Most homeowners in the city of Charleston would be allowed to have an apartment on their property -- a small house in the backyard, or an apartment in the garage, for example -- under proposed rule changes aimed at increasing the amount of affordable housing in the city.

In some cases, multiple "accessory dwelling units" would be allowed.

Concerns about where the tenants of such units would park could result in some opposition to the plan, as it has in the past, but city planners and affordable housing advocates are hopeful. Mount Pleasant passed a similar ordinance a year ago, and Charleston used it as a model.

"If you increase the supply of housing, you decrease the price -- and rents are very high on the peninsula, out of the reach of many working folks," said Bob Holt, a local developer who served on a city affordable housing committee that helped create the plan.

"I cannot tell you how many people have told me, over the years, that they would love to find a small house downtown with a rental unit, to help pay the mortgage," Holt said.

Charleston's Planning Commission will hear the details at a meeting Wednesday.

While the plan was driven by a desire to increase affordable rental housing, the proposal could be a boon to people who would like to provide a small place to live for an older relative.

Christiane Farrell, director of Mount Pleasant's Planning Department, said the town's ordinance also was developed as a way to create what's often called "workforce housing" -- homes that middle-income workers can afford.

"It was about workforce housing, but also about seniors," she said. "A lot of things came up about elderly parents."

In downtown Charleston, examples of "accessory dwellings" are common in older homes. A carriage house, or the ground-floor apartment below a classic Charleston single home, or an apartment above a garage would be examples.

The city's proposed rule changes would allow any homeowner with enough space on their property to create such a rental property, with a maximum size of 850 square feet. A one-story home 20 feet by 40 feet would nearly hit that limit.

For those willing to follow the city's rules on affordable housing, which means renting to people with certain incomes and charging limited rents, up to three accessory dwellings would be allowed, and with no requirement to provide off-street parking.

"It's like Christmas for affordable housing," said Tim Keane, director of the city's Department of Planning, Preservation and Sustainability. "We want to provide as regulation-free as possible an environment to create these units."

Despite the potential changes to city zoning rules, rental units would not be allowed in communities with covenants and restrictions that prohibit them. The same is true in Mount Pleasant, where only the I'On development has changed its rules to allow accessory dwellings since the town adopted its regulations.

In Charleston, an earlier version of the proposal was rejected by a committee of City Council.

"People worried that neighbors could turn their homes into apartment buildings. That's not what it's intended to do," Holt said. "It's more about the apartment over the garage, which is an American tradition, but you don't see them now."

Reach David Slade at 937-5552 or dslade@postandcourier.com.