Dense Pack Insulation

How Does Dense Pack Insulation Work?

Dense Pack, or Drill and Fill, refers to a method of insulating the exterior walls of a home by blowing loose fiber insulation, usually cellulose, into the wall cavities at high pressure. Though it is necessary to drill holes into every wall cavity in order to fill the cavities, dense pack is by far the least invasive and lowest cost method for installing insulation into the walls of an existing home.

Cellulose Insulation Works Best

Cellulose, made from recycled paper, is by far the most common material used for dense-pack insulation. Unlike most other fibrous insulation materials, cellulose maintains its R-value (ability to resist heat transfer) under compression. In the last five years, some fiberglass insulation products have been developed to compete with dense pack cellulose, but cellulose remains the preferred material for dense pack. The cellulose is manufactured in bales of about 20 pounds, and is fed into a machine with a hopper and blower that discharges the unconsolidated fiber through a hose at high pressure. The tip of the hose is inserted into the wall cavity, filling the wall cavity with insulation. Unlike fiberglass batts and most other insulation products, when dense-pack cellulose is properly installed in a wall assembly, the insulation can do a good job of reducing air movement through the wall. This characteristic helps older homes achieve wall insulation quality that equals or exceeds most standard new construction. Since walls make up most homes’ largest exterior surface, many homes built before the 1970s were constructed without wall insulation, and reductions in air leakage, dense pack wall insulation often makes a bigger difference in energy savings and comfort than any other single measure, and often qualifies for rebates from utility programs that offset a substantial portion of the cost.

How Dense Pack Insulation is Installed

Dense pack insulation can be installed from the inside or outside of a home. If done from the inside, holes are drilled through the existing plaster or drywall, which are then plugged and will need to be refinished and painted after insulation work is complete. If done from the outside, installers will often remove siding or shingles and drill through the wall sheathing underneath the siding, replacing the siding after plugging the holes. It is also common for installers to drill through the exterior of stucco and older wood-sided homes, plugging the holes with stucco masonry or two part resin. In most cases, whether the siding is removed and reinstalled, or the outside of the house is drilled through, finishing and painting are typically required.

Dense Pack Insulation Being Installed Outside

Dense Pack Cellulose Can Be Blown In From The Exterior of a Home.

Dense Pack Insulation Being Installed Inside

Dense Pack Cellulose Can Be Blown In From The Interior of a Home.



Best to Coordinate with Other Work

Since finishing and painting are a required component of most drill and fill insulation projects, it is best to coordinate insulation with other improvements. If you are already considering repainting (inside or outside) or installing new siding, this is the best time to add insulation to your exterior walls. If you have plans to insulate, remember to factor in the cost of finish and painting into the equation – these services can be as expensive as the insulation, unless you plan to do the work yourself.


Copyright September 2014 by Advanced Home Energy

If you would like to use this article on your own website, please give Advanced Home Energy credit and a link.


Energy Upgrade California Participating Contractor

Lead Safe Logo

Efficiency First Founding Logo

CaliforniaFirst Registered Contractor