Alexei Volkov
Whether or not to use plastic sheeting as a vapour barrier before installing drywall on ceilings is a highly debated topic. Some people suggest that plastic sheeting is necessary to act as an air and moisture barrier, while others argue that it can trap moisture and cause mould problems. The decision may depend on the climate and building codes of the specific location, with some areas requiring a vapour barrier by code. Ultimately, it is essential to consider the potential benefits and drawbacks of using plastic sheeting before making a decision.
| Characteristics | Values |
|---|---|
| Purpose | Insulation, moisture barrier, and protection of drywall from moisture spots |
| Pros | Insulation, protection against moisture spots |
| Cons | Potential for trapping moisture and causing mould, inability to use drywall adhesives, may not be necessary in certain climates |
| Installation | Placed between the drywall and insulation or rafters |
| Thickness | 4-6 mil |
| Materials | Polyethylene, poly, visqueen |
| Climate considerations | Very cold winters, high summer humidity, varying climates |
| Building code requirements | Varies by location, e.g., standard in Ontario, Canada, but not in Ohio |
| Alternatives | Tyvek housewrap, ProClima Intello Plus, Isover diffusion foils |
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What You'll Learn
Pros and cons of plastic under ceiling drywall
Plastic sheeting is often used as a vapour or moisture barrier between the ceiling drywall and the insulation. While some people suggest that it is necessary to put up a plastic vapour barrier, others disagree. The decision to use plastic sheeting depends on various factors, including the climate, building codes, and the type of insulation used. Here is a detailed look at the pros and cons of installing plastic under ceiling drywall:
Pros of Plastic Under Ceiling Drywall:
- Insulation and protection: Plastic sheeting can act as a vapour barrier, helping to insulate the ceiling and protect the drywall from moisture spots. This is especially beneficial in areas with cold winters and low summer humidity.
- Compliance with building codes: In certain regions, such as Ontario, Canada, installing a vapour barrier is required by the building code. Checking with local building departments or insulation companies can provide clarity on specific requirements.
- Reduction of unwanted drafts: Plastic sheeting can help cut down on unwanted drafts in addition to its role in moisture control.
Cons of Plastic Under Ceiling Drywall:
- Trapped moisture and mould issues: One of the primary concerns with plastic sheeting is the potential for trapping moisture. This can occur against the backing of the drywall or within the wall structure, leading to mould problems. Mould removal can be expensive and hazardous.
- Incompatibility with adhesives: The use of plastic as a vapour barrier may not be compatible with drywall adhesives, requiring alternative installation methods.
- Climate-related considerations: In areas with high humidity, plastic sheeting may not be advisable as it can trap moisture vapour, leading to condensation issues.
- Installation complexity: Installing plastic sheeting adds another layer of complexity to the drywall installation process, potentially increasing the margin for error.
- Difficulty in removal: Once installed, removing plastic sheeting can be challenging, especially if it has been in place for an extended period.
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The type of plastic to use
In terms of the climate, if you live in an area with very cold winters and low summer humidity, a vapour barrier can help keep your insulation dry. On the other hand, if you live in an area with high humidity, there is a risk that the plastic will trap moisture and cause mould problems. For example, some people have noted that using plastic vapour barriers in Ohio, a state known for its hot, humid summers, resulted in moisture being trapped and mould forming.
The type of insulation you plan to use is also a factor to consider. If you are using faced insulation, it may already provide enough moisture protection, and a plastic vapour barrier may not be necessary.
It is important to check your local building codes, as some areas require a vapour barrier by code. For example, in Ontario, Canada, it is standard building code to install a vapour barrier in residential construction.
When choosing the type of plastic to use, the thickness is an important consideration. The most commonly mentioned thickness is 6 mil, which has been used successfully by several people. However, one person noted that they used 4 mil plastic in their moisture barrier, which became brittle and disintegrated over time.
Some people also mentioned using polyethylene foil as a vapour barrier, but this has been known to cause issues with moisture puddles building up on top of it.
It is important to carefully consider your specific circumstances and possibly consult with a local contractor or insulation specialist to determine the best type of plastic to use in your ceiling drywall installation.
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Building code requirements
Fire Resistance
Fire-resistance ratings are pivotal in specifications for ceiling drywall. These ratings indicate how long a ceiling assembly can withstand a standardized fire test, measured in hours. Fire-rated assemblies may have stringent fastening requirements, specifying closer spacing or specific screw types. For instance, coarse-thread drywall screws are recommended for wood framing, while fine-thread screws are used for metal studs.
Structural Integrity
Ceiling drywall installations must also meet requirements for load-bearing capacity and seismic considerations. Screw length is crucial, with screws penetrating framing members by at least ⅝ of an inch for wood and ⅜ of an inch for steel. Fasteners should generally be placed no more than 12 inches apart for ceilings.
Moisture Control
The need for a vapour barrier in your ceiling depends on local climate and building code requirements. Vapour barriers are more commonly recommended in colder climates where indoor air is typically warmer and more humid than outdoor air. However, in very hot and humid climates with air conditioning, a vapour barrier could potentially trap moisture and cause issues.
