Installing Dense-Pack Cellulose

1 of 16

This truck is equipped to install either damp-spray or dense-pac… Read More This truck is equipped to install either damp-spray or dense-pack cellulose.

The hopper that feeds material to the operator can be filled to … Read More The hopper that feeds material to the operator can be filled to the ceiling, providing enough material to last from 15 minutes to an hour, depending on the application.

Netting is stretched tight between framing members to minimize b… Read More Netting is stretched tight between framing members to minimize bulging of the cellulose.

Netting is fastened with a pneumatic upholstery stapler.

The closely spaced fasteners are driven at an angle just beyond … Read More The closely spaced fasteners are driven at an angle just beyond the outer edges of the faces of framing members. This “inset stapling” helps draw the material taut and prevents the cellulose from pushing beyond the framing.

The tension of the netting against electrical boxes is enough to… Read More The tension of the netting against electrical boxes is enough to prevent them from filling with insulation when the cavities are packed; the netting will later be cut by the drywall crew.

A skilled installer can snugly fit the netting around joists, co… Read More A skilled installer can snugly fit the netting around joists, collar ties, and other obstructions. As long as the material is tight and securely stapled, small gaps won’t leak significant amounts of insulation as the cavities are blown full.

In complex areas, like the peak of this Queen Anne tower (below)… Read More In complex areas, like the peak of this Queen Anne tower (below), netted dense-pack can be a cost-effective alternative to spray foam.

Wall cavities are filled first from the bottom to the midpoint o… Read More Wall cavities are filled first from the bottom to the midpoint of the wall.

Next, cavities are filled from the top back to the middle.

After a cavity is filled, the operator uses a remote control to … Read More After a cavity is filled, the operator uses a remote control to momentarily turn off the blower, then quickly inserts the hose into the next cavity before switching it on again.

Filled cavities are compacted with an aluminum roller to avoid b… Read More Filled cavities are compacted with an aluminum roller to avoid bulging drywall. A quick pass of the hand is enough to confirm that the insulation lies flush with the framing.

When filling rafter cavities, the usual insertion point is just … Read More When filling rafter cavities, the usual insertion point is just above the top plate. The natural curvature of the longer hose required tends to direct the flow of insulation to one side of the cavity, so filling it uniformly requires a second pass with the curve facing the other way.

The hose is visible behind the netting in the photo at right.

A strip of netting between a top-plate nailer and the facing joi… Read More A strip of netting between a top-plate nailer and the facing joist makes it possible to dense-pack this area of the band joist.

Netting stapled between the joist ends is filled with cellulose … Read More Netting stapled between the joist ends is filled with cellulose to form insulating and air-sealing “pillows”.

Blowing Wall Cavities

For most applications, the 3-inch hose from the truck is stepped down to 2 inches at the business end. Hoses as small as 11/4 inch can be used for narrow cavities (tighter cavities are filled with low-expanding one-part spray foam). The operator makes a small slit in the netting just big enough to provide an entry point for the sharply angled tip of the hose, which he pushes to the bottom of the cavity. A control box on a lanyard around the operator’s neck contains a combination switch that operates the blower and the cellulose feed mechanism. When both are turned on, cellulose quickly begins flowing into the netted cavity.

Judging when the correct density is reached is a matter of feel and isn’t easy to describe, but if the pressure on the blower is set correctly, the flow of material begins to slow and the sound will change, alerting the operator to begin withdrawing the hose while keeping the cellulose flowing. Once the cavity has been halfway filled and the end of the hose is just inside the insertion hole, it’s redirected upward, shoved to the top of the cavity, and then withdrawn as it fills from the top back to the middle.

When the cavity has been packed full all the way to the insertion point, the operator shuts off the blower, shoves the hose into the next cavity over, and repeats the process. There’s no need to plug the entry holes in the netting; properly installed dense-pack is so compact it won’t fall out on its own even if the netting is removed.

All of that happens fast, practically in one continuous motion. It has to, because if the hose is left in one place too long, the material inside it will begin to back up and bind together. An inexperienced or careless operator can pack the hose full all the way back to the truck, creating a mess that may take hours to clear.

You can tell when a cavity has been filled to the right density by feeling it through the netting with the palm of your hand. It should be solid but have some give to it, somewhat like a firm mattress. If everything has been done right, the netting shouldn’t bulge noticeably beyond the framing. But some bulging is unavoidable, so each cavity has to be rolled flat with a heavy aluminum roller — a task we jokingly describe as the company fitness plan. A couple of quick passes up and down is usually all that’s needed, but it adds up when you’re talking about a whole house, especially if there are sloped or flat ceilings to deal with.

Rolling may seem like an afterthought, but it’s something we take seriously. The one guy who can really hurt my business is the sub who comes on the job after I leave. If the drywallers complain to the GC about having to flatten the insulation themselves, it makes us look bad. Worse, if they ignore slight bulges and just hang the drywall over them, the pressure exerted by the cellulose will eventually cause the fasteners to pop through the paper facing, especially with 1/2-inch-drywall. That makes us, the drywall crew, and the GC all look bad. Taking the time to roll the cellulose really flat saves trouble all around.

Working Overhead

Blowing a cathedral ceiling is similar to working on a tall wall, except that there’s usually no way to start in the middle of the bay. The nozzle ordinarily goes in just above the plate and is pushed all the way to the peak, with work proceeding from the top down. If there’s no ridge board at the peak, we’ll push the nozzle high enough to let us blow material over the top and down the other side. This will fill the cavity most of the way, but we will still need to come into it again from the other side to “touch up” the density to the right level.

When the rafters are spaced 24 inches or more on-center, we make two passes along each cavity, because the natural curvature of the hose causes it to flop to one side, depositing more material there than on the back side of the curve. Once the hose has been withdrawn the length of that side, we twist it so the curve faces the other way and push it back to the peak, then pack the cavity to its final density.

It’s generally cheaper to insulate a ceiling with loose-fill than it is to dense-pack it, but overhead rafter cavities are sometimes insulated for soundproofing, or if an attic will be floored to provide storage space. Gravity makes it more likely that the insulation will bulge beyond the framing in the ceiling, but it’s difficult to use the roller overhead. To avoid putting any pressure on the ceiling drywall, we have the builder strap the ceiling after we’ve stapled netting to the undersides of the joists, but before we blow the cavities. That restrains the cellulose and ensures that any bulges that do form won’t push out against the drywall.

Another benefit of dense-packing the ceiling is that it insulates and helps air-seal the band joist area at the same time. Even if we’re not going to do the entire ceiling, we’ll usually net and fill between the two outermost joists that run parallel to an outside wall. To insulate and air-seal the spaces between the joist ends, we’ll often create “pillows” of material by folding and stapling netting into place before filling it with dense-pack. This requires some time-consuming origami, but it lets us do this part of the job on our own schedule with materials we already have available. It often means that we don’t have to bring in a foam sub at all, which saves time and money in the end.

Jonathan Tauer owns Cellu-Spray Insulation in Florence, Mass.