Alexei Volkov
Crawl spaces are often prone to moisture problems from water vapour that rises from the ground and gets trapped in the enclosed space. This can lead to mould and mildew, which can circulate into the living space and cause health issues. To prevent this, plastic sheeting can be added as a water vapour barrier to control moisture. This barrier is made of rolls of ordinary sheet plastic that are laid down on the ground in a crawl space to trap water in the ground from evaporating or condensing. The process of installing a vapour barrier in a crawl space is called crawl space encapsulation. The thickness of the plastic sheeting can vary depending on your budget and needs, with thicker plastic being more durable and long-lasting.
| Characteristics | Values |
|---|---|
| Purpose | To control moisture in crawl spaces and prevent water vapour from seeping into the house |
| Materials | Plastic sheeting, dehumidifier, fans, pump, garden rake, tape, concrete (optional) |
| Thickness | 6-23 mils (0.006-0.023 inches) or 10-20 millimetres, depending on budget, needs, and local code |
| Installation Process | Dry out crawl space, remove debris, level ground, lay plastic sheeting, cut to size, overlap seams, secure with tape, cover with concrete (optional) |
| Benefits | Prevents moisture damage, increases energy efficiency, lowers risk of mould and bacteria-related health issues |
| Cost | $0.15 to $0.50 per square foot for plastic; $2 to $4 per square foot or $1,200 to $4,000 for installation |
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What You'll Learn
Prepare the crawl space
Preparing the crawl space is a crucial step in ensuring the effectiveness of the plastic vapour barrier. Here are the steps to prepare the crawl space:
Firstly, locate the entrance to the crawl space. The entry hatch may be outdoors along the perimeter wall or inside in the basement, closet, pantry, or utility area. Once you've located the entrance, it's important to ensure the crawl space is as dry as possible. Use a dehumidifier, fans, and a pump to remove any standing water. If there is any mould or mildew, address it by following the necessary removal procedures.
Next, remove any debris, especially sharp objects that could puncture the plastic. This step is crucial as crawl spaces often contain discarded building materials and other items that can retain moisture and promote mould growth. After clearing the area, use a garden rake to level the ground as much as possible.
Before laying down the plastic, ensure you have the necessary materials, such as the plastic sheeting, tape, and any other recommended supplies. The plastic sheeting should be made of reinforced polyethylene plastic (poly) with a thickness of at least 6 mils. Choose a thicker option if you anticipate regular traffic in the crawl space or if the floor has sharp objects or uneven surfaces.
Finally, enlist the help of an assistant to facilitate the process. Having someone pass items through the crawl space door and help with rolling out the plastic and taping the seams will make the task more manageable. It is also recommended to wear a face mask to avoid inhaling any debris or damp moisture that may contain bacteria and mould.
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Choose the right plastic sheeting
When choosing the right plastic sheeting for your crawl space, there are several factors to consider. The most important factor is the thickness of the sheeting, which is measured in mils, where 1 mil is equal to 0.001 inches. The thickness of the sheeting will depend on the moisture level of your crawl space and the amount of traffic the space will have.
The most common thicknesses for plastic sheeting are 6 mil, 10 mil, 12 mil, and 20 mil. A 6-mil sheet is considered a Class 1 vapor retarder, which is the minimum recommended thickness for a crawl space ground cover. This thickness is suitable for a basic level of moisture protection but may not be as durable or puncture-resistant as thicker options.
A 10-mil vapor barrier is a thinner option that still provides decent protection against moisture. It is an economical choice, ideal for crawl spaces that aren't exposed to heavy traffic or substantial wear and tear.
If you require a higher level of protection, a 12-mil or 20-mil vapor barrier would be a better option. These thicker barriers offer superior resistance to punctures and tears, making them well-suited for high-traffic areas or situations where a higher degree of protection is necessary.
In addition to the thickness, it is important to consider the type of plastic sheeting. The most commonly used materials are polyethylene plastic sheeting and reinforced polyethylene plastic sheeting. Polyethylene plastic sheeting is a popular choice because it is durable, waterproof, and resistant to mold and mildew. Reinforced polyethylene is an upgraded version with added strength to prevent tears or punctures, making it suitable for high-performance applications.
Another factor to consider is the cost of the plastic sheeting. The price of vapor barrier sheeting can range from 15 cents to $1.50 per square foot, depending on the thickness and type of sheet. If you are installing the vapor barrier yourself, you will also need to budget for the cost of the installation materials, such as tape and stakes.
Finally, it is important to ensure that the plastic sheeting you choose meets the local building codes and ASTM E1745 standards. Using a cheap, recycled liner may not satisfy these requirements and could lead to issues with moisture control in the long run.
By considering the thickness, type, cost, and local regulations, you can choose the right plastic sheeting for your crawl space to achieve effective moisture control and protect your home from damage.
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Install the plastic sheeting
Installing plastic sheeting in a crawl space is a great way to control moisture and prevent water vapour from seeping into your home. The process is relatively straightforward, but it can be labour-intensive and may be tricky to do alone. It is recommended to have at least one other person to help pass items through the crawl space door and to assist with rolling out the plastic and taping the seams.
