Attic insulation sits on the attic floor joists and the backside of the drywall ceiling. A properly insulated attic keeps your home warm in the winter and cool in the summer. In addition to providing greater comfort, proper insulation could help lower your energy bills.
If you’re thinking about upgrading your attic insulation, the materials you install will significantly impact the project’s success. Read on to learn about the types of attic insulation best suited to make your home more energy-efficient.
The type of attic insulation best-suited to your attic depends on a variety of factors: attic accessibility, durability requirements, desired eco-friendliness, and project budget. But the most crucial factor to consider when choosing attic insulation is its R-value.
R-value indicates a material’s thermal resistance (in layman’s terms: the material’s ability to prevent heat from moving between two spaces). Measured in per-inch units, R-values range from 2.0 to 8.0. The higher the R-value, the better the insulation.
You’ll find the R-value listed on the insulation’s product packaging or the product description.
The material’s type, thickness, and density will determine the insulation’s R-value. The location and method of installation will also impact the R-value. Temperature, aging, and moisture accumulation can negatively impact R-value.
Determining Your Target R-Value
The amount of insulation your attic needs depends on the climate zone where your house is located.
The International Code Council (ICC) updates building codes listed in the International Energy Conservation Code (IECC) every three years.
Here are the IECC’s most recent recommendations for residential buildings, updated in 2021:
- Climate Zone 1: R-30
- Climate Zones 2 or 3: R-49
- Climate Zones 4 – 8: R-60
A higher climate zone number indicates a colder climate; a higher R-value indicates a greater degree of insulation. If you’re using multiple layers of insulation, calculate the total R-value by adding the R-values of each layer.
A material with a higher R-value doesn’t automatically mean it’s the best insulation material for your home’s particular insulation needs. You will need to consider other factors as well, particularly proper installation.
Also known as blanket insulation, batts are large insulation pieces of interweaving fibers and adhesive binders.
Along with loose-fill, batts are the most common option for do-it-yourself insulation. So long as your attic has enough headspace and minimal obstructions, batts provide the most straightforward installation.
However, for batts to provide adequate insulation, they need to fill the entire space between ceiling joists without any gaps. If you have a few obstructions in your attic, you can cut the material to fit tightly around them.
Unfortunately, the bulkiness of batts often results in ineffective installation… which in turn results in poor insulation.
(Be aware that you may have to install several layers of batts to achieve your desired R-value.)
Batts come in sheets or rolls, sized to fit the standard space between joists (16 or 24 inches). Faced batts are backed with foil or paper to provide vapor control. Unfaced batts are exposed on both sides.
Insulation batts come in several materials: fiberglass, cellulose, cotton, or mineral wool.
Composed of delicate glass fibers that look like cotton candy, fiberglass batts are the most common batt option. They are cheap, easy to find in stores, and don’t shrink over time.
Unfortunately, while fiberglass batts are the least expensive, they are also the least effective and can pose certain health hazards (more details in later sections).
Fiberglass is moisture resistant, although not totally impervious, making it less susceptible to mold. It is also noncombustible.
R-value per inch: 2.9 – 4.3
A limited number of manufacturers make cellulose batts constructed from recycled paper. Unfortunately, cellulose batts lose effectiveness and develop mold when exposed to moisture.
Cellulose collects and holds water by design, so these batts might not be your best option for attic insulation.
Although manufacturers treat cellulose with anti-flammable chemicals, these batts still come with a warning that they present a fire hazard.
R-value per inch: 3.7 – 3.8
Cotton batts are made from recycled denim fabric, making them the safest and most environmentally friendly insulation material. They are the most effective and most expensive of these materials.
In addition to insulating your attic, cotton batts can help block sound transmission.
R-value per inch: 3.7 – 3.8
Mineral Wool Batts
Mineral wool, also known as rock wool, is a fiber made from stones such as basalt rock and recycled steel slag. As an insulation material, mineral wool is more expensive than fiberglass but not as effective as cotton.
That being said, mineral wool batts are flame-resistant up to 1,800 degrees Fahrenheit and retain insulation ability when wet. Like cotton batts, mineral wool batts can also block sound. Despite these advantages, mineral wool batts are challenging to find.
Heads up – inhaling mineral wool during installation can potentially cause cancer.
R-value per inch: 3.0 – 3.3
If your attic has limited headroom, many obstructions, or irregular joist spacing, loose-fill insulation will provide a complete layer of insulation free from gaps.
Loose fill comes in bags and is installed either by hand or with a blower (a large machine that uses air to blow loose fill through a hose). You can rent a blower from a home center to achieve a more thorough and less labor-intensive job.
Loose-fill insulation is generally more expensive than batts, running about $1 per square foot.
There are three main types of loose-fill insulation: cellulose, fiberglass, and mineral wool. The material of loose-fill will impact the price.
Cellulose is the most common blow-in material and tends to be cheaper than fiberglass loose fill. Made of 85% recycled paper and 15% chemical treatment, cellulose loose-fill is dense and clumpy.
However, it has a consistency similar to down feathers, allowing it to conform easily around wires, ducts, and other obstructions.
Manufactures treat cellulose with borate to repel rodents and insects, although its ability to repel these pests remains questionable. This borate treatment also helps cellulose repel fire.
Cellulose has the highest R-value of the loose-fill options, making it suitable for cold climates. However, it can mold, so only use cellulose if your attic has proper ventilation.
Installing loose fill cellulose creates a lot of dust, but you can hire a contractor to apply wet-spray cellulose. Wet-spray application will help tamper the dust and increase the material’s R-value.
