stiffness, kXmm in MN/m with a cavity width of X mm and n ties/m2 is n.kXmm<4.8 MN/m3.