Question 1

How do I add insulation to existing walls?

Accepted Answer

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If you need to insulate behind finished walls, the best option will likely be to have an insulation professional install blown-in insulation. The installation requires small holes cut in your wall, after which the installer can blow loose-fill insulation into the void. After the installation, you’ll have minor drywall patching, which shouldn’t cost more than $100. Compared to ripping down the existing drywall, using a different type of insulation, and replacing and finishing the drywall, this should save you hundreds or even thousands, depending on the size of the room you’re insulating.

Question 2

Do you have to staple insulation?

Accepted Answer

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You don’t need to staple insulation, as your drywall and studs will hold it into place. But if you already have a staple gun and staples lying around, it can help keep the product in place and avoid any shifting. But, most experts agree it’s an unnecessary step.

If you’re adding a vapor barrier, you will need to staple that in place.

Question 3

How much does it cost to insulate or reinsulate an attic?

Accepted Answer

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On average, insulating an attic costs about $2,500, with a typical range of $1,500 to $3,500. The final price often depends on the attic's size, with costs generally falling between $1 to $3 per square foot. For example, insulating a 1,800-square-foot attic would likely cost between $1,800 and $5,400.

If the project involves removing old insulation, this can add an average of $900 to the total cost, bringing a full removal and reinsulation project to around $3,000.

Several factors influence the overall cost:

Insulation Type: Prices per square foot vary significantly by material.
Reflective: $0.50–$1.50
Blown-in: $1–$4
Batt: $2–$4
Loose-fill: $2–$5
Spray foam: $2–$5
Structural insulated panels (SIPs): $4–$7
Project Complexity: Factors like sealing air leaks, poor attic accessibility, and required inspections can add to the cost.
Removal Issues: The discovery of mold, asbestos, or pests during the removal of old insulation can substantially increase the price.

Question 4

Should you remove old insulation before adding new insulation?

Accepted Answer

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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.

Question 5

Does basement insulation need a vapor barrier?

Accepted Answer

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Yes, basement insulation needs a vapor barrier due to its susceptibility to moisture seeping in from the outside of the house. You should install a moisture barrier before you install insulation or purchase insulation that comes prebuilt with a moisture barrier to avoid water damage in your insulation and costly mold and water remediation expenses.