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Do Bathroom Walls Need a Vapor Barrier? (Answered!)

If you’re having water leakage issues, and molds in your bathroom, and you’re annoyed with how your bathroom is always wet and soaked in water.

Then you must know that to protect your bathroom walls from moisture, vapor barriers need to be installed.

Do bathroom walls need a vapor barrier?

Bathrooms are highly prone to water damage and moisture problems; hence, need vapor barriers to stop moisture from penetrating through the walls. A vapor barrier will stop any form of condensation and this process will eventually lead the water vapor and moisture back to the ambient air.

Is vapor barrier necessary in bathroom walls?

Reasons behind bathroom walls need vapor barrier are given below –


A vapor barrier prevents forming moisture in your bathroom walls. The bathroom tends to be hotter due to hot water and forms steam which may condense into water vapor.

A vapor barrier in the bathroom walls protects the dry part of the bathroom walls from getting moisture and dampness.

Climate conditions:

If the temperature difference outside your house and in the bathroom is a lot different during a whole season and less in a day.

It will cause the essential materials to act differently and the exposed area of your bathroom will catch vapor and condense accordingly.

Prevents mold or mildew growth:

The condition of your bathroom is much different than other areas of your house and it is most likely to grow mold or mildew due to damp and moist collection.

Since the bathroom always tends to be a wet place, it requires immediate drying of bathroom walls to give protection against mold. The vapor barrier plays a significant role in this regard.

Water damage:

Water damage is very common in the bathroom and the bathroom walls get easily rotten. Moreover, the surface coating gets worn out and comes off from your bathroom walls.

A vapor barrier can effectively protect your bathroom walls from such water damage.

Do I need a vapor barrier in my bathroom ceiling?

You will need a vapor barrier in your bathroom ceiling as well to maintain a controlled ventilation process. In colder climates, you can use sandwiched plastic vapor barriers between the interior surface and the insulation.

And in hotter climates, you’ll have to install a vapor barrier on the exterior part to protect humidity and moisture from entering the bathroom.

However, you have to seal and block if there’s any leak on the ceiling before installing a vapor barrier as it may trap the moisture inside and interrupt with ventilating.

Hence, some experts recommend not using a vapor barrier on the ceiling.

Do you need a moisture barrier under the tile?

Whether you need a moisture barrier under the tile depends on your climate and the type of flooring.

If you’re installing a subfloor over the concrete, you may want to place a sheet of plastic underlayment to protect the bathroom floor from extra moisture.

Moreover, in colder climates, or heavy humidity zones, you’ll require a moisture barrier to keep it free from dampness and moisture.

However, if you’ve already set up a sheet membrane over the tile substrate while building up the bathroom floors, you will not need a moisture vapor under the tile also.

Because moisture would get soaked by the liquid membrane on the floor surface and would never reach under the tiles.

Do I need a vapor barrier behind the cement board in the shower?

You will need a vapor barrier behind the cement board in the shower to stop the moisture from penetrating the studs and drywall behind the cement board. 

The cement board itself is very heavy and porous enough to absorb the moisture and prevent it from rotting and molding.

In addition, a vapor barrier behind the cement board protects the moisture from entering further into the infrastructure or other boards behind the concrete.

Showers tend to create more moisture and steam from hot water when meeting the cold air. A vapor barrier effortlessly acts as a shield to protect that area from moisture.

In fact, it even stalls the forming condensation and thus stops the moisture from infiltrating further.

Where do you put a vapor barrier in a bathroom?

A vapor barrier is essential to keep your bathroom hygiene and dry. Effective places to put a vapor barrier is given below –

On the surface:

This is the easiest and commonplace to install your vapor barrier on. If you’ve already built your bathroom and you’ve no plan on remodeling it anytime soon, but you’re enduring water damage.

You can simply just put a coating of liquid vapor membrane over the tile substrate with the help of mesh tape.

