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Insulation | Can It Be Left Exposed? (Code & Comfort)

Insulation is an important aspect of many homes with all the temperature regulating and energy-saving benefits it provides. However, some technical insulation aspects we end up needing to research.

Insulation can require covering, either for code compliance or from a comfort level, which might make the extra cost worthwhile. There are several issues related to uncovered insulation, including fire safety.  

Exterior insulation must be covered, according to the IRC, to protect the material and its R-value. Interior foam plastic insulation must be covered by a thermal barrier, but other materials might benefit from coverings from a comfort perspective.

Exterior Insulation

First, we are going to look at insulation on the exterior side of the house. Now, you are unlikely to leave the wall around your front door with exposed insulation. However, there are places where this choice is less obvious.

Code Says Exterior Insulation Must Be Covered

The International Residential Code (IRC), Section N1101.11.1, states that any insulation that is installed on the outside of basement walls, crawl space walls, and “slab-on-grade floors” must have a full covering that extends at least 6” below grade (which is the level of the ground).

Slab-on-grade means a shallow foundation that has the concrete slab directly on the floor: there is no basement.

Construction of slab on grade

This covering must be weather-resistant, opaque, and rigid to provide proper protection to the material. So, your exterior insulation cannot be left exposed.

Reason Why It Is Necessary

Coverings are used for exterior insulation to protect the insulating material in order to preserve its R-value for functionality.

Insulation is installed to help regulate temperatures in our homes and to prevent cooled or heated air from interacting with the unconditioned outside air, which will allow heat to get in during the summer or cause a loss of warmth in winter.

When you think about areas like basements and crawl spaces, you probably know that they are often too hot or too cold. This means they are often unpleasant to be in and can also ramp up energy bills by affecting adjoining and living areas of the house.

This makes them prime candidates for the thermal protection of insulation.

Unfortunately, these spaces and shallow foundations typically lack real estate, like wall cavities, for installing insulation.

Thankfully, there is an alternative: exterior insulation also serves the purpose of balancing your home’s thermal environment.

However, exterior insulation is vulnerable to the environment, which can impact your comfort fairly significantly. So, it is important that we protect our insulation from the elements that can damage and influence the material.


Exterior insulation can have trouble with something called “wind washing”.

Without a covering, wind can blow through and around the porous insulation. This helps increase the movement of air through the material and increases conduction, counteracting the purpose of insulation.

The material cannot function effectively, essentially lowering the thermal resistance the insulation can offer.


Exposed insulation can also get dirty and dusty. The trouble with this is that insulation typically relies on the air gaps in the material.

When the dirt particles sink into the insulation and fill the air gaps, which are necessary to slow conduction, the functionality of the insulation material is impeded because solid particles, like dirt, promote heat conduction.

Water and Leaching

Water from rain, snow, condensation, and any ground source also fills the gaps in insulation. The water transmits heat through the material faster, meaning that wet insulation is less effective at keeping heat in or out of your conditioned spaces.

Water filling the air gaps can also compress it, which lowers the R-value, and cause it to clump, sag, and displace.

Old and dirty insulation installed in a worn out crawl space

The final factor to consider is that any chemicals, like flame retardants, that the material is treated with can leach out (can be corrosive) when it gets wet.

Most insulation is treated with chemicals to deter pests. Pests can cause damage to the insulation by scratching at it, chewing it, eating it, or attempting to burrow into it. However, these chemicals can also be leached out by rain and dew, making them less effective.


When exposed to sunlight, insulation can degrade. Mineral wool insulation is the least susceptible to this damage and plastic foam insulation is the most susceptible.

Interior Insulation

IRC Looks Mostly at Foam Plastic Interior Insulation

In terms of insulation that is installed on the interior of your home, like attics, walls, around ducts, etc., the IRC only speaks about foam plastic (Section R316.4), with specific mention of spray foam insulation in Section R316.3.

Plastic foam is a category of foam-based insulation, including a lesser-known loose-fill (polystyrene beads) version that looks a little like packing peanuts.

Foam insulations are common ceiling insulation, along with fiberglass, but this category has an off-gassing consideration when damaged.

