The Cause

What is affordable housing?
The Department of Housing and Urban Development (HUD) considers housing to be affordable to a low-income family as long as the cost of housing, including rent or mortgage/tax payments plus basic utilities minus telephone and internet service, does not exceed 30% (before taxes).

How much does a household have to make annually to qualify as low
income?
Low-income is defined as a household whose annual income does not exceed 80% of the median income for the area, as determined by HUD. Other factors are considered on a regional basis where there may be great disparity between the wages earned by high and low income families.

What is the "Fair Market Rent" (FMR)?
Fair Market Rent, or FMR, is a geographically-averaged rent estimate including basic utilities (excluding telephones and internet).  A property owner looking to rent can compare other properties in the area and the local FMR to determine an appropriate rental amount to charge.  This amount is also used to determine the affordability of housing in the general area.

Considering this...
I currently live in Stevensville, part of Queen Anne's County, MD.  For 2014, the 50th percentile fair market rent (FMR) for an efficiency apartment in Queen Anne's County is $847/mo, and for a one-bedroom the FMR is $1001/mo.

The minimum wage in Maryland is set to the federal rate, which as of January 1, 2012 is currently set at $7.25/hr.  At $7.25/hr, 40 hrs/week, and 52 weeks/year (not including federal holidays), this is an annual salary of $15,080.  Just to reach the current FMR in Queen Anne's County for an efficiency ($847), a person would need to be working ~90 hrs/week at minimum wage.  In fact, you will find by further investigation that in no county in the US can an individual afford a two-bedroom apartment at the FMR by working full-time at the minimum wage.  Likewise, excepting a handful of counties in Washington and Oregon states (where the state minimum wage is above the federal minimum), there are no other counties in the US where that same individual could afford a one-bedroom apartment at the FMR.

I encourage everyone to take a quick look at the Out Of Reach 2013 report by the National Low Income Housing Coalition, which gives a great summary of all of this information and a ton of state-specific values on the cost of housing.  For instance, at the estimated mean hourly wage for renters in Queen Anne's County of $7.99/hr, the "affordable rent" is a measly $416/mo for a full-time employee.  At this wage, the renter would have to be working 2 full-time jobs to afford an efficiency apartment at the local FMR ($847), or up to 3 jobs for a 2-bedroom apartment.