Cellulose Insulation in the Bay Area

Everything You Need to Know About Cellulose Insulation

Cellulose insulation is made mostly from recycled paper, largely newsprint, shredded into fine fibers and treated with borate compounds. That treatment is what makes it practical: it helps the material resist fire, discourages insects, and helps inhibit mold on the fiber. Cellulose ships in compressed bags and is installed with a blowing machine, either as loose-fill on an attic floor or packed tightly into closed wall and floor cavities. As loose-fill it typically provides roughly R-3.2 to R-3.8 per inch, more than loose-fill fiberglass at the same depth.

Dense-packing is cellulose's signature application. To insulate a finished wall without removing drywall or plaster, the installer drills a small hole into each stud bay, inserts a tube, and blows fiber in at high density until the cavity is full and firm. Packed that tightly, the material resists settling inside the wall and fills around wiring, blocking, and irregular spaces. For older Bay Area homes built before wall insulation was common, it is one of the few ways to insulate exterior walls without a major remodel.

Density gives cellulose an edge in how it handles air. Its fine fibers sit close together, so a cellulose layer resists air moving through it better than a fluffier fiberglass layer of the same thickness. That helps cut down small drafts and air currents within the insulation itself. It doesn't replace proper air sealing, which still has to happen at the ceiling and top plates, but it does mean cellulose holds its performance well once installed. Inside walls, the same density provides a modest sound-dampening benefit.

Loose cellulose settles after installation as the fibers compact under their own weight. Manufacturers account for this by printing both an initial installed thickness and a settled thickness on the bag for each R-value. Installers blow to the higher initial depth so that, once the layer settles, it still reaches the target, and attic depth rulers make that easy to verify later. Dense-pack in walls behaves differently: because the fiber is compressed tightly as it goes in, there is very little room left for it to sink.

Cellulose vs. Blown Fiberglass, and What to Watch For

Compared with loose-fill fiberglass, cellulose usually reaches a given R-value in fewer inches, and its heavier layer does more to slow air movement. Fiberglass, on the other hand, is much lighter, settles less, and doesn't soak up water. Cellulose also kicks up more dust during installation, while fiberglass fibers are the bigger skin irritant. Neither is universally better. The right choice depends on the space, the ceiling below, and how reliably dry the attic stays from one year to the next.

Moisture is cellulose's main weakness. Paper fiber absorbs water, and wet cellulose clumps, loses much of its insulating value, and can hold dampness against wood framing and drywall. That is why any roof leak, plumbing drip, or condensation problem needs fixing before cellulose goes in, and why a good inspection looks closely for water staining. Most Bay Area attics stay fairly dry, so this is rarely a dealbreaker, but it is a reason to keep up with roof maintenance after the insulation is installed.

The borate treatment gives cellulose good fire resistance for a paper product, but it is still treated fiber, not stone, so it can char and smolder under enough heat. Clearance around non-IC recessed lights and flues applies just as it does with other insulation. Borates discourage insects, though they won't stop rodents from tunneling through. Weight is another consideration: cellulose is heavier than fiberglass, so a deep attic layer over thin ceiling drywall on widely spaced joists is worth checking first.

Other Services Homeowners Ask About

Most projects involve more than one service. These are the ones our Bay Area crews pair with this work most often:

• blown-in attic insulation
• attic insulation removal and replacement
• Rockwool insulation
• attic cleaning and cleanup

We do cellulose insulation across the Bay Area from four offices, on the Mid-Peninsula, in the South Bay and East Bay, and in the North Bay, San Francisco and Oakland.