Homes are often built with multiple types of insulation:
- Outside the walls and under theslab, closed cell extruded polystyrene (XPS) rigid foam board is commonplace. Also,insulated concrete forms (ICFs), aerated autoclave concrete blocks, Air-krete, Hebelblock, and Durisol have become popular over the last 20 years.
- For the exterior walls, we often find fiberglass batts, cotton or wool batts, blown incellulose, rock wool, vermiculite, straw or straw clay, rigid foam and structural insulatedpanels (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 sunfrom heating the attic space.
Factors to consider
Choosing the quantity and right type of insulation is one of the most important decisionsthat affect the comfort and energy efficiency of a home.
Key factors worth consideringare:
- Thermal efficiency
- Indoor air quality
- Adequate ventilation
- Moisture control
- Sustainability factors
- Availability and cost
EFFICIENCY. Thermal insulation, as defined by BuildingScience.com, is "any material whichsignificantly slows down or retards the flow or transfer of heat.
- Building insulationtypes are classified according to form (e.g., loose-fill, batt, flexible, rigid, reflectiveand foamed-in-place) or material (mineral fiber, organic fiber, foam plastic).
- All typesare 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 notfactored in.In a famous experiment comparing fiberglass to cellulose conducted at OakridgeNational Laboratories in Tennessee, two identical buildings were built side by sideusing R-19 insulation.
- Both thermostats were set to the same temperature and all otherenvironmental conditions were the same.
- Over the same period, one home using celluloseout-performed fiberglass by approximately 30%!! Why was that? After all, they wereboth 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 collectivelycould drastically alter the energy performance by more than 30%.
R-values are only theoretical measures that don't take everything into account as provenby this experiment.
IAQ. Just because a product keeps out cold or keeps in heat doesn't mean it's safe or goodto breathe.
- Fiberglass is well known to cause respiration issues both during and afterconstruction.
- Some fiberglass still contains formaldehyde, which is considered hazardousto your health.
- Spray foam, which is primarily petroleum-based, off-gasses for daysor weeks and, if burned, can create a deadly smoke.
- Some insulation when wet mayfacilitate the growth of mold and mildew, while others may contain questionable anti-microbial chemicals designed to prevent it.
VENTILATION. According to BuildingScience.com, "In order to design and build safe, healthy,comfortable and affordable buildings, airflow must be controlled. Airflow carriesmoisture that impacts a material's long-term performance (serviceability) and structuralintegrity (durability), behavior in fire (spread of smoke), indoor air quality (distributionof 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 insulationcontrols airflow the same way. Some is much better than others. It is well known that airinfiltration accounts for 30% of all heat loss.
MOISTURE CONTROL. Each type of insulation allows moisture to permeate differently, depending on itsporosity, mass and chemical nature.
Insulation often comes with vapor retarders orbarriers, which may be useful in preventing condensation if used correctly. Insulationsuch as fiberglass, cotton, cellulose or wool has a high perm rating, which meansmoisture diffuses easily. As long as there is no moisture retarder added, this insulationtends to wick out excessive moisture naturally.
However, the wrong use of vaporretarders can trap moisture or create condensation, which may eventually create mold andmildew.
SUSTAINABILITY. Green insulation is a highly debated topic because definitions vary widely dependingupon what it's made from and how it performs.
- Insulation that contains bio-based components may be renewable, but doesn't necessarilyperform better or worse than those with recycled content or those with syntheticingredients.
- Also, beware; just because its bio-based doesn't mean there are no hazardouschemicals. Blown in soy-based foam insulation is considered partly bio-based and isexcellent at reducing air infiltration, but it's made primarily of petroleum-based materialsthat are not sustainable.
Just about every type of insulation has some amount of recycled content that keepshundreds of millions of pounds of waste out of landfills. This is a good thing, but how itis recycled may require more or less energy and where it is imported from may increaseor decrease its carbon footprint. Slag wool, cotton and cellulose have the most recycledcontent, but so does fiberglass.
INSTALLATION. Installation requires knowledge and experience, and--because it is one of those criticalcomponents that can't easily be undone--it must be done right the first time.
- Cutting abatt 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., cancause serious consequences.
- The California Energy Commission, for example, found thata 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 environmentalattributes.
- One might be initially inexpensive, yet end up costing far more in the long runand create poor indoor air quality.
- Others may insulate very well, but be way overkill andhave diminishing returns for the money spent.
- Still others could be expensive up frontbut save you money month after month and offer excellent accoustical and environmentalbenefits.
In other words, insulation is part of a system, and you have to understand all theparameters that affect heat loss and gain, initial and long term cost, indoor air quality andoverall thermal performance.
So, whenever I'm asked about what is the best insulation product to use, it always leadsinto 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 andwindows and other features that might affect heat loss.
All of this information is neededBEFORE choosing the right insulation.
Here are some important questions to ask:
- What is the R-value? According to the Department of Energy, this is a theoreticalmeasure of the heat transfer resistance--the higher R-value the greater the insulatingeffectiveness.
- Does the R-value remain constant when the temperature drops? Some insulation retainsits R-value while others lose R-value when the temperature drops below 20 degrees. Forexample, Fiberglass loses R-value as the temperature drops below 20 degrees F. Makesure you're getting what you pay for!
- What effect does moisture have on R-value? If it rains and water gets inside does theinsulation 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 formold 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 mostinsulation. 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 insurancecompanies 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, howmuch 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. Willinstallation create moisture problems or air pollution problems? Some require seriouscleaning; others require almost none.
- How does it affect indoor air quality during and after installation? Some produce off-gasor 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 wearoff or cause other problems.
- How well does it insulate against noise? Most are good, but some are superior, and workwell between floors and between rooms. This is especially important when sharing ahome or apartment or office. These are good areas to use a type of insulation better suitedto the task.
- Are energy credits available from the local utility or from the state or federalgovernment? If the R-value is higher, does it pay for itself within a few years? In mostcases a more efficient insulation will cost more up front but it will payback money in theform 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. Someinstallers charge by the board foot or square foot, some by the hour, some will bid thewhole 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.