Does foil insulation need an air gap?

Author: Prof. Tony Heathcote  |  Last update: Monday, April 14, 2025

Foil insulation is particularly effective at reflecting radiant heat, which can be beneficial in both summer and winter. However, in order for it to work effectively, there needs to be an air gap between the foil layer and the surface it's installed on.

Does foil insulation need air gap on both sides?

Radiant heat moves through the air, so when you install a radiant barrier foil, you need an air space on at least one side of it to work properly.

Does foil board need an air gap?

Does Foilboard need an air gap? In most applications, foil insulation requires an air gap of at least 25mm in order to insulate effectively for radiant heat. Installed without an air gap, and the effective R value of the boards will be close to zero.

Can foil-faced insulation be left exposed?

Kraft or foil facedFaced insulation is a batt or roll of fiberglass insulation with an attached kraft paper or foil facing. Kraft and standard foil facings can burn and must not be left exposed.

Does reflectix work without air gap?

With multiple layers of product and airspaces between each layer, enhanced performance will be gained. If the product is simply “doubled” (with no air space between the layers), a very minimal benefit is obtained, (R-1.1 (per layer) for the Reflective/Double Bubble product).

Radiant Barrier Foil Insulation - Why Is Air Gap or Space Required?

Do you need a Vapour barrier with foil insulation?

Typical insulation works in a basement but you have to use a good vapour barrier along with it. This is where foil faced insulation takes its place. The best way to insulate a concrete wall is with foil faced rigid foam boards.

Are air gaps necessary?

Without a dishwasher air gap, contaminated water can flow back into the dishwasher. A dishwasher air gap prevents this from happening by ensuring that the water flows in one direction: out of the dishwasher and into the garbage disposal.

What are the cons of foil insulation?

It is also worth to point out 3 main disadvantages of foil faced insulation such as:
  • It is generally more expensive due to being a metal-based product.
  • It is also important to note that in order for foil insulation to work correctly, it must be kept free of any dust.

Does foil faced insulation need to be covered?

AP™ Foil-Faced insulation must be covered with an approved thermal barrier and cannot be left exposed.

What insulation can be left uncovered?

ECOCELL Blankets can be left exposed or even painted. Unlike other insulation materials, ECOCELL does not have to be covered with gypsum board. Leaving ECOCELL exposed is another reason ECOCELL is the cost effective solution for insulating basements and crawlspaces.

What happens if you don't have an air gap?

The use of an air gap is required by plumbing codes for certain plumbing fixtures, such as dishwashers, to prevent the backflow of potentially contaminated water into the clean water supply. If contaminated water backflows, it can cause serious health risks.

Which side of foil board faces out?

Install the Foilboard® GREEN rigid insulation panel to the external face of the studwork, ensuring the anti-glare side is facing out, measure the area you require. Tape all penetrations, joints and gaps using the Foilboard® green PVC tape, ensuring the stop of cold / hot air transfer.

Is foil faced insulation an air barrier?

Polyiso provides one of the highest R-values per inch of any rigid insulation (R-6.0 at 1 inch). Furthermore, when properly installed, AP Foil-Faced Polyiso Continuous Insulation functions as a water-resistive barrier, vapor barrier and air barrier, eliminating the need to install additional components.

Does Foilboard need a gap?

Foil insulation is particularly effective at reflecting radiant heat, which can be beneficial in both summer and winter. However, in order for it to work effectively, there needs to be an air gap between the foil layer and the surface it's installed on.

Can you board over foil insulation?

If you plan to add an extra layer of insulation, you can install insulated plasterboards over the foil insulation.

Does foil insulation keep cold out?

Foil insulation is known as an extremely effective way to keep your home warm and to cut energy costs at the same time.

Is it OK to leave faced insulation uncovered?

Fire Risks

While the insulation isn't flammable, most fiberglass has foil or paper that can easily catch fire. Because of this, fiberglass shouldn't be left exposed without a special flame-resistant facing. Otherwise, it's best to protect your home by using a thermal barrier.

Do you need vapour barrier with foil backed insulation?

With the insulation built into the plasterboard, there is no need for an additional installation process, saving time and money. One of the key benefits of insulated plasterboard is the option for foil-backed varieties, which serve as a built-in vapour barrier.

Can foil faced insulation get wet?

It is made of closed-cell foam, which means that it is composed of tiny cells that are filled with gas. However, because the cells are not totally watertight, PIR insulation is not waterproof. The foil facings on both sides of the PIR Insulation board further protect the insulation from getting wet.

Does foil insulation have an R value?

Foil insulation can provide an additional R-value when installed within an air cavity in the building frame. Roof sarking is installed in homes to reduce summer heat gains and reduce cooling costs. Aluminium foil insulation is a highly reflective material that rebounds radiant heat rather than absorbing it.

What are the disadvantages of foil?

Health Risks of Aluminium Foil
  • Leaching of Aluminium into Food: When food is wrapped in aluminium foil, especially hot, acidic, or spicy foods, aluminium can leach into the food. ...
  • Kidney and Bone Damage: Prolonged exposure to aluminium has been linked to kidney and bone damage.

How effective is attic foil?

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. These figures are for the average reduction in heat flow through the insulation path.

How do I know if I need an air gap?

If you live in a state where air gaps are mandated by law, even a new dishwasher will require one to be installed. A drain hose that is connected to house plumbing lower than 20 inches above the floor will need an air gap. Check your local codes and requirements.

What is the main disadvantage with the air gap technique?

Limitations of the air-gap technique include potentially increasing patient dose and geometric blurring (unsharpness) 3.

What are the two requirements for the air gap?

How Measured: Air gaps shall be measured vertically from the lowest opening of the water supply outlet to either (1) the flood level rim of the fixture or receptor served, or (2) the maximum elevation of the source of contamination.

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