An excellent question from Patricia in Ohio on wall cavity insulation (BTW, folks, you can feel free to post your questions here rather than emailing them. Chances are, other people have the same question, too. We’ll do our best to post an answer.):
“Wouldn’t packing your walls with old newspapers [i.e. cellulose insulation] increase the fire risk in a wood-framed house?”
Counter-intuitive as it may be, the answer is a resounding NO! Use of cellulose insulation, which is made out of recycled newspapers, actually reduces fire risk, and addresses a host of other problems. Here’s why:
The recycled newspaper (or other paper fiber) is treated with a fire retardant called borate, which is a naturally occurring non-toxic mineral. This means that the insulation is effectively non-flammable, so when it comes into contact with a flame it forms a scorched crust, which actually slows the progression of fire. Additionally, correctly installed cellulose is packed so densely into the wall cavities that it inhibits the movement of air. We all know that fire needs oxygen to burn, so densely packed cellulose slows the progression of fire in two ways.
If you’re not convinced, or you just want to see some firemen burning some houses down, take a look at this great video that compares how quickly fire consumes otherwise identical un-insulated, fiberglass insulated and cellulose insulated houses. The cellulose insulated house took about 25 minutes longer to succumb to fire – that’s translates to a lot of extra time to save your house, and seconds count to get yourself and your loved ones to safety.
As if that wasn’t enough, the borates in the cellulose product can kill insects, and squirrels, rats and other rodents don’t like to nest in it, so by insulating with cellulose you are taking a step towards eradicating pests.
Insulation is good—and cellulose is a great choice for many applications. Fiberglass and foam insulation each have their places, too–we use them both in addition to cellulose. What is important is to understand the needs, abd the correct application of whatever you’re using. And for goodness sake, remember that insulation doesn’t work properly without air-sealing.