do you need a vapor barrier behind cement board

Do You Need A Vapor Barrier Behind Cement Board?

Do You Need A Vapor Barrier Behind Cement Board? When considering a tile or stone floor, the options can be endless. Do you want to go with a classic look like ceramic tile or something a little more flashy, like natural stone?

If you choose plywood, you may be wondering if you need to take extra steps to protect your floor from moisture. The answer is: it depends. Let’s look at some factors to consider when deciding if you need to add a vapor barrier behind your cement board.


Do You Need To Put A Vapor Barrier Behind Cement Board?

The main reason behind installing a vapor barrier is to prevent moisture from penetrating the cement board and reaching the plywood. One factor would be the relative humidity in the room where the tile will go. Even if your home is sealed up tightly, humidity can still get in through cracks around windows and doors. This humidity will affect the moisture content of the air in your house, which may be enough to damage plywood that is not adequately sealed.

Do You Need To Put A Vapor Barrier Behind Cement Board?

Vapor barriers are almost always unnecessary if you’re putting flooring on a concrete slab or another hard surface. This is usually true for above-grade substrates that are not exposed to the elements, such as cement board or wood siding.

Does Cement Board Need A Membrane?

If you have a concrete subfloor, then no extra measures are needed. The concrete will act as its vapor barrier. This means that places where moisture can penetrate your floor, such as joints between the boards, don’t need to be sealed off with mesh tape or similar products before laying out the cement board. If you have plywood, adding a vapor barrier can cost less than $10.

By taking the time to install a membrane, you’ll be protecting your plywood subfloor from moisture damage for years to come.

How Do I Know If I Need A Vapor Barrier?

A vapor barrier is similar to a membrane, but its main purpose is to keep moisture out of the subfloor. If you have plywood subflooring, this product can last up to 50 years with little maintenance required. The membrane usually gets installed over the cement board before laying tile or stones on it. If you want to install your cement board, you’ll need to buy a membrane separately.

Can You Put A Vapor Barrier On Top Of Plywood?

Your plywood subfloor is protected by the vapor barrier. By installing the product first, you can be assured that your floor will last for many years and require little maintenance. The barrier isn’t required if you don’t have plywood subflooring.

How Do I Know If I Need A Vapor Barrier?

If you’re not sure whether or not to install a vapor barrier, consult your local building code. You may find that your city or state has rules that determine what types of products are acceptable for certain installations.

Is Cement Board Waterproofing Necessary?

If you have a cement board subfloor, you can avoid installing a vapor barrier by simply installing the tile over the cement itself. You’re using the concrete as its moisture barrier and avoiding extra installation costs by doing this. Also, remember that most floors at or above grade don’t need membrane protection because of their surroundings.

Frequently Asked Questions (FAQs)

Does Hardie board need a vapor barrier?

There is a huge debate about this. In most cases, it does not make the flooring any more water-resistant.

However, it will dramatically help prevent mold from growing behind the tiles and jacking up your energy bills due to condensation under the tile.

In humid areas such as Florida, it is highly recommended if you are going to install a tile floor with grout joints or any porous tile for that matter.

In most cases, it is not required in Northern climates such as Michigan and New England.

If you install adhered sheet goods such as hardwood laminates over a concrete floor, there is no need for a vapor barrier.

However, if you were to install a floating engineered floor over the concrete, I would recommend using a vapor barrier.

Do you need a waterproof membrane on the cement board?


The cement board is waterproof. If installed properly with fasteners in between panels, there should be no need for a waterproof membrane.

The membrane that requires adhesives for installation would not be recommended due to the possibility of delamination later on down the road when it comes time to replace your living room flooring.

Do you need a green board behind the cement board?

No, a Green board is not required behind a cement board. We would recommend a green board for ceramic tile installation over plywood or backer boards because it provides a smoother surface for the tiles to “key” into. The surface will also clean easier with soap and water. It’s known as “green” because of its light color compared to the cement board.

Does tile need a vapor barrier?

Yes, if you install any type of tile over a concrete floor with grout joints, you must use “kraft paper” behind the tiles before installation.

Do you need drywall behind the cement board?

No, drywall is not recommended behind the cement board. A vapor barrier would be required if drywall were to be installed over the cement board. Cementboard is waterproof and can cause mold contamination in humid or underwater areas. Also, grout joints will absorb water like a sponge causing tiles to pop off the wall if not protected.

The tile is waterproof and does not require a vapor barrier, but the “kraft paper” will act as a barrier to mold growing behind tiles down the road.

Final Verdict: Do You Need A Vapor Barrier Behind Cement Board?

Do You Need To Put A Vapor Barrier Behind Cement Board? Do you need a vapor barrier behind the cement board installation?

Yes, depending on the area. It may be necessary to use one if your house is located in an area with high humidity or dampness, then it may be necessary to use one to prevent mold and mildew from growing inside your wall cavity.

This can occur if water leaks into the drywall and concrete, which will eventually cause damage over time. It’s not required, but we recommend it for areas with higher moisture levels like coastal towns or where there are swampy conditions nearby.

“It’s kind of like insurance; even though you hope you never have a fire, having smoke detectors, fire extinguishers and homeowners’ insurance helps provide peace of mind,” says Karen Fauskett.

Having trouble deciding whether or not to install a vapor barrier? Use our free Do I Need A Vapor Barrier Calculator to find out now!


Leave a Comment

Your email address will not be published. Required fields are marked *