Insulated Vinyl Siding: Does It Really Work?

A deeper look at energy savings, moisture management, and durability

Insulated vinyl siding has been around since the mid-1990’s and has been installed on over half a million homes. Despite this track record, many people are not familiar with what insulated vinyl siding is, how it works, and if it’s the right siding product for them. When they take to the internet for research, they may run into exaggerated claims or inaccurate opinions about the product. Which brings us to the question does it really work?

As the inventors of insulated vinyl siding, it’s our responsibility to accurately represent the facts, pros, and cons of the product so you can determine if it’s right for your unique project.

In this article, we will address three primary areas of questioned performance:

• energy savings
• moisture management
• and durability

Energy Savings with Insulated Vinyl Siding

Why Is Insulation Necessary Under New Siding?

The United States Department of Energy (DOE) says “when new siding is to be installed, it is a good idea to consider adding insulation under new siding.” Continuous insulation has become a popular recommendation to help reduce energy loss.

There may be an invisible energy leak in your walls that is costing you money every day. The source is the wooden studs in the wall. Although there may be pink batt insulation in between, the studs themselves are not insulated. Energy transfers across these studs from the warm interior of the home to the cold exterior (or vice versa in the summer) through a process called thermal bridging. And because studs make up 25% of a home’s wall space, it’s like having one entire wall of the home without insulation.

Even though you may have R-19 pink insulation in the cavity, this is only the “nominal r-value,” a rating provided by the manufacturer. “Effective r-values” are actual thermal resistances provided by the insulation in an actual assembly, accounting for any losses attributed to thermal bridging.(1)

Adding continuous insulation to the outside of the home when new siding is installed covers those studs in an energy-saving blanket of insulation, helping to stop thermal bridging and reduce energy loss.

What is the Effective Energy Savings of Insulated Siding?

Many insulated siding panels provide r-values of 2.0 - 3.5, comparable to the most commonly used flat foam insulation options.

As new building and insulation materials have entered the market, confusion over the nature and meaning of "R"-value has raised questions among building professionals and consumers alike. What exactly is "R"-value? Is it an effective and objective measure of the thermal performance of an insulation product or construction system?

The published r-value of insulated vinyl siding is true effective r-value. Even though there are seams between the panels of siding, the r-values are tested in an as-installed state using a hot box apparatus test.

This procedure ensures that the R-value claimed for an insulated siding product represents the actual thermal insulation value that will be delivered to the home.

When considering insulated siding for a home renovation project, most people ask, “How much will it reduce my energy bills?”

Third party energy modeling has shown that insulated siding can reduce heating and cooling costs by up to 16%, depending on your home style and climate zone. Because every home is different, as well as the behaviors of its inhabitants, it is impossible to accurately estimate potential energy savings without doing appropriate blower door testing on the home.

Managing Moisture with Insulated Siding

In the past, we have been asked, “does insulated vinyl siding absorb moisture?” Insulated vinyl siding does not absorb or hold moisture, or contribute to mold or mildew growth in any way. In fact, third-party testing that proves insulated vinyl siding is a great exterior cladding option for managing moisture in a home.

Craig Drumheller, Senior Energy Engineer with Home Innovations Research Labs (HIRL), completed a one-year field study titled Effect of Cladding Systems on Moisture Performance of Wood-Framed Walls in a Mixed-Humid Climate.

In this study, Drumheller compared insulated siding with eight other wall assemblies, including traditional vinyl and fiber cement sidings, and concluded that “Insulated vinyl siding demonstrated the best moisture performance in the study, with the overall driest wall assembly regardless of indoor moisture conditions.”

The thermal resistance of insulated siding provides a double benefit: reduced heat flow in the wall assembly, thereby saving energy, and a higher wall cavity temperature, resulting in increased drying capacity.

In addition, a technical bulletin published by the EPS Molders Association highlighted third-party testing conducted by SGS US Testing Company Inc. to evaluate EPS’ resistance to fungi and mold growth. Using ASTM C1338-08 Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings, the research indicates that under a 28-day incubation period, the EPS had no trace of mold growth. EPS insulation is a closed-cell foam, and exposure to moisture has little, if any, effect on its thermal performance and dimensional stability.

Does Insulated Vinyl Siding Actually Improve Durability?

Increased durability is one of the most unique benefits of insulated vinyl siding. Although you can insulate a home with blown in for flat foam insulation, the contoured insulation of insulated siding provides support to the siding panel for ultimate durability.

Most siding products are made with one primary goal in mind - to make a home look great - but they aren’t all designed to protect the house. For instance, traditional vinyl siding creates a hollow void between the back of the siding and the wall. This leaves the siding susceptible to damage from impact due to hail, baseballs, rocks thrown from the lawnmower, creating a compromised exterior that no longer looks beautiful.

Insulated vinyl siding has contoured foam that acts as a shock absorber for the siding, protecting it from impact and preserving the appearance.

Check out these impact videos that push insulated vinyl siding to the limits of durability:

Summary

In summary, insulated vinyl siding is an effective way to insulate a home when adding new siding. Although comparable energy savings can be achieved with cheaper alternatives such as foam board insulation, these flat alternatives do not provide additional benefits such as maximum moisture management and superior durability.

It is important to determine the goals of your project when considering insulated siding. If you want maximum energy savings, combining options such as flat foam insulation under insulated vinyl siding could provide high r-values with all the additional benefits of contoured insulation.