BUILDING ENVELOPE – INSULATION
It would be hard to find a more critical decision than your choice of insulation. In addition to R-value, you also need to look at these materials’ relationship with the rest of the building envelope. Though the fundamentals of building heating and cooling are unchanging, new products and evolving best practices allow insulation to play an increasingly important role in whole-house system design.
A comprehensive insulation strategy takes into consideration the products’ efficiency, cost, application techniques, and environmental impact. One also needs to factor in comfort and durability. Some of the products and practices being used to insulate today’s high-performance homes are outlined below.
Thermal Resistance Defined
Thermal energy travels from hot to cold, so we lose heat from inside to outside in cold months and lose our cool in the summer as heat tries to move indoors.
Insulation’s job is to slow down that transfer of heat. R-value is a measurement of a material’s ability to resist the transfer of energy; as we all know, the higher the R-value, the more effective the insulation (a chart of typical R-values is available in the R-Value Table section link here). By doubling the thickness of an insulating material, we can double its R-value, cutting energy transfer in half; however, the law of diminishing returns means that the same resources applied over again yield half the net change. Looking at a complete wall assembly design and its energy analysis is the only way to find the right balance between construction cost, long-term energy savings, and overall environmental impact.
Below is a brief review of the major types of insulation, from simplest to more complex and from least cost to most. Remember: As we improve our thermal enclosure, we also can reduce the complexity and size of our heating and cooling systems. This reduces first cost and saves on long-term operating cost. In a Life Cycle Assessment of this approach, higher-performing insulation will result in the best choice.
BATTS: If you are considering using batt insulation, select high-density batts with a higher insulating value. Remember that careful installation is vital; too often, poor installation techniques, design complexities, framing challenges, and other factors can cause gaps and voids between and around batts, seriously deteriorating their performance over time.
LOOSE-FILL SPRAY: Fibrous spray insulations are an innovative use of some traditional blown insulation products or recycled materials all using low-toxicity binders. These loose-fill solutions can be sprayed when mixed with moisture or binding agents. Some are intended for filling cavities while others are designed to adhere to exposed surfaces such as joists and floor pans. Correct installation requires careful management of moisture content and carefully watching the installed density. Cellulose-based solutions such as Green Fiber’s Cocoon System are made from recycled newspaper and incorporate EPA-registered fungicide. Some companies are fine-tuning their blends to emphasize fireproofing and acoustical attenuation along with energy-saving insulation.
SPRAY FOAM: Foam-in-place technology is playing an increasingly important role in establishing a tight building envelope. Historically, most of these products utilized high-density, closed-cell polyurethanes, which involved exposure to potentially hazardous chemicals during application. Today they usually flash their VOCs quickly and become fairly innocuous after a short time. Closed-cell foams are very effective at managing air leakage and can have high R-values of up to 7 per inch. Unfortunately, most still use HCFCs as blowing agents (with some notable exceptions such as SuperGreen).
But there are now a number of non-ozone-depleting, open-cell products available. These open-cell foams have lower R-values, but manufacturing them requires fewer hydrocarbon resources. Some are managing to replace petrochemicals with bio-based raw materials. The Icynene insulation system has a very long track record and is the most widely installed open-cell foam used today. BioBased 501 is a polyurethane foam with a soybean-oil base that uses carbon dioxide as a blowing agent. These products seem to be gaining rapid acceptance as builders look for alternatives to traditional insulation.
SIPS: An alternative to installing traditional insulation, Structural Insulated Panels (SIPs) are typically constructed of OSB sandwiching a foam core. Pros appreciate the ease of assembly and the improved performance SIPs can provide. Typical wall system R-values are from 22 to 30; these walls actually perform remarkably well as they have less framing materials thus reducing thermal bridging. This would eliminate the conventional framing approach and provide a faster and very tight enclosure. Still, these are not perfect either and require some training to install them correctly.
Regardless of the system you choose, remember that structural framing has a significant impact on insulation performance. The space between the studs may be R-22, but the studs, trimmers, headers, and rim joists themselves are only R-7 or R-8. Also remember that complex framing designs increase the building envelope’s surface area, and more surface area means more energy loss. Design the building shell with less surface area, and you’ll be miles ahead before you even start thinking about insulation.
