Building Insulation

Thermal insulation used in building construction is the subject of this article. The goal of insulation is to use Heat-transfer resistance to slow down heat transfer to and from the exterior.

The phrase “thermal envelope” refers to the conditioned or living space in a house. The attic and basement can be unconditioned space, but either, or both, can be part of the conditioned space. To prevent heat loss and/or gain in a building, it is important to make the building envelope airtight. Airtightness must be built in. Stopping air infiltration is a first step in insulating a building, as it has been estimated that up to 40% of a building's heat loss or gain is due to air leaks to the outdoors. Source: http://www.ornl.gov/sci/roofs+walls/whole_wall/airtight.html Quality of work is key. Gaps and cracks inside exterior walls are too deep to be considered a function of weatherproofing, or weatherization.

Once airtight, a building needs a system, passive or active, to manage air, to prevent humidity buildup. If not, then most materials used as insulation become far less effective than expected. Furthermore, water (moisture, humidity) stored in or near these materials then harbours conditions enabling mold, fungus and rot to thrive.

Buildings have different types of insulating materials in various places; each type of insulation is deemed suited to specific tasks and not others. Most residential insulation materials are deemed effective primarily because they have low thermal conductivity; some are primarily effective at blocking heat radiation or convection. Some materials, for example, foil-faced rigid panels, reduce heat transfer effectively in more than one way.

Adobe, earth, stone, and concrete can regulate indoor temperature by damping the daily swings in outdoor temperature. This is because of the principle of thermal mass at play. The substances used are actually poor insulators.

Two indications that a house is poorly insulated and poorly ventilated:

* Dew and frost forms on cold surfaces in the attic, such as on the underside of the roof sheathing, during the winter.
* The attic is oppressively, almost unbearably hot in the summer.

Methods of insulation in buildings

Radiant barriers

These materials reduce radiated heat, rather than conducted heat. For this reason, trying to associate R-values with radiant barriers is difficult and inappropriate. The R-value test does not control the amount of heat transfer due to conduction / radiation respectively. There is no standard test designed to measure the reflection of radiated heat energy alone. Radiated heat is a significant means of heat transfer; the sun's heat arrives by radiating through empty space and not through conduction. At night the absence of heat (i.e. cold) is the exact same phenomenon, described mathematically as the linear opposite. Roofs and exterior walls thus need radiant protection. Heat and cold are resisted in equal measure; i.e. radiant cold and radiant heat.

* Metal roofs, e.g. aluminum or copper.
* Glass windows with low-emissivity (low-E) coating. Low-E glass has an invisible metal coating suspended between layers of glazing that reflects radiation that would normally escape, back into the house, and reflect radiation that would normally enter, back to the outside. Thus, they keep the house warmer in winter and cooler in summer. They work similar to the way that a Dewar flask works, in which the metal is in contact with a near-vacuum, greatly reducing the conduction and convection that would normally occur, while taking advantage of the metal's superior radiative properties.
* Foil-faced polyurethane or foil-faced polyisocyanurate panels.
* Foil-faced polystyrene. this laminated, high density EPS is more flexible than rigid panels, works as a vapor barrier, works as an excellent thermal break. When using metalized plastic facing is a more effective reduces surface conductivity. Uses underside roof sheathing, ceilings, and on walls. for best results, this is not a cavity fill type insulation.
* Foil-backed bubble pack. This is thin, more flexible than rigid panels, works as a vapor barrier, and resembles plastic bubble wrap with aluminum foil on both sides. Often used on cold pipes, cold ducts, and the underside of roof sheathing.
* Light-colored roof shingles and reflective paint. These help to keep attics cooler in the summer and in hot climates.

Batts and blankets

These come in various thicknesses, depending on how much insulation capacity you need. Batts are precut, whereas blankets are available in continuous rolls. Blankets are ideal for covering joists and studs as well as the space between them. If you don't cover joists and studs with insulation, heat will tend to flow through them (known as "bridging" or "short-circuiting"), since they are the path of least resistance. Similarly, you can install batts in two layers across an unfinished attic floor, perpendicular to each other, for increased effectiveness.

