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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.

While there are many different kinds of insulation, spray foam, blown-in, foam board, and batt and roll are the four types you’re most likely to see. That doesn’t mean they’re alike, though. Each one varies drastically in terms of cost, materials used, and how they’re installed—not to mention, how well they limit heat transfer.

The lifespan of crawl space insulation depends on how well you maintain your insulation and the type of insulation. Fiberglass will need replacing every 15 to 20 years on average if you don't have a vapor barrier in place. If you do have vapor barriers in place, then your insulation could last much longer. Spray foam insulation can last anywhere from 80 to 100 years.