Today in the US, most houses and apartments are built using light framed wood construction. This system consists of load bearing walls made from 2x4s or 2x6s, which support a wood-framed floor or roof - usually either trusses, joists, or engineered i-joists. This system is a variant of a framing style known as balloon framed construction, and though it may not look particularly impressive, it’s one of the most important developments in the history of building technology.