Attic insulation around a skylight

Which Attic Insulation is Best?

No matter how big your house is or what material it’s made of, every house needs to have a properly insulated attic in order to keep the temperature regulated and the energy bill down.  And if you live in a region with particularly cold and snowy winters, that last sentence applies to you in bold font and all caps.

But which attic insulation is best? There isn’t a “one size fits all” answer, as there are several factors that come into play. Read on for everything you need to know about the different types of attic insulation, and how you can go about choosing which one is right for you.


First, an Overview of R-Value

Any conversation about proper attic insulation must begin with a firm understanding of R-Value, the unit by which the strength of insulation is determined. R-Value is a material’s capacity to resist the transfer of heat. A material’s R-Value is generally affected by the following four factors:

  • Type of material (more on this shortly)
  • Thickness
  • Density
  • Where and how it’s installed

The higher an attic’s total R-Value, the better it will be at trapping heat and keeping your home from turning into an iceberg in the winter or sauna in the summer.

Generally speaking, the US Department of Energy recommends maintaining the following overall R-Value levels in your attic:

  • R30 in hot climates (like California)
  • R38 in temperate climates (this is typically the desired level for residences in California)
  • R49 in cold climates (note: if you live in a region where the temperature regularly drops to “every shop in town is closed today because it’s so cold outside” levels during the winter, maintaining a specific R-Value in your attic may be required by state law)


Types of Attic Insulation Material

Though R-Value is a “the higher, the better” measurement, the insulation material with the highest R-Value isn’t necessarily the best choice for your house. Different insulation materials have unique strengths and weaknesses, and some attics will be more suited for certain material than others.

Here’s an overview of the most frequently used insulation material, the pros that made them so popular with consumers, and the cons you should consider before you buy:


Fiberglass

Fiberglass is like the McDonald’s Big Mac of insulation material: it’s certainly not the highest quality option, but it’s easily the most popular. Its R-Value ranges from as low as 2.2 to as high as 4.3 in the case of specially manufactured high-density fiberglass. 

The fact that fiberglass has been a staple of new construction and Extreme Home Makeover-like gut renovations is easy to track. It has many advantages, including the following:

  • It’s cheap and highly accessible
  • It’s adept at resisting moisture, which is why it’s particularly sought after in regions with high humidity
  • It doesn’t shrink over time
  • It’s fire-resistant
  • Insects will avoid nibbling on it


Cellulose

Cellulose insulation generally comes from either wood or recycled paper, which makes it even friendlier to the environment than fiberglass.


With an R-Value between 3.2 and 3.5, cellulose is about par for the course in heat resistance capability compared with other insulation options. But from a performance standpoint, cellulose boasts a few positives, like:

  • Versatility – The thick, dense consistency of cellulose enables it to fit in enclosed areas or conform around obstructions like pipes or wiring.
  • Fire-Resistance – Due to the fact that cellulose fibers are tightly packed and treated with innocuous boric acid prior to packaging, cellulose is fire-resistant, not to mention inedible for insects.

Even with its impressive aspects, cellulose remains an inexpensive commodity and is typically up to 25% cheaper than fiberglass. But it’s not without its drawbacks, such as:

  • They’re a Glutton for Moisture – Any insulation is rendered useless as soon as it becomes wet. Because cellulose is designed to collect and hold water, it waves the white flag in the presence of moisture quicker than any other insulation material. This can cause cellulose insulation to not only slip in effectiveness, but also develop mold and mildew, and even rotting. And if cellulose does become wet, the boric acid used to treat it goes from being harmless to corrosive.
  • Settling – Cellulose also tends to settle and sag over time, which takes away its superpowers. Thankfully, this is less of a problem with attics and pertains more to walls throughout the house.
  • Dust – If you’re in the attic while cellulose insulation is being installed, strap your respiratory mask and goggles on extra tightly. Cellulose creates a whole lot of dust when first installed.


Mineral Wool

Featuring melted down stone and recycled slag from steel mills, mineral wool batts are more widely utilized in Canada and Europe but are currently enjoying a resurgence in the US.

Compared to fiberglass, mineral wool is costlier, but you get what you pay for due to the following advantages:

  • Fire Barrier – Mineral wool doesn’t even begin to burn until it reaches temperatures of 1,8000 degrees Fahrenheit. In the worst-case scenario of a house fire, this will buy the fire department crucial, potentially home-saving extra minutes to arrive at the scene and take care of business.
  • Water Warrior – In addition to being fire-resistant, mineral wool is also water-resistant, able to continue insulating even in the face of the worst moisture leak.
  • Wall of (No) Sound – Mineral wool is extremely effective at blocking outside noise from entering your home.

There’s really only one drawback with mineral wool insulation, but it’s a significant one: inhaling it during insulation can be potentially cancerous. Proceed with extreme caution if you’re present for the installation.


