Pros And Cons Of Flash And Batt Insulation

You want effective insulation in your home but don't want to break the bank. You heard about an insulation method called flash and batt, which combines the performance of spray foam with the low cost of fiberglass. While you've heard some good reports about flash and batt, you aren't sold yet. Will combining spray foam and fiberglass provide the results you need?

South Central Services has insulated hundreds of homes with spray foam insulation. While we install both spray foam and fiberglass batt insulation, we do not offer traditional flash and batt insulation. Traditional flash and batt insulation can have devastating results for homeowners in our climate zone.

Flash and batt is a controversial insulation option. We want you to be confident in your insulation decision, so we’ve compiled all the potential benefits and problems of traditional flash and batt so you can decide for yourself.

By the time you finish reading, you'll know whether flash and batt is an option for your home. Specifically, you will know:

• Benefits of flash and batt compared to insulating with spray foam
• Benefits of flash and batt compared to insulating with fiberglass
• Problems flash and batt insulation can create

What Is Flash And Batt Insulation, Again?

Flash and batt insulation is a broad term in the construction industry. Many resources may refer to flash and batt as simply a method combining spray foam and batt insulation. In our service area, flash and batt insulation is most commonly one inch of closed cell foam with a batt of insulation.

This article weighs the pros and cons of flash and batt by this strict definition. We will compare the cost and performance of one inch of spray foam combined with batt insulation.

Pros Of Flash And Batt Insulation (Compared To Spray Foam)

You may consider flash and batt insulation because spray foam alone is expensive. Can you cut costs on your exterior wall insulation without compromising insulation performance?

This section covers the two main benefits of flash and batt compared to spray foam.

1. Flash And Batt Is More Budget Friendly Than Spray Foam Alone

To properly insulate an exterior wall in our climate zone, Climate Zone 5, you would need an average of 2 to 3 inches of closed cell or 4.5 inches of open cell spray foam. At our rates, closed cell spray foam would cost about $4.35 per square foot, and open cell spray foam would cost about $2.00 per square foot.

While the cost could be higher or lower, that is still a high price tag per square foot.

For traditional flash and batt insulation, only one inch of closed cell spray foam is applied. While we do not perform flash and batt, you can use our rates to estimate what flash and batt might cost. With only an inch of foam, the cost per square foot for the “flash” would be between $1.15 and $1.75.

The cost of fiberglass batts must be added to a flash and batt estimate. Fiberglass tends to be the cheapest insulation material. The lower the R-value, the less expensive fiberglass batts will be. You can estimate spending about $1 to $3 per square foot on the fiberglass for a flash and batt application.

Flash and batt would cost anywhere from $2.15 to $4.75 per square foot, while spray foam alone would cost $4.35 on average.

2. Flash And Batt Offers Better Sound Attenuation Than Closed Cell Spray Foam

Closed cell spray foam is commonly used in flash and batt applications. While closed cell foam has many features and perks, sound control is not one of them. The cell structure that creates rigid closed cell foam does not allow sound to be absorbed or quieted.

Other insulations, like open cell spray foam and batt insulations, can absorb and quiet noise pollution.

Sound control would be limited if you were to insulate your exterior walls with closed cell spray foam alone. However, the fiberglass batt layer can trap and quiet neighborhood noise in a flash and batt application.

Pros Of Flash And Batt Insulation (Compared To Fiberglass Batts)

You may also consider flash and batt insulation because you want a better performance than fiberglass batts. Can an inch of closed cell spray foam make your wall insulation more effective?

Compare the two main benefits flash and batt offers compared to fiberglass.

1. Flash And Batt Offers An Air Barrier That Fiberglass Cannot Achieve Alone

Fiberglass batts may be one of the cheapest and most popular ways to insulate, but there are better-performing insulation products. One of the reasons that fiberglass cannot compete with spray foam is its lack of air-sealing ability.

Traditionally, insulations are measured by R-value, which determines how well materials prevent conductive heat flow. But heat can also travel through the air with convection and radiation.

An insulation that air seals can prevent heat from traveling through the air, which boosts its performance. Air sealing is also desirable because it preserves air quality and supports HVAC equipment in the home.

With the flash and batt method, spray foam can create an airtight layer in your exterior walls. There would be no air barrier if exterior walls were only insulated with fiberglass.

In an area of the home with a lot of heat transfer potential, fiberglass alone would compromise performance. Adding a spray foam layer gives an air barrier and boosts the performance of flash and batt compared to fiberglass.

2. Flash And Batt Has A Higher R-Value Than Fiberglass Alone

We've already established that fiberglass batts perform poorly because they cannot create an air barrier. However, fiberglass batts also have lower R-values than other insulation products.

