The best attic insulation is the one that does the best job for your circumstances. Trussed attics, wide open attics, vaulted attics, or attics cluttered with HVAC, plumbing, and electrical require different insulation approaches.
Best Attic Insulation
These are some of the best attic insulations available. One of them is almost certain to work for your particular situation.
Best Overall Attic Insulation: Greenfiber Cellulose Loose Fill
Cellulose loose fill blown in attic insulation has an R-value of R-3.2 to R-3.8. Settling does not affect the R-value. When blown properly it provides a complete blanket of insulation–filling around obstructions and eliminating gaps and thermal bridging. It can reduce heating and cooling costs by 20%. Reduces noise by 60% when also applied to walls.
Cellulose insulation is made from 85% recycled materials and is treated with borates–making it fire and insect resistant. It is easy to apply over existing insulation and is suitable for use in any climate.
Pros:
- R-3.7 per inch.
- Meets Class 1 fire rating.
- Simple DIY application with machine rental (may be provided free).
- No itch formula.
- Reduce heating costs by up to 20%.
- Can be installed over existing insulation products.
- Limited lifetime warranty.
Cons:
- Very dusty while being installed. Not dusty after installation.
Best Batt or Blanket Insulation: Owens Corning Fiberglass Roll Insulation
Fiberglass insulation is available in batts or rolls. It is also manufactured in various thicknesses with R-values between R-2.2 – R-4.3 per inch. The rolls are an excellent choice for flat unobstructed attic floors. Easy to place. Fewer gaps.
Fiberglass rolls should be installed in two layers–the second one perpendicular to the first to eliminate gaps. The rolls can also be installed over existing insulation to add R-value and cover existing gaps.
Pros:
- Less expensive than most attic insulation options.
- Recovers thickness instantly when opened.
- Can be installed over existing insulation.
- DIY-friendly installation.
- Less mess. No dust. Fast clean-up.
- Rolls leave fewer gaps because of fewer joins than batts.
Cons:
- Difficult to install in truss-built attics and/or attics with HVAC, electrical, or plumbing.
- Difficult to eliminate gaps.
- Can irritate sensitive skin.
Best Spray Foam Insulation: Dow Froth Pak 650
Widely considered the best insulation available, spray foam can be used on attic floors or the undersides of roofs. It fills cracks and gaps; then expands and dries to completely seal air leaks. Spray foam insulation is available in open-cell (R-3.5) or closed-cell (R-7) formulations.
Spray foam does not settle and retains its R-value regardless of temperature changes. Some foam may shrink over time or gaps may form as wood framing expands and contracts. It is waterproof, mold, and mildew resistant. Spray foam can release toxic chemicals while curing, but becomes inert when cured.
Pros:
- R-7.0 per inch.
- Cures in minutes.
- Class A flame spread rating.
- No HFCs. Low odor.
- Moisture, mildew, and mold resistant.
- Available in disposable kits or refillable, returnable cylinders.
Cons:
- Can be a difficult DIY project. May require professional installation.
- Most expensive attic insulation option.
Best Reflective Insulation: US Energy Products Radiant Barrier
Reflective insulation is also known as foil insulation or bubble wrap. It is most effective on the undersides of pitched or vaulted roofs and unventilated cavity walls in hotter climates but ineffective and even counterproductive in colder climates.
Reflective insulation has little or no R-value. Its effectiveness comes from the ability to keep heat out of the attic. It must have at least one inch of air space on the warm side and should be kept dust-free for best performance.
Some manufacturers claim an R-value of up to R-21. This may be true in very specialized situations. Not always. Please read the fine print.
Pros:
- Reflects up to 97% of heat.
- Tear resistant.
- Class 1, Class A fire rating.
- 4’ x 250’ (1000 sq. ft.) rolls
- Ideal for attics.
Cons:
- None – when installed properly and used for the purpose it is intended.
Best Rigid Foam Insulation: Styrofoam SM 2” Scored
Rigid foam board insulation provides R-5.0 per inch. Installing rigid foam between vaulted roof rafters provides very good insulation. It can also be used efficiently on the floors of open attics. The gaps and cracks between the foam and framing should be filled with spray foam to complete the installation and complete the vapor barrier.
Install foam board between the floor joists and seal the joints. If another layer is to be installed it should be perpendicular to the first. Rigid foam is difficult to install and seal in attics with HVAC, electrical, and/or plumbing.
Pros:
- R-5.0 per inch extruded polystyrene foam.
- Provides vapor barrier when 2” thick and gaps are sealed.
- Effective in all climates.
- Scored to snap easily at convenient sizes.
- Easy DIY product.
Cons:
- Difficult to fit around obstructions.
- All gaps must be foamed to achieve a good seal.
What to Consider Before Insulating
Spend a few minutes inside the attic with the different insulation options in mind. Which insulation will do the best job? How difficult is installation? DIY project or not? Is the attic ventilated? Do I insulate the attic floor or the vaulted roof? Can I add to what is there now? Cost?
Difficulty
Some attics are easy to insulate with any product. They are wide open with no trusses with little or no clutter to impede installation. Often these are vaulted attics. Trussed attics with lower slopes are difficult to move around in. Low-slope attics are even worse. Attics containing HVAC, electrical wiring, and/or plumbing pipes are difficult to insulate properly.
DIY or Not?
Do-it-yourself attic insulation can be done by most competent DIYers. It requires patience, attention to detail, and in some cases no claustrophobia. (Some products are dusty or toxic. Safety equipment is required.) Professional insulation contractors do a good job quickly but cost more.
Ventilation
If the attic has soffit ventilation extra care needs to be taken to keep them open. Air chutes will need to be installed to allow the air to circulate. Ventilation moves air and humidity out of the attic and keeps the insulation dry.
Floor or Roof?
Insulation can be applied to the floor of the attic or to a vaulted roof. Either option is usually acceptable but some products only work in one location.
Add or Remove?
Removing the existing insulation is usually not necessary. In many cases removing insulation only adds cost. Most products can be installed right over what is there.
One exception is asbestos insulation–often vermiculite–which is benign if undisturbed. Working in the attic can stir up the tiny fibers that can be breathed in. It is best to have it removed professionally. (Some jurisdictions make professional removal and disposal mandatory.)
Cost
Insulation costs can vary between $0.50 and $7.00 per square foot for material only to supply and install.
How We Chose the Best Attic Insulation
To choose the best attic insulation we took into consideration versatility, R-value per inch, cost, and ease of installation. All of the types of insulations listed are available in multiple sizes, styles, and thicknesses. Different manufacturers produce similar products.
Attic construction and situations vary. For instance: fiberglass roll insulation works very well in open attics but fiberglass batts may be a better choice for attics with trusses or mechanical services.
It may be beneficial to use two types of insulation in an attic. Such as cellulose on the floor and reflective insulation on the undersides of a vaulted roof in hotter climates.
