How to Blow In Attic Insulation

Every bag lists coverage at a given R-value on the label — for example 'covers 32.4 sq ft at R-49'. Divide your attic square footage by that number and add 10% for settling and waste.

As a rough check: a 1,500 sq ft attic going from bare to R-49 usually takes 55–75 bags of cellulose or 70–90 bags of fiberglass. Rentals are typically free with 10–20 bags purchased, so DIY almost always beats renting for cash.

Air seal, install baffles, dam off recessed cans and flues, and staple depth rulers to the framing every 8–10 feet. Once the hose is running you will not be able to see the joists.

Lay a walk board or insulation stilts across the joists. Stepping between joists puts a foot through the ceiling — the classic and expensive mistake.

One person stays at the machine on the ground or in the garage, cutting bags and feeding the hopper steadily. The other works in the attic with the hose. Use phones or two-way radios; the machine drowns out shouting.

Start at the far corner and back out toward the hatch. Hold the hose at about a 45-degree angle roughly 2–3 feet above the joists and sweep — do not point it straight down or you will build hills and valleys.

Blow the perimeter first while you can still see the top plates, filling right out to the wall but not into the baffles. The eaves are where heat loss and ice dams start.

Finish flat across the field of the attic and check your depth markers from several angles before you shut the machine down. Returning a half-used bag is easy; renting the machine twice is not.

Vacuum the hatch area, shower in cool water, and wash work clothes separately. Cellulose dust is not itchy like fiberglass but it is filthy.