Everyone wants "affordable" housing. But few people know what that is.

The U.S. Department of Housing and Urban Development has defined affordable housing as no more than 30 percent of a household's income.

That means you shouldn't be paying more than 30 percent of your income for housing — whether mortgage payments or rent — plus utilities each month.

"People think affordable housing means just one thing. But it doesn't," said Sandra Hamameh, program director for the Sacramento Housing Alliance. "It means being able to afford a place to live, at whatever stage you're in in your life."

Levels of affordability are also based on an area's median incomes. The median incomes for Sacramento County, based on 2009 figures, are $50,950 for a single person, $58,250 for a two-person household and $72,800 for a family of four.

For housing to be affordable, that single person should pay no more than $1,274 per month; the couple, or parent and child, household shouldn't pay more than $1,456; and the family of four should pay $1,820 or less, according to the California Department of Housing and Community Development.

Income levels that fall below the median include low income, very low income and extremely low income.

Low incomes are those at 80 percent of the median:
• $40,800 for a single person, making affordable housing no more than $1,020 a month;
• $46,600 for two people, and $1,165 a month for affordable housing;
• $58,250 for four people, and $1,456 a month for housing.

Very low incomes are those at 50 percent of the median:
• $25,500 for a single person, and $637 a month for affordable housing;
• $29,100 for two, and $727 a month for housing;
• $36,400 for four, and $910 a month for housing.

Extremely low incomes are those at 30 percent of the median:
• $15,300 for a single person, and $382 a month for housing;
• $17,500 for two, and $437 a month for housing;
• $21,850 for four, and $546 a month for housing.

Affordable housing may include subsidized housing projects such as multi-family apartments or single-family homes built or leased through public-private programs.

Single-resident occupancy units, or SROs, boarding houses and other arrangements offer housing for extremely low-income residents, but little of such housing exists, said Hamameh.

HUD has a housing choice voucher program known as Section 8 for elderly and disabled people, very low-income families, and homeless or otherwise-eligible veterans. Recipients use the vouchers to rent or buy housing.

Extremely low-income housing may also be occupied by people whose only income comes from monthly supplemental security income (SSI), Social Security or disability checks. A person getting $474 monthly SSI checks can afford rent of no more $142. A widow who now gets $718 a month in Social Security and $240 from her husband's retirement fund can afford rent of $287, Hamameh said.

In 2010, fair market rent for a one-bedroom apartment in Sacramento County is $852, according to HUD. Some people who can't find safe, quality affordable housing end up renting from private owners who still charge "fair market rate" for substandard housing, said Hamameh, whose organization has been advocating for affordable housing since 1989.

Suzanne Hurt is a staff reporter for The Sacramento Press.

Read the story about the proposal for the biggest SRO in Sacramento here .