Q&A: Choosing Cellulose Insulation

A.Bill Rock Smith, building consultant and former contractor, responds: The thermal performance and installed costs for dense-pack cellulose and damp-spray cellulose are similar. With both methods, the quality of the job is considered "installer sensitive," since cellulose needs to be installed at the correct density to avoid settling.

The disadvantage to damp-spray cellulose is the addition of moisture to the wall. Because of this added moisture, cellulose manufacturers recommend waiting at least three days before hanging the drywall. Since dense-pack cellulose is installed dry behind a netting or reinforced polyethylene, the drywall can be installed immediately. However, since it takes extra time to install the netting or poly, the total time required for a dense-pack installation can be about the same as a damp-spray job with the drying period.

Dense-pack cellulose is prone to creeping onto the face of the framing or pushing the netting or poly beyond the face of wall, which can make drywall installation difficult. This is rarely a problem with damp-spray, since the excess material is scraped flush with the framing face using a scrubber.