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.
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.
Lastly, the geographic location of the construction needs to be taken into careful consideration when deciding the proper placement of a vapor barrier in relation to the wall assembly. Properly placed vapor barriers should be installed on the warm, humid side of a wall.
When using this approach, it is important to ensure that the vapour barrier is installed correctly. The vapour barrier should be installed on the warm side of the insulation to prevent moisture from penetrating the insulation and potentially causing damage or reducing the insulation's effectiveness.
Vapour control layer building regulations
12 require that all new builds have an approved VCL fixed to the warm side of all insulation and cover the external framed wall area. It must be fitted at 250mm centres to the top and bottom of frames, around openings, at laps and wherever there has been any damage.
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.
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.
This is because an air gap provides an additional layer of insulation that helps to prevent heat from passing through the barrier and into the living space. If you are installing a radiant barrier, it's recommended to leave an air gap of at least 25mm (1 inch) between the barrier and the surface it's installed on.
If installed on top of attic floor insulation, the foil will be susceptible to dust accumulation and may trap moisture in fiber insulation, so it is strongly recommended that you NOT apply radiant barriers directly on top of the attic floor insulation.
In colder climates, where the home's heating system sees more use, the vapor barrier should typically be installed on the insulation's interior side. In warmer climates, where the home is often kept cooler, the vapor barrier should usually be installed on the exterior side.
Being an inert material, it is a non-viable food source for mold and will not support mold growth. Fiberglass insulation cannot fight the battle against moisture intrusion alone, however. Vapor barriers applied over the face of the insulation provide additional benefits in the fight against moisture.
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.
It's the first line of defence against high vapour pressure air entering the roof structure and causing interstitial condensation. Because of this, the VCL always sits at the warm side of the insulation.
Location: Floor underlayment is positioned between the subfloor and finished flooring, whereas floor vapor barriers are typically installed beneath the underlayment or directly on top of the subfloor, depending on the specific requirements of the flooring system.
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.
When installing house wrap with rigid foam, it should typically go under the insulation. However, it's best to follow your contractor's advice, as not all professionals agree on the order.
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.
A Vapour Control Layer, or VCL for short, is a plastic layer that restricts the movement of warm, moist air from inside a property into the fabric of the building. VCLs prevent excess moisture entering a wall's cavity, behind the insulation.
Vapour barriers are installed along, in or around walls, ceilings and floors to prevent moisture from spreading and potentially causing water damage.
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. Under flooring: When installing wood flooring over concrete, a moisture barrier protects the wood from moisture damage.
Vapor barriers are installed along, in, or around walls, ceilings, and floors.
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.
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.
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.
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.