Frequently Asked Questions


How much R-value do I need?

Visit our Insulation Calculator at for the recommended and minimum amounts of insulation you need for any part of your house, no matter where you live in the United States.

What do I do if my insulation gets wet?

Simply allow it to dry out. Once dry, it will assume its original R-value.

Which way does the vapor retarder face?

For most areas, vapor retarders should be installed on the warm-in-the-winter side of the insulation (toward the interior). For some warm and humid areas, vapor retarders – if used – should be installed outside of the heating or building envelope. It is not appropriate to install Kraft faced fiber glass with the facing toward the exterior. Check local practice and/or building codes before installation.

What do I do about vapor retarders in my basement?

If it is entirely below grade, it’s generally best to use an unfaced product or one faced with our MemBrain™ material. If it’s partially below grade, the portion that is above grade should be treated as the floors above.

Do I fasten the vapor retarder flanges to the face of the stud, or do I inset staple?

Either method may be used. Inset stapling allows drywallers to have a clean slate on which to fasten the wallboards. However, CertainTeed recommends face stapling the insulation for more uniform and complete vapor barrier coverage.

Is the Optima fabric a vapor retarder, and is it fire-rated?

Optima fabric is not a vapor retarder, but it is fire-rated. It may be left exposed in enclosed areas where it will not be affected by UV rays.

How do I insulate my crawl space?

Basically, you want to put a sheet of 6 mil or greater polyethylene on the dirt floor, having at least a 6-inch overlap of the poly on the dirt side. These "seams" are taped with a waterproof tape. The poly should be installed so it goes up the exterior wall on the inside of the crawlspace 12 inches and securely taped and fastened. It is not recommended to use faced insulation in the crawlspace unless required by code. CertainTeed recommends the use of MemBrain Smart Vapor Retarder over unfaced insulation. MemBrain is installed using cap nails (commonly used nails for roofing with a plastic cap to prevent moisture intrusion). Install the faced insulation so the facing is against the sub-floor. Then use chicken wire or metal rods to hold the insulation in place. The insulation is commonly installed with the facing down because it’s easier to install, but this is not the correct method.

What's the difference between your sound batts and regular batts?

Nothing. All fiber glass products provide both thermal and acoustical performance. The products marketed as sound batts are usually unfaced and/or sized for typical sound applications (i.e. interior walls, suspended ceilings, etc.)

How do I know if the contractor blew in enough loose fill insulation?

Contractors should install paper attic rulers prior to blowing in loose fill insulation. These rulers give the R-value of the insulation job. Make sure the insulation is evenly installed and that attic baffles have been installed where soffit ventilation exists. We have coverage charts online that tell you how many bags should be used in a particular space to achieve a desired R-value.

I have existing insulation in my attic floor. Can I just put batts right on top?

You may, but they must be unfaced. You do not want to sandwich an attached vapor retarder between 2 pieces of fiber glass, as that might trap moisture within that area. It’s also incorrect to face the kraft paper up.

Can I put your batts right up against the underside of my roof deck?

If you have soffit-to-ridge ventilation in place, you’ll want to use baffles to keep the batts away from the underside of the roof deck, so as not to inhibit the required air ventilation from the soffit to the ridge.

What is that odor coming from the insulation?

The smell is a by-product of the manufacturing process that occurs from time to time. Though it may be initially strong, it is not hazardous and will generally dissipate within a few weeks.

I'd like a higher R-value than my framing will allow. Is there a downside to compressing fiber glass insulation?

Compressing the insulation decreases the R-value, and compressing it too much renders it less effective than a product designed for your cavity depth. Depending on your situation, you may want to consider using CertaSpray Closed Cell Foam or installing a hybrid system.

Will my health be compromised if I inhale the fibers?

No, unless you have a specific allergy to fiber glass. The reason we recommend respirators is to mitigate any irritation the fibers could have in your throat or chest.

Are your products formaldehyde free?

Our batts & rolls are made with no formaldehyde added . The amount of detectable formaldehyde in the finished product is minimal and meets or exceeds the most stringent air quality requirement with GreenGuard Gold certification. In fact, there is probably more formaldehyde in your furniture or dry-cleaned shirt than in the insulation.