Fill those empty spaces!

Insulate walls, save money

Insulating his first home in Schenectady kept this columnist warm throughout New York’s harsh winter.

Insulating his first home in Schenectady kept this columnist warm throughout New York’s harsh winter.

Photo by Greg Kallio

Sustainable Space columnists Lori Brown and Greg Kallio are professors in the College of Engineering, Computer Science and Construction Management at Chico State University.

Several people have recently asked me about insulating exterior walls in their homes. My reply? Fill ’em up! I suspect many older homes in the area have empty 2-by-4 walls. Insulating them can cut heating/cooling bills by up to 30 percent, and reduce the likelihood of condensation in the wall cavity. Based on a cost-benefit analysis, insulating the attic to at least R-30 is most important, followed by insulating walls and replacing single-pane windows. Insulating the floor is usually less important, especially in moderate climates such as ours.

Here’s the drill
In a previous Sustainable Space, I described my adventure of insulating the walls of our first home in chilly Upstate New York by renting a machine to blow cellulose insulation into each stud space. The laborious effort involved drilling holes through the brick facing of the house and later patching the holes with mortar. I drilled two holes per cavity and filled from a lower hole until insulation spewed out of the upper hole. Then I filled from the upper hole to increase the packing density. I don’t necessarily recommend that you do this yourself. Hiring skilled professionals will probably result in a higher R-value due to their expertise in achieving a uniform and optimum packing density. Make sure to get several quotes before hiring someone, as the price and method may vary.

Hire a pro
In Chico, I found three vendors who will insulate existing walls: Chico Insulation & Fireplaces, Loerke Insulation and Meek’s. Each primarily uses blown-in, loose-fill fiberglass that is specially prepared for this application, such as Certainteed Optima and Knauf Perimeter Plus.

The injection process can be done from inside or outside the home, depending upon the exterior siding, interior wall covering, and the preference of the vendor and customer. Drilling through stucco siding presents some special considerations since the water-resistant membrane will be perforated. Any holes should be patched and flashed in a way to prevent subsequent water infiltration. Be sure to discuss this before contracting to determine who is responsible for the patching. One vendor prefers inside wall injection in this case to avoid the problem altogether.

The blown fiberglass insulation can produce an R-value of about R-14 in a 2-by-4 wall if the optimum packing density is achieved. (An empty 2-by-4 wall has an R-value of about R-3!) Properly insulated, your home may be noticeably quieter since there will be some sound-dampening benefit. Within every home lie obstructions in the wall due to blocking, electrical wires, and pipes or ducts. It is up to the vendor to detect these obstacles and work around them to fill up the cavities to the optimum density. This may require some additional holes.

Price tag
Of course, the cost depends on the total wall area. Local vendors gave ballpark estimates of around $1-plus per square foot of wall area for 2-by-4 construction. This equates to about $1,000-$1,500 for an average-sized home. Keep in mind that PG&E will pay a modest rebate of 15 cents per square foot. With a typical payback of around five years, it’s a no-brainer!