Vapor barriers resist moisture penetration, keeping humid interior air from reaching cold surfaces where it could condense. In cold climates, vapor barriers go on the warm side of insulation. In hot, humid climates, they go on the exterior side.
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.
Direction Matters: The vapor barrier should always face the warm side of your insulation. In the UK, that's usually the inside of your building.
Kraft-faced insulation includes a paper vapor retarder, which helps prevent mold and mildew. Kraft-faced insulation should be installed in exterior walls, exterior basement walls, and attic ceilings by pressing the product into the wall cavity with the paper side facing outward, towards the installer.
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.
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.
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.
Therefore, when installing foil faced insulation always fit the foil side where the temperature difference is greatest. So, any time you use a single side foil insulation, the foil needs to be facing toward the living space.
In finished attic rooms with or without dormers, insulate (2A) between the studs of "knee" walls, (2B) between the studs and rafters of the exterior walls and the roof, (2C) and ceilings with unconditioned spaces above. (2D) Extend insulation into joist space to reduce air flows.
More than likely, installing an additional layer of poly over kraft facing won't cause any problems — it's no more risky than if the wall had only unfaced batts and poly — and the risk of using poly on the interior is relatively low in a cold climate like New York's.
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.
The first is stapling Original AtticFoil to the bottom of the roof rafters via the Staple Up Method. The second is laying SuperPerf™ AtticFoil® out on top of the existing attic floor insulation like a blanket. Alternate methods like the Flat Top and the Hybrid are just modifications of the standard Staple Up method.
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 general water vapor moves from the warm side of building assemblies to the cold side of building assemblies. This is simple to understand, except we have trouble deciding what side of a wall is the cold or warm side. Logically, this means we need different strategies for different climates.
Should I Put Vapor Barrier Plastic Over Insulation Before Drywall? Yes, covering your insulation with a vapor barrier plastic before installing drywall is crucial. It prevents moisture buildup that can lead to mold, rot, and even structural damage.
Our view is that for mixed climates (aka heating dominated climate zones) the best place for a smart vapor barrier is inboard of the insulation because it will prevent conditioned air from entering the insulation layer and really help minimize or eliminate condensation.
If you're wondering whether to put the foil side of foam insulation board shiny side in or out, consider whether you want to make the space inside warmer or cooler. If you want to make the space warmer, the foil should face inside so it can reflect radiant heat back into the room.
One of the most important rules of insulation installation order is to install the thickest layer of insulation first, and then add thinner layers on top of it. This is because the thicker the insulation, the higher the R-value, and the more effective it is at preventing heat transfer.
One of the key benefits of insulated plasterboard is the option for foil-backed varieties, which serve as a built-in vapour barrier. However, it's important to keep in mind that ensuring the continuity of the vapour barrier at joints can be a challenge.
At this point, you may ask, “Which way should insulation face in a crawl space?” Install faced insulation with the paper backing against the subfloor and the material side facing into the crawl space.
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.
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.
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.