How Do I Install Mineral Wool Insulation in Floor Joists?

Written by michelle raphael
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Floor joists are horizontal elements spanning from one wall to another. They are beamlike structures that support a floor. However, unlike beams, floor joists are narrow. These construction elements offer a practical place for installing insulation since they form a closed, semi-empty space, usually between the living area and the attic, or between the living area and the basement. If you want to improve your home's thermal isolation index, you may want to know how to install mineral wool insulation between the floor joists.

Skill level:

Things you need

  • Measuring tape
  • Caulking gun
  • Utility knife
  • Metal ruler or wooden slate
  • Synthetic, rubber-based adhesive
  • Staple gun

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  1. 1

    Measure the floor joist spacing or the area between the floor joists to see how much material you'll need, using a measuring tape.

  2. 2

    Apply a bead of silicone caulk in the places where plumbing, other pipes and electrical wires penetrate through the joists, using a caulking gun. Apply the caulk around each pipe or wire. Be precise to assure that you made the floor joist area airtight.

  3. 3

    Measure the space between the joists again and cut the pieces of mineral wool so that they fit perfectly in between, using a utility knife. If you have mineral wool that fits the width of the joists' spacing, simply cut the needed lengths. To assure that the cut is straight, lean the utility knife on a metal ruler or wood slate. This method is for batting, rolls of blankets of mineral wool only.

  4. 4

    Apply synthetic, rubber-based adhesive to the back side of the mineral foam. Lightly press the insulation for a minute or two to secure it in its place on the band joist. Do not press firmly, because you might compress the mineral wool, decreasing its R-value. Cut holes for the piping and the wires in the mineral wool, using a utility knife. Pipes and the wiring have to stay visible, for easy access in case of repairs and to prevent overheating.

  5. 5

    Staple the wool insulation in place with a heavy-duty staple gun.

Tips and warnings

  • If your floor joists are hard to reach, use loose-fill insulation instead of rolls and blankets. The blow-in method of insulation assures that the loose material fills the space between the joists and completely conforms to that space.
  • Always wear protective work gloves, safety goggles and a mask when installing mineral wool insulation.

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