Reaching $205.46 per square foot as of April 2013, the 25-metropolitan-area RPX Composite price was up 13.1% from the April 2012 level and 2.7% higher than its March 2013 level, Radar Logic Incorporated reported in its RPX Monthly Housing Market Report for April. 

From its post-crash low of $169.62 in January 2012, the RPX Composite price has increased 23.7%, but remains 26.2% below its all-time peak in June 2007. 

Of the 25 metropolitan areas included in the RPX Composite, 23 exhibited year-over-year price appreciation. 

The increase from March to April 2013 was driven largely by seasonal factors, as prices typically increasing off seasonal lows in April. However, this year’s increase more significant than in the past. In fact, prices haven’t increased this much since April 2005. 

One reason behind the stark increase in home prices is the lower-than-normal inventory. The inventory of homes for sale dropped 10.1% year-over-year to 2.22 million, a 5.1-month supply, according to data from the National Association of Realtors. 

Reluctance from homeowners, paralyzed by low home prices at the bottom of the market, has kept supply constrained. As prices have started to increase over the past year, many homeowners have held out, anticipating receiving a higher price in the future.

Widespread negative equity has also kept inventory tight, with an estimated 10.2 million out of a total of 50 million homeowners in the country owing more on their mortgages than their homes are worth. 

The slow rate of housing construction over the past five years has also been a huge damper on supply as well. According to data from the U.S. Census Bureau, housing starts reached historic lows between 2009 and 2011. Since January 2012, housing starts have increased 27% on a non-seasonally-adjusted basis, but remain 29% below the long-term historical average. 

Demand is being aided by the shortage in inventory, home price appreciation, low mortgage interest rates and an increased investor demand for single-family homes. Because of this, the 25-MSA RPX transaction count rose 10% year-over-year in April. 

"The market factors driving the recent increase in home prices will not persist forever. Eventually, rising prices will reduce demand and attract supply to the market and reduce the rate of price growth. However, it is not clear how long this will take," Radar Logic Incorporated said in the report.