Insulation is highly susceptible to failure over the lifetime of a house. Always install it according to manufacturers' recommendations and in conjunction with effective moisture control practices, including vapor barriers and indoor ventilation.

Environmental Context
A large share of the energy used for heating and cooling in Minnesota comes from burning coal and natural gas, which has serious negative environmental impacts, such as greenhouse gas emissions and air pollution. Using insulation to reduce the amount of energy needed to heat and cool homes will reduce this environmental damage year after year. All insulation will eventually save more energy and pollution than it takes to manufacture. For a given R-value, insulation with minimal energy input, such as blown cellulose, will start to accrue net energy savings more quickly than insulation with high embodied energy, such as spray polyurethane foam. Other ecological considerations include the amount of recycled content and the ability to reuse or recycle the insulation.

Options and Analysis

Insulation Type R-value per inch Durability Cost/sf/R-value Practice
fiberglass, batt 3.2 may slump in walls; typical warranty 25 yrs $0.037 standard
mineral fiber, batt 3.2 may slump in walls $0.039 standard
fiberglass, blown 2.2 no significant concerns $0.044 standard
cellulose, blown 3.4 settling to 80% original volume (usually accounted for at time of installation); susceptible to mold with water damage $0.033 standard
Rigid Board
expanded polystyrene (EPS) 3.85 UV light degrades board; warranty 5-10 yrs $0.130 standard
extruded polystyrene (XPS) 5.0 no significant concerns; warranty 20 yrs $0.140 standard
polyisocyanurate 6.25* R-value declines to stabilized value; warranty 20 yrs $0.100 standard
Expanding Spray Foam
closed-cell spray polyurethane (SPF) 6.45* R-value declines to stabilized value $0.140 special training required for installation
open-cell polyicynene 3.6 may hold significant moisture $0.117 special training required for installation

Cost information based on Means Cost Works 2007, except expanding spray foams which are based on averages from local insulation contractors.

The quality and the design of the wall assembly significantly affect and R-value of all insulation types.

*Denotes a stabilized R-value

Insulation cost should be understood in the context of lifecycle costs and potential energy savings. In many cases, a thicker or more expensive insulation will easily compensate for its higher initial costs. That said, loose-fill, blown, and batt insulation materials have a substantially lower cost per R-value than rigid board and spray foam materials. A thicker application of these low-cost insulations can be an inexpensive way to lower energy costs. However, thicker insulation materials may require thicker wall assemblies, driving up framing costs. In this case, the higher first cost associated with premium insulation materials, such as spray foams and rigid boards, can prove less expensive in the long run.

Product Life
The R-value of most insulation materials decreases over time. Loss of R-value can be attributed to several factors. Batt and blown insulation can slump in wall cavities, and most insulation, with the exception of some rigid boards and spray foams, can be damaged by excessive moisture. These effects can be limited by proper construction and detailing. Blown cellulose settles, decreasing its effectiveness. The effect of settling on R-value can be quantified and installers are typically required to account for it at the time of installation. Blown fiberglass is typically not subject to settling. Rigid insulation can shrink and/or dry over time. This leads to gaps in coverage, reducing the effective R-value. Some rigid boards (such as polyisocyanurate) and spray polyurethane foams lose R-value as the blowing agent leaks out over several months, or possibly years. Such products require testing at long time intervals to determine an ultimate stabilized R-value. Spray polyicynene, however, has greater R-value stability.2 In general, all insulation is meant to last the life of the structure. However, long life is contingent on proper construction and detailing techniques.

Prolonged contact with moisture can cause the paper backing on batt insulation to deteriorate. Moisture can also mat down batt and blown insulation, reducing the effective R-value of the material. With cellulose insulation, high levels of moisture can foster mold growth and reduce R-value. Rigid insulations are generally impervious to water damage, but can suffer degradation if left exposed to sunlight and/or abrasion.

