Know the Lingo
R-Value: A measure of how effectively a material resists heat flow. Thus, higher numbers are better.
Batt: A length of insulation that is precut to fit certain wall cavity dimensions. Typically sold in a pre-cut roll.
Unfaced/Faced Insulation: Faced insulation (typically a fiberglass batt) includes a vapor retarder on the interior face that restricts movement of moist air into wall cavities. Unfaced is simply a batt without a vapor retarder.
Ridge Vent: An opening covered by a rainproof vent that follows the peak of the roof, typically required by code. Some insulating methods, however, negate the need for a ridge vent. Clear it with your local code official first.
Blow-In: Method of introducing loose fiberglass, cellulose or mineral wool to framing cavities or attic space, typically using a machine with an attached hose.
Blower Door: Equipment used to test the effectiveness of a home’s insulation and air sealing systems.
Stud Cavity: The space between the vertical members of a conventionally framed wood or lightweight steel home. Common stud spacings include 16” and 24” on center (of stud).
IF YOU'VE EVER opened up the wall of a home built before about 1950, you’ve probably been shocked to find little or no insulation—or at best some crumpled newspapers. And even the earliest serious attempts at insulation with fiberglass look quaint now. Cavities were often only partially filled. Water from outside often leaked in around windows and doors and damaged the insulation. Of course, homes were so leaky prior to the 1960s that walls dried out quickly, so mold wasn’t a big problem.
The rules of the game are very different today. Homes are built tight—with no tolerance for sloppy insulating.
Building scientists (a new breed of experts) now have a deep understanding of how insulation works. They’ve learned that factors such as air infiltration, dampness and age can dramatically affect performance.
But they also recognize that insulation is part of an energy saving system, not a standalone solution. Good results can be achieved with any insulating material, if it’s combined with the right housewraps, tapes and construction details. Here’s an overview of the latest advances in insulation technology.
Fiberglass insulation in batt form is probably the most familiar insulating product. Changes in recent years have affected the composition of chemical binders that hold the product together, along with the size of the glass fibers. Many brands have removed or reduced toxins such as formaldehyde from their products. Some of the largest manufacturers of fiberglass products now offer hybrid systems that include an air-sealing component. They have improved the performance and handling of blown-in fiberglass, and added to the percentage of recycled content in all product lines (up to 40 percent).
Insulating walls and ceilings with spray foam is relatively expensive, typically more than twice the cost of fiberglass batts, and most often it’s a job best handled by pros. Why is foam green? Not because of what’s in it. Even the most eco-friendly brands replace only a small percentage of their petroleum-based chemical mix with biological products such as soy. But the energy performance of foam is hard to beat. Some brands offer insulating value of more than R-6 per inch, at the same time sealing against air infiltration. This makes spray foam a dual-duty system, ideal for both new and retrofit construction.
Cellulose has a good green story to tell, especially from the manufacturing side. It’s made primarily with recycled paper, typically newspapers, and most brands are treated with boric acid as a fire retardant. Research on the health effects of boric acid suggest that it is a minor irritant in small doses. Cellulose can can be installed wet or dry. If installed wet, it should be allowed to dry properly before covering with drywall (typically less than 48 hours). The insulating value of cellulose is about the same as blown fiber glass (roughly R-3.7 per inch).
Although mineral wool looks like fiberglass, it’s made from basalt rock and slag, not glass. The resulting product, either batts or loose fill, is non-flammable, requiring no chemical flame retardants. As a result, offgassing emissions tend to be low. Mineral wool includes high levels of post-industrial recycled content waste (up to 90 percent), reducing the environmental impact of its production.
You may have seen contractors in your area putting green or blue insulation right over the wood siding of an old house. Chances are, they’re applying extruded expanded polystyrene (XEPS) or polyisocyanurate closed-cell foam. Both products are dense and durable. Some building experts suggest that foam used this way can an act as water resistive barriers (WRBs), negating the need for housewrap, but we recommend playing it safe and using housewrap as well. Rigid foam also is a good choice for insulating basement walls.