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Spray Foam Insulation vs. Wet Blown Cellulose

If you’re reading this blog, chances are you have some familiarity with spray foam insulation. But what about other insulation options that might be available to you, like wet blown cellulose? For those of you who don’t know about this product, it is ground up, recycled newspaper that has a dry adhesive that is activated with water when it is blown into place. While it is very different from spray foam insulation, some builders will use it as an alternative to spray in foam insulation.

Before we go on, watch the short video below to get an idea of how wet blown cellulose is installed:

As you can see, this product installation is on the messy side! That’s because about 50% of the weight of blown cellulose is water. If you’re thinking that all that moisture could potentially cause moisture issues, you would be right! This study conducted by The Canadian Housing Information Centre on “Wet-Sprayed Cellulose Insulation in Wood-Frame Construction” found the framing material can have the moisture content more than double and that it may take as long as five months to get the framing back to pre-installation levels.

To put this in perspective, imagine it is in the middle of a humid summer. If you spray a product that is 50% water into your new home, does this seem like a good idea? Are you willing to potentially put your project behind or on hold for several months to allow for proper drying?

You can conduct a practical test of this on your own in just a few minutes. Take some newspaper and weigh it. Then add the amount of water needed to double its weight. Once saturated, place it in your garage or basement and see just how long it takes to dry out.

Pit Falls of Wet Blown Cellulose

The study also concluded wet blown cellulose is not an effective air barrier. Related to this, we have seen some cellulose contactors still using small cans of spray polyurethane insulation to air seal new homes!

With respect to wood moisture, the study reported “Sections of the frame adjacent to the dry insulation showed normal absorption and drying rates. After the wet-sprayed cellulose was installed, the plywood’s sheathing moisture level increased to 26% after 30 days, decreased to near original levels (15%) after 160 days and dried 1% more by the end of the test (420 days).”

Moreover, it concluded the “wet-sprayed cellulose insulation nearly saturates wood framing, but within six months the framing will dry almost to the level before installation, even during winter.”

Now, keep all of this in mind and let’s add a 3mil sheet of plastic to serve as a vapor barrier over the wet-sprayed cellulose to meet vapor barrier building code requirements. According to CertainTeed Corp., one of the largest insulation manufacturers in the county, adding vapor retarders significantly slow the drying process.

Another potential problem caused by wet-sprayed cellulose is moisture damage. For one, it doesn’t seem like a good idea to have all that moisture on the fasteners, wiring, duct work or plumbing, as it poses a risk for rust.

And then there’s the issue of mold. To create mold growth, you need:  a food source, water and the right temperature (32°F to 120°F). When you choose wet-sprayed cellulose, you have all of these points covered, with the paper and wood framing serving as the food source, and the water used during installation as the water source. Are you ready to cover your walls with plastic and dry wall and potentially lock mold behind your new walls? Knowing that mold can lead to health problems, it’s important to prevent exposure in your home when possible.

We know you have a variety of products to choose from when selecting an insulation product for your home or building. And each comes with its own set of pros and cons. We just recommend you consider these points before you decide which insulation system to use. If we can help answer any questions you may have, let us know!

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