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Yes, you can install insulation behind drywall yourself, but only if your walls are not finished. If your studs are exposed, installing fiberglass insulation in roll or batt form is very straightforward and just requires a few tools and some safety equipment. If your walls are already finished and you’re looking to add insulation, it’s better to hire a professional, as you’ll likely need blown-in insulation, which can be dangerous to work with and a challenge to get into the proper areas in your wall voids.

While not every wall requires a vapor barrier, if you do need one and don’t install it, moisture can get between the walls of your home. This can lead to water damage from mold growth or rot, and the excess moisture could also attract pests, including termites, cockroaches, or ants.

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.

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.