What is Insulation R-Value? – A Simple Guide to R Value

What is Insulation R-Value A Thorough Look

Insulation R-value is heat resistance value. It is a unit of measurement used to determine how well insulation can resist heat from flowing through it per each inch of material. For any insulation material, the thicker it is, the higher the R-value. But insulation R value differs significantly from one material to another.

If we look at it in terms of how much insulation your home has in various areas - the attic, walls, or floor, R-value is a way to think about how much heat loss (or heat gain in summer) your home is experiencing in any given area.

There is a lot that goes into finding the insulation R value. For more information, keep reading this comprehensive article!

Navigation Guide:

  • What is R-value? A Thorough Look
  • Types of Insulation and Their R-values
  • DIY Friendly?

What is Insulation R-Value? A Thorough Look

Contractors use complex testing and math to determine the R-value of the insulation already in your home, as well as the insulation needed. If you enjoy crunching the numbers, this article explains the technical side of determining R-value. Whether you do the deep dive, it is important that you understand what goes into finding the R-value.

It’s typically dependent on three things:

  1. The type of insulation being used. Different insulation types have different weights and thicknesses, which affects R-value, aka insulation R value.
  2. The insulation’s thickness. To find the R-value of an insulating material, you’ll need to calculate its heat-resistance per inch of that material.
  3. The material’s density. Density is referring to compactness. How compact is the material in the area needing the insulation? This is something of a subset of #1.

But you should also note that there are additional factors that influence what specific R-value is ideal for your home:

  1. Climate temperature. Homeowners living in very cold and extremely hot climates will need insulation with higher R-values to compete with the weather.
  2. Your home’s age. Older homes can be drafty, meaning air moves more freely in and out, if they haven’t been updated with house wrap and new windows. They need to be approached differently than modern homes.
  3. Your HVAC system. Moisture control is significant for R-value. If your home is frequently humid, you will need insulation with a higher R-value.
  4. The specific location. Each type of insulation works best in specific conditions. For example, if moisture is high, then foam is prefered to other insulation types.. You’ll need to choose the type of insulation best for your project.

The higher the R-value, the more heat-resistant the insulation will be. And the more insulation you install in an area, the R-value will naturally increase. This is because the additional material strengthens the insulation barrier, making it harder for heat to pass through.

The result of a proficiently insulated home is less wasted energy and more financial savings over time. In fact, bringing your home’s insulation up to recommended levels has a tremendous return on investment, ROI, also called Cost to Value in the building industry. Installing additional insulation in an attic will pay for itself in less than five years. After that, the savings are a bonus.

Types of Insulation and Their R-values

Refer to the R value chart below to compare each insulation material. Here’s the R value insulation offers based on type.

Insulation materialR-values per inch (thickness)
FiberglassBatts and rolls: 2.9 to 3.8
Loose-fill: 2.2 to 2.7
Blown-in: 2.2 to 4.3
CelluloseLoose-fill: 3.1 – 3.8
Blown-in: 3.1 – 3.9
Mineral wool (rock wool, slag wool)Batts and rolls: 3.3 – 4.2
Loose-fill: 2.2 – 3.3
Natural fibers (cotton)
Batts and rolls: 3.0 – 3.7
Spray foam (open/closed-cell)
Open-cell: 3.5 – 3.7
Closed-cell: 6.0 – 7.2
Polystyrene (foam)Expanded: 3.6 – 4
Extruded: 4.5 – 5.0
Polyisocyanurate/Polyurethane (foam)5.5 – 8.0

1. Blanket Batts and Rolls

Blanket Batts and Rolls Insulation

Blanket insulation can come in two forms: bats or rolls. This insulation type is most commonly made of glass fibers, known as fiberglass; although, it can also be available in plastic fibers, cotton, rock wool, and slag wool.

Batts and rolls are the least expensive types of insulation to install, and homeowners may be pleased to know that they are DIY-friendly, especially in comparison to other types of insulation.

Blankets of insulation are designed to conveniently fit the standard widths between wall studs, attic rafters and floor joists. Size can be easily cut down with a utility knife for smaller spaces whenever needed.

Batts and rolls are used for unfinished walls (including basement walls), ceilings, floors, crawl spaces, and attics.

Insulation materialsAverage cost per sq. ft.Installed cost per sq. ft.
Fiberglass$0.52 – $0.77$1.30 – $2.60
Mineral wool (rock/slag)$1.00 – $1.11$1.80 – $2.25
Natural Fibers (cotton)$0.70 – $1.50$1.50 – $3.35

2. Blown-in/Loose-fill

Blown-in insulation (also referred to as loose-fill) is best used for adding to existing insulation in a finished area of the home, for irregularly shaped spaces, and for in hard-to-reach spaces. A mechanical blower is used to distribute the insulation, which looks like small paper bits and is most commonly cellulose. Recycled newspaper is a common component of blown-in insulation.

Blown-in insulation does not proportionately increase its R-value with added thickness. This is because the insulation’s weight makes it more compact, increasing its density. And the more compact any insulation is, the less R-value it has.

The U.S. Department of Energy recommends that homeowners in most northern (colder) climates use insulation with a minimum insulation R value of 49 (R-49) in the attic and that homeowners in most southern (hotter) climates use R-38. Using more insulation - up to R-60 in any climate - is recommended for optimal energy and cost savings.

