Mass masonry walls have always been the standard for building weather-resistive structures. A thick, redundant masonry wall acts as a blotter absorbing wind-driven rain through the exterior exposed surfaces and by its shear mass. The wall eventually dissipates the force (wind) and pressure differentials, maintaining a dry interior. While there are as many variations to these basic design principals as there have been architects, mass masonry has proven to be a most durable basic building wall system.

The first adobe hut included the extension of a thatched roof to over sail the mass masonry walls below. This arrangement provided the wall protection from above, and an architect asked, “Why don't we stop the roof on the interior face of the wall and hide it?” Thus, the parapet (vertical extension of the mass masonry wall) was invented.

This milestone in the evaluation of the building envelope added considerable complexity to construction, design, and maintenance in several ways.

  • The roof (horizontal water management system) had to interface into the parapet on the blind side in a water tight manner.
  • Provisions to drain the roof had to be incorporated by the inclusion of roof drains or scuppers to preclude ponding and minimize loadings imparted by standing water, ice, and snow
  • The wall extension (parapet) had to include a coping with or without flashing to protect the horizontally exposed portion of the parapet from water infiltration above.
  • The parapet is exposed on two sides and must resist twice the amount of wind-driven rain. In cold climates, inboard surfaces of the parapet can be in contact with melting ice and snow for extended periods.
  • The masonry parapet is more susceptible to thermal variations, which accelerate cracking and result in breaches that allow more wind-driven rain to enter the assembly.