Cotton

Interestingly, cotton insulation comes from recycled blue jeans. And aside from the novelty of having former blue jeans hung up in your attic, cotton insulation is a viable choice for the following reasons:

  • High Performance – With a typical R-Value of about 3.7 and up, cotton traps heat with the best of them.
  • Safety – Whereas both fiberglass and mineral wool present safety hazards both in the physical handling of them and the fibers they release into the air, cotton couldn’t be safer to handle or install. No need to worry about it irritating your skin or the consequences of accidentally breathing it in during installation.

Similar to mineral wool, the perks that cotton insulation comes equipped with cost you extra.


Foam

When it comes to performance, foam is the MVP of insulation material. There are two types of foam insulation:

  • Open cell, which has an R-Value of about 3.5
  • Closed cell, which hits a whopping R7!

Foam has just about everything going for it, including:

  • Top-Notch Air Leakage Prevention – The only difference between foam and the 1986 Chicago Bears’ defense is that foam can’t do the Super Bowl Shuffle dance. Foam is the stingiest of defenders against air coming in or out, able to expand quickly and form an airtight seal over cavities that other insulation materials couldn’t handle. This airtight seal also discourages airborne contaminants from spreading.
  • Pushing the Envelope – A house’s building envelope is the physical separation of conditioned space (where people move and breath) from unconditioned space (where they don’t). Foam is the only insulation material that allows you to expand your building envelope to your attic’s roofline. This is a particularly clutch option if your HVAC system (heating, ventilation and air conditioning, for the layman) is located on the floor.
  • Equally Tough on Water – Foam insulation is impermeable to water, which means it neither lets water in nor absorbs it. And as if that couldn’t make mold and mildew feel any less welcome, foam also contains a polymer that deters their growth, which means they don’t have a prayer of setting up shop around foam.
  • Durability – Foam never settles or loses its efficiency, even in the face of severe temperature drops. You can leave it up for literally decades without having to worry about maintenance.
  • Dual-Purpose – When you apply foam to your rooflines, the effect is two-fold. It not only fortifies your home’s structure but also serves as an unrivaled sound blocker.

Once again, the many perks that foam has to offer will hit you in the wallet. But aside from the obvious downside of cost, there are other drawbacks with foam to consider, such as:

  • Shrinkage – Though the R-Value of foam never diminishes, it does shrink over time in some cases.
  • Professional Installation or Bust – When foam isn’t installed properly with expert attention, it’s likely to fold over itself and create voids that the naked eye can’t see. Even worse, you run the risk of exposing yourself to the foam before it fully cures and becomes non-toxic, a mistake that can have potentially life-threatening consequences.


Popular Installation Methods

Typically, insulation material will be installed in an attic in one of three ways:


Batts

Batts come packaged in rolled-up sheets featuring interweaving fibers. These fibers are usually held in place by adhesive binders in the form of either paper or reflective foil backing, both of which can serve as a vapor barrier. 

The majority of batts are either fiberglass or mineral wool, and occasionally cotton.

 


Because batts cover such extensive real estate, they are ideal for attics that fit the following description:

  • Expansive area with little to no obstructions on the floor and plenty of headroom for the installer to maneuver around
  • No prior insulation is in place
  • The area features joists (the horizontal structural wooden rods running between two beams in open space) that are spaced out evenly


Blown-in

Also known as loose-fill, blown-in insulation comes in tiny chunks packaged in large bags, and entails using a blowing machine to fill in necessary spaces. Fiberglass, cotton, and mineral wool can all work as loose-fill material, but the far and away top choice for blown-in insulation is cellulose.

Contrary to batts, blown-in cellulose insulation is perfect for filling in tight voids around wiring, pipes, or any area with awkward framing.


Spray

The spray can is the exclusive home of foam insulation. 


Let Attic Construction Help You with All Your Insulation Needs

While attic insulation can be performed by DIY’ers, it certainly doesn’t mean it should be, especially in the case of installing spray foam. 

At Attic Construction, we’re dedicated to working with you and your budget to assess which type of insulation best suits your unique attic, and how much of it you’ll need. And when you rely on our expert team of installers, you can rest easy knowing that the installation will be done right and done safely.

If you have any questions, need a quote generated, or just want to gather a bit more information, reach out to one of our experts! Contact us today. We’re happy to discuss any and all things related to attic insulation. 


Resources

1) “Batts, Blown or Sprayed? What’s the Best Attic Insulation?” by Allison Bailes
https://www.energyvanguard.com/blog/46480/Batts-Blown-or-Sprayed-What-s-the-Best-Attic-Insulation

2) “Attic Insulation Types” by Rueben Saltzman
https://www.constructionprotips.com/tools-materials/attic-insulation-types/

3) “Read This Before You Insulate Your Attic” by Mickey Goodman
https://www.thisoldhouse.com/ideas/read-you-insulate-your-attic