In addition, foam plastic (including spray foam and foam board) insulation must have a thermal barrier separating it from the interior of your home. This can be gypsum, wood, or any other material (i.e., drywall) that is approved by the National Fire Protection Agency (NFPA 275) according to their fire tests:

  • The Temperature Transmission Fire Test: measures how well the barrier can prevent the covered surfaces from temperature increases and how well it protects against ignition.
  • The Integrity Fire Test: a room airtightness test that looks at whether fire prevention system gas will be kept concentrated enough to extinguish fires. Since insulation doesn’t necessarily act as a vapor barrier, the thermal barriers will compensate for that.

Rockwool Insulation | Does It Need A Vapor Barrier?

Some Exceptions

There are a few exceptions in Section R316.5 of the IRC, which permit a lack of coverage if there is a masonry, concrete, or wood barrier between the material and the building’s interior.

Another exception is that if your attic or crawl space is infrequently accessed, then only an ignition barrier is necessary.

  • Ignition barrier: helps protect insulation from conditions that could make it combust. Meaning it increases the time it takes for the foam insulation to light.
  • Thermal barrier: also extends the time until your insulation ignites, but it is also a physical separation of the insulation from your living space.
Ignition barrier and thermal barrier of a house

Other Insulation Types

Since the building codes, which aim to regulate the best and safest practices concerning homes, do not mention the need for barriers with other insulations, we can assume they are not required. Technically, you can be code-compliant without a covering for your insulation.

However, beyond foam plastic insulation, experts at Phoenix Insulation Pros recommend covering fiberglass because if left exposed the glass fibers can cause adverse health effects.

Fiberglass can be covered with mesh or a poly membrane since the goal is to keep the fibers in place.

Coverings for other insulation types, like fiberglass, are only absolutely necessary if they are in a space that will be more frequently disturbed, but in terms of comfort, you might want to cover them anyway.

Fire Considerations

Sections R302.10.1 and R302.10.4 of the IRC contain a lot of terms and numbers that mean little to most homeowners, but we can all understand the basic function here: fire safety. The insulation material needs to meet certain fire standards in terms of flame spread and surface burning.

Now is when we trust in the experts who make the codes with these standards, adapt state codes, and make and install the products.

Any non-foam plastic products that are approved by the IRC comply with the relevant safety standards. Otherwise, correct protective measures (i.e., needing a thermal barrier) would be detailed in the IRC as with the foam plastic insulation.

I recommend contacting and consulting a local professional to help you determine the best and safest practices for your insulation if you are unsure.

Problems With Exposed Interior Insulation

Any insulation within a living space should be covered to prevent a variety of problems.

Health Risks

There is a reason we wear protective gear when installing insulation, so you want to keep insulation and associated particles out of your living spaces.

Between things like dust (which cellulose is known for) and fiberglass, insulation can cause irritation to the lungs and respiratory system, skin, and eyes.

The less you have to deal with these particles, the better, especially if you have a pre-existing condition like asthma or dermatitis. A covering assists in protecting you if you cannot leave the insulation undisturbed or would be more comfortable knowing it’s contained.

You also want to keep it out of reach of children, which coverings help to do. Any curiosity of little explorers can increase the potential exposure risks.

Insulation Damage

The more exposed the insulation is, the easier it is to damage. If it gets moved, broken, or compressed, this can decrease the effectiveness of the insulation. Loose-fill insulation is particularly easy to disturb.

A covering will help contain the material and physically protect it.

Materials and components of walls, floor and roofing

Spray foam insulation can have issues with off-gassing if it gets damaged or if it is exposed to UV rays, which can be harmful to you.

Another way that insulation can be damaged is by water. A covering helps to keep moisture away from the material, which also helps to prevent mold issues.

Fire Risks

Insulation has a high heat tolerance, meaning the heat it must be exposed to before it will ignite is rather extreme. However, insulation has a different and higher fire risk when it comes to an open flame.

In that case, insulation can catch fire, which is why a covering can be important. Thermal barriers will help protect them from the flame and from the heat to delay the material from burning.


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