As an expert in the field of insulation, I can confidently say that you rarely need to remove existing insulation before adding new insulation, unless you have a specific or personal reason. Removing old insulation requires more time and labor, so it's usually not worth the extra cost. The main reasons for removing old insulation are that it can impede air flow into the attic, promote mold growth, and be dirty. The old floor insulation has been exposed to outside air because the attic is ventilated. Foam insulation is beneficial for sealing attic ventilation, and it's important to remove the old insulation from the attic floor.
If airflow is blocked, there will be a temperature difference between the attic and the rest of the house. That old insulation could cause more problems than it's worth and hinder the ability of aerosol foam to effectively insulate the attic.
Attic insulation
is essential for getting most of your home's heating and cooling without driving up your energy bills. Before applying spray foam, any old insulation must be removed from the attic floor. The work will take approximately eight to ten hours, depending on the size of the attic and if you have more than one attic. The old insulation of the attic floor will almost always be cellulose or fiberglass, which are fibrous materials that have been shown to retain moisture and promote condensation, along with moisture problems.So, if you find that your attic needs more insulation, even if the existing old insulation still has some value left over R-value, insulating the attic floor with spray foam is a great way to isolate it from the rest of the house and create an air seal. Finally, if a rat has been in an area, a trail of excrement will follow, and the insulation must be removed and the attic disinfected before installing new insulation. This is one of the main reasons why old attic floor insulation should be removed when insulating the roof cover with aerosol foam.
