What Are Insulation R-Values?

Date Published: August 11, 2022

When it comes to optimizing in-home climate control, increasing energy efficiency, and saving money, one of the most important aspects of the home is insulation. In fact the EPA calculates that, by sealing homes and insulating properly in the appropriate areas, homeowners can save up to 15% on yearly heating and cooling costs.

There are several different types of insulation, all of which can be useful when utilized in the right scenario. So, how do we determine when to use what type of insulation? The answer lies in the R-value.

What is an R-Value?

The R-value of insulation indicates its resistance to heat flow. In other words, R-value measures how well insulation prevents heat from flowing inside and outside of a home.

A higher R-value means a higher heat flow resistance and better performance. This value is affected by various factors, including type of material, density and thickness.

When it comes to choosing insulation and selecting R-values, it’s not a one-size-fits-all kind of situation. Depending on where you live and what in-home components you are insulating, recommended R-values may vary.

The US Department of Energy recommends R-Values that vary from region to region. Generally, the colder the area, the more effective the insulation should be; and thus, the higher its R-Value should be. For instance, a homeowner in Bismarck, North Dakota will utilize higher R-valued insulation than one in Miami, Florida. The map below shows the USA broken down into different “R-value regions.”

R-Values US map

Image sourced from: https://www.homedepot.com

Additionally, different R-values are recommended for different parts of the of the home. For instance, a higher R-value is going to be recommended for attics than for floors, walls or crawlspaces. The chart below shows the recommended R-values for the various climate zones in the US (zones indicated on the map above).

Chart showing recommended R-values for different parts of the home.

Image sourced from: https://www.homedepot.com

So, when hiring an insulation professional or doing your own DIY installation, it is important to be aware of your regional R-values. Insulation materials vary in cost, and you don’t want to end up paying more for a material with an unnecessarily high R-value. Now let’s take a deeper dive into the various insulation types.

Insulation Types and Their R-Values

Blown-in Insulation

Blown-in insulation is a process that uses a specialized machine to blow small insulation particles into a given space. It has proven to be a very handy technique, especially when trying to insulate hard-to-reach or irregularly shaped areas. The primary materials used for this process are fiberglass or cellulose. Both of these materials have their own pros and cons.

Blown in insulation

Blown in insulation. Image sourced from: https://www.parkerandsons.com/

As indicated in its name, fiberglass contains a percentage of glass, which makes it a more sustainable and recyclable material. Also, it is resistant to moisture absorption and can combat problematic issues such as mold, mildew and fungus.

Standard loose-fill fiberglass has an average R-value of R-2.2 to R-3.8 per inch of thickness.

This type of blown-in insulation generally does not do much to reduce air leakage. Additionally, airborne fiberglass particles have been proven to be a health risk to individuals who are installing the product.

Cellulose is made from recycled newspaper and cardboard then treated with chemicals to make it fire-retardant. This material’s chemical coating acts as a deterrent to pests, and it is generally less desirable to rodents and insects than fiberglass.

Contrary to fiberglass, the composition of cellulose has been proven to help combat air leakage. In fact, during our blower door tests, we have found that dense-filled cellulose has shown the highest resistance to air leakage (aside from spray foam insulation).

Cellulose R-values are higher than that of fiberglass ranging from R-3.2 to R-4.0 per inch.

On the down side, cellulose is usually harder to install, making it a little less DIY friendly than fiberglass. Additionally, cellulose might begin with a higher R-value than fiberglass. But overtime, it is more prone to settling and packing, which ultimately decreases its ability to resist heat transfer.

Insulation Blankets

Insulation blankets are usually one of the cheapest options for insulation. These blankets generally come as pre-cut “batts” or rolls that need to be cut to length. They are super user-friendly because they are meant to fit into the standard lengths between wall studs, floor joists or attic rafters. This type of insulation will commonly be composed of fiberglass, though it can sometimes contain less common materials, such as plastic, cotton or sheep’s wool.

