Alexei Volkov
Covering a crawl space with plastic sheeting is a great way to insulate your crawl space and prevent moisture from seeping into your home. The process involves laying down a vapor barrier, which can be made of plastic sheeting, directly on top of the entire dirt or gravel floor surface. This will help to keep humidity down, avoid termite and wood rot problems, and prevent the growth of mould and mildew. Before laying the plastic sheeting, it is important to remove any pieces of wood or cardboard, as well as any standing water, from the crawl space. The plastic sheeting should be sealed with duct tape and construction adhesive, and can be capped with concrete or covered with gravel or sand for added protection.
Characteristics and Values of Covering Crawl Space with Plastic
| Characteristics | Values |
|---|---|
| Why cover crawl space with plastic? | To prevent water vapour from seeping into the crawl space and to keep humidity down. |
| Materials | Polyethylene/poly sheeting, duct tape, bricks, gravel or sand, insulation, vapor barrier, concrete |
| Preparation | Remove all items from the crawl space, especially wood and cardboard. Clean any visible mould or mildew with a mixture of detergent, bleach and warm water. Smooth out uneven ground with a tamper or a 2-by-4. |
| Installation | Unroll the first row of polyethylene along the longest foundation wall and cut to length. Apply double-sided bonding tape 3 inches below the top of the wall. Press the polyethylene against the tape and hold in place with a termination strip made of wood and masonry nails. Trim excess plastic and seal with urethane caulk. Lay the next row of polyethylene, overlapping at least 6 inches with the first row. Seal the seams with duct tape. Place bricks to hold the plastic in place. |
| Additional Tips | Check local building codes for applicable requirements. Cover the foundation walls with insulation to prevent moisture. Lay a layer of gravel or sand over the plastic to absorb moisture and stop drips. |
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What You'll Learn
Prepare the crawl space
To prepare a crawl space to be covered with plastic, there are several steps to follow. Firstly, clear out the crawl space. Remove everything inside, especially items made of cardboard or wood, as these can grow mould and mildew due to the damp conditions. If there is any standing water, remove it as it can breed insects and bacteria. Wear a protective mask during this process. If there are signs of mould or mildew, create a mould killer by mixing detergent, bleach, and warm water, and apply this to the affected areas.
Next, measure the length and width of your crawl space to determine how much plastic sheeting you will need. You can purchase plastic sheeting in various widths, typically ranging from 6 to 40 feet, and up to 200 feet in length. Ensure you have enough plastic sheeting to cover the entire crawl space floor, and consider whether you also want to cover the walls. Some sources recommend extending the plastic sheeting at least six inches up the foundation wall, while others suggest covering the entire wall. Check your local building codes for applicable requirements; for example, California requires a Class I vapour retarder for exposed earth in crawl spaces.
If your crawl space has a dirt floor, it is recommended to smooth the ground with a tamper or a 2-by-4 if it is uneven. This will create a more even surface for the plastic sheeting to lie on.
Now you are ready to begin laying down the plastic sheeting. Unroll the first row of polyethylene next to your longest foundation wall and cut it to the length of the wall. Apply double-sided bonding tape a few inches below the top of the wall, leaving an uncovered area for future visual inspections for termites. Press the top of the polyethylene against the tape and secure it with a termination strip made of wood. You can also use masonry nails hammered through pressure-treated lumber to hold the plastic in place. Trim any excess plastic, and seal the edges with urethane caulk.
If you are using multiple sheets of plastic, ensure there is an overlap of at least six inches between each sheet. Seal the seams with duct tape or construction adhesive. You can also use a pressure-treated nailing strip to secure the plastic to the foundation wall.
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Measure and cut the plastic sheeting
To measure and cut the plastic sheeting for your crawl space, begin by measuring the length and width of your crawl space. Compare these measurements to the dimensions of a roll of plastic sheeting. Rolls of plastic sheeting can vary in size, with widths ranging from 6 to 40 feet and lengths up to 200 feet.
Once you have selected a roll of plastic sheeting that is large enough to cover your crawl space, unroll the sheeting and cut it to size. If your crawl space has a rectangular or square layout, you will need to cut two pieces to length and two pieces to width, ensuring that the pieces are slightly larger than the crawl space dimensions to allow for overlap and a tight seal.
If your crawl space has an irregular shape, you may need to cut the plastic sheeting into multiple pieces to ensure full coverage. Overlap the seams of the plastic sheeting by at least 6 inches and seal them with duct tape or construction adhesive. You can also use a pressure-treated nailing strip to secure the plastic sheeting to the foundation wall.
When measuring and cutting the plastic sheeting, it is important to consider the thickness of the material. For crawl spaces, it is recommended to use plastic sheeting with a thickness of 6 to 10 mil. This thickness will provide an effective vapour barrier and protect your crawl space from moisture and humidity.
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Seal the plastic to the walls
Sealing the plastic to the walls is a crucial step in encapsulating your crawl space. This process will help prevent moisture and odours from seeping into your crawl space and creating issues like mould, mildew, and unwanted odours. Here is a step-by-step guide to sealing the plastic to the walls:
Prepare the Walls:
Start by checking for any signs of pests, mould, or mildew and address them accordingly. Ensure the walls are clean and clear of any debris. If your crawl space includes masonry columns, prepare them in the same way you will prepare the foundation walls.
