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.
General rule of thumb is that the WATER barrier goes on the exterior wall, just under the outer cladding, and the VAPOR barrier goes on the warmest side of the wall, up against the sheathing. You can have only one water barrier, and only one vapor barrier, so you would need to remove the existing one.
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 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.
In walls, the air barrier (e.g., OSB or rigid foam sheathing) should be aligned with the exterior vertical surface of the insulation in all climate zones and also at the interior vertical surface of the wall insulation (the drywall) in Climate Zones 4-8.
Vapor barrier materials are installed on the warm side of the insulation in a building assembly, as determined by climatic conditions. In warm climates, it will be on the exterior and in cold climates, it will be on the interior.
Quite simply an air barrier reduces the flow of air, a vapor barrier reduces the flow of water vapor and a water resistive barrier reduces the flow of liquid water. Each function is completely different.
Add a vapour barrier on the warm side of the wall within the first third of the thermal resistance value of the overall wall insulation.
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.
Extend vapor retarder at least 6 inches up walls, columns, and footings. Use physical attachments where practical and necessary for long-term adhesion of vapor barrier to vertical surfaces. Overlap all seams at least 12 inches using a reverse or upslope lapping technique.
If doing an encapsulation (including the crawlspace in the building envelope and making it conditioned space) the experts agree that the vapor barrier should extend up the wall, stopping four to six inches below the sill plate to allow for an unobstructed pest control inspection area.
The common taboo against a double vapor barrier arises from a very real concern: If you have a Class I vapor retarder (less than 0.1 perm) on both sides of a wall, that wall has virtually no drying potential in either direction.
Even if there is no huge water leak such as from a hole in the roof, the steam and moisture of showers, bathtubs, and boiling pots can potentially affect the structure and safety of a house or building. This is why vapor barriers are needed in areas that are more moisture-prone.
In cold climates, vapor barriers go on the warm side of insulation. In hot, humid climates, they go on the exterior side. Even with faced insulation appropriately installed, it's wise to have a separate vapor barrier facing the heated space. This layer adds extra moisture protection.
Not to be confused with a vapor barrier—which is placed on the warm side of the wall just in front of the insulation and behind the drywall— a moisture barrier goes against the basement wall and behind the insulation and framing.
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.
Wall installation for vapour control layers
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. The VCL is stapled to the timber studwork with the insulation wedged between the timber studs.
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.
Standard Crawl space vapor barrier thicknesses range from 6 mil to 20 mil, with 6 mil being the bare minimum and 20 mil being the most heavy duty and puncture-resistant.
Because a vapor barrier is a low permeable barrier, it keeps moisture from passing through. This is beneficial to keep moisture away from a dry surface but will trap moisture behind it if installed on a water-damaged concrete wall, causing the wall to fail further.
In conclusion, Warm Wall construction is a roofing term used to describe a construction method that places insulation on the exterior side of the wall or roof assembly. This method of construction can significantly improve energy efficiency, durability, acoustics, and fire resistance.
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.
Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter. Whether or not you need a vapor retarder hinges on three main factors your climate, your home and the location of the wall you're insulating.
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.
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.