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The Insulation Lab

Dense Pack Cellulose – Cellulose Reborn

Jeff Aderholdt - Thursday, August 25, 2011

As energy costs have increased, so has interest in improving insulation techniques. One such insulation technique that is gaining popularity is what is called “dense-pack cellulose”. Dense-pack cellulose is a technique that allows an insulation installer to blow cellulose insulation into wall cavities of new homes during the construction, before the interior paneling or drywall is installed. In a 2 X 6 wall, dense-pack provides an R-value of about R-21. With the dense-pack technique, the performance advantages of cellulose insulation is now available for the new home builder. That's right! Cellulose, it's not just for remodeling anymore!


Cellulose – A Brief History

Cellulose has been an insulation contractors mainstay in retrofit insulation applications for decades. What made cellulose initially attractive was the cost, due to its being made from recycled materials. It soon became apparent that cost wasn't the only advantage. This was especially noticeable in blowing cellulose insulation into walls.

The first noticed advantage that cellulose had in a retrofit wall insulation application was how well it filled in voids. Blown fiberglass had a tendency to hang on to nails and other obstructions in the wall cavities. This would create uninsulated pockets. The more obstructions, the more potential for missed voids. This was especially a concern with older houses with lathe and plaster walls. Unlike fiberglass, cellulose would flow nicely around most voids and provide an uniformly insulated wall.

In order to eliminate settling problems that early techniques had, insulators starting installing the cellulose insulation in a way that packed it in the wall cavities. If packed at greater than settled density, the insulation wouldn't settle. This made another advantage of cellulose apparent. When cellulose was packed in this manner, the houses were noticeably less drafty. Studies showed that when cellulose was packed in such a way air movement through it was virtually eliminated. Fiberglass, though it slowed the air movement, could never reach this level of performance. The less air leaks, the less the heat loss. The less heat loss, the lower the energy bills. The lower the energy bills, the happier the customers.

Cellulose in New Construction

When the performance benefits of cellulose became apparent, many insulation contractors started thinking, “how can we use this on a new house?”. Attic insulation wasn't a problem, but what about walls? Some inventive contractors starting experimenting with a variety of methods. One man made plastic panels with holes in them that he would anchor against the walls, blow the cellulose through the holes until packed, then take down the panel and move down the wall (no, the insulation didn't fall out). Others developed a wet-spray technique: the cellulose was dampened with a mixture of water and adhesive and shot in the open cavities, then the excess would be trimmed flush to the studs. It seemed promising, but, especially in cold climates, there were concerns over cold weather application and the trapping of water inside the walls. Though there are those that still use wet spray for some applications, many cellulose installers and manufacturers backed away from it, especially in cold climates. Installers started looking for ways to install cellulose in new walls without the water.

The first incarnation of dense-pack cellulose involved installing heavy reinforced poly to the walls, stapling a lot with roofing staples, cut a hole big enough for an insulation pipe and blowing it full. When you were done blowing, you would tape and repair the holes in the poly. For a few years, that was the way to do dense-pack. One drawback became apparent. The air involved in blowing did not have anywhere to go. This lead to excessive stretching and bulging of the poly. The air pressure also had a tendency to push the insulation down from the top creating voids at the top plate. An installer needed to watch for these so they wouldn't be missed. That lead to the second incarnation of dense-pack.

The next incarnation of dense-pack cellulose was almost the same, but with one significant difference, the heavy poly was replaced with a fabric that let the air out during the blowing process. Because air pressure was being released, the stapling required with the reinforced poly was no longer needed. Conventional staplers replaced the roofing staplers. Because the fabric was not stretchy like the poly, the bulging, or pillowing was greatly reduced. When the blowing was completed, a layer of conventional construction poly was installed for a vapor barrier. Thus was born dense-pack cellulose insulation as we know it today.

Why Dense-Pack Cellulose

Because of the extra labor involved, dense-pack cellulose is a little more expensive than fiberglass batting. So why do it? Is it really worth it? As mentioned in the “Birds, Bees and Energies” article, the most important aspect of an insulation job is to control convection, air movement. This is something fiberglass just can't do. Dense-pack so effectively controls convection that it rivals spray foam in performance, for a fraction of the cost. So, rather than comparing dense-pack to fiberglass, one needs to compare it to spray foam. When put in perspective, comparing cost and performance, dense-pack cellulose proves to be a value in home construction.

At NTC, we have worked with a variety of techniques, including dense-pack cellulose. We know what will work best for your home. Give us a call and ask us about dense-pack cellulose by NTC for your home, or have your building contractor give us a call. Let us show you why NTC is the best choice for all your insulation needs.

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