Dedicated to sustainable,
high performance building

Insulating walls with dense pack cellulose

Time for some respect

In 2005, Metric Homes of Carp, Ontario designed and built Canada’s first Energy Star labelled home in Canada. This home was built with dense-packed cellulose as the wall insulation of choice. Their intent was to produce a better built home with a goal of creating “a proper balance between additional efficiency and price such that it would be attractive to future clients “.

By Phillip MacCallum


Dense pack cellulose insulation can be a superior product to commonly used batt insulation, but somehow it has developed a bad reputation in Canada. Cellulose fibre insulation [CFI] is like the Rodney Dangerfield of insulations, it “can’t get no respect”.
When done right, dense blown cellulose is a highly efficient option for insulating exterior walls.  It gives good thermal performance [R3.5-3.8/inch], and slows air flow through walls making your house cheaper and easier to heat and cool. In addition, the high density of packed cellulose can provide a better sound barrier than batt insulation.

Modern CFI production began in the 1970s and has been commonly used in roofs across the globe, and in walls throughout the US and Europe. When cellulose is densely packed [3.0lbs/ft3 or 48kg/m3 or greater], it is an excellent wall cavity insulation that provides good R value at a reasonable cost. However, it is seldom used in Canada despite its reasonable cost and efficiency.
It has been unfairly criticized for its ‘settling’ issues, and risk of mould and flammability. These criticisms are largely baseless, and dense blown cellulose for wall cavities should be more common in Canada than it is today.

The concern of cellulose in wall cavities settling is probably the biggest misconception, though it is one that originates legitimately because that’s what used to happen when it was blown into walls loosely, as it presently is in ceilings. Cellulose in walls is packed in so that it is, in effect, under pressure and cannot settle, thus maintaining the overall performance of its installed R-value. Any warnings on packages of settling refers to cellulose loose-blown in ceilings.

CFI is commonly manufactured with borate, which is a fire retardant that also resists mould and and insects. In fact borate, in small amounts, has been determined to be largely harmless. Most common foods contain borates at concentrations of 1-20 ppm, so we ingest up to 1 mg/day in our normal diets,2  and it is certainly less harmful than many toxins found in various adhesives and finishes commonly used in housing construction.

Phillip MacCallum is a contributor to ecoHouse Canada affiliate website