In 2017, 37,000 homes were built as rentals, according to the National Association of Home Builders. That grew to 43,000 last year, or just under 5% of total single-family housing starts. But that is just homes built and held by builders for rent and doesn't include those sold directly to investors, so the numbers are likely larger and growing more quickly.
The only operating expense for landlords is the landscaping. In addition, the rents for single family are growing fast at 4.5% annually now compared with 3% rent growth for multifamily apartments, according to John Burns Real Estate Consulting. There is also much less turnover in single-family rentals, and the rental market is much less volatile than the home sales market.