What Is Home Insulation & Why Is It Important?

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What Is Home Insulation & Why Is It Important?

We’ve been insulating the homes we live in for thousands of years with the primary goal of keeping us warm when it’s cold and cool when it’s hot.  Some of the earliest forms of insulation include mud and straw plastered between the logs used to build homes.  In medieval times, homes were made of stone and thatched roofs that were miserably damp and drafty, but some inventive folks would hang tapestries on walls to help make their home a little more bearable.

Fast forward to the early 20th century and Dale Kleist stumbles on the invention of fiberglass while working at the Owens Illinois Glass Company (now Owens Corning).  Around the middle of the century, cellulose (which is made from cardboard, cotton, newspaper, sawdust, and straw) came onto the scene and grew in popularity when manufacturers were able to add a fire retardant to reduce its flammable properties.  Around the same time, the military developed a new chemical compound called polyurethane, which would eventually be used as insulating spray foam.  Fiberglass, cellulose, and foam are the most popular forms of home insulation today.

Technically, home insulation is the use of insulating material for the purpose of acoustic, fire, impact, or thermal insulating properties.  However, when people think of home insulation, they are most often thinking of thermal insulation. The reason is simple, heating and cooling your home makes up the largest portion of your utility bill and properly insulating your home can provide substantial reductions in energy use and some of the quickest paybacks in terms of home energy improvements.

Not only can proper insulation save you money, but along with home sealing it will also play a critical role in combating climate change and getting the world to net-zero carbon emissions by 2050.  Part of getting to net-zero involves upgrading HVAC systems to electric options such as mini-splits and geothermal heat pumps. But regardless of your fuel source, a poorly insulated home means your HVAC system is working too hard and using too much energy.

Here’s what we’ll cover in this guide – feel free to jump to the section you’re interested in.

  1. Benefits of Home Insulation
  2. R-Values in Insulation
  3. Types of Insulation for Homes
  4. Where to Insulate in a Home
  5. Cost to Insulate a House

Benefits of Home Insulation

Alright, so there are all these different types of insulation to choose from, but what are the real benefits of insulation?  There are three primary benefits of insulation:

  1. Insulation will reduce your energy costs – heating and cooling your home is typically the most expensive part of your utility bill and properly insulating your home can reduce your energy usage from 20% to 40%.
  2. Insulation can improve your health – a study conducted by researchers at the Harvard School of Public Health found that properly insulating our home would translate into the following health benefits; 240 fewer deaths, 6,500 fewer asthma attacks, and 110,000 fewer restricted activity days per year from emission reductions of fine particulate matter.
  3. Insulation helps protect the environment – properly insulating your home will use less energy, which reduces your personal carbon footprint helping us get to net-zero carbon emissions.

R-Values in Insulation

Depending on where you live, you’ll need to insulate to a higher or lower R-Value.  The “R” in R-Value, stands for resistance and is how insulation is rated.  The higher the R-Value the more resistance it has to heat flow (how well it keeps heat from entering or leaving your home).  The minimum guidelines for what R-Value your home should be insulated to is determined by The International Energy Conservation Code (IECC).  The first energy code was first published by the IECC in 1998 and is updated every three years.  Local governments use the energy code to establish regulations for builders to meet certain minimum insulation requirements.  As homeowners, we can use the guidelines too when determining the R-Value we should insulate our homes too.

Central to the energy code are the Climate Zones.  The U.S. is divided into 7 Climate Zones based on the general weather patterns of the region.  The weather patterns have to do with the average temperature in the winter and summer as well as the amount of humidity and rainfall a given region experiences.  Below is a map of the 8 climate zones and a table of the recommended R-Values for each zone.

Recommended insulation levels for retrofitting existing wood-framed buildings
Zone Add Insulation to Attic Floor
Uninsulated Attic Existing 3-4 inches of Insulation
1 R30 to R49 R25 to R30 R13
2 R30 to R60 R25 to R38 R13 to R19
3 R30 to R60 R25 to R38 R19 to R25
4 R38 to R60 R38 R25 to R30
5 to 8 R49 to R60 R38 to R49 R25 to R30

Wall Insulation – Whenever exterior siding is removed on an:

Uninsulated wood-frame wall:

Drill holes in the sheathing and blow insulation into the empty wall cavity before installing the new siding, and

Zones 3-4: Add R5 insulative wall sheathing beneath the new siding

Zones 5-8: Add R5 to R6 insulative wall sheathing beneath the new siding.


Insulated wood-frame wall:

For Zones 4-8: Add R5 insulative sheathing before installing the new siding.