Apply Double-Sided Tape:
Use double-sided construction tape and apply it firmly and evenly to the masonry walls. If your local building code requires it, leave a small gap of about three inches at the top of the walls for termite inspection. Make sure the tape is applied smoothly and securely, as it will form the base for the plastic barrier.
Unroll the Vapor Barrier:
With the tape in place, it's time to unroll the vapor barrier. Start by attaching it to the tape on the walls, ensuring that the barrier extends higher than the tape. Smooth out any wrinkles or creases as you go.
Secure with Mechanical Fasteners:
Once the vapor barrier is securely attached to the tape, use mechanical fasteners like termination bars to further secure the plastic to the walls. If your walls are concrete, you may need to pre-drill holes for the fasteners. This step ensures that the plastic is tightly sealed to the walls.
Seal with Tape:
After the vapor barrier is attached and secured, use seaming tape to seal any remaining seams or openings. Tape down all seams and openings tightly, including around pipes or other penetrations. This step ensures that your crawl space is completely sealed off from moisture and soil gases.
Optional: Concrete Layer:
While not necessary, some people choose to add a layer of concrete over the plastic sheeting for added protection. Pouring a thin layer of concrete will protect the plastic from any potential damage and allow you to access the crawl space without fear of puncturing the plastic.
Remember to follow local building codes and recommendations when encapsulating your crawl space. The steps outlined above will help you seal the plastic to the walls effectively, creating a protected and healthy environment for your home.
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Add a layer of concrete
Adding a layer of concrete to your crawl space is a method that has been used traditionally to seal off the area. It involves first installing a plastic vapour barrier seal, which is then covered with concrete. This method provides a rigid and durable floor, which is especially useful if you frequently access the crawl space or store heavy objects there.
Before adding concrete, it is important to address drainage and level the surface. This can be done by bringing in a layer of pervious fill and ensuring the ground is even. If the ground is uneven, use a tamper or a 2-by-4 to smooth it out. You will also need to remove any organic soil and fill the area with sand before pouring the concrete.
Next, install a plastic vapour barrier seal. This will act as a physical shield to repel moisture and prevent it from entering your home. The recommended thickness of the plastic sheeting is 6 to 10 mil. Cover the entire crawl space floor with the plastic sheeting, using a wide roll to minimise the number of pieces needed. Overlap all seams by at least two feet and seal them with duct tape. Extend the outside edge of the plastic sheeting up the foundation wall by at least six inches.
Finally, pour the concrete over the plastic sheeting. A typical crawl space floor will only require a concrete layer of 2 to 3 inches thick, and a rough "float" finish is sufficient. The concrete will provide a level surface and a finished look to the crawl space.
While concrete creates a durable and level surface, it may not be the best choice for air quality due to the moisture it can trap. Concrete is also not always suitable for retrofit applications, as it requires stable soils and proper pouring techniques.
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Maintain and inspect
Maintaining and inspecting your crawl space is crucial for the health and safety of your home and family. Crawl spaces can be tricky to maintain as any problems that arise can affect the rest of your home. Here are some essential steps to maintain and inspect your crawl space:
Regular Inspections
Firstly, regular inspections of your crawl space are necessary to prevent issues. It is recommended to have your crawl space inspected annually by a professional. If you choose to inspect it yourself, ensure you wear protective clothing and equipment, such as comfortable clothing, goggles, gloves, and a respirator. During your inspection, check for the following:
- Discolorations on exterior walls and exposed wood.
- Dampness on the walls and wood.
- Pooled or standing water, which could indicate a drainage issue.
- Hanging or lying insulation, which can cause drainage problems.
- Rodent droppings and pin-like holes in exposed wood supports.
- Signs of pests, mould, mildew, dust mites, wood rot, and asbestos.
Preventative Measures
To prevent issues, it is important to seal off areas that could allow moisture and damp air to penetrate. Install a heavy plastic vapour barrier on the floor and attach it to the walls, sealing all vents and openings with foam board or spray foam. Focus on sealing gaps and cracks, including plumbing penetrations, band joists, wiring, and HVAC drain line runs.
Attend to Problems
If you notice any issues during your inspection, it is important to address them promptly. Issues in your crawl space can lead to costly repairs and negatively affect your home's value. Attend to problems with drainage, insulation, and pest infestations. If you are unsure how to resolve an issue, consult a local professional.
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Frequently asked questions
Covering your crawl space with plastic helps to prevent water vapour from seeping into your crawl space and causing excess humidity, a mildewy smell, and wood rot.
You should use a plastic vapour barrier, such as polyethylene or poly sheeting. The thickness of the plastic sheeting should be 6 or 10 mil.
First, remove everything from your crawl space, especially pieces of wood or cardboard that can grow mould and mildew. If there are visible signs of mould or mildew, mix a mould killer using 1/3-cup of detergent, 1/2-gallon of bleach, and 2-gallons of warm water, and apply it to all areas of the crawl space. Next, lay down the plastic sheeting, covering the entire crawl space floor. Use a wide roll of plastic sheeting to minimise the number of seams. If you need to use multiple pieces of plastic, overlap the seams by two feet and seal them with duct tape. Extend the plastic sheeting up the foundation wall by at least six inches. Finally, seal the plastic to the foundation wall with construction adhesive or a pressure-treated nailing strip.
Check with your local building department to learn about applicable codes for crawl space vapour barriers. For example, California requires a Class I vapour retarder for the exposed earth in crawl spaces.
Alternative methods to seal off a crawl space include using concrete or gravel.
