Blown-In Insulation in the Bay Area

Everything You Need to Know About Blown-In Insulation

Blown-in insulation, also called loose-fill, arrives as small tufts of fiber rather than pre-cut pieces. A hopper machine breaks up compressed bales and pushes the material through a long hose, so the installer can lay down an even layer across a wide area from one spot. The two common materials are loose-fill fiberglass and loose-fill cellulose. Both are well suited to attic floors, where the insulation simply rests between and over the ceiling joists instead of having to stay upright inside a wall.

With loose-fill, R-value comes from installed depth and density, not a number printed on a blanket. Every bag carries a coverage chart listing, for each target R-value, the minimum thickness, the minimum weight per square foot, and how many bags a given area should take. Loose-fill fiberglass typically delivers roughly R-2.2 to R-2.9 per inch, so it needs more inches than cellulose to reach the same rating. Depth rulers stapled to the framing let you climb up afterward and confirm the coverage matches the plan.

The work done before the hose comes out matters as much as the insulation. Fibrous insulation slows heat flow but does little to stop air, so the attic floor gets sealed first: gaps along top plates, holes for wiring and plumbing, recessed light housings, and bath fan boxes. Next come baffles at the eaves, which keep loose-fill from spilling into the soffit vents and choking off attic ventilation. Skip these steps and you can end up with a thick, tidy-looking layer that still lets conditioned air escape.

Some things in an attic have to stay uncovered. Recessed lights that aren't rated for insulation contact need open space around them, typically about three inches, and furnace or water heater flues need a sheet-metal dam holding material back at the clearance the manufacturer and code require. The attic hatch gets a raised dam too, so insulation doesn't pour down when it opens. All loose-fill compacts slightly after installation; manufacturers' charts account for this, and blowing to the listed depth keeps the layer on target once it settles.

Blown-In vs. Other Options for Your Attic

Batts work well where joists are evenly spaced and the attic is easy to move around in, but every seam, cut, and obstruction is a chance for a gap. Loose-fill has no seams. It flows around wiring, blocking, and cross-bracing and fills odd-shaped bays without trimming. Blown deep enough, it also buries the tops of the joists, cutting the heat that conducts through the wood framing. In attics with tight corners or a low roof pitch, those advantages usually tip the decision toward blown-in.

Picking between fiberglass and cellulose loose-fill comes down to a few trade-offs. Cellulose packs more insulating value into each inch, and its denser layer slows air movement better, but it weighs more and settles more over time. Loose-fill fiberglass is light, shrugs off moisture, and settles very little, though it needs a deeper layer for the same R-value. Either performs well when blown to the correct depth over a sealed attic floor, and we will explain which suits your framing, ceiling, and attic conditions.

If the existing insulation is dry, clean, and free of rodent droppings, new loose-fill can usually go right on top of it. If it is contaminated, water-stained, or packed down from years of storage and foot traffic, removal is the better path, because burying a problem under fresh material keeps it in the house. Both situations are common in older Bay Area homes whose attics were insulated decades ago. Houses without an attic, such as many Eichlers with low-slope roofs, are a different case, since there is no attic floor to blow onto.

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:

• attic insulation removal and replacement
• cellulose insulation
• batt insulation installation
• attic cleaning and cleanup

We do blown-in attic 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.