Home improvement corner: Insulating your walls
With the arrival of warmer weather, home insulation might not be at the top of your summer-time to-do list. But a little bit of time invested now can pay big dividends over the next several years in terms of year-round comfort and savings on your energy bills.
When people talk about adding insulation to an existing home, the attic is usually the first thing that come to mind. In most homes it's an easy space to access and add the most insulation. But when retrofitting an older home, the walls should not be overlooked. Most homes built before 1930 had no insulation at all.
With some of the insulation options available today, you don't have to tear off siding or drywall to get to the empty stud cavities. Blown-in cellulose or chopped fiberglass allow homeowners to add significant insulation to their walls through drilled holes as small as one inch.
Last summer, as I considered insulation options for my family's renovated 1920s schoolhouse, this was an important consideration. Because we are living in the house as we renovate, tearing out the plaster and gypsum board of the interior walls out wasn't an option; we were already entering the last stages of renovating the interior. Our exterior renovations were only just beginning, so I decided we would insulate the house from the outside, using blown-in cellulose.
Cellulose insulation is made from up to 85% recycled paper fibers. Much of this comes in the form of shredded newsprint. The fibers of cellulose insulation are much finer than fiberglass. When cellulose is blown or dense-packed into walls and ceilings, cellulose takes on almost liquid-like properties that let it flow into cavities and around obstructions to completely fill walls and seal cracks and seams. It easily flows around wires, electrical boxes and pipes and conforms to odd-shaped cavities. So, in addition to adding significant insulation value to walls, it can stop drafts and cold air infiltration during the winter months.
If you think blowing a product made primarily from finely-shredded paper into your walls would be a recipe for fire, you'd be wrong. Cellulose insulation is treated with a flame retardant-usually low-toxicity boric acid. If a fire occurs, the blown-in cellulose and its flame retardants can actually slow the spread of fire and create a two-hour firewall. Studies by the National Research Council of Canada have shown blown-in cellulose insulation increases a wall's fire resistance by anywhere from 22 to 55 percent.
Cellulose insulation in walls once earned a bad reputation for settling over time and leaving gaps at the top of wall cavities, but using the "dense-pack" method to install it both minimizes the potential for settling and wrings the highest r-value from the insulation. Most manufacturers list their recommendations for dense-pack installation. Typically, the method is to drill a series of holes along the height of each wall cavity, every few feet, and fill these working from top to bottom, using plenty of air in the blowing machine to drive the insulation into the cavity.
To get the job done, you'll need to estimate how much insulation you'll need (it's typically sold in 20-pound bales). Again, most insulation manufacturers have data sheets on their websites that give the particulars on estimating the amount of their product needed for a project. You'll also need to rent a blower, which is usually available from the place where you'll buy your insulation. Other necessary tools and materials include eye protection, a dust mask, a ladder, a drill, bits for drilling the size of hole recommended by your insulation's manufacturer, plugs for the holes and a nozzle to funnel the insulation from the blower's hose into the drilled holes in the walls. Some manufacturers sell their own nozzle kits. In my case, I was able to get a 20-ounce drink bottle the same diameter as the hose, secure it to the hose with duct tape, and cut the tapered, capped end of the bottle to the diameter of the holes I drilled in the wall.
And doing an insulation retrofit with blown-in celloluse means drilling holes. Lots of them. In our particular case, the walls are 12 feet tall, with studs on 16-inch centers. All of our exterior walls have blocking in the framing-2x4s that run horizontally between studs-at two and four feet from the floor level, where the schoolhouse's interior wainscoting is secured. There is also some diagonal bracing at the corners of the house. All of these odd cavities require their own holes. Additionally, cavities that are 8' or greater in height should have holes spaced every three-to-four feet along their height, with the last hole being about one foot from the top. For our modest little schoolhouse, this translated into about 280 1-inch holes.The size of the holes you drill will depend on the insulation manufacturer's instructions. For the the particular brand of insulation I chose, the recommendation was a 1-inch hole.
