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You do not always need to remove old insulation before adding new. If the existing insulation is in good condition—not wet, physically damaged, moldy, or infested with pests—you can add new insulation directly on top of it for a compounding effect. You can also mix different types, such as adding blown-in insulation around existing fiberglass batts.

However, removal is recommended if the old insulation is compromised by water damage or pests. You should also remove it if you plan to install a different type of insulation, like switching from roll or batt insulation to spray foam. If the existing insulation is very old or damaged, you will likely get more benefit from removing it and starting fresh.

Ideally, you can add new insulation to your existing insulation. However, some circumstances require you to remove old insulation before adding any new insulation: 

• If the insulation is over 15 years old

• If the insulation is wet or moldy

• If it is vermiculite insulation

• If you see signs of pest infestation

Removing old insulation is best left to a pro who can safely dispose of potential moldy or asbestos-ridden insulation.

Mineral wool wraps are the most affordable and effective insulation for crawl space ducts. They are easy to cut, last for a long time, and healthier for humans. Meanwhile, fiberglass wraps are cheaper but more hazardous and difficult to handle. If you do choose to use a fiberglass wrap, make sure you are wearing long sleeves and wear proper protective gear.

Drywall insulation costs around $1,800, on average, but prices can range from $500 to $4,500, depending on a few different factors. The following things are important considerations to make when pricing out your insulation project:

• Square footage of insulation

• Type of insulation 

• Climate in your area and the insulation R-value required

• Whether or not your walls are already finished

• Accessibility of the area 

• Whether or not you need old insulation removed first