Types of Insulation for Homes

As we mentioned earlier, fiberglass, cellulose, and foam are among the most common types of materials used in insulation, but within the world of insulation, there are many variations to choose from.  The primary factors that guide your decision around which type of insulation to use are: 

  1. Where in your home do you need to insulate
  2. The R-Value you plan to insulate to
  3. The budget for your insulation project
  4. Whether you plan to insulate yourself or hire a professional

Below is an overview of the most common insulation types, their advantages, and where they are typically installed.

Blanket: batts & rolls – usually made of fiberglass, mineral (rock or slag) wool, plastic fibers, or natural fibers. Installed between studs, joists, and beams in unfinished walls, floors, and ceilings.  Its primary advantage is that it’s relatively inexpensive and you can do it yourself.

Concrete block insulation and insulated concrete blocks – foam board applies on the outside wall for new construction or inside walls for existing homes.  Requires professional installation.  Blocks are either dry-stacked and surface-bonded or mortared in place and can provide substantial increases to R-Values compared to conventional concrete.

Foam board or rigid foam board – usually made of polystyrene, polyurethane, phenolic, or polyisocyanurate, these boards have a very high insulating value given their thickness. You can use foam insulating boards on unfinished walls, including foundation walls, floors and ceilings, and unvented slope roofs.

Insulating concrete forms (ICFs) – foam board or foam blocks that are installed as part of the building structure.  ICFs achieve a high thermal resistance by providing insulation built right into the home’s walls.  ICFs are most commonly used in new construction applications.

Loose-fill and blown-in – usually made of cellulose, fiberglass, or mineral (rock or slag) wool and is blown into place using specialized equipment. Loose-fill or blown-in insulation is commonly used in home energy retrofits e.g. attic floors, adding insulation to finished areas, areas with obstructions or irregular shapes.

Reflective system – foil-faced kraft paper, plastic film, polyethylene bubbles, or cardboard are typically fitted between wood-frame studs, joists, rafters, and beams on unfinished walls, ceilings, and floors. While you can do this work yourself it is typically applied during new construction and has the advantages of effectively preventing downward heat flow.

Rigid fibrous or fiber insulation – usually made of fiberglass or mineral wool (rock or slag) and is fabricated either on the job site or at a shop by HVAC contractors.  The primary advantage of rigid fibrous or fiber insulations is that they can withstand high temperatures.

Sprayed foam and foamed-in-place – typically made or cementitious, phenolic, polyisocyanurate or polyurethane and is applied in using small spray containers or in larger quantities as a pressure-sprayed application.  Sprayed foam or foam-in-place is good for adding insulation to finished areas, areas with obstructions, or irregular shapes.

Structural insulated panels (SIPs)

Structural insulated panels (SIPs) are panels of foam, liquid foam, or straw that contractors fit together to form walls and the roof of a home.SIPs provide uniform insulation and faster build times compared to more traditional construction methods.

Where to Insulate in a Home

When you are thinking about where to insulate your home, you really need to consider the entire building envelope, but you can get more bang for your buck with a focused approach if you can’t afford to properly insulate your entire home to the recommended R-Values for your region all at once.  There are a couple of things to consider before digging into an insulation project.  First, do you know the R-Values in your home currently?  Second, do you know the air exchange rates in your home?  If you are unsure, then you may want to get the help of a professional home energy auditor to get an independent evaluation.  Before tackling insulation projects making sure your home has a proper air seal will improve the effectiveness of your insulation and will save you money.  We tackle air leakages and how to create an air seal for your home later in this article. Below are some of the more common places you will need to insulate.

Attic Insulation – The 2021 energy code calls for R-Values ranging from 30 to 60 depending on your climate zone for ceilings.  Making sure your attic has sufficient insulation is one of the most important insulation investments you can make given the amount of heat loss and gain flowing through your roof.  Most commonly batt or loose-fill insulation is installed in attics.  Loose-fill insulation can provide better coverage and is typically more cost effective.  It is important to tackle any roofing repairs you may need before addressing attic insulation.  Because attics often contain mechanical equipment such as ducts, HVAC, and water heating systems additional sealing and insulation of these systems may be necessary as well as insulating rafters.

Ceiling Insulation – Most ceilings will interface with the attic, however, cathedral ceilings provide some unique insulation challenges.  A cathedral ceiling matches the roof’s pitch and depending on how it was built may or may not be easy to insulate.  Properly insulating cathedral ceilings will help provide even temperature distribution throughout your home.

