Two-story homes are still more popular among homebuilders than single-story homes, but that gap is shrinking.

According to newly released analysis by the National Association of Home Builders, the share of new homes with two or more stories fell from 55% in 2017 to 53% in 2018, while the share of new homes with one story grew from 45% to 47%.

That means that the ratio between single-story and multiple-story homes is decreasing.

Although one-story homes were found more common in non-metro areas and two or more story homes were found more common in metro areas, 2017 and 2018 saw a rise of one-story homes in both.

The rise in one-story homes was heavily concentrated in the South, where the shares of two or more stories homes climbed 9%, 7% and 7% in the South Atlantic, East South Central and West South Central, respectively. The West North Central is the only division for which the share of single-story homes declined from 2017 to 2018.

The Midwest also saw a demand for single-story homes; 57% of new homes started were one story. New homes in East South Central and West South Central were 55% and 60% one story, respectively.

The NAHB also found that home height preference varies by generation, and more notably, the desire for a one-story home rises with age. Only 35% of Millennials want a single-story home, while 55% said they wanted a two-story home.

Due to aging in place concerns, 80% of Baby Boomers said they wanted to live in a single-story home, as well as 53% of Gen Xers and 74% of Seniors. Only 38% of Gen Xers, 17% of Boomers and 21% of Seniors said they wanted to live in a multiple story home.

Put simply, as age increases, desire to climb stairs decreases.