Ethan Clarke
When it comes to home improvement, one common query is whether to install a plastic vapour barrier between the ceiling and drywall. This decision depends on various factors, including climate and building codes. In cold climates, a vapour barrier can help keep insulation dry, but it may also trap moisture and cause mould issues if not properly installed or in climates with high humidity. Some local building codes, such as in Ontario, Canada, require a vapour barrier for residential construction. Additionally, the order of installing drywall on the ceiling and walls is debated, with some recommending the ceiling first for ease of installation and others suggesting walls first to provide support for the ceiling drywall.
| Characteristics | Values |
|---|---|
| Placement of plastic | Between the studs and the drywall |
| Plastic in exterior walls | Should not be used in exterior walls that are below-grade, like basement walls |
| Plastic in interior walls | Used as a moisture barrier to prevent moisture from getting to the insulation |
| Plastic in cold climates | Recommended in severely cold climates with poor attic insulation to prevent moisture buildup |
| Plastic in warm climates | May not be necessary; vapor barriers may be more effective in allowing moisture escape and house ventilation |
| Plastic in humid climates | May cause moisture buildup and black mold issues; controlled ventilation recommended |
| Drywall installation order | Ceiling drywall before wall drywall to create a tight joint and reduce gaps |
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What You'll Learn
Vapor barriers are necessary in cold climates
Vapor barriers are necessary to prevent assemblies from getting wet. In cold climates, condensation is limited on the interior side of the vapor barrier. This is due to the installation of thermal insulation on the exterior side of the vapor barrier. Vapor barriers are also a drainage plane, so any moisture that condenses on the exterior side will be drained to the exterior.
Vapor barriers are especially important in very cold climates and in hot and humid climates. In cold climates, the vapor barrier goes on the warm side of the insulation, meaning the interior. This is because the vapor barrier is meant to keep the insulation dry. If the vapor barrier is placed on the cold side, it will trap and keep moisture in the insulation, reducing its effectiveness.
In hot and humid climates, the vapor barrier goes on the exterior of the building. This prevents humid outdoor air from entering the building cavities and causing condensation.
However, it is important to note that vapor barriers can also prevent assemblies from drying. Vapor barriers installed on the interior of assemblies prevent them from drying inward. This can be a problem in any air-conditioned enclosure or below-grade space, especially if there is also a vapor barrier on the exterior.
Additionally, the use of vapor barriers is very situational and depends on the specific climate and construction of the home. In some cases, other forms of moisture protection, such as faced insulation, may be sufficient, and a vapor barrier is not necessary.
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Vapor barriers are not needed in hot and humid climates
Whether or not to install a vapour barrier depends on the climate and the construction of your home. Vapour barriers are materials that reduce the rate at which water vapour can move through walls, floors, and other parts of a building. They are typically used in colder climates to prevent moisture from entering and condensing within the wall cavity, which could lead to dampened insulation and the growth of mould.
In hot and humid climates, the placement of a vapour barrier is critical. If placed on the wrong side of the insulation, it can trap moisture and cause mould issues. In these climates, the vapour barrier should be placed on the cool (exterior) side of the insulation to allow moisture to drain to the exterior.
However, some sources suggest that in hot and humid climates, a more permeable barrier should be used instead of a vapour barrier. This allows for some moisture vapour diffusion and prevents moisture from becoming trapped.
In the case of drywall ceilings, the general consensus is to not install a vapour barrier on the ceiling, especially if the attic above is not heated. This is to allow vapour to work its way up into the attic space and be vented through the vents. Instead, a vapour barrier should be installed on the walls, with proper ventilation in the room.
Therefore, while vapour barriers are an important part of moisture control strategies, they may not be necessary in hot and humid climates, especially when considering ceiling installations. Instead, more permeable barriers or construction products specifically designed to allow some moisture vapour diffusion may be more suitable.
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Vapor barriers are not always installed properly
Vapor barriers, also known as moisture barriers, are materials that prevent water and moisture from passing through walls, floors, and other parts of a building. They are essential in home construction to protect against water damage and mould growth. However, installing them incorrectly can lead to moisture problems and even legal issues.
Firstly, it is important to distinguish between a vapor barrier and a moisture barrier. While the terms are often used interchangeably, they refer to different concepts. A vapor barrier is designed to stop the movement of water vapor by diffusion, while a moisture barrier focuses on preventing liquid water intrusion. The placement of these barriers is critical. If placed on the wrong side of the insulation, they can trap moisture and lead to potential damage. For example, in a cold climate, a vapor barrier should be placed on the warm side of the insulation to prevent condensation and allow moisture to escape.
