The benefits of homeownership are clear and undisputed. The accumulation of wealth or what is called a "forced savings plan," is often the most favorable result of homeownership, especially among low-income families that have no other asset building strategy. Since owner's payments on mortgage principals are retained as equity in a comparatively illiquid asset, wealth is accumulated to the extent that the constant-dollar value of the owner's equity exceeds any decline in the home's value. The single-family house is the only architectural type driven almost entirely by the commodity practices of a market economy; a condition which encourages standardization and thus stifles architectural innovation. Dire trends over the past forty years, however, demand new architectural solutions as homes have consistently decreased in quality, diversity and affordability. Current lending practices, land use strategies, and production methods have made homeownership unaffordable for households with two median in nearly all major US cities.