All homes need to have some air leakage in order to building building code standards, but too much air leaking into your home can cause moisture problems. With today's building standard it's preferred to control this leakage with an ERV or HRV. If a home has not been air sealed the leaks will cause issues like moisture damage to attics and indoor air quality problems in the home. Before you insulate your attic all the excess air leaks need to be sealed to prevent damage to your home.