I’ve seen this question pop up a number of times, and in each case different numbers are floated as the answer. So why not throw out another?

According to the Federal Reserve the aggregate market value of all the residential real estate in the US, as of Q1 - 2008, was (a) $19.718 trillion. In addition, there was (b) $10.601 trillion in mortgages against that real estate. Chart of growth below (click for larger view):

The estimate replacement cost of residential real estate structures at Q1-2008 was (c) $14.283 trillion. And here is a graph of the change in replacement cost of those residential structures over the period - this should provide some idea of the amount of value injected into the economy as a result of residential real estate construction (inflation notwithstanding):

Note: There are probably a few apples versus orange discrepancies as it relates to values, mortgages, and replacement costs on farm households, mobile homes, and second homes, as well as second liens taken out against properties. Also, multi-family residences were excluded where possible, as I could not ascertain what might be purely rental property.

Source: The Federal Reserve Flow of Funds Statements
(a) B.100 Balance Sheet of Households and Nonprofit Organizations - line 4
(b) L.100 Households and Nonprofit Organizations - line 25
(c) B.100 Balance Sheet of Households and Nonprofit Organizations - line 42