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Complete Roof Insulation Guide for 2022

With winter coming on and natural gas prices on the rise, it makes sense to ensure our homes are as well insulated as possible. Insulation can take many forms, but some materials work better than others.

Often the location of the needed insulation will dictate which version to use, but some materials will work essentially anywhere.

To help clarify what insulation is and what it does, today we will discuss the insulation materials commonly in use in today’s modern construction industry and offer a few pros and cons of each design.

Why Should You Insulate Your Roof?

Roof insulation is one of the best investments a homeowner can make. As energy prices rise, the return on investment provided by insulation increases as well. There is a point of diminishing returns, however, as the cost of insulating can outpace the cost of heating and cooling.

Many times this cost is justified because the homeowner plans to stay in the home for many years. As a rule of thumb, most building codes require a minimum of R-38 insulation in an attic, but some northern US states may require as much as R-60.

Depending on the design of the home, adequate insulation can reduce energy costs exponentially, not to mention the environmentally friendly reduction of energy use. As we know, warm air rises and cool air falls, so we want the most insulation where it will be the most effective, which is the roof. 

How Does Roof Insulation Work?

Insulation works by resisting thermal transfer. Simply stated, this means that the primary function of insulation is to keep cool air separate from warm air. With most types of insulation, the main benefit comes from the air trapped inside the material, not the material itself.

Interestingly, the air is one of the best insulators available. Other gases, such as argon, are also very efficient at resisting thermal transfer. Many modern windows, for example, employ argon between two panes of glass, separating the interior pane from the exterior pane. 

Roof insulation can take several forms and each form has its pros and cons, depending on where it is installed. Often, a combination of different forms will provide the best overall performance for a roof, especially if the design uses vaulted or cathedral ceilings.

The best roof insulation design will typically include a balance of R-value, elimination of drafts, and initial cost.

What Are the Benefits of Insulating a Roof? 

  • Reduced Energy Costs

Without question, the main benefit of roof insulation is energy conservation. For homeowners, this essentially equates to saving money on the utility bill. The return on investment will vary from home to home, but as a rule, the more insulation, the better. In many cases, this makes installing insulation directly proportional to the energy savings.

  • Vapor Barrier

Some forms of insulation, like fiberglass batting, not only reduce thermal transfer but also resist moisture. These batts are usually paper-backed, meaning one side includes a moisture-resistant layer that retards moisture from passing through. Reducing moisture will help prevent mold and mildew problems while helping the fiberglass fibers encapsulate the air pockets in the batts. 

  • Increased HVAC Lifespan 

Most homes use some form of forced air HVAC system, which will have moving parts that will eventually wear out. Roof insulation extends the useful life of a mechanical forced air system by reducing wear and tear on the vulnerable parts such as the fan, air handler, and compressor. These components do the bulk of the work, so keeping them in good condition will result in ownership savings.

What Are My Roof Insulation Options?

Most forms of roof insulation can be categorized as blown in, foam, or batts. Blown-in insulation takes advantage of machinery to install large quantities of insulation material very quickly.

This is particularly useful in attics, where thickness is directionally proportional to effectiveness. Here we will discuss the common blown-in insulation options and a few pros and cons of each:

Option 1. Loose Fiberglass

Loose fiberglass insulation is typically sold in a large bale, which is blown into the attic space using a machine called a hopper. These machines chop up the bale, helping the fibers become airborne. Then a powerful blower pushes the fiberglass through a hose, where it can be directed into place.

Protective gear must be worn during installation to avoid breathing in the fiberglass fibers, as these fibers can contain irritants to the skin and lungs. As such, wearing safety gear, including a respirator, is required. To reduce the risk, some manufacturers have reduced or eliminated the irritating chemicals often found in fiberglass insulation, such as formaldehyde. 

Option 2. Cellulose

Cellulose is relatively inexpensive and works better the colder it gets. Cellulose is a paper product, which like loose fiberglass, is fed into a hopper and blown into the attic space. This allows the cellulose to be used in sufficient quantities to attain the required R-value for the region.

As a rule, more cellulose will be required than loose fiberglass to achieve the same R-value, but the initial costs tend to be similar. Proper safety gear is required when using cellulose, as the airborne fibers can irritate both skin and lungs during installation.

