Everyone wants to build a home that lasts. Using a moisture barrier (or vapor retarder) on your walls, ceilings and floors is a good way to keep your house in tip-top shape for a long time. You might be asking, is it really necessary to use a barrier even on floors? To help you answer this question, we've taken the liberty of listing below some important points about when to use moisture barriers on floors.

You will need to apply moisture barriers on your floor when you have one or a combination of any of these three things: Mixed-humid climate, below-ground floor foundations, and concrete subfloors.

In this article, we'll take a closer look at each of these conditions and what they mean for your home. We'll also look at the best moisture barriers for hardwood floors, what happens if you don't use underlayment, and more. Read on to learn all about it!

When to use moisture barriers

According to the U.S. Department of Energy, ensuring that a moisture barrier carefully seals the seams and areas of penetration in your floors is central to effectively controlling moisture. We've seen that you should use moisture barriers in certain climates and with certain types of floors, but let's take a closer look at each condition.

 Mixed-humid Climate

If you live anywhere from New York to Oklahoma, then weather-wise you have it all -- The long humidity of summer and the dry coldness of winter. The key to a sturdy house is proper moisture control. This can be tricky in states in mixed-humid climate zones as the summer humidity is not particularly house-friendly.

 Foundation Floors

Floor foundations, such as basements and crawlspaces, that are below ground level are usually dark and cold. Add damp and this becomes the perfect mold-nourishing environment. Not having a moisture barrier installed on the walls and floor is an open invitation to molds. A mold infestation can start a house rot and cause undesirable health effects.

 Subfloor material

Concrete is a porous material and, therefore, allows moisture from the ground to penetrate. If you already have or plan to use concrete for your subfloor, it is wise to install a moisture barrier with your underlayment.

Is underlayment the same as moisture barrier?

The terms "underlayment" and "moisture barrier" can be confused as the same. Although there are underlays that have a pre-installed moisture barrier, they are different in their purpose. In the book, Fundamentals of Building Construction: Materials and Methods, underlayment is defined as the substrate that is placed over a subfloor to act as a stiff backing, with a smooth surface for the application of the floor covering. Meanwhile, a moisture barrier is a membrane that has the distinction of being water-repellant and moisture-resistant.

Depending on your purpose, there are different types of materials used as underlayment:

 Particle boards

These are compressed wood strands glued together with a smooth surface used as an underlay for resilient flooring.

 Plywood

Plywood that is lightly sanded makes good material for either a subfloor or floor underlayment. It gives the substrate a matter and smoother surface without compromising its structural performance.

Fiber Boards or Cement Boards

These are eco-friendly materials. They are usually made from organic matter like wood and vegetable fibers. Recycled papers are also used to make fiberboards for carpeted flooring.

Orient-Strand Board (OSB)

OSB is similar to particle board in that it is engineered wood made by gluing and compressing wood strands together. The difference is that OSB doesn't always provide as smooth a surface as other materials.

Panels or Tile Underlay

Panels or tile underlay are easy to install. They are pricier than other types of underlay but it also acts as a moisture barrier. They are ideal for carpet or laminate flooring.

Foam or Cork

These are floating underlays detached from the subfloor. Floating underlays allow room for expansion and do-it-yourself installations.

Felt/Fiber Underlayment

 Felt/Fiber underlayment gives you the best value for your money. Its 6mm thickness acts as a moisture barrier while providing sound absorption and floor insulation.

Rosin Paper

This is the cheapest among the underlays. It is a thin, recycled paper that keeps the floor from dust and too much squeaking. However, it neither offers moisture protection nor insulation.

The market is abundant with underlayment options. At least now, you have an idea of what materials best suit your preference and complement your home.

What happens if you don't use underlayment?

Regardless of whether your floor is wood or concrete, the ideal floor anatomy from the bottom up should be the subfloor, moisture barrier, underlayment, adhesive, and floor cover.

Now you may think that's a lot of layers. Maybe skipping on the less critical parts, like the underlayment, is alright plus that's savings. That thinking right there is anything but a good idea.

Underlays are important because they serve five major purposes:

1. Cushion – if you like going around the house bare feet, it wouldn't hurt to have soft flooring underfoot.
2. Sound absorption – underlayment made from felt/ fiber performs well as soundproofing media.
3. Insulation – this comes particularly beneficial for those living in cold places. A warm floor in cold weather is not a bad deal.
4. Better adhesion – this is helpful to keep tiles or stone floors from popping out of place. Underlays are not prone to expansion, thereby making them a good medium for applying floor adhesives.
5. Moisture protection – Some underlays come pre-installed with a moisture barrier. It may cost a bit more than other types of underlayment but your investment will go a long way.

All these considered, two things will happen if you forego the use of underlayment: (a) you will settle yourself in discomfort, and; (b) sabotage the life span of your house.

 Should I seal my subfloor?

Installing moisture barriers on the floor is useful when you are still building your home or revamping your interiors, but what if your house is already built without the promise of a make-over soon? Can you still protect your floors from too much moisture? That's where sealants come in.

Accumulation of moisture and dirt can cause damage over time. Floor sealing is a method that uses a polymer-based coating to cover all pores and cracks in the subfloor. This sealant dries to a clear, smooth surface that is water and dirt-resistant. However, polymer sealants can be toxic, so location, ventilation, and floor material are things we need to consider before using sealants.

 What is the best moisture barrier for hardwood floors?

When installing wooden floors, you will want to make sure that your subfloor and flooring are protected from moisture. The best set-up would be installing a plastic sheeting on top of the dirt under the subfloor.

Between the subfloor and hardwood, you will need a material with a perm rating of 0.7 to 50 as recommended by the National Wood Flooring Association, which will also meet the standards of ASTM D 4869 or UU-B-790.

For hardwood, the perfect material would be an #15 asphalt-saturated felt paper which is underlayment and moisture barrier in one.

Many hardwood soundproofing underlayments also include a moisture barrier, such as the one below.

Click here to see this underlayment/ moisture barrier on Amazon

Conclusion

To make absolutely sure that the installation of a floor moisture barrier is necessary, any of these three things must be present: Mixed-humid climate, below-ground floor foundations, and concrete subfloors. Ultimately, to ensure the right material is chosen and proper procedure is observed, it is safest to consult with professionals. 

If you found this article helpful, be sure to check out these great posts:

Should You Use a Vapor Barrier on Basement Walls?

How to Install Vapor Barrier on Concrete Basement Floor