Q: Can you install a radiant barrier under insulation?

• <div><p>It&rsquo;s best not to install a radiant barrier directly under insulation because it requires an air gap on at least one side to work properly. Instead, you should install the radiant barrier over your existing insulation to create an air space to reflect the radiant heat. </p></div>

Question 1

Does an attic floor need a vapor barrier?

Accepted Answer

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Vapor barriers in attics are a bit outdated and most areas no longer recommend them for attic spaces.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.

Question 2

Can you install a radiant barrier under insulation?

Accepted Answer

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It’s best not to install a radiant barrier directly under insulation because it requires an air gap on at least one side to work properly. Instead, you should install the radiant barrier over your existing insulation to create an air space to reflect the radiant heat.

Question 3

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.

Question 4

How much does a radiant barrier cost?

Accepted Answer

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The cost to install a radiant barrier ranges from $700 to $2,800, depending on the size of your roof and the type you choose. Most people pay an average of $1,700 to install a radiant barrier. Foil options, both single- and double-sided, cost between $0.10 and $0.90 per square foot, while spray-on options start at $0.60 and go all the way up to $1 per square foot—which can add up quickly.

Question 5

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.