Not only are fiberglass batt R-values often lower, their R-value can also be easily compromised during installation. If a fiberglass batt gaps during installation or sags over time, more air flow and heat transfer can occur. The conditioned air that you pay for can escape.

With the addition of a layer of spray foam, the insulating capabilities of a wall cavity are boosted. Instead of having an R-value of only R-13, R-19, or even R-38, one inch of closed cell foam can add R-7 to the wall cavity.

Cons Of Flash And Batt

We've addressed the positives of flash and batt and why the method exists. For homeowners leaning towards fiberglass, the technique is meant to boost some performance without breaking the bank. For others considering spray foam, flash and batt is supposed to save a little money and offer some sound control.

However, the flash and batt method is controversial for a reason. South Central Services does not install traditional flash and batt because of the risks in our climate zone. For our customers, there are better solutions with fewer problems.

Let's examine the issues that traditional flash and batt insulation can create in more detail.

1. Flash And Batt Can Create Condensation Problems

Flash and batt insulation most often uses closed cell spray foam for the “flash” portion of the installation. One of the features of closed cell spray foam is its ability to create a vapor barrier at two inches thickness. Vapor is water in its gaseous state. You can think of the humidity in the air as a vapor: literal water content in the air.

Air can only hold so much water vapor. The colder the air temperature, the faster vapor reaches its max capacity, or dew point. When air can't hold any more vapor, the water condenses from its gaseous state to a liquid form.

Why does this matter? With a vapor barrier, the water content in the air cannot pass through your walls. If the vapor cannot condense inside your walls, then mold and mildew issues are prevented.

Flash and batt insulation does not install enough closed cell spray foam to create a vapor barrier. Closed cell spray foam can only create a vapor barrier at two inches or more. The traditional flash and batt only uses one inch of closed cell spray foam. The air barrier of spray foam is intact, but vapor can travel, settle, and condense within walls.

2. Flash And Batt Can Have Gapping Problems

The most common issues with fiberglass batts are gapping and sagging. Since fiberglass is manufactured and pre-cut, it only sometimes fits its cavity. Sometimes, the batt is bigger than the cavity and can be cut to the correct size. Other times, the batt is smaller than the cavity, and gaps are left behind.

Spray foam insulation adheres to the surface it is sprayed against. The adhesion is part of its air-sealing ability. Fiberglass insulation does not adhere to surfaces. It is placed or stuffed into cavities.

When the flash and batt method combines spray foam and fiberglass, it does not solve the fiberglass gapping or sagging problem. A gap can exist between the layer of spray foam and the fiberglass batt. Over time, the fiberglass batt may settle or sag. The wall areas no longer covered by both foam and fiberglass may not have enough R-value to insulate properly. The ineffective insulation could lead to cold spots.

These gaps can also be problematic given the condensation issues we've already addressed. A space between foam and batt could be an ideal area for mold to grow if there are condensation problems.

3. Flash And Batt Is Tricky To Install Correctly

Spray foam insulation is a complex product that requires a trained installer for an effective result. While readily available for homeowners to install, fiberglass batt insulation must fit cavities perfectly to offer its advertised R-value.

When you combine these two insulation products into one method, you double the difficulties in creating an effective result.

Let's say you work with a competent contractor who is confident in this method and knows how to handle its weaknesses. Even the most well-trained spray foam installers do not install perfectly even layers of spray foam.

Have you ever tried spraying an even layer of cooking spray onto a pan or baking sheet? Inevitably, some areas of the pan have more coverage than others. In a traditional installation, certain areas could have less than one inch of foam, meaning not even the air barrier is intact.

Some resources claim that flash and batt is easy to install and that most contractors can pull it off without concerns. These statements are inaccurate. Not only do contractors debate how the flash and batt method should be used in construction, but an effective application requires excellent attention to detail.

Is Flash And Batt Your Solution For High-Performance Budget Insulation?

South Central Services does not offer traditional flash and batt insulation. With only an inch of closed cell spray foam, the potential complications and severity of the risks are too high. No one should worry about mold in their walls or needing to replace or correct their insulation. In our climate zone, vapor barriers are necessary.

If you are still interested in flash and batt insulation, we encourage you to research your contractor options carefully. The greatest chance of success with this method is by working with a trustworthy contractor who is knowledgeable about the problems that can arise with flash and batt insulation.

Now that you know the potential problems with flash and batt insulation, your next step is to:

• Weigh the pros and cons of the hybrid insulation method, which includes a vapor barrier
• Compare spray foam and fiberglass insulation as individual options
• Estimate the cost of spray foam insulation alone