How to Add a Vapor Barrier to an Outdoor Deck

Enclosing your deck gives you a space that you can use for much of the year, not just when it's warm outside. With the addition of a heater, you can even use the space during the winter. Whenever you're enclosing a new space, it's a wise idea to add a vapor barrier to the walls and floor. To add a vapor barrier to the floor of a deck, treat the floor as a subfloor. Cover it with the vapor barrier, and then install new flooring over it.

Sandpaper or surform tool
Pressure washer or scrub brush
Wood deck or concrete cleaner
Vapor barrier
Scissors or utility knife

Instructions

- 1
  Remove any splinters from the deck by sanding them down with sandpaper or a surface-forming tool.
- 2
  Pressure wash the deck floor with wood deck or concrete cleaner to remove all debris and grime. If a pressure washer is unavailable, scrub the floor with the cleaner and scrub brush. Rinse the deck floor after washing it, and then allow it to dry.
- 3
  Set a roll of vapor barrier at one side of the porch, with the exposed flap lined up with the outer edge of the deck floor.
- 4
  Unroll the vapor barrier slowly toward the other side of the deck, stretching the material to keep any wrinkles or buckles from forming. As you unroll the vapor barrier, apply at least two evenly spaced beads of adhesive in the same direction as the vapor barrier.
- 5
  Cut the end of the vapor barrier so that it is even with the opposite edge, using scissors or a utility knife.
- 6
  Restretch the material to ensure that it is taut.
- 7
  Continue adding subsequent rows of vapor barrier in the same manner until the deck is completely covered. Overlap each row by 4 inches. Press down on the beads of adhesive as you overlap each row.
- 8
  Apply a bead of foam adhesive all along the outer edges of the deck floor, under the vapor barrier. Press the edges onto the bead of glue to seal the ends.

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