You may have known this intuitively, but a new poll is confirming what’s on many San Franciscan’s minds: Voters here are overwhelmingly concerned about the affordability and availability of housing, particularly for families, artists and middle class residents.

The survey of 400 likely voters was conducted earlier this month by David Binder and Associates for TODCO, a nonprofit housing development firm that helped craft a proposal for the November ballot that has developers and Mayor Ed Lee all in a tizzy.

That proposal, authored by District Six Supervisor Jane Kim, would seek to ensure that 30 percent of all housing units are below market rate by holding market-rate developers to more rigorous and time-consuming scrutiny anytime the ratio of affordable housing in the city’s development pipeline slips below the 30 percent threshold. Market rate developers, however, are predicting that the proposal would lead to a reduction in housing construction. And Lee recently introduced a competing ballot measure that would essentially invalidate Kim’s if it received more votes. Kim has said she’s open to a compromise measure, but no deal has been reached.

Enter TODCO with a poll — released Thursday, the same day Kim and Lee’s proposals were the subject of a public hearing at a Board of Supervisors committee — that the firm’s CEO, John Elberling, said shows strong public support for at least the idea behind Kim’s proposal.

For example, the survey found that 64 percent of respondents want at least 30 percent of future housing to be affordable to low- and middle-income households, and one-third think as much as half should be. Voters expressed concern not just about the cost of housing, but about how rising costs and gentrification are changing the character of San Francisco neighborhoods. Seventy five percent said they have noticed significant changes to neighborhoods over the past three years, and a majority of those people said those changes have had a negative impact.

Perhaps most importantly, Elberling said, “Voters clearly aren’t satisfied with what City Hall has done around this issue so far.” A strong majority — 59 percent — said they disapprove of the job city government has done addressing the rising cost of housing, with people between ages 30 and 39 the most concerned.

He said the poll indicates that the “sentiment is there to support” Kim’s proposal, but acknowledged that whether supporters can sell voters on the details remains to be seen.

The poll shows sharp differences among different groups. Those under the age of 30, those who make more than $100,000 a year and those who have lived in San Francisco for less than five years were overwhelmingly positive about the city’s direction, while those who make less than $99,000 a year and those between the ages of 30 and 49 are far more split about whether the city is going in a negative or positive direction.

The poll was conducted between July 7 and 11 and surveyed 400 likely San Francisco voters. The margin of error was 5 percent.

Marisa Lagos is a San Francisco Chronicle staff writer. E-mail: mlagos@sfchronicle.com, Twitter: @mlagos