Vapor barriers are essential in preventing moisture from entering building assemblies, such as walls, floors, and ceilings. They are typically installed on the interior of assemblies to prevent drying inward, which can be problematic in air-conditioned enclosures, below grade spaces, and when there is also a vapor barrier. Faced insulation, made of materials like kraft paper, foil, aluminum foil, or vinyl, is another type of insulation that includes a vapor barrier.
Drainage systems should be implemented to direct water away from the wall, minimizing moisture penetration. A good rule of thumb is to install a vapor barrier on the outer face of an exterior wall in hot and humid climates, while in colder climates, the vapor barrier should be on the internal side of an exterior wall.
There are three different classes of vapor barriers: Class III, which are the most permeable, brick, gypsum board, concrete, and impermeable vapor barriers (retarders) made of thin plastic sheets. These barriers resist moisture diffusion through ceiling, wall, and floor assemblies.
The best vapor barriers for walls include 6 Mil White Dura-Skrim® Reinforced Plastic Sheeting and 10 Mil Dura Skrim® Fire Retardant Reinforced Plastic Sheeting. These materials are designed to prevent the diffusion of vapor (water molecules in the air) through a home’s wall assembly, ensuring a comfortable living environment.
📹 How Vapor Barriers Work
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When should you not use a vapor barrier?
In the majority of other climate zones, the use of an interior plastic sheet is not necessary, nor is the application of one on the interior.
Do exterior walls need a vapor barrier?
Building codes based on climate zones require vapor barriers on a structure’s interior or exterior. In Marine 4-8 climate zones, Class I or II vapor retarders are required on the wall’s interior frame. Climate zones 1 through 3 do not require vapor retarders. ASTM E96 assigns a material’s ability to restrict moisture by assigning a class of barrier or retarder. Vapor barriers stop vapor diffusion, while vapor retarders slow it. Class I vapor retarders are 0.
1 perm or less, while Class II vapor retarders are 50 to 100 times more moisture than vapor diffusion. A superior air barrier system, like Polyguard’s, is needed to limit or prevent moisture accumulation and condensation in the building envelope.
Can I use plastic sheeting instead of Tyvek?
While plastic can be employed as a vapor barrier in below-grade basements, it is not recommended for this purpose. Polyethylene can be utilized between drywall and wall studs to create a more compact wall structure, thereby preventing the accumulation of moisture. Nevertheless, the utilization of plastic as a vapor barrier is inadvisable, given that concrete has the potential to draw in moisture, which could result in the proliferation of mold.
Can I just use plastic as a vapor barrier?
The efficacy of plastic sheeting as a vapor barrier is contingent upon the manner of its installation and compliance with pertinent building codes. The advantages of this material include cost-effectiveness, ease of installation, and availability in hardware stores. It should be noted, however, that not all types of plastic sheeting may meet the requirements set out in the relevant building codes.
What can I use instead of a vapor barrier?
Vapor retarders are thin, flexible materials used in building materials, such as membranes and coatings. They are typically mechanically fastened and sealed at joints, and can be found in rolls or integral parts of building materials like polyethylene sheeting and aluminum- or paper-faced fiberglass roll insulation. Paint-like coatings also retard vapor diffusion. In mild climates, materials like painted gypsum wallboard and plaster wall coatings can impede moisture diffusion.
In extreme climates, higher-perm vapor diffusion retarders are recommended for new construction. They perform best when installed closest to the warm side of a structural assembly in cold climates and toward the exterior in hot/wet climates.
Can I use plastic sheeting as a vapor barrier?
While plastic can be employed as a vapor barrier in below-grade basements, it is not recommended for this purpose. Polyethylene can be utilized between drywall and wall studs to create a more compact wall structure, thereby preventing the accumulation of moisture. Nevertheless, the utilization of plastic as a vapor barrier is inadvisable, given that concrete has the potential to draw in moisture, which could result in the proliferation of mold.
How do I choose a vapor barrier?
