The IRC requires either a Class I or II vapor retarder on the interior side of frame walls in climate zones 5, 6, 7, 8 and Marine 4 (see climate zone map).
A vapour barrier is placed on the inner side of the insulation and is designed to stop moist air from passing through it. A breathable membrane, by contrast, is installed on the outer side of the insulation. Breathable membranes must repel water from the outside while still allowing moisture from the inside to escape.
If you live in a mixed climate – hot and humid with several heating months in the winter, you probably need a vapor retarder. Specifically, if you live in climate zones 4C (marine), 5, 6, 7 and 8. Not sure your climate zone? You can check here.
The IRC requires Class I or Class II vapor retarders on the interior side of most above-grade frame walls in Climate Zones 5, 6, 7, 8, and Marine 4. It is permitted to use Class III vapor retarders if continuous exterior insulation is installed in accordance with IRC Table R702.
Exterior walls: In exterior walls, moisture barriers keep outdoor moisture out and prevent indoor moisture from condensing within the wall. In cold climates, the barrier goes on the warm (interior) side of the insulation. In hot, humid climates, it's placed on the cool (exterior) side.
Don't: Put Vapor Barriers on the Bottom of the Floor Joist in the Crawl Space. Because vapor barriers are good at retaining moisture, putting plastic sheeting on the joists can cause moisture to build up under the floor.
Vapor barriers are installed along, in, or around walls, ceilings, and floors. Of course this is done to prevent moisture from spreading and potentially causing water damage.
Vapor Retarders in Cold Climate Zones (5, 6, 7, 8 and Marine 4): The IRC requires either a Class I or II vapor retarder on the interior side of frame walls in climate zones 5, 6, 7, 8 and Marine 4 (see climate zone map).
Install a New Vapor Barrier
If your vapor barrier was damaged or not installed correctly, it's important to replace it with a new one. This will help prevent moisture from seeping into your crawl space and creating the perfect environment for mold growth.
Is DuPont™ Tyvek® a vapor barrier? No, DuPont™ Tyvek® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.
In Most Cases, Attic Insulation Does Not Need To Provide A Vapor Barrier. The good news is that blown-in insulation should not need a vapor barrier. Blown-in is primarily used on the attic floor, and vapor barriers are not a concern for attics in our climate zone.
You can use plastic if you put polyethylene between your drywall and the wall studs. This way, you should get a tighter wall without trapping moisture inside the exterior walls. If you are framing out a below-grade basement, however, do not use plastic as a vapor barrier.
An average vapor barrier installation costs $2 to $4 per square foot or between $1,200 and $4,000 for materials and labor. *Labor costs to install add $1.50 to $3.00 per square foot on average.
The majority seem to agree that insulated, unheated garages, should be allowed to breathe. If the garage is heated, you will need a vapor barrier, otherwise you will get frost and mold.
Both are designed to keep moisture out of your home and can be made from various materials. But there are a few key differences, the most apparent being that moisture barriers are better at keeping out liquids, and vapor barriers are better at keeping out water in its gaseous state.
Thickness: The vapour barrier must possess a minimum thickness of 0.2mm (200 µm) and demonstrate resilience against impacts, punctures, and moisture penetration. Installation Standards: The film should provide a 200mm overlap at all joints, with penetrations meticulously sealed or taped using a snug-fitting sleeve.
The Cons of Vapor Barrier Installation
Although vapor barriers aim to prevent moisture from entering the structure, they can also trap moisture inside. If not properly installed or upheld, this could result in the proliferation of mold and other issues related to moisture.
Insulating an unheated garage alone may not necessarily cause mildew, but the risk of mildew increases if there isn't proper ventilation. Insulation can trap moisture in the garage, especially in humid climates, creating a perfect environment for mildew growth.
Vapor barriers should only be used in areas where there is water or moisture such as kitchens and bathrooms. The interior kitchens and bathrooms specifically need a vapor barrier installed during the building process.
In climates that are hot and humid, a vapor barrier should be installed on the warm side (for walls, this would be just beneath the exterior cladding, over the insulation). For very cold climates, the warm side is the interior, so the insulation should have a vapor barrier separating it from the interior wall.
Wall installation for vapour control layers
Generally speaking when you install a VCL to the walls of existing properties, you are installing a stud wall with insulation. If you use permeable insulation material such as sheep's wool, rockwool or fibreglass, the VCL is installed to the warm side of the insulation.
Yes, covering your insulation with a vapor barrier plastic before installing drywall is crucial.
On most projects where insulation meets the under-slab vapor barrier, we have found that the project teams elect to install their insulation first and to lay the vapor barrier over top. Various industry leaders have commented on the advantage of placing the vapor barrier directly beneath the slab.
A crawl space vapor barrier is crucial to the long-term care of a home because it prevents the growth of mold and prevents the introduction of hazardous gasses, like radon, into the air inside the building.
For example, House wrap by itself is not an air barrier, it is a vapor barrier. However, IF installed properly, which is rare, with taped seams, bottom, top edges, and no tears, it acts as an air barrier. So primarily it acts as a vapor barrier, but installed properly can do both; vapor barrier and air barrier.