DIY Blown Insulation For Attic Joists

Choose a type of loose fill insulation. Compare costs and insulating values, measured in R value for resistance to heat, of cellulose, fiberglass or rock wool. Cellulose has R value of 3.2 to 3.8 per inch and requires 10 to 12 inches to reach the desired level of R-38. Fiberglass pellets are 2.2 to 2.7 and need 14 to 17 inches for R-38. Rock wool is 3 to 3.3 and needs 11 1/2 to 13 inches for R-38.

Get the square footage of the attic using a tape measure. Multiply length by width, then factor in the number of inches needed to determine how much material to buy. Most manufacturers label bags with coverage per bag, which will vary with the type of material and manufacturer. Fiberglass, for instance, may require fewer bags than cellulose even though the insulation value per inch is less.

Cover the vents at the edge of the attic, usually into a soffit on the eave of a roof. Seal all other areas of the attic where air might leak in or insulation might seep out. Shield electrical outlets such as ceiling lights and block off chimneys or heat exhaust vents with fire-resistant material. Make sure no loose fill insulation comes in direct contact with heat sources.

Rent equipment to blow in insulation from an equipment rental or building supply outlet. These machines have a hopper where insulation is dumped in, with a blower motor and a long flexible hose which is used to guide the insulation into place. Wear full protective material; polystyrene or similar coveralls, a dust mask, goggles and ear plugs. Lay 2-by-12-inch boards or plywood panels across roof joists or truss bottom chords to prevent accidentally stepping onto ceiling material.

Get the hose into the attic, through some opening; attics often have pull-down stairs or similar entries from inside a house or you can pull the hose through a side vent. Make sure all impediments are removed. Set rulers upright in various parts of the roof to help judge the depth of insulation. Start at the farthest point from the attic entry and spray insulation into cavities between joists, moving the hose from side to side.

Have a helper fill the hopper as needed; keep it as full as possible. Hold the hose parallel to the floor and close to the floor. Move to new sections as joist cavities are filled to the proper depth. Work on the temporary support boards and remove them as you fill cavities to that location. Remove the rulers and vent covers once the cavities are full.