Picking the right face with fiberglass insulation containing a vapor barrier facing is crucial. The facing has a thin asphalt layer acting as a vapor barrier to block moisture. It can also have Kraft paper or foil attached on one side. Proper installation is critical to getting the expected performance from the insulation. Follow these best practices when installing faced insulation in your home.

Best Side Forward

The insulation should always face the warm-in-winter side. Use faced insulation with the paper facing the heated living space. So, in cold climates, it should face the interior; in hot, humid climates, it should face the exterior.

Also, cut the insulation batts to fit between the ceiling joists. Leaving gaps enables warm air to escape in winter or hot air to enter in summer, reducing your insulation’s effectiveness. Take time to custom-cut each piece for a snug fit. If insulating an attic space, make sure you’re familiar with how to place faced attic insulation before proceeding.

Problems with the Wrong Side

Incorrectly installing insulation leads to problems. Here is what happens when the vapor barrier ends up on the wrong side:

  • Moisture gets trapped inside wall cavities, causing condensation buildup.
  • You get a musty smell.
  • You get wood rot.
  • It promotes severe mold issues, impacting your indoor air quality.

Condensation happens when warm, humid air contacts a cold surface. With the vapor barrier on the wrong side, moisture cannot escape and pools inside the walls or attic. Over time, constant dampness rots structural materials like wood and drywall. Mold spores thrive in moist environments and can trigger allergic reactions or respiratory problems when inhaled.

The Fix

If you installed insulation wrong side up, remove it immediately and inspect for moisture or mold before reinstalling or replacing it. Look for dark or discolored areas and musty odors. Use a moisture meter to check the moisture content. If mold exists, have a professional perform mold remediation before adding new insulation.

Replacing upside-down insulation in time prevents permanent damage. But you must act quickly once you realize your error. Leaving the vapor barrier incorrectly installed traps moisture and can lead to mold within weeks in some cases. Immediate removal gives the materials a chance to dry before rot sets in.

Hiring a Professional

While a DIY approach seems straightforward, proper insulation installation requires building science and moisture control knowledge. Consider hiring an insulation contractor, especially for dense-packing wall cavities. They have the tools and experience for proper insulation coverage and air sealing.

Professionals access industrial insulation materials and can install specialty options like spray foam, doubling as a vapor barrier. They know how to find and seal all the gaps and air leaks, letting conditioned air escape. This expertise ensures you get the insulation’s full performance benefits.

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So, Is Proper Installation Crucial for Insulation?

Yes, correctly installing insulation is vital to gain energy efficiency and moisture control benefits. Faced insulation, in particular, must be oriented with the vapor barrier on the right side. Taking the time to install insulation properly avoids issues with mold, rot, high energy bills, and poor indoor air quality. Before beginning the project, ensure you know how to apply a vapor barrier to attic insulation. Consider hiring a professional if you lack the building science expertise to do it yourself.

FAQs About Installing Insulation

What are signs I installed the insulation wrong?

Signs that you installed your insulation incorrectly include musty, damp smells and rotting,  discolored, or moldy materials. Other signs are an obvious buildup of condensation and high moisture readings inside the walls or in the attic.

How soon do I need to fix improperly installed insulation?

You should fix improperly installed insulation as soon as possible — within weeks. Leaving the vapor barrier on the wrong side traps moisture and can quickly lead to mold growth and rotting structural materials.

Can I install faced insulation in all climates?

Yes, you can install faced insulation in any climate, but the orientation changes. In cold climates, face it toward the heated interior. In hot, humid climates, face it toward the exterior.

What if there is already mold present?

If you have mold already present, have a professional perform mold remediation before installing new insulation. The spores must be killed and removed for healthy indoor air.

Is it better to hire a pro?

You’re almost always better off hiring a professional to install insulation. Insulation contractors train in building science and proper installation methods. Their expertise can ensure optimal insulation coverage and prevent issues.

Editorial Contributors
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Elisabeth Beauchamp

Senior Staff Writer

Elisabeth Beauchamp is a content producer for Today’s Homeowner’s Lawn and Windows categories. She graduated from the University of North Carolina at Chapel Hill with degrees in Journalism and Linguistics. When Elisabeth isn’t writing about flowers, foliage, and fertilizer, she’s researching landscaping trends and current events in the agricultural space. Elisabeth aims to educate and equip readers with the tools they need to create a home they love.

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Sabrina Lopez


Sabrina Lopez is a senior editor for Today’s Homeowner with over 7 years of writing and editing experience in digital media. She has reviewed content across categories that matter to homeowners, including HVAC services, home renovations, lawn and garden care, products for the home, and insurance services. When she’s not reviewing articles to make sure they are helpful, accessible, and engaging for homeowners like herself, Sabrina enjoys spending time with her family and their two parrots.

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