Stabilizing cellulose insulation in an attic is the process of applying the insulation at a density which limits settling to less than 5%. Stabilizing an attic requires more than installing a cellulose product labeled “Stabilized.” A stabilized product must contain a dry adhesive and you must add water during the installation process. Most manufacturers suggest six pounds (approximately 3 quarts) of water to a 30 lb. bag of stabilized cellulose insulation material. However, it is important to note that you should always check with the manufacturer for the recommended ratio of material to water as this will vary from manufacturer to manufacturer.
It is essential to understand the difference between stabilized cellulose products and dry-blown loose-fill products. These two products are governed by different standards. Stabilized products must be tested to ASTM C1497 (Standard Specification for Cellulosic Fiber Stabilized Thermal Insulation) and loose-fill products must be tested to ASTM C739 (Specification for Cellulosic Fiber Loose-Fill Thermal Insulation). The other important difference is the two products have completely different cover charts that are not interchangeable.
For example, here is a stabilized coverage chart at R-19:
R-Value Installed Thickness Settled Thickness Max. Net Coverage Bags/1000 ft2
19 5.38 5.26 58.2 17.2
By comparison, here is a loose-fill chart at R-19:
R-Value Installed Thickness Settled Thickness Max. Net Coverage Bags/1000 ft2
19 6.1 5.4 53.2 20.7
As you can see, at first glance the stabilized coverage chart looks noticeably better than the loose-fill chart. The major difference between the two charts is the loose-fill chart accounts for settling while the stabilized chart infers that settling will be greatly reduced due to the addition of water. A stabilized chart gives a lower “installed thickness” because the material is applied within 5% of its settled density (again-this is only possible by adding water according to the manufacturers instructions). Imagine if you performed a dry installation using this chart. You would install less material than necessary to achieve the desired R-Value. Therefore, if you install attic insulation dry, or with only enough moisture to reduce dust, you must use a product that is designed for loose-fill application and has a loose-fill chart. If you use a stabilized chart for dry-blown loose-fill applications, you will not achieve the specified R-Value and you will cheat the customer.