Secondly, the type of barrier selected must be suitable for the application. Using a barrier that is too impermeable or too permeable can cause issues. An overly impermeable barrier may trap moisture within the structure, while an overly permeable barrier may allow excessive moisture to pass through, failing to provide adequate protection. The choice of barrier should consider the specific climate and construction of the home.
Thirdly, improper sealing and inconsistent overlapping during installation can create weak points in the barrier system. Moisture may bypass the barrier entirely if seams, edges, and penetrations are not properly sealed. Non-uniform overlapping of seams can result in gaps that compromise the barrier's integrity. Additionally, vapor barriers are not always necessary, and in some cases, they may cause more harm than good. For instance, in certain climates with varying levels of humidity, the use of vapor barriers can trap moisture and lead to mould issues.
Finally, it is crucial to follow local building codes and regulations when installing vapor barriers. Different areas have specific rules and requirements for moisture barrier installation based on the local climate. Failing to comply with these codes can result in legal repercussions and may even require the removal and replacement of drywall to correct the mistake.
In summary, while vapor barriers are essential in controlling moisture and preventing damage in buildings, they must be installed correctly and in accordance with local regulations. Improper installation can lead to moisture problems, mould growth, and legal issues. It is always advisable to consult with professionals and refer to local building codes to ensure the proper selection and placement of vapor barriers.
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Drywalling the ceiling first makes it easier to butt wall sheets
Starting with the ceiling means that you can lift the wall sheets to create a tight joint. If you drywall the walls first, you would have to sculpt every edge to make it fit tightly, and you may end up with gaps that need to be filled before taping. However, if you are drywalling a basement, some people suggest doing the walls first, as it is often necessary to cut into drywall to fix water leaks or run electrical lines.
If you decide to drywall the ceiling first, you can use "dead-men" to support the ceiling sheets while you work. Dead-men are similar to clothesline props but are T-shaped and made from 2x4 scrap wood. Once the ceiling is done, you can butt the upper sheets to the ceiling and the lower sheets to the upper sheets, leaving a gap at the bottom that will be covered by trim.
If you are drywalling a basement, you may want to consider using a different ceiling material, as it is often necessary to cut into the ceiling to access plumbing and electrical mechanicals.
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Drywalling the walls first can result in unsupported ceiling drywall
Drywalling the ceiling first is generally recommended by contractors and plasterers. This is because drywalling the walls first can result in unsupported ceiling drywall. If you install drywall on the walls first, the ceiling drywall will be unsupported along the entire length of the wall. However, if you install the ceiling drywall first, the wall drywall will be supported by the ceiling drywall.
There are some exceptions to this. For example, if you are drywalling a basement, some people recommend using a drop ceiling instead of drywall so that you can easily access wires and pipes in the future. Additionally, if you are using 4-foot-wide sheets on a 9 or 10-foot wall, it may be helpful to place the narrow strip near the floor to avoid cutting for switches or outlets in the upper sheets.
The main advantage of drywalling the ceiling first is that it can help to avoid cracks in the ceiling and top corners. This is because the perimeter of the ceiling drywall can be left floating over the last 8-12 inches, which provides extra flexibility and reduces the likelihood of cracks. Drywalling the ceiling first can also make the installation process easier. For example, if you are using full sheets, drywalling the ceiling first means that any cuts will be hidden above the wall panel and will require less precision and effort.
Overall, while there may be some exceptions depending on the specific situation, drywalling the ceiling first is generally recommended to avoid unsupported ceiling drywall and to make the installation process easier.
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Frequently asked questions
The decision to install a plastic vapour barrier before drywalling depends on the climate in your area. If you live in a severely cold climate, a vapour barrier may not be necessary, as the heat loss from your house will be enough to warm the attic and remove moisture. However, if you have a well-insulated attic, a vapour barrier may be necessary to prevent moisture build-up.
A plastic vapour barrier can help to keep your insulation dry and prevent moisture damage. It can also reduce unwanted drafts and control the ventilation in your home.
Yes, one potential issue is that the plastic may trap moisture, leading to mould problems. Another issue is that the plastic may disintegrate over time, especially if it is not installed properly. It is important to consult with a professional and follow the building codes in your area to ensure that the plastic vapour barrier is installed correctly and is suitable for your climate.
