The advantages of a well-insulated home are threefold:
To take advantage of those characteristics, you have several types of insulation to choose from. The material you use should take into account the weather patterns where you live, the level of performance you want, and how accessible your structure is. With a new home, the sky’s the limit--any insulation can be specified. In an old house, however, where you have to “drill and fill,” your options may be more limited.
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, such as Owens-Corning, have introduced products that are more comfortable to handle, 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. Creating spray foam is chemically intensive, but the energy performance of foam is hard to beat.
Some brands offer insulating value of more than R-6 per inch. One technique to consider with spray foam is combining closed cell and open cell foam in the same cavity, a system especially suited for the roof cavities in unvented attics.
Another efficient and money-saving option is to apply a shallow layer of closed cell foam to seal off air leaks, then fill the remaining space with fiberglass, cellulose or stone wool.
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. Companies such as Greenfiber have fine-tuned these products in recent years.
Cellulose 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 fiberglass (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. Rigid exterior insulation made from mineral wool is now available as well, an excellent choice for wildfire risk regions.
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 act as a water-resistive barrier (WRB), negating the need for housewrap, but we recommend playing it safe, and using housewrap as well.
Rigid foam is also a good choice for insulating basement walls. Recent research has found that adding just an inch or two of rigid foam to a roof deck can make a tremendous difference in the amount of heat absorbed into the building. We are currently testing this principle on a remodeling project called ReVISION House Scottsdale, located in Arizona. Temperatures there often exceed 115 degrees Fahrenheit.
Extra-thick layers of exterior insulation can greatly improve the energy performance of homes, but installation requires some special techniques.
For thinner insulation, the cladding can often be attached directly through the rigid insulation, nailed or screwed into the structure. The practical limit of this approach is around 1-½” of rigid insulation, due to the limited fastener lengths for many pneumatic nail guns.
For thicker insulation, vertical wood furring strips can provide a cladding attachment location. This approach also provides a drainage and ventilation gap behind the cladding, which helps manage water. To adequately support the cladding, the furring strips should be attached back to the structure using #10 or larger wood screws that are sized to maintain a 1-¼” minimum embedment into the structural framing.
Some claddings, such as stucco and adhered stone veneer, may require additional support between the structural furring strips to facilitate the installation. Wood shingles require a continuous nail base, which is best provided by installing another layer of structural sheathing directly over the insulation in place of wood furring strips.
One of the simplest, most affordable ways to ratchet down your heating or cooling bills is to zip up your attic access stairs. If you don’t access the attic frequently, we recommend one of these low cost systems; Owens Corning makes a similar product.
If you’re in and out of the attic on a regular basis, however, you may want to invest in a pricier, sturdy unit such as this one, used as insulated service doors for roof access. Bilco offers one that should hold up for years of regular use.
Available for under $40 on Amazon, the Attic Stairs Insulation Cover pictured above can reduce energy loss into your attic dramatically.
Publisher’s Note: This content is made possible by our Today’s Homeowner Campaign Sponsors. These companies take sustainability seriously, in both their products and their operations. Learn more about building and buying homes that are more affordable and less resource intensive.