It is of the utmost importance to select a vapor barrier that exhibits low permeance, high tensile strength, high puncture resistance, and chemical resistance. This is essential for the effective functioning of moisture and vapor barriers, while simultaneously maintaining their physical integrity throughout the course of use.
What is the best material to use for a vapor barrier?
The best vapor barrier for crawl spaces is a Class 1 polyethylene vapor barrier with a thin concrete slab over it. Encapsulating the crawl space, including the floor, support posts, and walls, with the best vapor barrier system is crucial. The Polyguard ® TERM® Underslab WaterTermite Barrier is the industry’s best and thickest vapor barrier for crawl spaces, providing a durable physical barrier against water, termites, and radon. This high-strength barrier consists of an 8.
5 mils polyethylene backing laminated to a 69-mil thick TERM barrier sealant integrated into a high-strength non-woven geotextile fabric top layer, resulting in a total factory-controlled thickness of 95 mils.
What is the difference between a moisture barrier and a vapor barrier?
Moisture and vapor barriers are often used interchangeably, but they have distinct differences. Moisture barriers block both liquid water and water vapor, while vapor barriers only block water vapor. To choose the right barrier for your project, consider factors such as climate, materials, and construction nature. It’s essential to understand the specific purpose of your barrier and choose the appropriate option for your specific needs.
What is the difference between interior and exterior vapor barrier?
A vapor barrier is a material used to slow or reduce water vapor movement through a material. It is installed on the warm side of insulation in a building assembly, depending on climatic conditions. Vapor barriers can be mechanically fastened sheet-material, adhesive membranes, fluid-applied materials, insulating board stock, or medium density spray polyurethane foam. The thickness of the material determines its vapor barrier status. However, water vapor may be transported by air leakage, which should be addressed by installing a proper air barrier.
What is a house wrap vapor barrier to exterior walls?
Housewraps are a protective layer that resists external liquid water and allows water vapor to escape the assembly, thereby enabling the wall to “breathe.” This occurs during heating season, when water vapor is driven from the interior to the exterior.
📹 Vapor Barriers: Need one or not?
Vapor Barriers – When to use them, & when to NOT.. On this special edition of the Build Show Matt takes us on a guided tour …
Great topic. I’m in Northern California. Very dry and super hot in the summer. Fairly wet in the winter and very rarely does it get below freezing. Our typical new construction house is built using using only Forti-fiber on the exterior and then either a scratch, Brown and color coat of stucco or Forti-fiber and then 1″ of rigid foam and then one coat brown mud, then the color coat. The ladder method usually results in lots of cracks around windows and doors. I wish our local contractors would start using delta’s dimple mat under the paper.
Of course I find this article AFTER i put Poly sheet and hang it up on one wall. I’m redoing my garage, the drywall was full of holes and overall ugly. Figured I’d get mineral wool batts while I had access. (Found a 1980 penthouse magazine) and couldn’t decide if I needed to get a vapor barrier. I trust Matt’s advice when It comes to all building matters. So looks like I’m gonna get a can of spray foam and caulk to seal up some possible air gaps and get to drywall. Its for the garage anyways, so I don’t really see any reason moisture is going to be a big deal when the door opening throws everything wack again.
Texas – You’d still want one where a shower stall shares an exterior wall, right? Lots of warm humid interior air combined with tiny grout cracks in the tile. I had to gut the shower of a 1997 house that was built with tile on greenboard (don’t get me started on that shit), and most of the mold was between the brown side of the greenboard and the poly. A little bit got past the poly through nail holes, but otherwise the studs were OK. Good info.
Matt Risinger, great article. ive been researching a lot about poor air quality in my home due to a lack of make-up-air, i now im coupling that knowledge with the information you present about vapor barriers. i have a question for you? here in the cold northern wisconsin climate, should i be worried about mold growth behind my walls because of vapor barriers and negative house pressure? Thanks.
