Yes, you can use black plastic as a vapor barrier. However, it is primarily recommended for ground-level applications, such as over dirt crawl space floors or under concrete slabs.
For the best results, use polyethylene plastic sheeting. The ideal thickness and type depend on where you are installing the barrier:
Black plastic is generally superior for crawl space and ground-contact vapor barriers due to its UV resistance and longevity, while clear plastic is suitable for indoor wall applications. The most critical factor is the thickness (typically 6-mil to 10-mil+), not the color, for moisture resistance.
Plastic Degrades When Exposed to Repeated Heat
This is especially true of plastic sheeting installed under siding on south-facing walls. It's likely to become brittle in just a few years.
Yes, but with significant caveats. While 4 mil plastic is acceptable for temporary use or light-duty general projects, it tears very easily. Professionals and building codes generally prefer or require 6 mil plastic for durability and long-term performance.
While 3-mil plastic can function as a temporary moisture barrier, it is generally not recommended for permanent, code-compliant vapor barriers. Industry standards usually require at least 6-mil polyethylene sheeting for walls and ceilings to prevent tearing and ensure low permeability.
Don't Skip Sealing Seams, Edges, and Penetrations
A vapor barrier with unsealed seams fails at every gap. Moisture and soil gases enter through even small openings. Overlap panels by at least 12 inches and tape every seam.
Measured in g/m²/24 hours or g/100 in²/24 hours, the MTVR shows how much moisture can enter a plastic bag during one day. A low MVTR means very little moisture can enter so a barrier like aluminum foil laminate is down to 0.001 g/m²/24 hours and a normal LDPE bag might be as high as 16-23 g/m²/24 hours.
Yes, mold can absolutely grow under a vapor barrier. While vapor barriers are designed to block moisture, any moisture that gets trapped beneath the barrier—due to a plumbing leak, groundwater seepage, or poor installation—will create a prime environment for mold to grow, out of sight.
No! Don't use plastic sheeting as a vapor barrier. This video provides an incredible explanation why you shouldn't and provides proper recommendations for most applications. Vapor retarders function like plastic barriers, but allow moisture to escape, which is essential to avoid buildup behind your walls.
Yes, you can use black plastic sheeting for a vapor barrier, particularly in crawl spaces and under concrete slabs, provided it is polyethylene film with a thickness of at least 6 mil (0.0060.0060.006 inches). Black plastic is often preferred for crawl spaces because it is durable, resists tearing, and can block sunlight, which helps prevent weed growth.
4 mil plastic is thicker.
A 6-mil vapor barrier meets minimum building code requirements, but it is rarely enough for optimal, long-term protection. Because 6-mil polyethylene tears and punctures easily, experts generally recommend upgrading to 10-mil to 20-mil barriers depending on your specific project.
Black plastic is generally superior for crawl space and ground-contact vapor barriers due to its UV resistance and longevity, while clear plastic is suitable for indoor wall applications. The most critical factor is the thickness (typically 6-mil to 10-mil+), not the color, for moisture resistance.
When using unfaced insulation, you need a separate vapor barrier. The best options are a continuous sheet of 4 to 6-mil polyethylene plastic or a smart vapor retarder like CertainTeed MemBrain. Install this barrier on the "warm side" (the interior-facing side) of the wall before hanging drywall.
You should avoid using a traditional, impermeable vapor barrier (like polyethylene plastic sheet) when it traps moisture instead of letting the wall system dry. If moisture gets into a wall, the barrier prevents it from escaping, leading to mold, mildew, and wood rot.
The vapor barrier must sit directly beneath the concrete, not embedded in the fill. Ideal placement is above the compacted base and below any insulation or reinforcement. Incorrect placement exposes the barrier to damage and reduces its effectiveness.
To kill mold permanently, you must combine chemical treatment with moisture control. Mold will always return if its food and water sources remain.
How to Tell if Your Vapor Barrier Is Failing
Polyamides (nylons) generally show higher water absorption than other engineering plastics. This leads to dimensional changes to finished parts, a reduction in strength, and also to changes in electrical insulating characteristics.
Yes, Ziploc bags keep moisture out and prevent outside humidity from affecting your stored items. They act as an excellent water-resistant barrier that protects dry goods from dampness or humidity. However, they are not 100% airtight and will not block out moisture completely over an extended period.
Yes, smells can pass through plastic. While plastic stops visible liquids and heavy gases, it is microscopically porous. Odor-causing molecules can dissolve into the plastic, pass through it over time (a process called permeation), and escape into the air on the other side.
Invest in a dehumidifier.
It's a game-changer for removing those damp, musty odors in your basement. There it is... a beautiful dehumidifier. And not just any dehumidifier—it's the SaniDry Sedona.
Mold is generally at its worst from early spring through early fall (specifically July through October), peaking during the warmest and most humid months. Mold thrives in warm temperatures (60∘F to 80∘F) combined with relative humidity levels above 60%.
Unfaced insulation is great for new construction, remodels, walls, floors, ceilings, basements, attics and crawlspaces. It's best used for interior wall applications that do not face the outside and also in rooms that don't need moisture control, like living rooms, dining rooms and studies.