Most wall insulation is traditionally installed in wood stud cavities, but adding insulation on the outside of the frame can significantly improve building performance if traditional framing is used. Besides adding additional insulation value, insulating the exterior of the enclosure also reduces dew-point potentials in cold climates and condensation potentials in high latent-load cooling climates. Exterior insulation also reduces the thermal bridging effect that studs have in a wall.
Because steel-stud exterior walls lose much more heat than wood-framed walls, they have the additional need to be sheathed in extruded or expanded polystyrene. The Department of Energy specifies the application of a minimum 1- to 2-inch layer over steel framing members to prevent thermal transfers that bypass the insulated cavities. In most climates, I would recommend installing at least 2 to 3 inches of foam if steel studs are being used. Enclosing the box with rigid insulation also can tighten up the envelope and will keep framing materials warmer and drier. Remember, in all but the most extreme climates a house enclosed in foam sheathing should not have an interior polyethylene vapor barrier. (More on this topic in the next issue.)
Put It All Together
With all of these approaches, real success comes from paying attention to the details. When wall and roof assemblies effectively connect with improved insulation products, we achieve synergistic gains. As our industry increases understanding of and respect for the fundamentals of building science, it is leading to many significant product innovations. Keep your eyes and knowledge tuned to improving our buildings’ performance.
INSULATION: PRODUCT REVIEW
Sometimes finding the right insulation can be extremely tricky. Fernando Pages Ruiz wrote a great article for ecohome magazine that lays a comprehensive list and product review of most insulations available:
Insulation represents an inherently green building material because it is designed to save energy. Still, while any insulation is better than none, the many choices present a broad range of benefits, with certain products inherently more ecological than others.
Here is a sampling of the major types of insulation, their properties, and their sustainability beyond simply saving energy.
Ubiquitous and economical, fiberglass represents the largest share of the market, comprising more than 50% of the insulation installed in the U.S. in 2007, according to the North American Insulation Manufacturers Association (NAIMA). It’s available in loose form for blown-in installation and in blankets, rolls, and batts for compression installation. Depending on density, both blown and stuffed fiberglass products provide R-13 to R-15 in a 2×4 wall cavity. Medium-density fiberglass designed for 2×6 constructions now provides R-21. In a 9?1/2-inch (2×10) cavity, high-density fiberglass can deliver a whopping R-38.
All fiberglass insulation manufacturers use 25% to 40% recycled glass in their products, according to Paul Bertram, director of environment and sustainability for NAIMA. The balance is sand, an abundant natural resource, with chemical binders added to create loft and a cohesive mat in the case of batt-style insulation.
One ecological issue with fiberglass is that glass and sand have to bake at extremely high temperatures to produce fibers. On the flip side, a typical pound of fiberglass insulation “saves 12 times as much energy in its first year in place as the energy used to produce it,” says Bertram.
Most of the health concerns and allegations made about fiberglass insulation have been retracted or disproved. The National Academy of Sciences (NAS) reported in 2000 that epidemiological studies of glass-fiber manufacturing workers indicate “glass fibers do not appear to increase the risk of respiratory system cancer.” NAS now supports the exposure limit of 1.0 f/cc that has been the industry recommendation since the early 1990s. And as of 2001, the International Agency for Research on Cancer (IARC), on which the California standards for Proposition 65 are based, no longer classifies fiberglass as a human carcinogen.
Perhaps the biggest objection to fiberglass batts in green building circles comes from the binders used to glue the glass fibers into a cohesive mat. These binders usually contain formaldehyde, a chemical known to cause sensitivity in certain people and classified as a human carcinogen by the IARC and as a probable human carcinogen by the EPA.
Most manufacturers insist that the low levels of formaldehyde used in manufacturing fiberglass batts makes any health concern exaggerated when compared to many other building products and naturally occurring off-gassing from raw materials, such as wood. In fact, some fiberglass batt insulation with added formaldehyde has gained Greenguard certification.
But if you are concerned, loose fill or blown fiberglass insulation requires no binder, which means no formaldehyde. For those using batts, Johns Manville offers the only fiberglass batt product line with no added formaldehyde. “We don’t consider the formaldehyde binders in insulation to be a big contributor to indoor air pollution, but since we can use alternatives without formaldehyde, why not do our little part to improve the environment?” explains Erick Olson, a senior technical product specialist for Johns Manville.