Batts come in standard widths designed to fit snugly between framing (joists, rafters, studs) on 16-inch or 24-inch centers in ceilings, floors, and walls, and are generally easier to handle than blankets. However, batts can be challenging and unpleasant to install between joists under floors. You can run straps, or staple cloth or wire mesh across joists, to prevent insulation from sagging or falling down. Compressing batts reduces their effectiveness. Cut them to accommodate electrical boxes and other obstructions, and do not leave items resting on the batts.

Batts and blankets are susceptible to poor installation. Installers tend to leave bypasses (air gaps) that drastically reduce their effectiveness. Warm air and moisture always find their way to these bypasses. Even if you close all bypasses around batts and blankets, they remain poor barriers to air infiltration and are susceptible to convection loops, especially when there are large temperature differences on either side of the insulation (such as during cold weather). You can reduce air infiltration by adding a layer of cellulose loose-fill on top of the fiberglass. The only way to virtually eliminate air infiltration is with a near-perfect vapor barrier. An attic that only has fiberglass batts to keep out warm, moist air, but a poor or nonexistent vapor barrier, will probably not keep out the warm, moist air.

Batts as the prefered choice of insulation

There are many types of insulation, but Batts have become the preferred choice for domestic situations. This did not come about by accident. At the start of the 1970's in response to oil shock's, the US state governments sought to cut home heating oil usage by increasing building code insulation requirements for all new housing.

At the same time, Owens Corning fiberglass lobbied intensively to convince the building officials who wrote and administered the four separate building codes then used in the USA. They also aimed to eliminate every other kind of housing insulation material (such as polyurethane) on safety or hazard grounds. The result was that Owens Corning successfully lobbied for mandatory 2" x 6" (50 x 150 mm) wall framing with fibreglass insulation. This suited the timber merchants just as well as it suited Owens Corning.

Loose-fill materials can be blown into attics, finished wall cavities, and hard-to-reach areas. They are ideal for these tasks because they conform to spaces and fill in the nooks and crannies. They can also be sprayed in place, usually with water-based adhesives. They frequently consist of recycled materials, and therefore, are relatively inexpensive.

General procedure for retrofits:

• Drill holes in wall with hole saw, taking firestops, plumbing pipes, and other obstructions into account.
• Pump loose fill into wall cavity, gradually pulling the hose up as the cavity fills.
• Cap the holes in the wall.

Advantages of loose-fill

• Ecological
• R-Value 3.4 - 3.6
• Class I Fire Safety Rating
• No Formaldehyde-based Binders
• High Recycled Content
• Less Harmful to Installer

Commonly used loose-fill

* Rock and slag wool, also known as mineral wool or mineral fiber. Made from rock (basalt, diabase), iron ore blast furnace slag, or recycled glass. Usually gray with black specs, or white, and more brittle, denser, and more resistant to airflow than fiberglass. Clumps and loses effectiveness when moist or wet, but does not absorb much moisture, and regains effectiveness once dried. Nonflammable. Older mineral wool can contain asbestos, but normally this is in trace amounts.
* Fiberglass. Usually pink, yellow, or white. Loses effectiveness when moist or wet, but does not absorb much water. Nonflammable (because the fibers are not in a plastic resin, unlike the fiberglass used in cars and boats). See Health effects of fiberglass.
* Cellulose. Usually gray and consists of recycled, shredded newspapers, boxes, waste paper, and wood pulp. Cellulose, like rock wool, is denser and more resistant to air flow than fiberglass, but cellulose settles (and therefore, loses effectiveness) much more than fiberglass and rock and slag wool. Persistent moisture can weaken the flame-retardants in cellulose. Dense-pack cellulose is highly resistant to air infiltration and is either installed into an open wall cavity using nets or temporary frames, or is retrofitted into finished walls. However, dense-pack cellulose blocks, but does not permanently seal, bypasses, as a closed-cell foam would. Furthermore, as with batts and blankets, warm, moist air will still pass through, unless there is a near-perfect vapor barrier. Wet-spray cellulose is cellulose mixed with water and adhesive to help the cellulose bind to the inside of open wall cavities, and to make the cellulose more resistant to settling. Wet-spray cellulose must be allowed to dry completely before sealing up the wall with a vapor barrier and drywall. Moist-spray cellulose uses less water to speed up drying time. Cellulose insulation is regulated as a recognized fire hazard by the Consumer Product Safety Commission (CPSC), which requires labeling of cellulose insulation to inform installers and consumers about the threat of fire. (See 16 C.F.R. 1209, 1404)
* Natural insulations such as granulated cork, hemp fibres, grains, all which can be treated with a low toxicity fire and insect retardants