Insulation Type Global Warming Potential lbs CO2 Life Cycle Analysis metrics Resource Consumption Recycling/Reuse Potential
fiberglass, batt 0.0743 energy consumption (Btu) 649 materials acquired through open pit mining; most include 30% recycled content recyclable, but no program currently exists; reuse possible but rare
weighted resource use (lbs) 0.127
air pollution index 0.0111
water pollution index 0.0000
mineral fiber, batt 0.1856 energy consumption (Btu) 1037 made from molten slag, a waste product of steel production reuse possible but rare
weighted resource use (lbs) 0.295
air pollution index 0.0305
water pollution index 0.0000
fiberglass, blown data not available materials acquired through open pit mining; most include 30% recycled content recyclable, but no program currently exists; reuse possible but rare
cellulose, blown 0.0102 energy consumption (Btu) 95 most contain 75-85% post-consumer recycled content; up to 100% is possible recyclable but no program currently exists; reuse possible but rare
solid waste (lbs) 0.068
air pollution index 0.0006
water pollution index 0.0000
Rigid Board
expanded polystyrene (EPS) 0.1071 energy consumption (Btu) 1034 derived from non-renewable resources, crude oil and natural gas recyclable into packing foam, but non cost effective
solid waste (lbs) 0.068
air pollution index 0.0091
water pollution index 0.000
extruded polystyrene (XPS) 0.1645 energy consumption (Btu) 1587 derived from non-renewable resources, crude oil and natural gas recyclable; high reuse potential if not damaged
solid waste (lbs) 0.101
air pollution index 0.0144
water pollution index 0.0000
polyisocyanurate 0.2229 energy consumption (Btu) 1104 derived from non-renewable resources; contains at least 9% recycled content (PET bottles) recyclable, but no program currently exists; reuse possible but rare
solid waste (lbs) 0.116
air pollution index 0.0155
water pollution index 0.0003
Expanding Spray Foam
closed-cell spray polyurethane (SPF) data not available can be made from recycled products like PET bottles not reusable or recyclable because of bonds with wall
open-cell polyicynene data not available more resource efficient than closed-cell foams not reusable or recyclable because of bonds with wall

Life Cycle Analysis information is based on Athena 3.0.3. Values are given on a per square foot per R-value basis.

Resource information is from the Sustainable Design Resource Guide—AIA Colorado and the AIA Environmental Resource Guide

Life Cycle Analysis

Life Cycle Analysis information is based on Athena 3.0.3. Values are given on a per square foot per R-value basis.

Global Warming Potential
In manufacturing, extruded polystyrenes still use blowing agents containing HCFC's. HCFCs are less damaging to the ozone layer than their predecessors, CFC's, but they still have significant ozone depletion potential. In addition, they are potent global warming gases with global warming potentials hundreds to thousands of times greater than carbon dioxide. Expanding spray polyurethane foams are typically blown with HFCs. HFCs have a zero ozone depletion potential, but remain strong global warming gases, similar to HCFCs. Rigid polyisocyanurate and expanded polystyrene now use alternative blowing agents, such as pentane, which do not deplete the ozone layer or act as a significant global warming gases. Some expanding spray foams like polyicynene use only water or carbon dioxide as blowing agents. These are considered the safest, most environmentally friendly blowing agents.3

Indoor Air Quality
In climates where heating is dominant, insulation should be installed with an air barrier and moisture retarder between it and all living spaces. If installed properly and left undisturbed in wall cavities and attic spaces, insulation poses no threat to human health.4 Off-gassing is not an issue when insulation is separated from living spaces by properly constructed and detailed air barriers. However, during installation, respiratory masks should be worn when handling fiberglass and mineral wool batts because they may release fibers into the air. Fiberglass dust is listed as a possible carcinogen. Up until 2001, fiberglass dust was listed as a possible carcinogen. More recent studies have convinced the International Agency for Research on Cancer (IARC) that fiberglass is not classifiable as a human carcinogen.5 If indoor air quality is still a concern, look for insulation that is certified by GreenGuard. This ensures that off-gassing from binders, fire retardants, and other chemicals is minimal.

Future Recycling
Blown insulation can be recovered easily for reuse or recycling. Cellulose insulation can be composted if the fire retardants and other chemical sprays used in their production are environmentally safe. Batt insulation can also be recovered for recycling, although no recycling programs currently exist. Rigid expanded polystyrene (EPS) can be ground up into packing material, but other rigid board insulations currently have no recycling programs. Expanding spray foams typically cannot be recycled or reused because they bind to the frame of the house, making removal difficult.

With the exception of expanding spray foam insulations, which require training and professional installers, all insulation types are considered common practice.

Other Resources


Web Sites

1 "Air Sealing: Building Envelope Improvement." U.S. Environmental Protection Agency and ENERGY STAR, Dec 2000. 7 Jul 2008.
2 "Benefits of Icynene." Heim Insulation Web Site. 29 Jul 2008.
3 Wilson, Alex. "Insulation: Thermal Performance is Just the Beginning." Environmental Building News. Jan 2005.
4 Wilson, Alex. "Insulation Materials: Environmental Comparisons." Environmental Building News. Jan 1995.
5 Wilson, Alex. "Insulation: Thermal Performance is Just the Beginning." Environmental Building News. Jan 2005.