Any stuffed insulation requires excellent on-site quality control to perform at its rated R-value. A few missed cuts, gaps, or cracks left between batts, and the R-value plummets. Blown and foamed insulation usually provide a more foolproof system to prevent air infiltration, but an excellent sealing job using a well-aimed caulk gun and a few cans of foam sealant coupled with a craftsmanlike batt installation can yield low-cost insulation results comparable to the blown systems.
Non-fiberglass batts can be made of cotton, sheep’s wool, or mineral (rock or slag) wool. All of the alternative batt insulation products are made almost entirely from recycled or renewable materials. They offer similar thermal performance as fiberglass but at a slight cost premium. They come unfaced and need the addition of a separate vapor retarder in extreme-cold climate zones.
To make them fire resistant and prevent mold and insect infestation, most alternative batt (and cellulose) insulation fibers are coated with ammonium sulfate or borate. Although one manufacturer advertises its product as so safe a child could eat it, both sulfates and borate are used as pesticides and have toxic properties. At a minimum, a respirator should be worn when installing any kind of insulation.
Although the broad category of cellulose insulation includes a variety of products such as granulated cork, hemp fibers, straw, and grains, the most common and readily available cellulose insulation is made almost entirely from recycled newspapers, cardboard, waste paper, and wood pulp. Cellulose insulation is perhaps the best example of a significant recycled product in widespread use. Most is approximately 90% post-consumer recycled waste paper, with fire-retardant chemicals and, in some products, acrylic binders added.
“Mineral fiber materials take at least 25 to 30 times more energy to make than cellulose of equivalent R-value,” says Daniel Lea, executive director of the Cellulose Insulation Manufacturers Association, citing cellulose’s low-intensity manufacturing process and high recycled content.
Nowadays, blown cellulose is applied dry or merely damp, eliminating the extended drying times required for older, “wet” applications. Because of its relative high density and fire suppressants, this recycled newsprint product increases the fire resistance of building assemblies by 22% to 55%, per the Canadian National Research Council. It also provides a better air seal than fiberglass because of its higher density and slight dampness when applied, which tend to push the material into framing member penetrations.
As with cotton and wool, cellulose is an organic and flammable product that requires added biocides and flame retardants, usually borate and ammonium sulfate. Most cellulose installations are done by contractors using special equipment, but loose fill is also available that anyone can simply pour out of a bag. As with all other insulation products, installers should wear proper respirators as recommended by the manufacturer, especially since some people have sensitivity to newsprint ink. Foam
Although R-values remain close to equivalent across all insulation products, expanding foam has an added benefit because of the excellent air seal it provides. Foams are two-part products that are mixed through a blowing mechanism and sprayed into the framing cavity. The two chemicals react and expand. As the foam expands, it fuses tightly around all pipes, ducts, and wires, creating an airtight seal that yields much higher thermal performance than R-value alone would suggest.
The adhesive quality of foam offers another benefit rarely associated with insulation: High-density foam insulation provides improved structural integrity that helps make a building a little stronger. Nowadays, most foams use HCFCs as blowing agents, which are less destructive to the ozone layer than the old, and now banned, CFCs but still considered environmentally detrimental. Foams that do not use ozone-depleting blowing agents include Icynene, which uses carbon dioxide and water; Air Krete, a foam produced from magnesium oxide (derived from sea water) and compressed air; and BioBased, which uses compressed air.
As a builder of low-cost houses, I look for the least expensive option to achieve the best possible results. For this reason, I often use high-density fiberglass batts coupled with an excellent sealing job. But when my company set out to build a LEED for Homes–certified demonstration house, we chose BioBased insulation as a high-performance alternative.
Depending on market niche, the variety of insulation products available lets a builder distinguish his house as a comfortable, energy-efficient, and environmentally safe place to call home.
Owens Corning. The manufacturer says its entire line of fiberglass insulation products has been certified by Scientific Certification Systems to contain an average of 35% recycled content, 5% of which comes from post-consumer sources. ProPink fiberglass insulation carries Greenguard certification, including its highest level with Greenguard Children & Schools product emission standards. 800.438.7465. www.owenscorning.com.