I am near the coastline in Hoboken, NJ and I’ve got an extension made of cinder block, whose exterior is stucco and open to the elements, which I am in the middle of remodeling. This extension was built 30+ years ago and after removing the drywall and insulation, I noticed a plastic vapor barrier against the cinder block, between the cinder block and the 2×4 framing. My question is whether I should remove vapor barrier completely and just put in new insulation and the drywall back alone or replace it/leave it in and put the insulation and drywall back on? From what I see from this fantastic article, I should do the former, but wanted to check if my particular context would suggest something different? Thanks in advance!
Hi Matt. Awesome article! In my current situation I am insulating a shed (in the cold north so only heated and never air conditioned) and will not have any drywall overtop of the insulation. In that case, since the drywall will not be there slowing down the vapor, I definitely want a vapor barrier correct? Thanks again!
Love your articles. Would love to see more on caribbean homes built with Bricks. Typically what they use for modern built homes here is vented roofs with gypsum air barrier in attic. Typically metal ducting or ducting board is used I think resulting in a lot of problems. Let me know if you need more info. thanks.
Not at all geeky. This is essential knowledge to anybody attempting to build anything insulated and airtight. You get it wrong and it will rot. And of course a building inspector should know better than that. To enforce vapour barrier even if it is detrimental is not his job. Great article and an excellent topic : )
Great advice We are just in the start stage of a new house in lower michigan zone 5 my plans are,drywall – 6in fiberglass paper less – osb – 1.5 in foil-faced r10 or so and strapping for siding to hang on, my ceiling will be drywall caulked sealed as best I can and 18in fiberglass hope this is a good way for a michigan climate any thoughts or advice would be helpful
We had the same problem in Canada in the summer in our unfinished basement when a/c is on the basement walls have pink insulation with vapor barrier over it and the moisture gets really bad and soaks insulation to the point where i have cut vapor barrier to let air flow to stop or slow this down ..now im just wondering about the rest of the house that has it and drywall is hiding this moisture issue..hopefully because of our climate it hasn’t caused that much damage as we only have air conditioning on for approximately 3 months
Thanks for this. I’m building garden rooms in the UK. I’m using ICF’s with warm flat roof. Permitted development only allows a maximum roof height of 2.5m I’m trying to construct a hybrid roof with 12mm ply, 50mm pir and 18mm osb3 covered in epdm for the outside and putting 50mm mineral wall slab up against the underside between the wooden joists. Between the joist and the plasterboard (drywall) I was going to use Siga Marjex 200. Do I need it now?
What would you recommend for a pole building? I will be heating it via radiant. I currently have Tyvek on the roof between the steel and trusses but nothing on the walls. I certainly want to keeps costs down but also only do it once. Do I need something against the steel first ? I considered rookwool in the studded “flush wall” between poles. I am just above MD. That’ said no vapor barrier correct?? Any advice Matt is greatly appreciated !!!
Question: I live in the south texas. I have a finished garage, that does not have insulation. My garage faces the west side, it can very hot and humid over 100 degrees. I recently add insulation to my garage door and purchased unfaced insulation for my ceiling attic. Did I made a mistake by purchasing unfaced insulation?
Very helpful but one question. I have 3/4″ furring strips not 2x4s attached to the cinder block wall in my bathroom. There is pink insulation between the strips. The 6 mil plastic then drywall (green). When the baseboard showed dampness, I opened the wall. All the furring strips were very damp and extensive mold on them. No mold on anything else.. This is in the DC area. Am I correct that the solution is to reinstall new furring and not use the insulation or plastic? We are in the DC zone. brick house
Matt. Building my house in climate zone 7 in PEC Ontario above code here because of you. Siding (mix of metal and composite wood.)/1 inch treated wood strapping / halo 1 inch foam house wrap (R5) taped / 1/2″plywood / 2×6 16C /3 inch Sprayfoam (vapour barrier and R 20) / Roxul comfort batt (R14) / 5/8″ drywall on road side and 1/2″ all around. @jtrenovation