Basement Vapor Barrier for Better Basement Insulation

Basement vapor barrier wall insulationOne of the best vapor barrier for basement wall insulation is the use of spray-in-place foam insulation. Nevertheless, spray foam insulation can be costly in some projects. That why we have come up with the cheapest way to insulate basement walls. It is a hybrid insulation detail that uses a blend of rigid foam insulation and fiberglass insulation.

The idea behind the use of this detail is to install a layer of rigid foam board insulation. It is then followed by carefully sealing it to create a vapor barrier adjacent to the concrete. Then, frame a wall and fill the openings with fiberglass insulation to generate an R-value that meets the design. Here is a step-by-step procedure for insulating basement walls with fiberglass.

  • Install a rigid foam insulation board with a minimum width of 1-1/2 inches.
  • The vapor barrier for insulation must be installed from the slab up to the top of the wall. That should include the top surface of the exposed concrete wall. Note that using a thinner section of the foam board will be risky because the result may not perform as an effective vapor barrier.
  • Cautiously seal all the seams in the foam board. You can combine Tyvek Tape, Dow Construction Tape, and spray foam in a can. This step is very crucial because it creates an effective vapor barrier.
  • Frame a wall directly ahead of the foam board, leaving an inch gap to allow for airflow around the studs. It is prudent to ensure that you use a pressure treated bottom plate to avoid decay. When installing a basement wall insulation vapor barrier, it is preferable to install the PT bottom plate on top of composite decking material to prevent any wicking of moisture into the framing.
  • Fit the fiberglass insulation in the wall cavities to generate a final composite R-value that meets the energy code requirements.

Installation basement wall insulation vapor barrierThe real question remains whether or not to install a vapor barrier over the fiberglass and behind the drywall. Typically, we do not recommend a vapor barrier if you have installed at least 1-1/2 inches of rigid foam. It is likely that if you install a thinner layer of foam, the surface of the foam could be cool enough to encourage condensation if water vapor moves from the conditioned room and hits the surface of the foam board.

For this reason, we recommend a vapor barrier if you have used less than 1-1/2 inches of foam when maximizing the purpose of vapor barrier on insulation.

Do you need a vapor barrier in basement walls? Contact us, and we shall have our experts on the ground for an excellent vapor barrier installation.

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