R-values for insulation blankets range from R-2.9 to R-4.3 per inch of thickness.

While these thick blankets can help to cut down on air leakage, they are not made for it. Significant air leakage can still occur with insulation blankets, especially around their corners and edges. In fact, during our blower door tests, we have found that insulation batts provide the worst air leakage control of all the insulation methods.

insulation in a basement

Insulation batts in a basement. Image sourced from: transicionenergeticaycc.org

Spray Foam Insulation

Spray foam insulation is unique in that it is the only technique designed to effectively increase insulation and reduce air leakage. It is a combination of chemicals that, when sprayed, react with each other, expand and harden.

This type of insulation is ideal for sealing wall cavities, attics, crawlspaces, gaps and cracks. Depending on the type of spray foam (Open or Closed cell), its R-value can range from R-3.5 to R-6.5 per inch.

Spray foam insulation has one of the highest R-values per inch of any insulation technique. It is proven to be long-lasting, provides excellent coverage even in those hard to reach nooks and crannies. And as stated above, its air-tightening capabilities are second to none, helping to drastically minimize air leakage and boost energy efficiency.

However, its good qualities do come with a price…literally. Spray foam insulation is one of the priciest insulation methods with costs ranging from $1 t0 $1.5 per board foot. On top of that, spray foam can over-tighten a home, increasing the need to bring fresh air into the home using mechanical methods. This is generally a good problem, but we like to outline the trade-offs you make.

Spray foam insulation being applied to a home

Spray foam insulation. Image sourced from: dunlapconstructioninc.com

Foam Board Insulation

Similar to foam spray, foam board insulation is another method that yields a high resistance to heat flow. It has R-values that range from R-4.0 to R-6.5 per inch of thickness.

Foam board’s tight-pored structure makes it highly resistant to moisture intrusion. As a result, it is commonly utilized for unfinished basement 0r foundation walls, floors and ceilings.

The biggest benefit of foam board insulation is it covers the entire wall creating a continuous insulation barrier that isn’t broken up by framing. This material is also commonly used around exterior slabs.

Foam boards usually come in rigid rectangular shapes that can be cut to size, which make this type of material relatively user-friendly. However, its rigid qualities prove to make it ineffective at sealing cracks and holes. Thus, this type of insulation method alone will not entirely solve air leakage problems.

Basement with foam board insulation

Basement with foam board insulation. Image sourced from: buildwithhalo.com

How Does Insulation Play a Part in HERS Ratings and Energy Efficiency?

As we strive towards increasing energy efficiency in homes, one of the most widely implemented processes is the Home Energy Rating System (HERS). In many Colorado counties, the International Energy Conservation Code (IECC) is requiring newly built homes to earn a satisfactory HERS rating.

When performing a HERS rating service, one of our certified HERS raters, will observe multiple aspects of the home. One of the primary points of observation will always be the insulation.

The inspector will consider questions such as: Is there a sufficient amount of insulation? Is the insulation installed properly? Does it have the optimum R-value?

Insulation with the appropriate R-value will, in turn, help to contribute to a sufficient HERS rating.

Home inspector inspecting insulation in attic.

In addition to HERS testing and insulation inspections, we also offer blower door testing. Blower door testing is another key procedure required by the IECC to assess the air leakage of a home.

As discussed above, insulation styles like spray foam and and dense-fill cellulose can really help to reduce air leakage. Properly installed insulation with the right R-values can be a prime contributing factor to a house’s overall energy efficiency.

Interested in evaluating the energy efficiency of your home? We’ve got you covered! Visit the Scott Home Inspection website now for a comprehensive list of our energy services.

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About the Author: Chris Kimmel

Chris Kimmel worked as an Associate Home Inspector for two years, handling numerous services including sewer scope inspections, pest inspections, mold air sample testing, radon testing, and water quality testing. Chris now works with Scott Home Inspection as a Content Writing Specialist.

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