Demilec. Sealection Agribalance open-cell, semi-rigid, polyurethane spray-foam insulation contains more than 10% renewable, agriculture-based products, says the firm. The material expands to fill the cavity, sealing cracks, gaps, and voids. It provides an R-value of 4.45 per inch. 877.336.4532. www.demilecusa.com.
CertainTeed. Designed for attic areas, InsulSafe SP blown-in fiberglass insulation is manufactured with no formaldehyde and is Greenguard certified. The product offers up to 20% better coverage versus competitors, the company says, with one bag covering up to 67 square feet. InsulSafe SP installed in the attic at 113/4 inches is R-30 and 141/2 inches is R-38. 800.233.8990. www.certainteed.com.
Advanced Fiber Technology. AFT cellulose insulation is made from 85% post-consumer recycled newspaper and cardboard. The pulp is ground into a fine, fluffy powder, then treated with primarily boric acid and borax to render it fire resistant. The higher density of this cellulose insulation makes for a tight seal, second only to foam products in blocking air infiltration and sound deadening, says the company. The blown-in insulation provides an R-value of 3.8 per inch. 419.562.1337. www.advancedfiber.com.
Thermafiber. Thermafiber mineral wool insulation is made with up to 90% post-industrial recycled content. It exceeds the California purchase specifications for total volatile organic compounds and general emissions with formaldehyde concentrations of 12 ppb, exceeding the California standard of 20 ppb maximum for formaldehyde concentration. Thermafiber can provide high sound-transmission coefficients that improve indoor environmental quality. The product also offers fire resistance of more than 2,000 degrees F for more than five hours, the maker says. 888.834.2371. www.thermafiber.com.
Air Krete. The company’s magnesium silicate, cement-based insulation is foamed or pumped into closed cavities. This insulation is purportedly hypoallergenic and popular with chemically sensitive people, the company claims. Since it is not temperature sensitive, it can be installed indoors under any weather conditions and tolerates contact with high-heat sources, such as exhaust pipes, without concerns for combustion. The product is fully recyclable and can be used for soil enrichment. Air Krete has an R-value of about 3.9 per inch. 315.834.6609. www.airkrete.com.
Icynene. Icynene water-blown foam insulation expands to 100 times its volume to fill cracks and crevices and minimize air leakage. It carries an R-value of 3.6 per inch. The product also is available in a pour-fill variation that expands upward to 60 times its original volume; it will not expand outward and damage the wall. The pour-fill version has an R-value of 4 per inch. 800.758.7325. www.icynene.com.
Johns Manville. Formaldehyde-free MR faced fiberglass batts use a water-based acrylic binder that meets California’s Section 01350 standards. The facing serves as an integral vapor retarder, chemically protected against potential fungi growth. The company claims to obtain its sand from sources close to the manufacturing plant to reduce transportation impacts, and 20% of its recycled content is post-consumer. 800.654.3103. www.jm.com.
Second Nature. Sheep’s wool is an insulation product commonly used in Europe and available in the United States through the Internet. A natural insulator, wool has a slightly higher R-value per inch than fiberglass and does not lose its insulating property when wet. It has inherent properties that resist both flame and many insects, but remains susceptible to moths, so it is treated with boron. Thermafleece comes in 2-inch-thick batts cut to friction fit within 16- and 24-inch stud spacing. They carry an R value of 3.8 per inch and can be layered to achieve the desired total R value. www.secondnatureuk.com.
BioBased 1701 BioBased Insulation. Unlike some traditional spray-foam insulation products that are petroleum-based and use HCFCs as blowing agents, BioBased 1701 is a soy-based, 100% water-blown, closed-cell polyurethane insulation. It has earned the Greenguard air quality certification. BioBased 1701 has an R-value of 19 at 3?1/2 inches. 800.803.5189. www.biobased.net.
Bonded Logic. Ultra Touch cotton friction-fit batt insulation can be used for 16- and 24-inch spacing. The product is made with 85% post-industrial recycled content. The line includes an R-30 batt that fits into 2×6 walls or joist cavities. Cotton insulation offers acoustic properties 36% higher than fiberglass, says the company, only slightly less than mineral wool. 480.812.9114. www.bondedlogic.com.