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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.

The most affordable way to insulate behind unfinished walls is to install fiberglass batts or rolls. These total around $0.75 per linear foot, with the width matching the gaps between standard studs perfectly. However, it’s important to consider the R-value of your insulation and the climate in your area, as fiberglass insulation isn’t the best in terms of preventing heat transfer. Plus, the most affordable option may cost more on electricity bills over time. The most affordable way to insulate behind finished walls is to leave them up and use blown-in insulation to avoid drywall replacement.

Vapor barriers in attics are a bit outdated and most areas no longer recommend them for attic spaces. For vented attics, the best method is usually to install drywall and cover it with latex paint before attaching insulation fiberglass, cellulose, or foam insulation. When renovating an attic to use as a living space, a contractor can guide you on the best way to cover insulation.

For your safety, you should always wear a mask when cutting batts of fiberglass insulation. We also recommend wearing eye protection, safety gloves, and long sleeves to protect your skin. Properly suiting up helps you avoid several fiberglass issues, such as cuts from the tiny shards of glass and inhaling small bits of fiberglass.