How to Achieve R-21 in a 2x4 Wall

Step 1: Install kraft-faced fiberglass batts.

- Use R-13 or R-15 kraft-faced fiberglass batts to fill the stud cavities.

- Ensure the batts are fully inserted and fit snugly against the studs.

- Stagger the joints of the batts to minimize gaps and air infiltration.

Step 2: Add foam board insulation.

- Cut the foam board insulation to fit between the studs.

- Insert the foam board insulation between the studs, making sure it fits tightly against the batts.

- Foam board insulation comes in thicknesses ranging from 1 to 2 inches. Choose a thickness that will help you achieve your desired R-value.

Step 3: Seal any gaps or cracks.

- Use caulk or spray foam to seal any gaps or cracks around the edges of the insulation materials, between the studs and the top and bottom plates, and around any electrical outlets or switches.

Step 4: Install a vapor barrier.

- Install a polyethylene vapor barrier on the warm side of the insulation, facing the interior of the room.

- Overlap the vapor barrier sheets by at least 6 inches and tape the seams to create an air-tight seal.

Step 5: Install drywall.

- Install drywall over the vapor barrier, securing it to the studs.

By following these steps, you can achieve an R-21 insulation value in your 2x4 wall, improving the energy efficiency and comfort of your home.