A Massachusetts ballot measure would require most cities and towns to allow single-family homes on lots as small as 5,000 square feet, challenging zoning rules that have helped limit the number and types of homes that can be built. The proposal, on this year’s ballot, does not apply to Boston, which has its own zoning rules. It would cover communities with water and sewer access, but opponents say it does not account for whether local systems have enough capacity for additional development. Supporters argue that allowing smaller lots could make it possible to build more modest homes and ease the state’s housing shortage. In many Massachusetts communities, zoning requires at least an acre for a single-family home—about 40,000 square feet. The measure would permit lots one-eighth that size. For Jamie Sharken, a 34-year-old renter who grew up in Massachusetts, buying a home feels out of reach. She shares a run-down house in Lexington with three other people and said saving for a down payment is difficult, especially for people carrying education debt. Sharken supports making room for smaller homes, saying large houses occupied by just one or two people leave too few options for others. Housing economist Andrew Mikula, who is helping lead the campaign, points to older neighborhoods in North Braintree where smaller homes sit closer together. He said many of those homes could not be built under current zoning. After World War II, minimum lot sizes grew in many communities, restricting housing construction and helping preserve low-density, single-family neighborhoods. The shortage has consequences beyond home prices. State data cited by supporters show that about 400,000 young adults still live with their parents. Jesse Kanson-Benanav, executive director of Abundant Housing Massachusetts, said workers in retail, health care and other service jobs often cannot afford to live in the communities they serve. He described the shortage as an “existential crisis” affecting people across generations, including seniors who want smaller homes nearby. But allowing smaller lots would not guarantee that the resulting homes are affordable to first-time buyers. In Lexington, a renovated house on a small lot was listed for nearly $1.3 million; another, larger home on a small lot sold for more than $2 million. Lexington Select Board member Jill Hai said the zoning change may not be as effective as local programs that tie rents to income or use town-owned land for affordable housing. She also questioned a statewide mandate, while acknowledging that her own adult children cannot afford to return to town. The Massachusetts Municipal Association opposes the measure. Its executive director, Adam Chapdelaine, warned that new development could strain schools, roads and water and sewer systems. He said communities may have to expand those systems, potentially passing costs on to existing ratepayers. The proposal is part of a broader push by states to loosen local restrictions as housing costs climb. Massachusetts has also required multifamily zoning near transit stations, allowed accessory dwelling units in areas zoned for single-family homes and committed billions of dollars toward housing programs. Supporters say smaller-lot zoning is one tool among several; opponents say local officials should retain more control over how growth is planned. The potential price of a smaller home remains uncertain, particularly near Boston, where land is expensive. Tobias Peter, a housing policy researcher at the American Enterprise Institute, said smaller lots can help builders offer lower-cost homes where land prices are more affordable. He suggested that even a home costing $500,000 or more might count as a starter home in Massachusetts, given the state’s high incomes and housing costs—a definition that could still leave many households priced out.