Option 3. Sheet Foam

Sheet foam is typically made from styrofoam, but most manufacturers add some features to the sheets, such as a vapor barrier. Sheet foam is often used in vaulted and cathedral ceiling designs where a mechanical connection to the roof framing is needed. Sheet foam is usually installed using staples or button cap nails, but it can also be glued into place.

Option 4. Spray Foam

Spray foam is a popular choice for new construction. Most of us know spray foam as a red can with a yellow lid, which normally expands as it dries. There are two common types of spray foam used in modern construction.

The first, called open-cell foam, tends to expand as it cures. Closed-cell foam is much denser than open-cell foam, only expands slightly, and can provide a vapor barrier once it is cured. This makes closed-cell spray foam the most popular choice among professionals.

Option 5. Fiberglass Batting

Fiberglass batting is probably what most of us think of when we envision insulation. This form has been around for decades because it is simple to install, does a great job, and lasts a long time.

However, in roof insulating, fiberglass batts are quite inefficient to install because there is no difference between installing the batts between rafters and installing them between wall studs. Unless the home has vaulted or cathedral ceilings, using fiberglass batts is often more expensive than blown-in insulation due to the installation costs.

Roof Insulation Installation Process

  • Loose Fiberglass

Loose fiberglass installation is straightforward, requiring only a few components. 

The process is very simple. The first step is usually to calculate how much insulation will be needed based on the size of the attic.

The next step is to install the depth gauges, which are just paper measuring sticks that are placed around the attic. These are used to keep the thickness as even as possible. Depth equals R-value, so the total amount needed will be a function of both the square footage and the thickness. 

The insulation is blown into the required depth, using the measuring sticks to keep the thickness consistent. In most installations, two people will make the process much faster. One person is in the attic, while the helper remains with the hopper.
The hopper is filled with as much loose fiberglass as it will hold, and the person in the attic uses a long hose connected to the hopper. In most cases, the hose will have a remote switch allowing the person in the attic to stop and start the hopper as needed.

  • Cellulose

Cellulose is installed exactly the same way as loose fiberglass, except that cellulose is usually more densely packed into the bale. This often requires breaking up the bale into pieces before placing it in the hopper.

Cellulose dust is also an irritant so safety gear, including a respirator, is required. Otherwise, the process, gauges, and even the hopper used are identical to loose fiberglass.

  • Sheet Foam

Sheet foam is usually installed with the help of either a stapler, button cap nails, or adhesive. Sheet foam is very light, so it can be surface mounted or installed between the ceiling joists and trusses.

Most professional installers use either an electric or pneumatic stapler, which makes the job very fast to complete. Button cap nails are basically drywall nails with an added “button”, or small plastic grommet added. This button increases the function of the nail head and has stronger holding power than a standard nail.

Adhesives are also commonly used, however, future removal can be difficult. In most situations, foam sheets will need to be stacked together to achieve the desired thickness, making adhesive a popular fastener choice.

  • Spray Foam

Spray foam is likely the most popular insulation method currently used in modern construction. In most applications, spray foam provides both a vapor barrier, crack sealing, and insulation once it is cured.

Installing spray foam involves a machine similar to a paint sprayer. This machine sprays very sticky liquid foam into the area and as the foam cures, it slightly expands filling in any voids. Spray foam is very fast and effective, but in most cases is not considered a do-it-yourself project, as the job requires safety gear, special training, and expensive machinery.

  • Fiberglass Batting

In contrast, fiberglass batting can easily be installed by a DIYer with a few tools. Batting is probably what we think of when we envision insulation. Batts have a paper-backed side (the vapor barrier) and an open side. When using batts, the paper-backed side always faces the heated space.

In practice, this means the paper side faces out, into the room. Batts are simply cut to length and installed between rafters or joists with staples, tape, or button can nails. Batts can also be stacked to increase the R-value.

Insulation Equals Savings

From an energy conservation point of view, installing too much roof insulation can be a challenge. Every BTU of energy saved is good news for both the homeowner and the environment.

However, many builders only install as much insulation as the local building code requires. It should be noted that building codes are generally based on minimum requirements, not necessarily the best option. Following the established EPA guidelines for any particular region will usually result in the most cost-effective insulation system dollar for dollar. 

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