You can still maintain the thickness continuity while securing any uneven places or joints. Apply another layer of fiber mesh tape to give it a smooth, professional touch.

Behind the concrete:

If you want to ensure 100% protection from moisture, it is recommended that you install a vapor barrier behind the tile substrate.

You can use plastic sheeting for this cause as this is the least permeable element and will minimize any leakage.

However, if you want more of a green option, you can go for 15lb felt paper and place it onto the wood studs and drywall. 

In the case of a non-continuous piece of tape, you can use water-resistant tape for the overlapping edges; ensure at least 2 to 4 inches of overlapping pieces.

Moisture Sandwich:

If you’re applying a liquid coating on the surface while building your bathroom, then you’ll be installing a vapor barrier by default.

On the other side, installing a plastic vapor barrier behind the substrate will make it a moisture sandwich condition. That is a vapor barrier on both sides of the walls.

What can I use for the moisture barrier in the shower?

Moisture barriers are often confused with vapor barriers. Be a little careful when you’re installing a moisture barrier in your bathroom.

The task of moisture barriers is to transfer any moisture penetrating through drywalls from steam, condensation, or leaks to the insulation.

You will need a moisture barrier if you’re using batt insulation in your bathroom to stop moisture. For moisture barriers, you can use the following things –

6-millimeter poly sheets:

These 6-millimeter poly sheeting will prevent moisture from entering the floors and basement of your house. Install the sheets on the walls above six to eight feet above the ground. A strip of woods would do fine in this case.

However, you cannot directly adjust them on the walls but by installing the poly sheeting on the wood strip. 

Rigid foam:

You can place the rigid foam on the corners and gaps of the walls to stop moisture from entering the drywall. They’ll need sealing from outside with the spray foam.

Exterior wrapping:

In this method, you will hang a piece of wood on the exterior side of the wall. Thus, it will direct any moisture onto the floor away from the insulation and prevent it from entering the walls.

What walls need a vapor barrier?

Not every wall of your house needs a vapor barrier. Whether you actually need a vapor barrier depends on your climatic conditions and the codes of your house.

However, in relatively colder climates, high-humidity zones, the temperature difference inside of your house and outside is a lot. In such cases, you’ll need a vapor barrier in your bathroom walls, basement walls, garage walls, shed walls, and so on.

You tend to use water the most, in the bathroom which causes this room to stay moist and damp. As a result, moisture and condensation occur.

The same dampness can be found in your basement and garage because of a lack of adequate air and light.

Can I use plastic sheeting as a vapor barrier?

Plastic sheeting is one of the excellent forms of vapor barriers as plastic is the least porous element. Hence, it will stop the moisture from penetrating through the walls. 

Moreover, properly installed plastic sheeting on the walls will hinder the form of any condensation on the internal surfaces. On top of that, the ambient air will reabsorb the condensation formed on this plastic sheeting.

Thus, giving full protection to your bathroom walls and minimizing water damage.

You can use plastic sheeting on the interior, exterior walls. Or you can follow the standard practices of installing vapor barriers that come in rolls.

Do vapor barriers cause mold?

The purpose of vapor barriers is to prevent moisture and moldings. However, low grade and improperly installed vapor barriers can cause mold due to window leakage, imbalanced pressure, airflow, lifestyle pattern.

Furthermore, when you install a vapor barrier on the interior, they are meant to prevent inward drying, which can potentially lead to other moisture problems like dampness and mold.

Does drywall act as a vapor barrier?

Drywall can at best act as an air barrier but no vapor barrier. That is, drywall can stop entering the outside air to your conditioned inside air. However, drywall cannot effectively prevent moisture from penetrating through it.

In cold climates, you must install vapor barriers to the interior walls as they tend to be more humid. Likewise, in the hotter climate, a vapor barrier on the exterior walls would effectively stop the water vapor and humidity from entering the drywall and studs.

That being said, to protect your bathroom walls from moisture, mold, and water damage, vapor barriers can be of great help to you.