Alan Greenspan accepts little if any responsibility for fueling the housing boom:

I do not doubt that a low U.S. federal-funds rate in response to the dot-com crash, and especially the 1% rate set in mid-2003 to counter potential deflation, lowered interest rates on adjustable-rate mortgages and may have contributed to the rise in U.S. home prices. In my judgment, however, the impact on demand for homes financed with ARMs was not major.
Demand in those days was driven by the expectation of rising prices--the dynamic that fuels most asset-price bubbles. If low adjustable-rate financing had not been available, most of the demand would have been financed with fixed rate, long-term mortgages. In fact, home prices continued to rise for two years subsequent to the peak of ARM originations (seasonally adjusted).