Insulation materialsAverage cost per sq. ft.Average cost per bag for installationInstallation cost per hour
Fiberglass$0.47 – $1.10$23 – $40$33 - $74
Cellulose$0.70 – $2.40$25 – $45
Mineral wool (rock/slag)$0.30 - $0.43$25 – $45
Natural wool$1.69 – $5.44$25 – $45

A DIY option is to rent the machine from the home improvement store. In fact, if you purchase enough bags of insulation, use of the machine for a half day to whole day is sometimes free.

3. Spray Foam

Blown-in_Loos

Spray foam is a liquid compound that, when applied, turns into a solid. It can be used in wet areas around the home without being ruined. It’s best used for finished areas (ceilings and basement walls) and around exterior faucets and vents.

Spray foam is available in two forms:

  1. Half-pound open-cell. It’s a weaker moisture barrier and is designed to expand in the area it’s applied. It is most appropriate for inside insulation jobs, such as filling crevices and crawl spaces, yet it needs a vapor retarder. Open-cell spray is cheaper than closed-cell.
  2. Two-pound closed-cell. It’s denser and does a better job at insulating, but it works best for exposed or exterior walls. Closed-cell usually has great performance, as it is designed to hold up well in extreme climates.

The cost for spray foam materials is much less than installation cost. The reason is that installation cost factors in the price for a professional’s labor, which includes the setup, prep work, trash removal, and cleanup. The price for installation will also vary considering spray foam doesn’t have a specified thickness like other types of insulation. As a rule, the thicker the foam, the more it will cost.

You’ll also notice that the materials cost is measured in “board foot.” A board foot is one square foot of insulation 1 inch deep. To calculate board footage, multiply the area (sq. ft.) you want insulated by the depth of the area in inches.

Insulation foamMaterials cost (per board foot)Installed cost per sq. ft.
Open-cell$0.39 – $0.70$1.95 – $6.00
Closed-cell$1.00 – $1.63$2.50 – $6.75

Cost to apply foam insulation, the Average Installed Cost, varies because the thicker the foam layer, the longer it takes to install.

4. Foam Board/Rigid Foam Panels

Foam Board_Rigid Foam Panels Insulation

Foam boards/rigid foam panels can be used for just about every part of your home and provide up to two times the heat-resistance of most other insulating materials of the same thickness.

Foam boards/panels are able to retain limited water, but the amount of water and the duration of time it can be exposed to water varies depending on which type of foam board you use. Expanded polystyrene (EPS) is very limited in what it can be exposed to; extruded polystyrene (XPS) has a better performance; polyisocyanurate (ISO), or polyurethane, performs the best.

Foam boards/panels are used for unfinished basement walls, exterior walls, floors, and ceilings.

Insulation materialsAverage cost per sq. ft.Installed cost per sq. ft.
EPS$0.33 – $0.40$1.40 – $1.85
XPS$0.38 - $0.46$1.75 – $2.90
ISO$0.66 - $0.78$3.00 – $3.85

5. Radiant/Reflective Barrier

Radiant_Reflective Barrier Insulation

Radiant barriers, also called reflective barriers, are installed over new or existing insulation in attics, unfinished walls, ceilings, or floors to increase the efficiency of both materials. In other words, radiant barriers are supplementary to insulation.

There are three types of heat: radiant, convection, and conduction. Insulation blocks conductive heat transfer, but radiant barriers reflect radiant heat. For this reason, they don’t have R-values.

Radiant barriers can comprise of four different materials:

  • Foil-faced kraft paper
  • Plastic film
  • Polyethylene bubbles
  • Cardboard

They can also come with one-sided or two-sided foil. Two-sided foil is the most expensive of the two options.

MaterialAverage cost per sq. ft.Average installation cost (per hour)
Radiant BarrierSingle-sided roll: $0.13 – $0.27
Two-sided roll: $0.80 – $0.92
$30 – $80

DIY Friendly?

It depends.

Insulation jobs requiring batts and rolls are typically DIY-friendly, and so is blown-in once you get the hang of it.

Cellulose and especially spray foam insulation aren’t good projects for the inexperienced or the handyman who is the jack of all trades but master of none. For those types, we recommend that you choose a pro for the installation. Professional contractors know how to effectively manage and apply the insulation to ensure all air-leaks, including hidden ones non-experts may miss, are sealed.

So that you don’t have any costly issues with your home’s insulation, we advise contacting a reliable contractor.

Here are some tips to keep in mind when hiring a professional:

  1. Obtain written cost estimates from multiple contractors to compare answers, find an average, and gain a better understanding of the R-value you need.
  2. Don’t be surprised if you find the cost estimates varying drastically from one contractor to another. Sometimes the prices vary by as much as 100%.
  3. Be sure to ask contractors about their air-sealing services and the cost for the service. It’s a good idea to have any air leaks sealed before insulating the area. In fact, reliable sources like Green Building Advisor suggest that stopping air leaks is more important than how much insulation you have. If air is changing rapidly in your home, there’s not much that insulation can do to stop the influx of heat in summer and the departure of heat in winter.

Make sure to tell each professional handing you a quote that he is competing for work. This way, you will be less likely to receive an overpriced estimate.

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