Installing a Vapor Barrier in Your Basement

a roll of waterproofing material
  • 5-15 hours
  • Beginner
  • 500-10,000
What You'll Need
Vapor barrier
Waterproof tape
Ladder (optional)
What You'll Need
Vapor barrier
Waterproof tape
Ladder (optional)

Installing a vapor barrier in your basement saves you money on your utilities and keeps your basement dry and free of mold and mildew, which is detrimental to your family’s health. A vapor barrier basement DIY project is not difficult, and it can potentially save you big on your energy costs in the long run.

What Does a Vapor Barrier Do?

Because air is constantly heating and cooling, it is hard to control how much moisture enters your home. That's where vapor barrier installation comes into play.

A vapor barrier basement protects your home from water damage. The barrier blocks vapor from accumulating and creates a waterproofing room envelope.

It is a plain fact that the more moisture enters your home, the more you will also find mold and mildew. Breathing in air saturated with mold promotes respiratory complications and can create serious health risks.

One of the best ways to prevent mold from happening is by installing a vapor barrier in the basement of your home. Mold prevention is much easier than mold treatment once this terrible stuff has taken root.

Another great benefit to a vapor barrier: it can also increase your home's energy efficiency. Sealing out moisture means sealing out air as well, after all.

A vapor barrier seals up the cracks in the basement. This prevents heat loss in the winter and cool air loss in the summer, which in turn reduces your energy bill.

Anything that makes your home more energy efficient will reduce your energy costs, and that’s always beneficial.

basement with moisture barrier

Types of Vapor Barriers

There are multiple types of vapor barriers. Plastic sheeting is common, but there are several other options to choose from.

Polyethylene plastic sheets, builder's foil, and foam board insulation are the most common materials used for vapor barriers. Rubber, sheet metal, plywood, and paper are all used as vapor barrier materials.

Vapor Barrier vs Vapor Retarder

There are a lot of products out there, and sometimes, information that seems to be conflicting. What are the pros and cons of a vapor barrier in the basement, and how does this differ from a vapor retarder?

There is a simple answer to how vapor barriers and vapor retarders differ: they don't. The proper name is vapor diffusion retarder but the term "vapor barrier? is still commonly used.

Anything that is marketed as a vapor retarder is a vapor barrier, so don’t worry about figuring out the difference between the two.

Where Are Vapor Barriers Needed?

There are many reasons why a vapor barrier is a good idea. Areas with high humidity from weather conditions or in areas with spas or swimming pools, or bathrooms can all benefit from a vapor barrier.

Vapor barriers are also helpful in cold climates where the barrier can provide energy efficiency and prevent heat loss. Likewise, vapor barriers are highly effective in hot climates.

Basement areas where moisture can seep in from the ground can also benefit greatly from vapor barriers.

How to Install a Vapor Barrier on the Basement Walls

Installing a vapor barrier as a DIY task is not so difficult. Once you get going, you'll know how to install a vapor barrier even before the job is done.

Start by cleaning the walls of any debris and filling in any cracks or holes with caulk. Seal around all the window and door frames with caulk, too.

Roll the vapor barrier out on the walls. Staple the top of each sheet with a staple every two feet and roll out each sheet so it extends 12 inches past the bottom of the wall out onto the floor.

Overlap each barrier sheet by four inches to ensure a tight envelope around the room. The best vapor barrier for basement walls is one that's well-sealed and installed properly.

Cut holes in the barrier for electrical outlets, pipes, windows, and so on. Seal the edges of these cut areas with a sealant.

Use seam tape to cover every seal of the vapor barrier, applying tape from top to bottom. Press down firmly as you apply the tape.

Check the vapor barrier for any signs of tears or rips. Cover these imperfections with foil or polyethylene tape or caulk.

Wall studs and insulation are installed over the vapor barrier. The overlapping ends of the barrier are then picked up and folded up over the insulation and stapled to the studs.

The drywall is then hung on top of the vapor barrier. Once the walls are painted, the room is complete, and the basement walls are sealed against moisture to protect you from mold and increase the home's energy efficiency.

Install a Vapor Barrier on the Basement Floor

worker installing moisture barrier on foundation

Clean the floor of any debris and remove or sand down any sharp areas that could rip or tear the barrier while you're installing it. Roll the barrier out over the floor, using a cutter to cut pieces to size and cut around piping, ductwork, and other infrastructure elements.

Tape all seams and tape the barrier to the bottom of the walls at the corners of the room. Use the tape to patch any tears or holes.

It will be difficult to place and tape the barrier because it is underfoot. You will need to be careful not to do any damage to the barrier with your feet or your footwear.

The floor is placed on top of the barrier, and the project is complete. The barrier will help keep moisture out of the basement and add a layer of insulation between the basement floor and the ground.

Installing a Vapor Barrier on the Ceiling

Installing a vapor barrier on the ceiling of a basement protects the home above from moisture damage. This is especially useful in basements where a sauna, hot tub, or bathroom may be present, as these areas tend to generate humidity.

Examine all ceiling joists and remove all nails, screws, staples or hanging chunks of wood that you find. You are removing any rough areas that may damage the barrier, so you might need to sand down any particularly sharp spots as well.

