Insulation over air leaks simply filters the heated air as it leaves the building. Consumers are often misled by home inspectors and insulation salesmen in this regard. They waste a lot of money and achieve none of the intended results.
Additionally, prior to air sealing … infiltration rates must be measured to ensure that sufficient ventilation remains for proper venting of poisonous combustion gases and that conditions conducive to mold are not created.
Any fool can recommend adding insulation to reduce energy bills … and most do.
It’s very sad for home owners who later discover (after consulting with a certified Building Analyst) that their new insulation must be removed or diminished in order to seal the air leaks that can actually cause up to a 45% loss of wasted energy (and money spent to buy it) … and then have to pay to restore it to the desired R value, again.
Air leakage is definitely to be addressed prior to insulating … and requires a blower door test to ensure that it is safely and efficiently done.
Home inspectors who discover missing or otherwise insufficient insulation can best serve their client by recommending that a certified professional perform a blower door test to measure air infiltration rates and locate leaks PRIOR to improving the insulation. They will save their client from wasting money while helping them to improve the energy efficiency and comfort of their new home.