Sidebar: Cellulose Insulation: An In-Depth Look at the Pros and Cons
Checklist and Recommendations for Use of Cellulose Insulation
General Recommendations:
1. Find an installer who uses fiberized cellulose. Fiberized material is less dusty and installs at a lower density, providing higher R-value and more coverage per dollar. Of importance to wet-spray applications, fiberized cellulose can be installed with less water. 2. Specify cellulose made with quality fire retardants. The best fire retardants are borax (sodium borate) and boric acid, used either by themselves or in combination with ammonium sulfate. Avoid cellulose made only with ammonium sulfate, and if ammonium sulfate is used, make sure it is commercial grade chemical, not agricultural grade. 3. Provide a continuous air barrier between the cellulose insulation and the living area (walls and ceilings). In northern climates, the best air barrier is a polyethylene vapor barrier. In southern climates where an interior vapor barrier is not desired, an interior air barrier can be achieved with airtight drywall (sealed edges and joints). 4. Make sure that installers and anyone else working in the house during cellulose installation wear adequate respiratory protection. Simple (single-elastic) dust masks are generally not considered acceptable, especially for men with beards.
Loose-fill Cellulose in Attics:
1. Use low-density, fiberized cellulose to maximize R-value. 2. If available, use stabilized cellulose to minimize settling or shifting of the insulation over time. 3. Do not install recessed light fixtures in ceilings that are to be insulated with cellulose. This is a good recommendation for all insulated ceilings, but especially important with cellulose insulation because of lingering questions about of the permanency of fire retardants. Even IC-rated light fixtures can heat up, especially if the ventilation channels get blocked. 4. If the installed insulation thickness is to be greater than about 12", care may need to be taken to ensure that ceiling drywall will not sag under the weight (either thicker drywall or truss/joist spacing less than 24" o.c.).
Wet-Spray Cellulose for Walls:
1. Design a wall system with adequate drying potential. The strategy you choose should depend on your climate. In northern climates, the cellulose should ideally be able to dry to the exterior, so the exterior sheathing and siding should be permeable to water vapor (e.g., natural wood, exterior gypsum, or asphalt-impregnated fiberboard sheathing, and wood siding). If plywood or OSB sheathing is to be used, it can be made more permeable by drilling holes through it every 2’ or so. In southern climates, the interior should be permeable (e.g. drywall with non-vapor-retarder paint) so that the cellulose can dry to the interior during the air conditioning season. Drying to the interior is also acceptable in intermediate climates as long as a whole-house cooling system is to be used. If the cellulose is installed without adequate drying, see #3 below. 2. Find an installer who installs wet-spray cellulose with a low water content. The installed moisture content should be below 50% on a dry-weight basis (weight of water divided by weight of dry cellulose). That means that water use should be less than two gallons of water per 30-pound bag of cellulose. Even better are processes with lower water use. By using fiberized cellulose and a binder that activates on contact with water, the moisture content can be as low as 28% (about one gallon per bag). 3. Do not cover installed wet-spray cellulose with an inner wall surface right away. Allow the insulation to dry for at least 48 hours—longer if it was installed very wet or if the wall system does not provide good drying potential. You may want to use a dehumidifier to speed up drying.
