Fiberglass vs. Cellulose Attic Insulation

Attic insulation is used to reduce thermal transfer through the walls and roof of your home. It can also be used on the floor of the attic to block cold air from entering into other living spaces. Fiberglass blankets and loose-fill cellulose are among the most popular types of attic insulation, with each offering its own benefits and drawbacks that should be considered before making a selection.

Features

Fiberglass insulation is made from spun glass fibers that are woven together to form blankets or batts. Some fiberglass products have a vinyl or reflective coating designed to improve thermal resistance, though these added features tend to increase the price of this material. Cellulose insulation is made by shredding recycled newspaper or wood scraps into small pieces, which are then treated with chemicals designed to resist fire and insect damage.

Installation

Cellulose insulation is installed using a loose fill or blown-in technique. It may be poured into available openings in the attic or blown through floor and wall openings using a specialty blowing machine. Most loose fill products are installed by professionals to ensure proper coverage. Fiberglass batts are cut to fit the spaces between wall studs or ceiling joists. They are fairly easy to work with and can be installed by most DIY homeowners.

Locations

Fiberglass batts are usually the best insulation material for new walls, as they can be installed before final wall coverings or drywall are complete. They are also the best choice for ceilings because of their ability to hold their shape when securely fastened. Cellulose works best in finished walls, as it can easily be installed through a space opening. It may also be used on attics that are inaccessible or in spaces blocked by obstructions.

Thermal Resistance

In most cases, cellulose offers better thermal resistance and more overall coverage than fiberglass. Experienced installers can pack cellulose tightly so it completely fills a space as needed for insulation. It is much more difficult to use fiberglass effectively, as it tends to sag over time and leave gaps where air can leak through. Though both of these materials have an R-value between 2 and 3.8 per inch, cellulose is more likely to achieve its maximum R-value, while fiberglass tends to fall at the lower end of that range.

Cost

According to This Old House, fiberglass batts cost about 40 cents per square foot uninstalled, while loose-fill cellulose costs about $1.20 per square foot installed. Depending on your level of expertise, the time involved in installing fiberglass may negate its lower price. Because cellulose is a more effective insulator, it may lead to energy savings over time that can justify its higher upfront costs.

References

• This Old House
• Attic Insulation
• Types of Insulation