What's new with insulation?

Asked by Eric Singer
Clarksdale, MS

Spray foam, traditional rolls, blown in, etc. What are 3 things I should know about new products/techniques I should know about?


Homes are often built with multiple types of insulation:

  • Outside the walls and under the slab, closed cell extruded polystyrene (XPS) rigid foam board is commonplace. Also, insulated concrete forms (ICFs), aerated autoclave concrete blocks, Air-krete, Hebel block, and Durisol have become popular over the last 20 years.
  • For the exterior walls, we often find fiberglass batts, cotton or wool batts, blown in cellulose, rock wool, vermiculite, straw or straw clay, rigid foam and structural insulated panels (SIPs).
  • In the attic, open cell spray polyurethane foam stops air infiltration well, as do SIPs. Finally, don't forget radiant heat barriers in the attic to reflect infra-red rays of the sun from heating the attic space.

Factors to consider

Choosing the quantity and right type of insulation is one of the most important decisions that affect the comfort and energy efficiency of a home.

Key factors worth considering are:

  • Thermal efficiency
  • Indoor air quality
  • Adequate ventilation
  • Moisture control
  • Sustainability factors
  • Installation
  • Availability and cost

EFFICIENCY. Thermal insulation, as defined by, is "any material which significantly slows down or retards the flow or transfer of heat.

  • Building insulation types are classified according to form (e.g., loose-fill, batt, flexible, rigid, reflective and foamed-in-place) or material (mineral fiber, organic fiber, foam plastic).
  • All types are rated according to their ability to resist heat flow (R-Value or RSI)".

These rating values, however, can be misleading when site conditions and construction techniques are not factored in. In a famous experiment comparing fiberglass to cellulose conducted at Oakridge National Laboratories in Tennessee, two identical buildings were built side by side using R-19 insulation.

  • Both thermostats were set to the same temperature and all other environmental conditions were the same.
  • Over the same period, one home using cellulose out-performed fiberglass by approximately 30%!! Why was that? After all, they were both rated at R-19.
  • The answer was due to the other factors such as settling, humidity, thermal bridging and air infiltration. Any one of these factors individually or collectively could drastically alter the energy performance by more than 30%.

R-values are only theoretical measures that don't take everything into account as proven by this experiment.

IAQ. Just because a product keeps out cold or keeps in heat doesn't mean it’s safe or good to breathe.

  • Fiberglass is well known to cause respiration issues both during and after construction.
  • Some fiberglass still contains formaldehyde, which is considered hazardous to your health.
  • Spray foam, which is primarily petroleum-based, off-gasses for days or weeks and, if burned, can create a deadly smoke.
  • Some insulation when wet may facilitate the growth of mold and mildew, while others may contain questionable anti- microbial chemicals designed to prevent it.

VENTILATION. According to, "In order to design and build safe, healthy, comfortable and affordable buildings, airflow must be controlled. Airflow carries moisture that impacts a material’s long-term performance (serviceability) and structural integrity (durability), behavior in fire (spread of smoke), indoor air quality (distribution of pollutants and location of microbial reservoirs) and thermal energy.“

One of the key strategies in the control of airflow is the use of air barriers.
Understanding air barriers is necessary in order to develop effective enclosure design, set achievable performance requirements and verify compliance."

Not all insulation controls airflow the same way. Some is much better than others. It is well known that air infiltration accounts for 30% of all heat loss.

MOISTURE CONTROL. Each type of insulation allows moisture to permeate differently, depending on its porosity, mass and chemical nature.

Insulation often comes with vapor retarders or barriers, which may be useful in preventing condensation if used correctly. Insulation such as fiberglass, cotton, cellulose or wool has a high perm rating, which means moisture diffuses easily. As long as there is no moisture retarder added, this insulation tends to wick out excessive moisture naturally.

However, the wrong use of vapor retarders can trap moisture or create condensation, which may eventually create mold and mildew.

SUSTAINABILITY. Green insulation is a highly debated topic because definitions vary widely depending upon what it's made from and how it performs.

  • Insulation that contains bio-based components may be renewable, but doesn’t necessarily perform better or worse than those with recycled content or those with synthetic ingredients.
  • Also, beware; just because its bio-based doesn’t mean there are no hazardous chemicals. Blown in soy-based foam insulation is considered partly bio-based and is excellent at reducing air infiltration, but it’s made primarily of petroleum-based materials that are not sustainable.

