The threshold change of equilibrium concentration of vacancies for reported void defect density change due to substitutional B and Sb doping is estimated. Changing point defect concentration by more than 10% for either B or Sb changes the void density. Thus, the threshold impurity concentration for changing void density is predictable for various dopants. The mechanism of void density change by the change of vacancy equilibrium concentration is discussed. Strain energies for the substitutional N, interstitial N pair and N2V proposed by the first principles calculation are calculated using the valence force field model. The role of stress in determining the configuration of N in Si and resultant point defect behavior is discussed.