Exterior Wall Insulation – R-values for exterior wood-framed walls range from 13 to 20+5, 13+10, or 0+20 to meet the 2021 energy code.  If your attic has been sealed and insulated to the current energy code, but your walls have not, then you may get some additional savings (especially in colder climates) by bringing your walls up to the current code.  However, insulating finished exterior walls are not cheap so make sure you calculate your payback window and evaluate that project relative to other energy retrofit options.  If and when you need to replace the siding of your home, it’s a great opportunity to look at insulating your exterior walls at that time.  

Existing Home Energy Retrofit – Usually, wall cavities are not easily accessible when doing a home energy retrofit so insulating exterior walls is usually done with cellulose blown-in insulation using the dense pack technique to maximize the R-value or an injectable spray foam insulation application.

Major Home Remodeling Project – if you are undertaking a major house remodeling project and your wall cavities are accessible then you can consider a two-part spray foam or wet spray cellulose insulation which will also provide air sealing benefits.

New Home Construction – with new home construction you have several insulation options to consider when thinking about the energy efficiency of your home.  Depending on the design of your home, you may want to consider structural insulated panels, insulating concrete forms, and insulated concrete blocks.  These building materials often have superior insulating qualities but are not for all residential home designs.

Floor Insulation – Some of the more common floor insulation problems come from the floors above or walls adjacent to unconditioned garages.  Car exhaust and other chemicals you may have in your garage tend to produce the most pollutants that can get into your living space so developing a good air sealing strategy is a good first step before tackling insulation.  From there, insulating floors to the same R-Value as your wall systems is a good rule of thumb.

Basement Insulation – Adding insulation to the exterior of the basement walls is impractical in existing homes, but there are benefits to adding insulation to the interior walls of a basement depending on how you plan to use the basement.  You have a lot of flexibility with the type of insulation you can use on interior basement walls, but there are a couple of important considerations you need to think about. Depending on how you plan to insulate your interior basement walls you will lose a bit of your usable space, typically it’s not a noticeable reduction in usable space.  Basements often have moisture problems, which may need to be addressed prior to any insulation efforts to prevent mold from developing.

Foundation Insulation – In new construction, you have the option of insulating the exterior foundation walls, which will minimize thermal bridging, reduce heat loss, provide some protection against moisture and insect infestation as well as tie the foundation into the rest of the conditioned space improving the overall efficiency and comfort of your home.

Crawl Space Insulation – Crawl spaces also present unique insulation challenges, but do offer some opportunities to improve home health, comfort, and performance.  Most building codes require venting to prevent moisture build-up.  However, in hot and humid climates an unventilated space is now considered a best practice when taking into account proper drainage, moisture control, rodent and insect prevention techniques. 

Cost to Insulate a House

Depending on the current R-Values and air exchange rates in your home, insulating up to the current energy code can give you one of the best paybacks of any home energy retrofit investments you can make.

There are several factors to consider when budgeting your insulation project.  Are you going to insulate your home yourself or hire a contractor?  Are you going to insulate all at once or one room at a time? What type of insulation will you choose?  The easiest way to get a rough estimate is to look at the average insulation cost per square foot, which can be broken out by type of insulation and labor to install if you are hiring a professional.

The following table shows a range of prices for some of the most popular insulation types.  Prices are for the insulation only, not labor to install the insulation.  Labor to install most insulation runs between $0.25 to $0.50 per square foot on top of the material prices below.  The following material costs are price per board foot, which is one square foot by one inch thick.  To calculate a rough price, multiply the prices listed below by the thickness you need.  

Insulation Type Price per Board Foot
Fiberglass Batting Insulation $0.30 – $1.50
Cellulose Blown-In Insulation $1.00 – $2.00
Spray Foam Insulation $.50 – $2.00
Radiant Insulation $0.20 – $1.00
Rigid Insulation $0.25 – $1.00
Polyisocyanurate Insulation $0.40 – $0.60
Expanded Polystyrene Insulation (EPS) $0.25 – $0.35
Extruded Polystyrene Insulation (XPS) $0.40 – $0.50
Structural Insulated Panel Cost (SIPs) $7.00 – $12.00*
Spray Foam Insulation (SPF) – Open Cell $0.35 – $0.55
Spray Foam Insulation (SPF) – Closed Cell $1.00 – $2.00

*SIPs come as a complete unit of roughly 4 inches of insulation between plywood or OSB, so this price includes the entire unit rather than multiplying the number of inches needed.

In summary, proper insulation is one of the most cost-effective upgrades to your home’s energy efficiency.  A properly installed home will save you money, help keep you healthy, and contribute to our collective reduction of planet-warming greenhouse gases.


Finding the right contractor can be the key to having Insulation installed correctly and safely, and is certainly easier than doing it yourself. Beyond word-of-mouth recommendations, local building inspectors or trade groups may have a list of licensed contractors in your area.

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