Omar Khalid
Whether or not to use plastic sheeting under Sheetrock is a highly debated topic, with many conflicting opinions. Some people claim that using plastic sheeting can help to reduce air infiltration and act as a vapour barrier, especially in cold climates. Others argue that it can trap moisture, leading to mould and other issues. The decision to use plastic sheeting may depend on various factors such as climate, building codes, and the specific situation of the project.
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What You'll Learn
Plastic sheeting under sheetrock in humid climates
Plastic sheeting under sheetrock is a common practice to insulate and protect the wall from moisture. However, in humid climates, the use of plastic sheeting under sheetrock becomes more complex. The decision to use plastic sheeting and the type of plastic sheeting used depend on various factors, including the specific climate, the presence of air conditioning, and the potential for flooding.
In southern, humid climates with air conditioning, it is generally recommended to avoid using a vapor barrier on the inside of the wall. Instead, the vapor barrier should be placed on the outside of the wall to prevent moisture buildup. This is because the warm, humid air from outside can condense on the cool, dry inside of the plastic barrier, leading to condensation and potential mold issues. Additionally, in areas prone to flooding, it may be advisable to avoid insulating the bottom few feet of the wall, as this can be more effectively insulated by the earth itself, and flooding can cause less damage.
However, in certain cases, plastic sheeting under sheetrock in humid climates can still be beneficial. For example, in a humid climate without air conditioning, a vapor barrier on the inner surface of the wall may be appropriate. Plastic sheeting can also help reduce air infiltration, especially when combined with proper air sealing techniques, such as sealing around outlets, ceiling lights, and windows.
The decision to use plastic sheeting under sheetrock in a humid climate should be made after considering the specific conditions and consulting local experts, contractors, and building codes. The type of plastic sheeting and vapor barrier used should also be chosen carefully to ensure compatibility with the climate and the presence of air conditioning.
Overall, while plastic sheeting under sheetrock can be beneficial in certain humid climates, it is essential to carefully consider the potential benefits and drawbacks to make an informed decision.
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Vapor barriers and their placement
Vapor barriers are materials used for damp proofing that resist the diffusion of moisture through wall, floor, ceiling, or roof assemblies. They are typically made of plastic or foil sheets. Vapor barriers are placed toward the interior, heated side of insulation in the assembly in building assemblies in most parts of North America, where winter heating conditions predominate.
In humid regions where warm-weather cooling predominates within buildings, the vapor barrier should be located toward the exterior side of the insulation. In relatively mild or balanced climates, or where assemblies are designed to minimize condensation conditions, a vapor barrier may not be necessary. An interior vapor retarder is useful in heating-dominated climates, while an exterior vapor retarder is useful in cooling-dominated climates.
In most climates, it is often better to have a vapor-open building assembly, meaning that walls and roofs should be designed to dry to the inside, outside, or both, so the ventilation of water vapor should be considered. A vapor barrier on the warm side of the envelope must be combined with a venting path on the cold side of the insulation.
The use of vapor barriers has been legislated within the building codes of some countries, including the US, Canada, Ireland, England, Scotland, and Wales. The placement of vapor barriers depends on the climate and the number of heating degree days (HDD) in an area.
It is important to note that vapor barriers should not be placed on the ceiling if the garage is heated and the attic above is not. This is to allow vapor to work its way up into the attic space and be vented through the vents.
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Plastic sheeting and the risk of mould
Plastic sheeting is often used in construction to prevent moisture infiltration and protect against mould. However, if not installed correctly, it can actually trap moisture and create an environment conducive to mould growth.
In general, the use of plastic sheeting as a vapour barrier depends on the climate and the specific building conditions. In cold climates, plastic sheeting can be effective in reducing air infiltration and preventing moisture buildup. On the other hand, in humid climates with air-conditioned buildings, vapour barriers are typically installed on the outside rather than the inside.
One common concern with plastic sheeting is the potential for moisture trapping, especially in humid environments. If there are two vapour barriers, such as using plastic sheeting with fibreglass batts, it can lead to increased moisture levels and promote mould growth. Additionally, in areas with both heated and non-heated spaces, such as garages, the use of plastic sheeting on the ceiling can cause moisture issues. The warm, moist air can condense and cause the sheetrock to become damp, creating an ideal environment for mould to thrive.
To mitigate these issues, it is crucial to understand the purpose of vapour barriers and the specific requirements of the building. For example, in some cases, it may be recommended to use plastic sheeting on the inside walls, ensuring that all seams are properly taped to prevent air infiltration. However, in other instances, alternative materials such as Kraft paper may be more suitable as a vapour barrier.