Health & safety issues

Fiberglass

Fiberglass is the most common residential insulating material, and is usually applied as batts of insulation, pressed between studs.

Fiber glass is now the most thoroughly evaluated insulation material in the market. The fiber glass insulation industry is committed to ensuring that fiber glass products can be safely manufactured, installed and used. This industry has funded tens of millions of dollars of research at leading independent laboratories and universities in the United States and abroad. The weight of the scientific research shows no association between exposure to glass fibers and respiratory disease or cancer in humans.

In October 2001, an international expert review by the International Agency for Research on Cancer (IARC) re-evaluated the 1988 IARC assessment of glass fibers and removed glass wools from its list of possible carcinogens by downgrading the classification of these fibers from Group 2B (possible carcinogen) to Group 3 (not classifiable as to carcinogenicity in humans). All fiber glass wools that are commonly used for thermal and accoustical insulation are included in this classification. IARC noted specifically: "Epidemiologic studies published during the 15 years since the previous IARC Monographs review of these fibers in 1988 provide no evidence of increased risks of lung cancer or mesothelioma (cancer of the lining of the body cavities) from occupational exposures during manufacture of these materials, and inadequate evidence overall of any cancer risk."

The IARC downgrade is consistent with the conclusion reached by the U.S. National Academy of Sciences, which in 2000 found "no significant association between fiber exposure and lung cancer or nonmalignant respiratory disease in the MVF [man-made vitreous fiber] manufacturing environment."

The World Health Organization however, has declared fiber glass insulation as potentially carcinogenic. The product is still required to carry a cancer warning label in the USA.

Miraflex is a new type of fiberglass batt that has curly fibers that are less itchy and create less dust. You can also look for fiberglass products factory-wrapped in plastic or fabric.

Loose-fill cellulose

Although cellulose is 100% natural, and usually made from recycled material, loose-fill cellulose is not as environmentally-friendly as some people would have you believe:

• Cellulose is treated with a flame retardants, usually boric acid and borax to resist insects and rodents. Some people think that the fire-retardant chemicals, insect repellants, dust, and newspaper ink in cellulose may be harmful to breathe and touch.
• One thing that has not contributed to mold problems is the growing popularity of cellulose insulation among knowledgeable home owners who are interested in sustainable building practices and energy conservation. Mycology experts (mycology is the study of mold) are often quoted as saying: “Mold grows on cellulose.” They are referring to cellulose the generic material that forms the cell walls of all plants, not to cellulose insulation.

• Unfortunately, all too often this statement is taken to mean that cellulose insulation is exceptionally susceptible to mold contamination. In fact, due to its favorable moisture control characteristics and other factors associated with the manufacturing process relatively few cases of significant mold growth on cellulose insulation have been reported. All the widely publicized incidents of serious mold contamination of insulation have involved fiber insulation materials other than cellulose.

U.S. Health and Safety Partnership Program

In May 1999, the North American Insulation Manufacturers Association began implementing a comprehensive voluntary work practice partnership with the U.S. Occupational Safety and Health Administration (OSHA). The program, known as the Health and Safety Partnership Program, or HSPP, promotes the safe handling and use of insulation materials and incorporates education and training for the manufacture, fabrication, installation and removal of fiber glass, rock wool and slag wool insulation products. (See health effects of fiberglass). (For authoritative and definitive information on fiber glass and rock and slag wool insulation, as well as the HSPP, consult the North American Insulation Manufacturers Association (NAIMA) website (www.naima.org).)