Before installing the plastic sheeting, it is important to ensure the crawl space is as dry as possible. Use a dehumidifier, fans, and a pump to remove any standing water. Remove all debris, especially anything sharp that might puncture the plastic. To the degree that it is possible, level out the ground using a garden rake.
Begin by laying down the plastic sheeting. Cover the entire crawl space floor, allowing 6 inches or more along the walls. Overlap the seams by at least 12 inches and secure them with poly PVC tape. You can also use construction adhesive or spray glue to affix the sheeting to the crawl space walls. If you are using thinner plastic, consider staking the plastic down with landscape fabric stakes or placing sandbags on top to keep it in place.
If your crawl space has a dirt floor, you may want to consider a concrete method. First, install a 6-mil plastic vapour barrier, then pump concrete into the area to cover it. The resulting floor will be rigid and durable, which is especially useful if you plan to store heavy objects in the crawl space.
Remember, the thickness of the plastic sheeting will depend on your budget, the intended use of the crawl space, and the type of floor. For long-term protection, a thickness of 10 mils or higher is recommended.
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Seal the seams
Sealing the seams of the plastic sheets in a crawl space is a crucial step in the installation process. Sealing the seams ensures that the vapor barrier effectively prevents moisture from penetrating or moving from one area to another.
To seal the seams, you will need to use adhesive seam tape or duct tape. Poly PVC tape intended for crawl space sheet installation, such as Dow Weathermate Construction Tape, is also an option. Before taping, it is essential to ensure that the plastic sheets overlap by at least 12 inches, with some sources recommending an overlap of two feet. This overlap is crucial to creating a tight seal and preventing moisture from seeping through.
Once the plastic sheets are overlapped, apply the tape generously along the seams to create a strong and secure bond. Make sure to smooth out any wrinkles or bubbles in the tape to ensure a flat and even surface.
In addition to taping, you can also use construction adhesive to seal the seams. This method involves applying the adhesive directly to the seams, creating a tight seal that may be messier but is equally effective.
For a more permanent solution, you can also use a pressure-treated nailing strip along the seams. This method provides a secure mechanical fastening that complements the tape or adhesive seal.
By following these steps and sealing the seams effectively, you can ensure that your crawl space is protected from moisture and the associated issues, such as mould, mildew, and rust.
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Maintain and replace
Maintaining your crawl space vapour barrier is essential to prevent moisture damage, increase energy efficiency, and lower the risk of mould and bacteria-related health problems.
To maintain your vapour barrier, ensure the crawl space is kept dry. Use a dehumidifier, set up fans, and remove any wet materials. You should also use a pump to discharge any standing water. Check for any holes or tears in the plastic barrier and repair these with tape. Poly PVC tape is recommended for this purpose. If you need to slide around on the plastic, it is recommended to use a puncture-resistant, single-layer vapour barrier. Alternatively, you can use landscape fabric stakes to keep the plastic in place.
If you are experiencing serious odours or mould in your crawl space, you should remove and replace the plastic. First, remove all debris and old plastic. Then, install a new vapour barrier.
To install a new vapour barrier, begin with a crawl space that is as dry as possible. Use a dehumidifier, fans, and a pump to remove any water. Remove all debris, especially anything sharp that might puncture the new plastic. Level out the ground using a garden rake. Lay down the plastic sheeting, allowing 6 inches or more along walls. Overlap the seams by at least 12 inches and secure them with tape. Seal the seams and affix the sheeting to the crawl space walls. You can use a variety of tapes to do this, including Poly PVC tape, duct tape, and Gorilla Tape. You can also use construction adhesive, such as Master Seal NP 1.
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Frequently asked questions
Attaching plastic in your crawl space is a great way to control moisture and prevent it from entering your home. Moisture can cause structural issues, rot and decay, and mould and mildew.
The type of plastic you use will depend on the intended use of your crawl space and the material on the floor. For example, if you will be entering the crawl space regularly for maintenance or storing heavy objects, you should use a thicker plastic such as 12 mils or higher. Polyethylene plastic sheeting (poly) is a common choice and is available in various thicknesses and strengths.
First, ensure your crawl space is as dry as possible by using a dehumidifier, setting up fans, removing wet materials, and using a pump to discharge any standing water. Then, remove any debris, especially sharp objects that might puncture the plastic. Next, lay down the plastic sheeting, allowing 6 inches or more along the walls. Overlap the seams by at least 12 inches and secure them with poly PVC tape. Finally, stake the plastic down with landscape fabric stakes to keep it in place.
While it may be tempting to leave the old plastic in place to save time and money, this is not recommended as old plastic can trap mould and debris underneath, leading to potential health hazards and compromising the effectiveness of the new barrier. Therefore, it is best to remove the old plastic and install the new plastic over old in your crawl space.
Installing a plastic vapour barrier in your crawl space can prevent moisture damage, increase energy efficiency, and lower the risk of mould and bacteria-related health problems. It can also help to keep out potentially dangerous chemicals and pests, such as rodents and bugs.