If you're going to be replacing your siding, you can tear it off and drill through the underlying sheathing. If you'd like to keep your existing siding, you can simply remove one row of siding at the height at which you need to drill your holes. For dense-pack installation, this means removing at least a couple courses of siding at different heights. If you have vinyl siding, most hardware stores carry a tool that will let you unzip a row of siding so you can get to the nails that hold it in place. If you have wooden clapboard or a shingle type of siding, you can score or cut the row to be removed along its top edge, where it meets the bottom of the next row, and carefully pry and snap it off. When you're finished with the insulation, you can then nail the siding back in place, then caulk and re-paint the cut edge.
My plan last summer was to drill through the existing clap-board. I knew I was going to replace it. I just hadn't yet decided on a material or method. As I drilled, I used an untwisted wire coat-hanger or my electrician's fish-tape to probe the cavities to check for any additional blocking or obstacles that would require additional holes. This was also helpful in making sure the holes I drilled were centered in the stud cavities, so they would fill evenly.
A word of caution: If you have electrical receptacles or light switches located on exterior walls in your home, be extremely careful about drilling near their respective locations from the outside. You don't want to damage their boxes or nick the insulation of their wiring with your drill bit and create a fire hazard. If you know wiring enters above or below a particular box, drill in the opposite location. And don't forget to turn off the breaker or remove the fuse that supplies power to the receptacle or switch in question.
With the holes drilled, you're ready to start blowing the cellulose into the wall. After all the prep, this is the easy part. With a friend breaking up the bales and feeding them into the hopper of the blowing machine, you place the nozzle into the hole and fill up the cavity.
Most cellulose blowers have a sliding door in the path of the hose connection that allows you to adjust the air flow that propels the cellulose through the hose and into the wall. For the first few holes, it may take some practice to get a feel for the right mix of air and cellulose to keep the hose and nozzle from clogging.
As you fill a cavity, you'll be able to tell that it's getting full when you start feeling some back-pressure build up and stiffen the hose. Eventually, you'll get enough resistance that the cellulose will stop flowing through the hose and you can let your helper know to turn the blower off so you can install a plug and move on to the next hole. The first few times-as you get the hang of it-the nozzle might pop off the wall and cast a nice little shower of cellulose insulation around you and your helper, which makes for a good laugh the first couple times it happens. It's also a good reminder that you should be wearing eye protection and a dust mask.
To complete the project on our house, which is about the size of an average ranch-style home, took two full weekends, with a helper. It was four days of work that have already made a noticeable difference in the past few seasons.
We use our electric baseboards-which supplement the heat from our wood stove-about half as much as we did last winter, and there are far fewer cold spots in our old schoolhouse. This means the house is staying more comfortable for much less money. With some of the warmer days we've experienced lately, the temperature inside our house is consistently cooler than it would have been in the past. I'm looking forward to seeing how the difference will play out in mid-July or August.
Interestingly, there was another benefit I hadn't anticipated. The number of those pesky asian lady beetles that found their way inside the house this spring was significantly less than in past years. The insulation has filled the cavities in the walls where they used to spend the winter, and the boric acid used to as a flame retardant in the insulation is also an insecticide.
If you want to read up on the subject before tackling an insulation retrofit, check out the websites of a few insulation manufacturers. Most have data sheets and installation guides available to download. And find a good book on the subject. Before doing our retrofit, I spent a lot of time with Bruce Harley's "Insulate and Weatherize" (The Taunton Press, 2002), which contains lots of detail about the dense-pack method and lots of additional tips on controlling temperature and airflow in the home.
Of course, as anyone working on an old house will tell you, you're never really "finished" with it. As we continue our work on the exterior this summer, we'll be adding some rigid foam insulation over our recently insulated walls as we prepare to install some new siding and sealing up the exterior surface of the house.
And next summer, I might insulate that crawlspace so the floors stay a little warmer. There's always something to do.