JOINT CENTER FOR HOUSING STUDIES OF HARVARD UNIVERSITY - 2019
Harvard released its comprehensive study on housing trends and the current state of housing.  The report begins with the Executive Summary:
With new construction still slow to recover from historic lows, almost 80 percent of the nation’s 137 million homes are now at least 20 years old and 40 percent are at least 50 years old. The aging of the US housing stock has been a boon to the home improvement industry, helping to lift the remodeling market to nearly $425 billion in 2017, according to the latest estimates from the Joint Center for Housing Studies. 
Indeed, in the years since the Great Recession, spending on improvements and routine maintenance to both owner-occupied and rental properties has not only increased the value of the existing stock but also contributed a dominant share of residential investment. In addition, the tens of millions of projects undertaken annually—from roof and window replacements to major kitchen and bath remodels—generated 2.2 percent of national economic activity in 2017.
Some of the recent strength of the remodeling market reflects a significant increase in spending by rental property owners. The surge in rental demand following the housing crisis prompted owners to invest in substantial upgrades to their units. Homeowners also had some catching up to do on maintenance and replacements deferred during the downturn, particularly on properties converted to rentals or left vacant for extended periods.
Get the full report here:  Harvard JCHS Housing Study