How to Insulate Your Attic

Go into your attic and measure the depth of existing insulation. Fiberglass batts are about R-3.2 per inch; loose-fill cellulose is about R-3.5 per inch. Check your climate zone on the DOE insulation map — most areas need R-38 to R-60 total. Calculate how many inches you need to add. For blown-in cellulose, the bags list coverage at different R-values per bag.

Before adding insulation, seal all air leaks from the living space into the attic. The biggest culprits: gaps around electrical wires and pipes penetrating the ceiling, the attic hatch perimeter, recessed light housings, and the tops of interior wall cavities. Use expanding foam sealant for gaps around pipes and wires. Use metal flashing and high-temperature caulk around anything that generates heat (exhaust flues, recessed lights).

If your home has soffit vents (vents in the eave overhang), install polystyrene rafter vents (baffles) in each rafter bay where the roof meets the attic floor. Staple them in place. These vents create an air channel from the soffit to the attic space, preventing insulation from blocking airflow. Proper attic ventilation prevents ice dams and moisture buildup.

Rent a blowing machine from the hardware store (usually free with a purchase of 10+ bags of insulation). Position the machine outside near the attic access. Feed the hose up through the attic hatch. One person operates the machine below, feeding bags of insulation into the hopper. The other person directs the hose in the attic. The machine breaks up the compressed cellulose and blows it through the hose.

Start blowing insulation at the farthest point from the attic access and work backward toward the hatch. This prevents you from having to walk over freshly blown insulation. Aim for an even depth — use a depth gauge (a marked stick) to check depth as you work. Fill all areas evenly, including around ductwork, plumbing, and between joists. Don't block soffit vents (the rafter baffles you installed protect them).

The attic hatch is often completely uninsulated — a major heat loss point. Cut rigid foam board to fit the back of the hatch and glue it on (two layers of 2-inch foam = R-20). Apply adhesive-backed foam weatherstripping around the hatch frame so the door seals when closed. If your attic access is a pull-down staircase, build an insulated box that sits over the opening from inside the attic.

Check the entire attic one final time for even coverage. No joist tops should be visible — insulation should be above the joist line everywhere. Verify rafter baffles are still unblocked. Remove the blowing machine hose and clean up any spilled insulation. Note the date and R-value achieved on a label stuck inside the attic hatch for future reference.