Does Spray Foam Insulation Lose Its R-Value?

If you're researching spray foam insulation for your home energy upgrade or new build house, you may be concerned about its longevity. Specifically, you wonder how long spray foam insulation delivers a high R-value. Can spray foam really offer a good R-value indefinitely, or does it lose some performance over time?

South Central Services has insulated hundreds of new and existing homes with spray foam. Spray foam insulation is one of the most high-performing products available for buildings. You need accurate information about your insulation choices to guide your decision.

The question of spray foam and R-value is a bit complicated, which we will dive into through this article. But for all intents and purposes, the answer to your question is no: spray foam doesn't lose its R-value.

By the end of this article, you will understand:

• What exactly R-value is
• What the difference is between aged R-value and advertised R-value
• How the R-value of spray foam changes over time

What Does R-Value Mean For Insulation?

So what exactly is R-value? R-value, or resistance value, is the traditional measurement of how well insulation can insulate. R-value measures the resistance to conductive heat transfer.

Materials with a high R-value are good at resisting this heat transfer method. Materials with a low R-value are more conductive, which makes them poor insulators.

When choosing an insulation material, the R-value must be taken into consideration. The necessary R-value will depend on your climate zone and where you are insulating.

Once you've established R-value, you can also check for air-sealing capabilities. Air-sealing is a more modern measurement of insulation performance. Heat transfers through conduction but can also transfer via convection and radiation. An airtight seal prevents convective and radiant heat transfer by stopping air from passing through.

Spray foam insulation delivers both a high R-value and an airtight seal. Since spray foam is spray-applied, it is literally seamless. As a plastic foam, it prevents air from sneaking through any crack or crevice.

R-value is the traditional measurement of insulation performance. Good insulations have high R-values. R-value is not the only measurement of insulation performance. It is also vital to consider air-sealing since heat can be transferred through three different methods.

Advertised R-Value And Aged R-Value Are Sometimes Different.

Now that we understand what R-value is, we can compare two variations in R-value: aged R-value and advertised R-value.

Both aged R-value and advertised R-value are straightforward. Aged R-value is what the R-value will be over time. In 10 years or 20 years, what R-value can this insulation deliver?

Advertised R-value is the R-value promised in marketing for the insulation product. What R-value is offered according to the manufacturer, home improvement website, or technical data sheet?

For some insulations, aged R-value and advertised R-value are different. The best examples are blown-in insulations and fiberglass batts. The advertised R-values for these products are the R-values they should deliver on day one, provided they were installed correctly. However, blown-in and batt are prone to sagging and settling. Over time, the R-value of these products is compromised because they are mobile. These insulations do not hold themselves in place.

When it comes to spray foam insulation, the advertised R-value and aged R-value are the same. Spray foam holds itself in place by adhering to the surface it was sprayed against. Spray foam insulation does not sag or settle.

The R-value that spray foam manufacturers promise in advertising is the same R-value over the lifetime of the insulation. Other insulations like batt and blown-in cannot deliver an aged R-value that matches the advertised R-value.

How Spray Foam R-Value Changes Over Time

Let’s examine the two possible changes in R-value over time: after initial application and over the lifetime of a building.

R-Value Change After Initial Application

When spray foam is initially applied, its R-value is higher than the advertised R-value. It depends on the product and manufacturer, but the initial R-value is technically different from the promised R-value.

However, that initial R-value isn't even disclosed because it is irrelevant. Within a short period of time, the spray foam stabilizes and reaches stability in its R-value, as well.

You could claim that spray foam loses R-value during manufacturing while it is stabilizing. While technically accurate, the change in R-value during that initial manufacturing period is not reflected in the aged or advertised R-value. Spray foam manufacturers account for this R-value change and only promote the aged R-value of spray foam insulation.

R-Value Change Over The Lifetime Of A Building

You may also hear the claim that spray foam loses its R-value over time, even after it has stabilized. This is another nuanced question.

Technically, it is accurate to say that the R-value of spray foam decreases over time. However, the amount of R-value loss is a fraction of a percent. It is almost immeasurable in a year-over-year comparison.

It is technically accurate to say that spray foam loses R-value over time. However, when that loss is accurately quantified, you can see that the R-value stays basically the same.

The Bottom Line About Spray Foam R-Value Over Time

Spray foam insulation is promoted as a permanent and high-performing insulation. It offers a high R-value and an airtight seal, setting it apart from other insulations on the market. While it is technically accurate to say that spray foam R-value changes over time, those changes do not impact the performance of the insulation.

From a manufacturer or installer's perspective, spray foam R-value changes. This change is a scientific fact we can measure. Spray foam is created through the science of a chemical reaction, so these changes are expected. They can be measured and quantified.

From the perspective of the person living in the home, your spray foam insulation will not lose R-value. A change in R-value will not undermine your investment. Whatever R-value you have after insulating is the same R-value as you'll have over the decades.

Now that you understand the nuance of how spray foam R-value changes, your next step is to:

• Read more about potential problems with spray foam insulation
• Find out if spray foam insulation can stop pest infestations