Should radiant barrier go over or under insulation?

Author: Prof. Misty D'Amore  |  Last update: Thursday, November 13, 2025

If installed on top of attic floor insulation, the foil will be susceptible to dust accumulation and may trap moisture in fiber insulation, so it is strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation.

Does vapor barrier go over or under insulation?

The sequence of construction steps is up for interpretation and may vary depending on your contractor or construction manager. Some builders swear by installing the vapor barrier first, while others claim that laying the vapor barrier over the insulation is better. Both may be correct.

Which way to install a radiant barrier?

The first is stapling Original AtticFoil to the bottom of the roof rafters via the Staple Up Method. The second is laying SuperPerf™ AtticFoil® out on top of the existing attic floor insulation like a blanket. Alternate methods like the Flat Top and the Hybrid are just modifications of the standard Staple Up method.

Can radiant barrier touch insulation?

Radiant barriers may be installed in attics in several configurations. The simplest is to lay the radiant barrier directly on top of existing attic insulation, with the reflective side up. This is often called the attic floor application. Another way to install a radiant barrier is to attach it near the roof.

Can you put radiant barrier over fiberglass insulation?

Installing a radiant barrier with fiberglass insulation is like getting the best of both worlds. When you install both, you maximize your energy savings and your family's comfort. Radiant barriers are your home's first line of defense against the sun's rays.

Reflective Bubble Foil Insulation/Does It Work???

Should radiant barrier go before or after insulation?

If installed on top of attic floor insulation, the foil will be susceptible to dust accumulation and may trap moisture in fiber insulation, so it is strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation.

What are the disadvantages of radiant barriers?

Moisture problems, air leaks, inadequate attic ventilation, dust accumulation, compatibility issues with existing insulation, and condensation are some of the common challenges associated with radiant barriers.

How much space is needed between radiant barrier and insulation?

Typically we suggest you have an air gap between 1/2″ and 3/4″ for the radiant barrier to work. Air gaps larger than this work well too – they promote ventilation on the foil and help keep the air dry and the air temps lower.

Does radiant barrier affect WIFI?

With Wi-Fi signals, unless the radiant barrier is between you and the router, there is unlikely to be any impact.

Can insulation touch roof membrane?

You definitely don't want any insulation to touch the roof membrane as it'll pull water inside. Netting shouldn't be necessary - if the insulation doesn't touch when it is installed it'll only settle in time and won't touch later.

How should a vapor barrier be installed?

Begin at one side of the crawl space and lay down 6-mil or thicker polyethylene plastic over the entire crawl space. Cut the sheets to size, allowing 6 inches or more along walls. Overlap the seams by no less than 12 inches and secure them together with the poly PVC tape.

How much does a radiant barrier reduce temperature in an attic?

The tests to date have shown that in attics with R-19 insulation, radiant barriers can reduce summer ceiling heat gains by about 16 to 42 percent compared to an attic with the same insulation level and no radiant barrier.

Should radiant barrier foil face up or down?

Radiant barrier sheathing panels have two sides: a foil surface and a skid-resistant surface. LP TechShield panels should always be installed with the foil side down and the skid-resistant side facing up.

How much gap between vapour barrier and insulation?

This is because an air gap provides an additional layer of insulation that helps to prevent heat from passing through the barrier and into the living space. If you are installing a radiant barrier, it's recommended to leave an air gap of at least 25mm (1 inch) between the barrier and the surface it's installed on.

Should vapor barrier go above or below underlayment?

Location: Floor underlayment is positioned between the subfloor and finished flooring, whereas floor vapor barriers are typically installed beneath the underlayment or directly on top of the subfloor, depending on the specific requirements of the flooring system.

What happens if you put a vapor barrier on both sides of insulation?

The common taboo against a double vapor barrier arises from a very real concern: If you have a Class I vapor retarder (less than 0.1 perm) on both sides of a wall, that wall has virtually no drying potential in either direction.

Can you put radiant barrier over insulation?

This is probably the easiest method to install Radiant Barrier AtticFoil™: lay the foil out over the existing insulation on the attic floor. This method can be used in any climate, though it has historically been most popular in colder climates.

What is the difference between a radiant barrier and a vapor barrier?

* vapor barrier or vapor retardant is a material which does not allow water vapor to pass through it. * non5perforated radiant barrier is a vapor retardant (vapor barrier) and if used, it will not allow water vapor to pass through.

How should radiant barrier be installed?

Before the roof sheathing is applied, the radiant barrier is draped over the rafters or trusses in a way that allows the product to droop 1-1/2 to 3 inches between each rafter. In Locations 3 and 4, the radiant barrier is attached to either the faces or bottoms of the rafters or top chords of the roof trusses.

What is the average cost of radiant barrier installation?

Installing a radiant barrier costs $1,700 on average, but often ranges between $710 and $2,840 depending on whether your pro uses a foil or spray on type.

Can drywall be installed over a radiant barrier?

Only if there is an air gap in the assembly; typically the air gap would be between the outer layer and the foil layer. If you are placing the drywall directly on top of the foil, then the other side of the foil must be open to an air gap, not insulation or some other material.

What is the R value of a radiant barrier?

Bubble foil does offer some R-Value because of the bubbles (because remember, radiant barrier does not have an R-value on its own). However, we see claims of up to R-14 for some bubble products.

Are radiant barriers worth it?

In theory, radiant barriers do seem useful for reducing the heat load during the summer. Theoretically, that would reduce your power bill. However, there is a lot more to air conditioning than keeping buildings cool, and radiant barriers can pose unique challenges to your comfort.

Which is better, spray foam or radiant barrier?

Spray foam insulation doesn't protect attic spaces from radiant heat, but does protect them from convection and conduction. In the summer, radiant heat is the biggest contributor to heated attic spaces, so spray foam insulation may not be as effective in keeping attics cool.

How long does radiant barrier last?

As long as homeowners or certified attic specialists install them appropriately, radiant barriers last anywhere from 80 to 100 years.

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