When purchasing a home, it’s easy to overlook what’s above the ceiling: the attic insulation. But this often-hidden detail can have a big impact on energy efficiency, and comfort. Attic insulation plays a crucial role in controlling indoor temperatures, reducing heating and cooling costs, and improving overall comfort. Here’s a breakdown of the different types of attic insulation you might encounter as a homebuyer, along with what to know about each type.
1. Loose-Fill Fiberglass
What It Is: Made of small glass fiber particles blown into the attic space to form a layer of insulation. This type of insulation has been in use since the 1930’s and is the most common insulation type used in Montana attic spaces. Loose-fill fiberglass is easy to install and ideal for complex or difficult to access attic spaces.
Typical R-Value per Inch: R-2.2 to R-2.7
How to Recognize It:
- Fluffy, loose cotton-like material, usually pale white or pink. Note – In older homes, it may appear dark grey or black.
Things to Know:
- Loose-fill fiberglass can fill irregular spaces, making it the most common choice for new construction as well as renovation projects.
2. Fiberglass Batt
What It Is: Pre-cut fiberglass sheets with a paper backing that fit between joists and studs. Fiberglass quickly became popular due to its effectiveness in trapping air, which makes it an excellent insulator. It was widely adopted in residential and commercial construction during the post-World War II building boom, especially in the 1950s and 1960s, as insulation standards started to gain more attention for energy efficiency and indoor comfort.
Typical R-Value per Inch: R-2.9 to R-3.8
How to Recognize It:
- Thick, roll-like sheets often backed with paper or foil, typically pink, yellow, or white.
Things to Know:
- Batts are cost-effective and durable, but they must be properly installed without gaps to ensure optimal insulation.
3. Loose-Fill Cellulose
What It Is: Loose-fill cellulose insulation has been used since the early 20th century, with its first recorded use around the 1920s. Made primarily from recycled paper products treated with fire-retardant chemicals, cellulose became a popular choice because of its low cost, ease of application, and environmentally friendly composition.
Typical R-Value per Inch: R-3.2 to R-3.8
How to Recognize It:
- Appears as dense, grayish particles resembling ground-up paper.
Things to Know:
- Good at air-sealing with a continuous application and eco-friendly.
4. Wood Fiber
What It Is: Loose-fill wood fiber insulation was commonly used in homes and buildings between the 1920s and 1950s, particularly in North America. It was an early type of insulation made from wood fibers, wood shavings, or cellulose. The material was treated with chemicals to improve fire resistance, but it eventually fell out of favor as more effective and durable options, like fiberglass and mineral wool, were developed in the mid-20th century. By the 1970s, wood fiber insulation was largely replaced by these newer materials due to their better insulating properties and durability.
Typical R-Value per Inch: R-2.5 to R-3.5
How to Recognize It:
- Coarse, brownish/orange fibers that look like compacted wood shavings.
Things to Know:
- Wood fiber has been treated for fire and pest resistance, giving it its orange color.
5. Vermiculite
What It Is: A lightweight, granular insulation that expands when heated. Popular mid-20th century but no longer used today due to asbestos contamination risk. It’s important to note that some vermiculite insulation, especially that sourced from the Libby, Montana mine, was found to be contaminated with asbestos. This has led to health concerns and the subsequent need for careful handling and removal in older buildings. If you suspect vermiculite insulation in a property, it’s advisable to have it assessed by a professional.
Typical R-Value per Inch: R-2.0 to R-2.4
How to Recognize It:
- Small, shiny, granular particles, often gray or silver.
Things to Know:
- Vermiculite may contain asbestos, so avoid disturbing it until it’s tested and deemed safe.
6. Spray Foam (Open-Cell and Closed-Cell)
What It Is: A high-performance insulation that expands on application, filling gaps for an airtight seal. Available in two types:
- Open-Cell Spray Foam: More flexible and less dense.
- Closed-Cell Spray Foam: Denser, with moisture resistance.
Typical R-Value per Inch:
- Open-Cell: R-3.5 to R-3.6
- Closed-Cell: R-6 to R-7
How to Recognize It:
- Firm, foamy layers, typically yellowish or off-white, applied directly to the attic floor, walls, or underside of the roof.
Things to Know:
- Spray foam offers excellent energy efficiency, especially closed-cell, but is one of the costliest insulation types.
Summary Table of R-Values per Inch:
| Insulation Type | R-Value per Inch |
|---|---|
| Loose-Fill Fiberglass | R-2.2 to R-2.7 |
| Fiberglass Batt | R-2.9 to R-3.8 |
| Loose-Fill Cellulose | R-3.2 to R-3.8 |
| Wood Fiber | R-2.5 to R-3.5 |
| Vermiculite | R-2.0 to R-2.4 |
| Open-Cell Spray Foam | R-3.5 to R-3.6 |
| Closed-Cell Spray Foam | R-6 to R-7 |
When evaluating insulation, consider both the R-value and the condition of the material. Even the best insulation won’t perform optimally if it’s damaged, compressed, or improperly installed.