Just about every type of insulation has some amount of recycled content that keeps hundreds of millions of pounds of waste out of landfills. This is a good thing, but how it is recycled may require more or less energy and where it is imported from may increase or decrease its carbon footprint. Slag wool, cotton and cellulose have the most recycled content, but so does fiberglass.

INSTALLATION. Installation requires knowledge and experience, and--because it is one of those critical components that can't easily be undone--it must be done right the first time.

  • Cutting a batt too short or too narrow, not filling the bay completely or producing the correct loft, forgetting to caulk or tape every seam, putting a vapor retarder on the wrong side, etc., can cause serious consequences.
  • The California Energy Commission, for example, found that a 4 % void reduces efficiency by 50%.

Consider your home

No insulation is perfect; each has its strengths and weaknesses for different
applications. There are always trade-offs in thermal performance, cost and environmental attributes.

  • One might be initially inexpensive, yet end up costing far more in the long run and create poor indoor air quality.
  • Others may insulate very well, but be way overkill and have diminishing returns for the money spent.
  • Still others could be expensive up front but save you money month after month and offer excellent accoustical and environmental benefits.

In other words, insulation is part of a system, and you have to understand all the parameters that affect heat loss and gain, initial and long term cost, indoor air quality and overall thermal performance.

So, whenever I’m asked about what is the best insulation product to use, it always leads into a deeper discussion about

  • envelope of the home,
  • what type of framing was used, 
  • the HVAC system,
  • how well it is sealed, as well as,
  • what type of vapor barriers and windows and other features that might affect heat loss.

All of this information is needed BEFORE choosing the right insulation.

Ask questions

Here are some important questions to ask:

  • What is the R-value? According to the Department of Energy, this is a theoretical measure of the heat transfer resistance--the higher R-value the greater the insulating effectiveness.
  • Does the R-value remain constant when the temperature drops? Some insulation retains its R-value while others lose R-value when the temperature drops below 20 degrees. For example, Fiberglass loses R-value as the temperature drops below 20 degrees F. Make sure you’re getting what you pay for!
  • What effect does moisture have on R-value? If it rains and water gets inside does the insulation shrink and lose its ability to insulate? How well does it dry out if exposed? Will it absorb and release water vapor well or does it trap it creating the environment for mold and mildew? Is a vapor barrier required? In some states they are outlawed.
  • How well does the insulation stop air leaks? Cracks around windows, doors, fireplaces, attics, between floors, etc. can drastically reduce the effectiveness of your insulation.
  • How well does it reflect or hold in radiant heat? Most infrared rays go right through most insulation. Will a radiant barrier in the attic or walls help reduce this loss in your climate?
  • Does the insulation carry a Class I fire rating? This is not required by insurance companies or local codes, but it sure helps. Are toxic chemicals produced when it burns?
  • Is it made from natural or recycled materials? Are toxic chemicals used in its production? Some natural products require huge amounts of chemicals for their growth. Also, how much energy is used in the production and distribution process?
  • How easy is it to install? Some are do-it-yourself while others require professionals.
  • How long does it take to install? Some take a few days, others one to two weeks. Will installation create moisture problems or air pollution problems? Some require serious cleaning; others require almost none.
  • How does it affect indoor air quality during and after installation? Some produce off-gas or create airborne particulates for weeks or months, while others produce none.
  • If your house settles, does the insulation move with the building or does it leave gaps? Some settle, others shrink, others fit snug. How well does it prevent air infiltration — especially around doors and windows?
  • Will it last as long as the house? Some may deteriorate over time and need replacement.
  • Do pests like to eat it? Some insulation may have added protective coatings that can wear off or cause other problems.
  • How well does it insulate against noise? Most are good, but some are superior, and work well between floors and between rooms. This is especially important when sharing a home or apartment or office. These are good areas to use a type of insulation better suited to the task.
  • Are energy credits available from the local utility or from the state or federal government? If the R-value is higher, does it pay for itself within a few years? In most cases a more efficient insulation will cost more up front but it will payback money in the form of lower heating and cooling bills later on — especially with rising energy costs.
  • What does it cost? Typical prices range widely from 45 cents to $2.00 per square foot. Installation prices also vary from 20 cents to 50 cents or more per square foot. Some installers charge by the board foot or square foot, some by the hour, some will bid the whole job including clean up and others will install for less if they supply the material. Choosing the right insulation for your home clearly requires doing your homework.


For more information:

Talk with energy officials, architects, government agencies, etc. Or visit some of these websites:

Read "Do you recommend bio-based soy foam insulation?" a Q&A answered by Andy Ault.

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