When dealing with mould remediation projects, plastic sheeting plays a critical role in containment. The United States Environmental Protection Agency (EPA) recommends either limited or full containment, depending on the size of the contaminated area and the level of contamination. Plastic sheeting is used to cover and seal the affected areas, including vents, doors, or pipes, to prevent the spread of mould and other hazardous materials during removal. The plastic sheeting should be a minimum of 6 mils thick and properly secured with airtight tape to ensure effective containment.
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Plastic sheeting and breathability
Plastic sheeting is often used in construction to protect against moisture and air infiltration. In some cases, it is placed under sheetrock or drywall to act as a vapour barrier. However, the effectiveness of this practice depends on various factors, including climate and the presence of other insulation materials.
Breathability is an essential factor to consider when using plastic sheeting in construction. Breathable films are polymer-based plastics that provide moisture control while allowing air and vapour to pass through. This breathability is achieved by creating uniform cavities or pores in the plastic film, which also enhances the strength of the material. Ground calcium carbonate is commonly added to breathable films as a functional additive to improve their breathability and other properties.
In certain situations, such as in humid climates, it may not be advisable to use plastic sheeting as a vapour barrier. In these cases, alternative materials like kraft paper or foam board may be more suitable. Additionally, proper installation techniques, such as taping all seams and ensuring no gaps, are crucial to the effectiveness of plastic sheeting as a vapour barrier.
The decision to use plastic sheeting under sheetrock should be informed by local building codes, contractors, and suppliers. Climate plays a significant role in determining the permeability required for the wall system. In some cases, it may be recommended to use plastic sheeting on the walls but not the ceiling to allow vapour to escape through the attic vents.
Overall, while plastic sheeting can provide benefits in terms of moisture and air infiltration control, it is important to carefully consider its breathability and potential interactions with other building materials before installation. Proper installation techniques and consideration of local conditions are crucial to ensuring its effectiveness and avoiding potential issues such as mould.
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Alternative methods to plastic sheeting
When it comes to alternatives to plastic sheeting under sheetrock, there are several options available. The choice of alternative methods depends on various factors, including the climate, building structure, and specific requirements of the space. Here are some alternative approaches:
Vapor Barriers:
The use of vapor barriers is a critical consideration in controlling moisture and humidity. In cold climates, vapor barriers are placed on the inside of exterior walls to prevent moisture from entering the building. However, in humid climates with air-conditioned buildings, the vapor barrier is placed on the outside. This approach helps manage condensation and prevents moisture-related issues like mould.
Air-Sealing:
Simple air-sealing measures and spray-applied sealants can significantly improve energy efficiency and comfort. By sealing gaps and penetrations, such as those around outlets, ceiling lights, plumbing, windows, and exterior doors, you can effectively reduce air leaks and minimize heat loss. This method is particularly effective in reducing heat loss caused by air infiltration.
Insulation:
Proper insulation is crucial in maintaining a comfortable indoor environment. In addition to using insulation materials like fiberglass, some builders recommend using Kraft paper as a vapor barrier in certain zones. However, it is important to note that the use of insulation and vapor barriers should be carefully considered together, as using two vapor barriers can lead to issues with mould.
Alternative Materials:
In some cases, alternative materials can be used instead of plastic sheeting. For example, foamboard can be used to cover cold spots on walls, providing insulation and reducing heat loss. Additionally, rubber mats on floors and plastic film over windows can further enhance energy efficiency.
Building Codes and Expert Advice:
It is always recommended to consult local building departments, contractors, and suppliers to understand the specific codes and requirements for your area. Building professionals can provide guidance on the appropriate methods and materials to use, ensuring that your construction meets energy efficiency and safety standards.
The choice of alternative methods to plastic sheeting under sheetrock depends on a variety of factors, and it is important to consider the unique characteristics of your building and climate to make the most suitable choice.
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Frequently asked questions
No, you should not put up a plastic vapour barrier under ceiling drywall. You should put a vapour barrier on the walls, but not the ceiling. This allows the vapour to work its way up into the attic space and get vented through the vents.
No, you should not use a plastic barrier behind greenboard. Make sure it's unfaced insulation behind the greenboard.
It depends on the climate. In southern, humid climates with an air-conditioned building, you should not put any vapour barrier on the inside. It goes on the outside. In colder climates, a vapour barrier on the warm side of a wall is standard practice.
Yes, you can use plastic sheeting to insulate your laundry room. However, if you do, you need to install insulation that does not have a vapour barrier.
Plastic sheeting can trap moisture in your sheetrock and cause black mould. Plastic has a history of causing moisture problems and some experts believe it traps condensation inside walls and ceilings, damaging the materials.
