As homes age, they require regular maintenance and renovation. Multifamily building contractors opine that it is easy to maintain a new house, but homes more than 20 years old often require complete renovation or at least one major expense each year in maintenance. Older homes need major roofing, electrical, and several plumbing upgrades to match the modern building code and to ensure that buildings remain safe and sanitary. The four major building codes of the USA are:

● The National Building Code by the American Insurance Association (AIA)
● The Basic/National Building Code (sometimes called the BOCA Code) by the Building Officials Conference of America (BOCA)
● The Southern Standards Building Code by the Southern Building Code Congress International, Inc. (SBCCI)
● The Uniform Building Code by the International Congress of Building Officials (ICBO)

According to a report published on the website of the National Association of Home Builders, the US Census Bureau has started the Rental Housing Finance Survey (RHFS). It was known earlier as the Residential Finance Survey (RFS) and was discontinued in 2001. Now in a new avatar, the RHFS will assess multifamily rental housing properties. The recent RHFS survey compared renovation expenses by property age.
 
Increasing renovation cost
According to the survey, the oldest buildings (constructed in 1920-30s) required the highest annual spending on renovation per unit, close to $1300 in 2011. On the other hand, newer properties (constructed in 2000s) had the lowest reported maintenance and renovation costs, around $500 per unit.

Renovation costs and income from rent
The survey also tried to establish a connection between renovation costs and income from rent. Annual renovation cost of old buildings (constructed in the 1970s) is $229 per unit, with per unit rent income being $1000. On the other hand, newer properties (constructed in the 2000s) require only $58 per unit in annual renovation costs and earn $1000 per unit from rent.
 
Thousands of multifamily properties are either under construction or renovation
Investors in Phoenix, Arizona have acknowledged the importance of multifamily properties. The Phoenix Business Journal reports that several risk takers who had invested in multifamily properties during the recession are now being rewarded with a high return on their investment. This has encouraged several multifamily property owners to invest in and renovate their old properties.
 
According to a NuWire report, investments in multifamily properties in the USA could break record of $105 billion investment in 2017. The report adds that the sales volume of multifamily houses jumped 28 percent in the 3rd quarter of 2014 from the same period last year to reach $27.5 billion.