Brutalism can be seen as having branched out from the International Style. It was originally started by the Smithsons and its first appearance can perhaps be traced to a design they did for a small house in Soho. This house was to be intended to have the structure entirely exposed and to have no finishes.
Brutalist architecture can be summed up into three principles, the memorability of the building as an image, the clear exhibition of a buildings structure and the valuation of its materials as they occur naturally.
During the middle decades of the 20th century the International style had become incredibly prevalent in architecture. All over the place cheap copies of buildings by le corbusier and other international style architects were being built. Raynor Banham stated that most modern buildings were beginning to appear as though they were constructed of white wash or patent glazing no matter what materials they were actually made of. Brutalism was a reaction to this mindless reproduction of the classic international buildings. Brutalism demanded a functional approach to architecture and advocated the return to functionalist principles in services materials and structure. Brutalist buildings were about truth. If a building was constructed of steel, concrete and glass then that is what it looked to be made of. There was no hiding of electrical or water amenities, the way in which these services were dlivered was not hidden but rather open for all to see.
Whereas the International Style is based on the aesthetics of the machine and expresses mass production through it?s similar elements and plain un-ornamented structures, Brutalism ignores the machine aesthetic and focus? on structural and material truth. Meaning that a building should look exactly how it?s built and what it?s made of.