Pertaining to the system-built house "Butterfly" two building systems combine: the masonry construction of the core area and the prefabrication of the pavilion annex, from which two architectural as well as functional configurations ensue. Whereas the heavy masonry of the core embraces basement, heating, kitchen, bathroom and living room-entrance hall, the light post-and-beam construction of the timber structures with infilling envelopes the living- and sleeping realms.