The Place for Sudbury's Citizen Reporters
The 2011 Sudbury Housing Production Plan offers an explanation of housing income limits. You can check the document here: Sudbury Housing Production Plan
From page 17:
Income limits are updated by HUD on a yearly basis. The 2010 income limits are:
State, Federal Housing Program Limits: Very Low Income (50% AMI) $45,900
Low Income (80% AMI) $64,400
CPA Housing Expenditure Limits: Moderate Income (100% AMI) $91,800
As explained in that document, AMI is Area Median Income, figured over the Boston-Cambridge-Quincy Metropolitan Area, which includes Sudbury. HUD is the federal office of Housing and Urban Development. HUD publishes the income limits--which is why 80% of $91,800 is $64,400 and not the $73,440 your calculator tells you. HUD's 80% is capped at 80% of the median income across the US, except under circumstances for which the greater Boston area doesn't qualify. While 80% of the AMI is the income cap for "40B affordable" units, CPA (Community Preservation Act) affordable housing funds can be used to provide housing for those with up to 100% of the AMI. The actual AMI numbers for 2011 from HUD will be different.
Affordable Housing is limited to low income residents (80% AMI maximum--where this is the "HUD 80%"). In order to "count" as part of the 10% affordable housing quota which indicates the community has fulfilled its obligations under 40B, the housing must be part of the SHI (Subsidized Housing Inventory) for the town, which is maintained by DHCD (the Massachusetts Department of Housing and Community Development). Houses must be sold by lottery, and the income limit is 80% (HUD-defined) of AMI.
Workforce Housing is available to moderate income residents (80% to 120% AMI), as described on page 42. Encouraging the creation of workforce housing is a goal (goal #8) of the Sudbury Housing Production Plan.
It's important to understand the difference between affordable and workforce housing--specifically, that workforce housing does not count toward the 40B 10% (unless it's also "affordable"), and has different income limits. You'll be hearing a lot about workforce housing during the upcoming Route 20 zoning discussions.
I'd recommend skimming the Sudbury Housing Production Plan just in general. I hadn't realized that the Maynard Road "affordable" units were actually workforce housing (page 21) (fortunately, CPA funds can be used for workforce housing) ; or which properties the Town was considering for "affordable housing development" (pages 49-53); or that the Village District Business bylaw--section 2230 of the Sudbury zoning bylaw allowing mixed use residential units in Mill Village--has produced no residential units under this bylaw due to the lack of sewage facilities on Route 20 (page 35). It's cited as a success, but we've never implemented any residential units using it. I was also interested to see that the 495/MetroWest Development Corridor Partnership, which created the compact discussed here: The 495/MetroWest Development Compact and Sudbury , chose to explore the issue of housing affordability in 2007 at the Melone gravel pit.
But definitely keep the distinction between affordable housing and workforce housing in mind during the discussions ahead.