[aclatuts]

I don't think there is much difference that's why all the projects plan for 20% low income units.

[dragonwriter]

You are misparsing the sentence: it is:

  ( 
    20% low-income or 
    100% middle-income
  ) and environmentally sound

Not:

  20% low-income or
  (
    100% middle-income and
    environmentally sound
  )