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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.

Installing sheets of plywood over attic insulation is a popular choice, especially in storage spaces. That said, insulation works by trapping hot air—so it needs extra space to expand and be effective, or you might reduce the energy efficiency of your home. 

It’s important that you never compress the insulation by installing flooring directly on top of it. In many houses, you’ll need to install a subfloor before putting plywood over insulation in your attic.

The best type of insulation for your home depends on your specific needs, climate, and the area you are insulating. For new construction, structural insulated panels are a highly energy-efficient option that is easy to install during the building process. In very warm climates, reflective insulation can be a cost-effective choice. For cold climates, fiberglass is an excellent option due to its high R-value and resistance to settling over time. Spray foam works well in humid environments because of its moisture-resistant properties. For standard attics, loose-fill, spray foam, or blown-in insulation are all suitable options.

Acoustic foam, fiberglass insulation, soundproof curtains, and specialized drywall are effective in reducing noise transmission.