R-value per inch: 3.2 – 3.8
Loose fill fiberglass is the go-to attic insulation in new homes. Fiberglass will provide better insulation as loose fill than in batt form, but both are made from spun glass.
In the past, loose fill fiberglass lost insulation value in temperatures below 20 degrees Fahrenheit. However, this is no longer an issue.
Fiberglass is the most lightweight of the three loose fill materials, so it settles the most. Unfortunately, this also means you’ll need to apply a thicker layer to achieve the desired R-value.
R-value per inch: 2.2 – 2.7
Mineral wool offers natural fire resistance as it is made from either rock or recycled slag. It provides a mid-range R-value, making it best suited to temperate climates.
However, it is more expensive than cellulose or fiberglass loose fill.
R-value per inch: 3.0 – 3.3
Spray Foam Insulation
Correctly installed spray foam creates a perfect air barrier and completely repels water.
However, spray foam is very expensive and difficult for non-professionals to install. Therefore, you will primarily find spray foam in commercial and industrial buildings rather than residential buildings.
If your HVAC system and ducts are located in the attic, you can use spray foam to move the boundary between conditioned and unconditioned space (known as the building envelope) from the attic floor to the roofline.
Unless absolutely necessary, it’s best to avoid using spray foam insulation. In addition to adding expense, applying spray foam creates toxic poisons that require proper off-gassing. Also, once it hardens, spray foam is difficult to remove.
Unlike other types of insulation, spray foam can maintain effectiveness for several decades. However, in some cases, spray foam can shrink over time.
In terms of eco-friendliness, spray foam does increase energy efficiency. However, it does contain polyurethane.
Additional Types of Insulation
Batts, loose fill, and spray foam are the most common materials for attic insulation. However, you can occasionally find a couple more types in attics: rigid foam panels and radiant barriers.
Rigid Foam Panels are structural insulated panels made from a piece of rigid foam insulation between plywood or OSB.
Made of polyurethane, polystyrene, or polyisocyanurate, these boards do not absorb much moisture and therefore do not risk mold growth. However, they are usually more expensive.
Radiant barriers are padded with reflective material and installed on the underside of roofing, helping to repel heat away from your house. Radiant barriers are technically not a type of insulation but are nevertheless useful in hot climate zones.
Other methods previously used to insulate attics include loose sawdust, shredded newspaper, and balsa wood. Read the following section to learn about the dangers of asbestos, a material commonly used to insulate houses until the 1980s.
Types of Old Insulation
Insulation can become ineffective over time due to several factors, such as settling and tearing. Keep reading to learn about certain insulation risks associated with older constructions.
Asbestos can cause serious health issues, including mesothelioma, lung cancer, and asbestosis. Asbestos exposure can also increase the risk of throat, esophagus, and kidney cancers.
Most countries banned asbestos in the late 1980s. But unfortunately, you can still find asbestos insulation in many older homes across America, primarily in vermiculite insulation and asbestos pipe insulation.
Vermiculite looks like loose gravel. Before 1990, most US-produced vermiculite came from a mine that contained an asbestos deposit.
So, if your home was built before 1990 and is insulated with vermiculite, that insulation probably contains asbestos. (Asbestos-free vermiculite is not dangerous.)
As the name suggests, pipe insulation is often found wrapped around pipes. It is a grayish color with an edge that looks like corrugated cardboard. This corrugated edge is the best indicator that it contains asbestos.
If you’re not sure whether or not your building contains asbestos, hire a professional to complete an asbestos inspection. Although this precaution will add to the overall cost of your insulation project, messing with asbestos can pose serious health risks.
Do not attempt to remove asbestos yourself. Instead, hire an asbestos abatement contractor.
Urea Formaldehyde Foam
Builders used urea-formaldehyde foam to insulate houses from the early 1930s to the 1980s.
However, this type of foam emits formaldehyde vapors while it is curing. These vapors can cause adverse health effects on the respiratory systems, eyes, nose, and memory.
Hardened urea-formaldehyde foam looks like yellowish, oozing liquid. Although the formaldehyde emissions decrease once the foam has cured, you should not attempt to remove the foam. Instead, removal must be completed by a qualified and licensed professional.
If you live in an older house, your house might contain large gaps between the walls to counter moisture accumulation. The gaps allow moisture to dry before it can accumulate and cause structural damage. If you fill these gaps with insulation, the insulation might absorb moisture and contribute to structural mold or rot.
Additionally, houses with wood-shingled roofs should not be insulated. Insulation along these surfaces will block the wood’s natural ability to breathe and dry when exposed to moisture.
If your attic contains outdated electrical wires or fixtures, do not place insulation near these components. Doing so will create a significant fire risk. Instead, have the electrical system replaced before you begin your insulation project.
Don’t Skip These Safety Steps
Hopefully, your attic project won’t involve wrangling asbestos. But even insulation projects on new-construction houses pose risks. We’ll go into more details on insulation in another article, but remember a few simple safety precautions before beginning any attic insulation project:
- Mask Up: Always wear appropriate safety equipment when handling insulation materials, especially fiberglass. This protective gear should include a mask or respirator, safety goggles, gloves, long pants, and a long-sleeved shirt.
- Stay cool: If you’re working in the summer, remember that heat rises, meaning attics can get pretty hot. Try to work in the morning or evening when the sun isn’t beating on the roof.
- Tread Carefully: Remember that the surface often referred to as the attic ‘floor’ is really only drywall. Only step on ceiling joists. If you need additional stability or movement flexibility, place kneeboards across three or more ceiling joists.
Once you have finished your work for the day, shower thoroughly and wash your clothes to remove hazardous fibers, then you can sit back, relax, and enjoy the extra comfort of a properly insulated attic.
Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.