How to Use 15 Pound Felt on Foundation Walls

Once called “number 15” felt because it weighed 15 pounds per 100 square feet, 15-pound felt has an average weight of 7 pounds to 12 pounds per square foot. This type of felt, sometimes called “tar paper,” is often used under roof shingles to help make a roof more water resistant. Instead of using a house wrap around foundation walls, some individuals use 15-pound felt as a drainage plane for walls and to add water resistance.

Laser level
Tape measure
Chalk
15-pound felt, type ASTM D226
Staple hammer
1-inch staples
Straight wooden board
Weatherization sealant
Utility knife
Contractor’s tape

Instructions

- 1
  Use a laser level to create a straight line along the foundation wall. Trace the line with chalk. The line will help you properly align the 15-pound felt. Keep in mind that the felt should extend to the bottom of the sill plate of the foundation walls.
- 2
  Roll out an 8-foot length of 15-pound felt.
- 3
  Starting at the bottom corner, secure the felt to the foundation wall using a staple hammer. Do not line felt flush with the corner. Instead, start at the 12-inch point so you can create a vertical overlap. Space the staples by 6 inches along the sides of the felt, but secure the bottom of the first layer of wrap to the wall using weatherization sealant.
- 4
  Push the felt into the corners of the wall with a straight wooden board before you secure the felt with staples. This technique will help the felt stay taut in these areas.
- 5
  Overlap successive panels of 15-pound felt by 6 inches. Overlap vertical joints by 12 inches.
- 6
  Cut the felt around window and door openings, using a utility knife, like you may find in a daylight basement.
- 7
  Seal the seams and any tears in the felt with contractor’s tape. In addition, tape around any window or door openings.

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