Comparing home insulations
Homeowners can select from a range of insulation materials, such as fiberglass, cellulose, foam boards, spray-in foam or recycled cotton. With so many different products in the market, how does one choose the best insulation for the job?
In general there are four aspects to consider when selecting insulation:
- Is it suitable for the intended purpose?
- Is it safe?
- Is it affordable, in terms of my budget?
- Is it environmentally responsible?
Suitability
Different parts of a house call for different insulation materials. For example, only rigid boards like extruded polystyrene (XPS) can be installed under a concrete slab or outside a basement wall. In an attic, both loose-fill and batt insulation works well. A complete insulation ‘package’ will include a variety of materials.
Insulation’s ability to slow heat loss is measured as "R-value". The higher the R, the better the insulation. R-value is measured in standard laboratory tests. However, in the real world, there are challenges to achieving full or tested R-value.
For example, today’s houses are usually built with wood framing, and framing cavities may be criss-crossed with wires, pipes, and ducts. These obstacles require batts to be carefully cut and fit around them, to achieve full R-value. By comparison, spray-in insulations will fill around such obstacles.
A weatherization contractor will have definite views about insulation he/she has used successfully. When selecting insulation, that experience can be most helpful.
Homeowners often ask about fiberglass vs. cellulose insulation. Both insulate well when installed properly, and both are safe for occupants of the home.
To help identify where insulation materials can be used, take a look at the "Insulation Comparison Chart" below.
Safety
For fire safety, insulation materials require a fire-resistant covering, such as drywall. The insulation itself will resist burning and/or generating smoke. The building code specifies both: how insulation must be installed, and what integral fire resistance it must have. Any insulation a homeowner is considering will be covered by the ‘fire and life safety’ building code, backed by testing of materials by organizations like Underwriters Laboratories (UL).
A more recent safety concern is potential off-gassing of chemicals from insulation into a home. For example, some fiberglass batts have contained formaldehyde. Manufacturers are aware of the concern and have modified their products to be safer. Some new products do not offgas any harmful chemicals. Ask for a ‘Material Safety Data Sheet’ or MSDS to review potential hazards.
Another concern is for the safety of workers who install insulation (and will someday remove it). Questions have been raised about the effect of inhaling insulation, such as glass fibers or blowing agents. These questions should be asked of the insulation supplier or manufacturer.
Finally, insulating a house usually reduces air leakage. This is a good thing, although care should be taken to ensure that there are no potential combustion safety issues. Older furnaces, water heaters and fireplaces may spill combustion byproducts, like carbon dioxide or smoke, if a house becomes too tight. A weatherization contractor can evaluate any potential risk. High-efficiency sealed-combustion furnaces and water heaters cannot spill combustion byproducts into a house.
Note than any pre-existing asbestos insulation, such as pipes or ducts, may be hazardous and should be evaluated before disturbing or removing.
Affordability
The cost of insulation should include both materials and labor needed to achieve full R-value. The cost of materials alone may be misleading. For example, a higher-cost material, like urethane foam boards, might be much quicker to install in odd locations, like a skylight well.
Lowest-cost options: loose-fill or ‘dense pack’ cellulose, fiberglass.
Moderate-to-high cost: fiberglass, cotton batts; EPS and XPS boards, wet-spray cellulose
Highest cost: spray-in foams, urethane and phenolic foam boards.
Environmental responsibility
There are many environmental variables, and each homeowner has different ideas about their respective importance. It can be confusing to weigh all the impacts.
For example, both fiberglass and cellulose usually contain recycled material. Fiberglass may include post-consumer and post-industrial glass, while cellulose may include post-consumer paper. However, recycling glass requires melting at high temperature, while recycling paper is very low-energy. If you think that energy use and greenhouse gas emissions are significant, cellulose would be the better option.
In general, look for transparency when evaluating products. If the supplier and manufacturer will answer your questions with factual information (not just claims or assertions), that’s a good sign they have nothing to hide.
Some products have an environmental certification, like GreenGuard. Usually a certification covers one aspect, like indoor air quality and safety, rather than a comprehensive green rating.
Some foam boards are made with blowing agents that contribute to global warming. Try to avoid using insulation containing HCFC-type blowing agents.
Hard to imagine, but someday your house will be deconstructed. When that time comes, will the insulation materials be recyclable?
In January 1995, Environmental Building News published a comprehensive evaluation titled "Insulation Materials: Environmental Comparisons." See it at:
Insulation Comparison Chart
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Insulation Type
|
R-Value
per Inch
|
Density (lb per ft3)(for Loose-Fill Only)
|
Where Applicable
|
Advantages
|
| |
|
|
|
|
|
Loose-fill:
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Anywhere the frame is covered on both sides, such as finished walls or cathedral ceilings, unfinished attic floors and hard-to-reach places.
|
Easy to use for irregularly shaped areas and around obstructions. ‘Dense-pack’ provides air sealing as well as insulation.
|
|
Cellulose
|
3.1-3.7
|
1.5-2.0
|
|
(dense pack)
|
3.4-3.6
|
3.0-4.0
|
|
Fiberglass
|
2.2-2.9
|
0.5-1.0
|
|
(dense pack)
|
3.4-4.2
|
1.6-3.0
|
|
Rock wool
|
2.2-2.9
|
1.7
|
|
|
|
Batts:
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All unfinished walls, falls, and attics--fits between frame studs, joists, and beams.
|
Do-it-yourself
Suited for standard stud and joist spacing, if there are few obstructions.
|
|
Fiberglass
|
2.9-3.8
|
|
|
Cotton (Recycled denim)
|
3.0-3.7
|
|
|
|
|
Sprayed insulation:
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Unfinished walls, attics, and floors.
|
Can provide air sealing as well as insulation.
Can provide complete coverage around obstructions.
|
|
Polyurethane foam
|
5.6-6.2
|
|
|
Icynene foam
|
3.6-4.3
|
|
|
Wet-spray cellulose
|
2.9-3.4
|
|
|
Spray-in fiberglass
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3.7-3.8
|
|
|
|
|
Foam board:
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Basement concrete or masonry walls, under slab floors.
Exterior walls under construction.
Exterior walls when adding siding.
|
High insulating value for relatively little thickness.
Covers wall framing, insulating studs as well as cavities.
|
|
Expanded Polystyrene (EPS)
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3.9-4.2
|
|
|
Extruded Polystyrene (XPS)
|
5.0
|
|
|
Polyisocyanurate
|
5.6-7.0
|
|
|
Polyurethane
|
5.6-7.0
|
|
|
Phenolic (closed cell)
|
8.2
|
|
|
|
|
Phenolic (open cell)
|
4.4
|
|
|
|
Sources: Lawrence Berkeley Laboratories, US DOE Insulation Fact Sheet, 1993 ASHRAE Handbook of Fundamentals, Loose-Fill Insulations
Additional Reading
