Blown-In Insulation

Cellulose is recycled paper fiber treated with borates for fire and pest resistance. Loose-fill cellulose runs roughly R-3.2 to R-3.8 per inch and packs tighter than fiberglass, which slows air moving through the layer. The borate treatment also helps it resist mold and insects, though it still has to stay dry.

It is the usual pick for dense-packing walls and for older attics with odd framing. Cellulose insulation installation is dusty work, so the attic hatch gets masked and the blowing machine stays outside with the hose run in.

Loose-fill fiberglass is spun glass fiber, lighter than cellulose at roughly R-2.2 to R-2.8 per inch, so it takes more depth to reach the same R-value. It does not soak up water the way cellulose does, and being lighter, it puts less weight on older ceiling drywall.

Fiberglass fits attic floors with plenty of height and top-offs where the existing layer is also fiberglass. Mixing the two over each other works fine when the old layer is dry.

Empty walls in older homes get filled without tearing off drywall or plaster. A hole goes into each stud bay, from outside under the siding or from inside, then a fill tube packs cellulose to about 3.5 pounds per cubic foot. At that density the fill will not settle, and it slows air leaks through the wall. Exterior walls in older homes are often completely empty, and that is where dense-pack makes the biggest difference.

Fire blocking and blocked bays get mapped first. Live knob-and-tube wiring is a stop: it gets flagged for an electrician before any wall is filled.

When the attic fill is dry and just thin, a new layer goes right over it to the target depth, after air sealing and baffles. Old batts on the attic floor can stay under the loose fill as long as they are dry and lie flat. The full attic checklist is on our attic insulation services page.

Filling an empty wall or floor cavity cuts airborne noise between rooms. Dense-pack cellulose and mineral wool batts both work, and a full cavity beats a half-full one.

Basement ceilings are the common request. Insulation between the floor joists quiets voices and TV noise from the rooms above. Footsteps travel through the framing, so impact noise needs resilient channel or a second layer of drywall as well, and we will say so up front.

Batts are pre-cut fiberglass or mineral wool blankets sized for 16 or 24 inch stud spacing. They work in open, square bays when they are cut tight around wires and boxes, and they leave voids when they are not.

Blown-in fills around obstructions and leaves fewer gaps, which is why it wins in attics and closed walls. In an addition with open framing, batts or spray foam insulation are the usual choice.