Plastic vapour barriers are often installed between drywall and rafters or insulation to act as an air and moisture barrier. However, there are concerns that plastic can trap moisture, leading to mould issues. In Ontario, Canada, building codes require a vapour barrier, but this does not lead to mould problems as there is always insulation between the vapour barrier and the outside of the house, keeping the barrier warm and preventing condensation.
Sound Transmission
Building codes also include standards for noise reduction between floors and units, ensuring better acoustic performance in buildings.
Material Selection
In moisture-prone areas like bathrooms, kitchens, and laundry rooms, specialized materials and techniques are required. Building codes specify the use of moisture-resistant (MR) or mould-resistant drywall in these areas. Cement board or other water-resistant materials may be necessary, especially in areas directly exposed to water, such as above showers.
Electrical Considerations
While drywall is not always necessary for ceiling joists or walls, it serves to protect electrical cables that are considered "exposed to damage." Overhead wires are typically not considered exposed to damage unless the ceiling height is low, bringing them within 8 feet of the floor. In such cases, protective measures like conduit and metal boxes with "exposed work covers" may be required.
Adhering to these building code requirements is crucial for creating safer, more durable, and compliant structures.
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Installation process
The installation process for plastic before ceiling drywall depends on several factors, including the climate, building structure, and local building codes. Here is a step-by-step guide on how to install plastic before ceiling drywall, taking these factors into consideration:
Step 1: Determine the Need for Plastic
Before installing plastic, it is essential to assess whether it is necessary for your specific situation. Plastic sheeting, typically a 6-mil poly vapour barrier, is used to prevent moisture accumulation and improve insulation. In regions with cold winters and low summer humidity, a vapour barrier can help keep insulation dry. However, in areas with high humidity, there are concerns about plastic trapping moisture and causing mould issues. Check with local builders or insulation experts to understand the specific needs of your region.
Step 2: Prepare the Ceiling Framing
Ensure that the ceiling framing is complete and secure. This involves installing ceiling joists or furring strips, typically made of wood, to provide a solid base for the drywall. The spacing and orientation of these strips may vary depending on local building codes and the type of ceiling being created.
Step 3: Install a Vapour Barrier
If a vapour barrier is required, carefully unroll the plastic sheeting and attach it to the ceiling framing. Overlap the seams of the plastic sheeting by at least 6 inches to ensure proper coverage. Secure the plastic using staples or nails, ensuring it is taut and flat against the framing. Tape the seams of the vapour barrier to make it airtight, which will enhance its effectiveness.
Step 4: Install Insulation
After the vapour barrier is in place, install the insulation. This may involve using fibreglass insulation, blow-in insulation, or another suitable type of insulation material. Ensure that the insulation is properly fitted between the ceiling joists or furring strips, creating an even layer.
Step 5: Install Drywall
With the vapour barrier and insulation in place, you can proceed to install the drywall. Measure and cut the drywall sheets to fit the ceiling, allowing for any necessary accommodations, such as electrical fixtures or ceiling angles. Secure the drywall sheets to the ceiling framing using screws or nails. Ensure that all seams between drywall sheets are tightly butted together to create a smooth surface.
Step 6: Finish the Ceiling
Finally, complete the ceiling installation by taping and mudding the seams of the drywall. This process involves applying joint tape and joint compound to the seams and screw holes, creating a smooth and continuous surface. Sand the dried joint compound to prepare the ceiling for painting or further finishing.
It is important to note that the provided steps serve as a general guide, and specific installation processes may vary depending on your location, ceiling design, and local building codes. Always refer to the instructions provided by the manufacturers of the materials you are using and consult with local building experts or contractors if you have any questions or concerns.
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Alternatives to plastic
Plastic sheeting is often used as a vapour or moisture barrier between the ceiling drywall and the insulation. However, there are mixed opinions on whether this is effective in preventing moisture build-up, with some suggesting that it may even trap moisture and cause mould issues.
If you are looking for alternatives to plastic sheeting, there are several options available:
PVC Panels
PVC panels are a durable and lightweight alternative to drywall. They are 100% waterproof and resistant to mould and mildew, making them ideal for areas with high moisture levels such as bathrooms, basements, and garages. PVC panels are easy to install, interlocking into place, and can last for over 100 years without requiring any repairs. They are also non-reactive to water or moisture, preventing any moisture from settling on the surface.
Tongue-and-Groove Planks
Tongue-and-groove planks are another DIY-friendly option that can be easily installed by snapping them into place. They provide a warm and inviting look to the space.
Metal Panels
Metal panels offer a striking aesthetic to the ceiling while being more manageable to install compared to drywall. They are also suitable for high-moisture areas as they resist water damage and mould growth.
Beadboard
Beadboard is a budget-friendly alternative that can add a simple upgrade to the space without being too expensive. It provides a warm and inviting look and is relatively easy to install.
Plywood
Plywood is another cost-effective option that can enhance the aesthetics of the space without breaking the bank.
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Frequently asked questions
It depends on the climate you live in. If you experience very cold winters, a vapour barrier can help keep your insulation dry. However, in places with high humidity, plastic can trap moisture and cause mould.
Plastic acts as a vapour barrier, which can help insulate your home and protect drywall from moisture spots. It can also cut down on unwanted drafts.
Plastic can trap moisture against the backing of the drywall, which can lead to mould growth. It can also be difficult to install drywall adhesive when using plastic.
