Does Expanding Foam Damage Wiring?

Expanding foam is a great way to quickly insulate your home or insulate hard to reach areas easily. The foam also expands to fill cracks and holes to provide an airtight, and even possible watertight, barries. Spray foam is perfect between studs and rafters or floor joists. If you have anything routed inside the cavity, like electrical wiring, you might wonder if the foam is safe.

Does expanding foam damage wiring? Yes, expanding spray foam can damage electrical wiring. Careful planning can prevent potential damage to wiring. Prepare any space you want to fill with expanding foam by routing wiring in conduit and ensuring not to overfill the cavities where spray foam is being applied.

We’ll explain how to properly prepare your space before you fill it with expanding foam and how to apply the foam to prevent any possible damage to wiring in your space.

Can You Put Expanding Foam Around Wires?

Because expanding spray foam is intended to provide insulation, the foam will insulate anything within the cavity it’s applied, including electrical wires.

Electrical wires used in residential construction have insulation around them already through the PVC material on the outside. This insulation helps protect from electrical shock and prevents fires by keeping the wires from touching flammable surfaces. Resistance in the wire material will cause the wires to heat up as current flows through them.

The PVC insulation sheathing causes the wires to be slightly less efficient, but the benefits are worth it. However, when expanding spray foam is applied around electrical wiring, the heat from the wires will not be able to dissipate. OldHouseWeb.com notes this could cause the wires to overheat and melt, resulting in a fire or power failure and is actually against many electrical fire safety codes.

There are several recommendations to prevent wires from overheating. Electrical wires are sized to carry current similar to how pipes are sized to carry water. Typically, to save costs, the wires are sized for the smallest size to conduct the current safely. When routed directly through a material like expanding spray foam, the wires can be oversized to reduce how much heat they will lose.

Another option to minimize fire risk is to route wiring through conduits. Conduits are lightweight metal pipes that can protect the wires from damage as well as provide an air gap between the wires and any flammable materials. Many homes do not have conduit around the wiring inside. Where homeowners choose to use expanding spray foam insulation, however, the conduit should be provided.

Types of Conduit

There are two categories of conduit: metallic and nonmetallic. Both types have flexible and rigid options. The Home Depot provides a guide for helping owners select a type of conduit for their project.

Rigid metal conduit offers the highest level of protection for your wiring but requires a lot of labor to install. The highest weight of a rigid conduit is called galvanized rigid conduit (GRC). Straight sections of conduit must be cut to length to attach to rounded, called radius, elbows. The radius elbows allow the wires to be pulled easily through the rigid conduit.

Flexible metal conduit is cheaper and easier to install than rigid conduit but is slightly more vulnerable to damage. The final installation is less tidy. A type of conduit between the two options is a type of bendable conduit called Electrical Metallic Tubing (EMT). Some flexible metal conduits can be bought pre-wired, to save the installer the trouble of pulling the wiring through the conduit.

Nonmetallic conduits are typically made from PVC or HDPE (high-density polyethylene). These types of nonmetallic conduits are great for outdoor installations or underground routing. Blue electrical nonmetallic tubing can be purchased in rolls from hardware stores.

How to Spray Foam Around Wiring

Make sure to prepare your target cavity before applying any expanding spray foam insulation.

For closed-cell, medium, and high-density spray foam applications, electrical wiring should be routed in conduit, which may require cutting holes between studs to route the conduit through the hole, bending conduits, or cutting and fitting pieces of conduit together.

If the conduit is omitted, then closed-cell spray foam should not be applied approximately three inches on either side of the wiring. Since the wiring isn’t rigid, the wiring may need to be carefully stapled into place, either on the studs or sheathing.

The person applying the expanding spray foam should apply the spray foam further than three inches away since the foam will expand towards the wiring. Overspray should be allowed to harden before being cut or scraped away from the wires for all types of insulation, including open-cell spray foam.

When applying spray foam to an existing wall cavity that cannot be opened, open-cell spray foam should be used instead of closed-cell. The open cell structure will prevent the foam from applying too much pressure to existing wiring inside the cavity. The low density of the open cell structure will also be less likely to over-insulate the wiring and may prevent overheating.

The person applying the insulation should be very careful not to overfill the cavity with too much insulation, which could make insulation too dense.

Types of Expanding Spray Foam

Expanding foam, or spray foam, insulation, is a product that expands when it comes in contact with air. The foam is used as an insulation for homes, vehicles, and other structures, to maintain better temperatures inside the space. The insulative value can vary depending on the products. Some may even be waterproof.

Since expanding foam will fill any shape volume, it is very useful for expanding into hard to reach areas. This could include existing walls that do not have insulation, but the wall can’t be opened up easily or cheaply to add board insulation. The foam can also expand around objects within the cavity, such as electrical outlets, nailing blocks, junction boxes, pipes, and other obstructions.

According to WhySprayFoam.Org, there are three different types of spray foam insulation: light density open cell, medium density closed cell, and high density, closed-cell.

Light density open cell insulation is lightweight insulation with a lower insulative value. Once applied, the foam is also very fragile and can be easily crushed with your hand. It can be easily manipulated if it was misapplied or overspray, or if additional building elements like conduit or plumbing need to be added at a later date.

This type should be used for attic spaces and interior walls to provide an air barrier or lightweight insulation, but it is not waterproof. It can even settle or shift over time.

The medium density closed cell type has a higher insulative value and is relatively rigid after application. The insulation value is higher than low density, but more beneficially, the closed-cell structure makes the foam rigid after application. This structure makes the foam water and moisture-proof. Care must be taken while applying as the foam is tough to remove once cured.

The high-density spray foam is the most durable and insulative and best suited for exterior walls. The benefits of high density are similar to medium density in that it can be used as a moisture barrier, air barrier, and sound barrier. The foam does not expand as much as the first two due to its high density, which means that much more material is required to provide a continuous application.

Final Comments

Spray foam can potentially damage wiring if injected directly into an existing wall. To avoid this from happening, ensure that your wiring is encased with a rigid conduit. A second alternative, though less desirable, is to attach the wiring to a fixed surface and spray around the wiring, maintaining at least a three-inch gap around the wires.

If you are dealing with an existing wall, these options can be a potentially costly exercise since the wall will need to be opened and existing wiring will need to be rerouted. In such cases, a third alternative is to use open-cell spray foam. A professional spray foam installer should be able to help you identify these issues and recommend the best course of action.