Measure the floor to get an accurate measurement for the ceiling without working up over your head, since you'll be doing that enough. Remember to add 12 inches to each panel to overlap the barrier and create an even more protective seal.

Hold the first panel of the barrier against the ceiling, starting in one corner. Attach the panel with staples, placing one every 4 to 6 inches.

Work back and across from that first corner, pulling the barrier tightly and stapling to a ceiling joist every 8 to 10 inches. Don't pull tight enough to strain the plastic but pull tight enough to get a taut barrier.

Overlap the seams as you place each new panel, applying a bead of calk between panels as you install them. Caulk at the corners of the ceiling as well.

Tape all seams of the barrier panels, pressing the tape firmly into place. Double back, folding the excess barrier back over the ceiling, and taping this in place as well to create a better seal.

Check for any holes or tears and patch these areas with tape to complete the project. The vapor barrier is now in place, and the ceiling can be installed.

A ceiling vapor barrier in the basement helps protects the floors above from being affected by basement temperature conditions, another nice feature of adding this barrier.

man installing basement ceiling

Basement Vapor Barrier FAQ

Installing a vapor barrier in your basement is not that difficult, particularly if you're in the middle of a new construction or a remodeling project already. Vapor barriers can be installed on the floor, the ceiling, and the walls to create a tight envelope around the space and protect against moisture while improving energy efficiency a great deal.

What Is a Vapor Barrier?

A vapor barrier is a water-resistant seal, usually in the form of plastic sheets, that can be installed on ceilings, floors, or walls in order to protect the home from moisture, mildew, and mold even as it increases energy efficiency overall. Any DIYer can use tools, sweat, and perhaps a helper or two to get this project done and make their basement far safer and more energy efficient.

Is a Vapor Barrier Necessary in the Basement?

A vapor barrier is never necessary but it can greatly reduce your chances of experiencing mold and mildew, and it can greatly reduce your energy bills, too. A vapor barrier can even help protect you against mild water damage that can otherwise seep in through the ground.

If you live in an area with extreme temperatures or in an area that has a lot of moisture in the soil, such as a swampy environment, a vapor barrier is not essential but it is a very good idea. In places where there is a lot of moisture present, you could experience a lot of moisture damage, mildew, mold and huge spikes in your energy bills during heat waves or cold dips.

No matter where you live, a vapor barrier can decrease your energy costs and decrease your chances of experiencing problems with mold and mildew, which can be very time-consuming and expensive to treat.

In every scenario, and no matter why you install a vapor barrier, you will ultimately get your money’s worth and end up saving money and potential problems as a result of this DIY project.

basement crawlspace with spray insulation

Should a Vapor Barrier Be Used on Basement Walls?

Installing a vapor barrier on basement walls helps prevent moisture damage, protects interior spaces against temperature changes outside and even adds a tiny bit of extra insulation against atmospheric conditions.

No one has to install a vapor barrier, but it is effective, and it will pay for itself in time due to the energy savings you will experience as a result. The mildew and mold protection you receive from a vapor barrier definitely can’t be measured, as they can cause long-term health problems and create unsafe living conditions.

Where Does the Vapor Barrier Go in the Basement Wall?

Vapor barriers are installed before the studs and before the insulation on the wall. They're installed right over the frame and the rest of the wall is added on top of it.

All vapor barriers are installed near the beginning of construction, going right on top of floor joists, ceiling joists and wall frames, along with piping and wiring infrastructure. Everything else goes on top of the barrier before the room is completed.

How Thick Should a Vapor Barrier Be in a Basement?

Vapor barriers are incredibly thin, though there is variation in thickness depending on the barrier material you choose. Vapor barriers can be as thin as a piece of paper, or they can be a thin layer of rubber or metal, among other materials, but in all designs, they are made to have a very small thickness.

To get an effective moisture block, pick barrier material at least 6 millimeters thick. If you have the budget, or if you live in a wet area, consider kicking that up to 12 millimeters.

Pro Tip: Vapor barrier thickness matters less than full coverage. Any gaps will eventually become entry points for moisture, so cover all the way down to your foundation and up to your ceilings, all the way across all the surfaces you want to protect.

What Can I Use for the Basement Vapor Barrier?

Vapor barriers are made with all sorts of materials. Plastic sheeting is common, as is foil and even latex and rubber. Shop around for the material that will work best with your budget and your DIY skills, as some materials are easier to work with than others.

How Much Does a Vapor Barrier Cost?

Adding a vapor barrier to any basement is not a huge expense, especially when you factor in the long-term savings in energy over time. On average, a vapor barrier costs around $0.50 to $0.70 per square foot and will end up reducing your energy bill so that it will pay for itself before too long.

Further Reading

Basement Remodeling Ideas & How Tos

The Benefits and Cost of a Floor Vapor Barrier for Hardwood Floors

How to Add Subflooring to Your Basement

How to Frame Walls for Basement Insulation

How to Insulate Your Basement Walls

Should You Add Drywall or a Drop Ceiling to a Basement?

Should You Insulate a Basement Ceiling?