The four eras of the wall
Great Mass Era: From early civilization into the late 19th or early 20th century, very thick stone, brick, log, adobe, and concrete walls provided defense against heat, cold, wind, earthquakes, and intruders, as well as primary structural support in buildings.
Curtain Wall Era: Upon the emergence of iron, steel, and concrete structural systems in the late 19th century, the exterior wall shed its load-bearing role and served primarily to enclose interior space.
Insulation Era: The invention of fiberglass insulation in 1938 allowed a 4" wall to offer similar protection from heat and cold as a 2' thick masonry or adobe wall. But as we insulated and sealed buildings more and more, they often developed problems with condensation and air quality.
Specialized Layers Era: The state-of-the-art building envelope has four layers that perform as an integrated system: water barrier (a cladding and/or membrane that protects against precipitation); air barrier (a membrane that minimizes seepage of exterior air into the building); insulation barrier (thermally separates interior and exterior); and vapor barrier (prevents movement of moist indoor air into a wall or ceiling cavity). Each layer should be continuous around a building.
