Do You Need A Vapor Or Moisture Barrier Over the Deck Floor?

Most people are misunderstood that the vapor barrier is the material for building walls only. It is used for walls and floors. A vapor barrier on the floor is called a moisture barrier. The materials are effective in avoiding floor damage.

For those who plan to have a deck in the house, a moisture barrier over the deck floor is something you must consider.

Before going far to buy this material, you must read some knowledge about the moisture barrier for the deck below.

What is Moisture Barrier?

Water vapor in the deck can cause severe damage without any good maintenance. The wet deck could cause mildew and mold, which later would destroy the deck floor. That is why installing a moisture barrier is crucial for all homeowners.

A moisture barrier is usually a plastic sheet. The function is to slow moisture from the subfloor. It is installed in areas with excess humidity or prone to dampness, such as under the deck floor. You can buy this barrier separately or choose the floor’s underlayment with a built-in moisture barrier.

The Difference Between Moisture Barrier and Vapor Barrier

The jargon used in the construction sector frequently confuses people who wish to improve their homes or businesses.

Moisture and vapor barriers are a bit of jargon. Still, they refer to essential treatment for building long-lasting buildings and meeting many new LEED (Leadership in Energy and Environmental Design) standards.

These two words fundamentally mean the same thing. Moisture and vapor barriers are made to stop water from getting through the building materials and into the air.

Most people call this a “vapor barrier.” But groups like the US Department of Energy say that “diffusion vapor retarders” is a better way to describe what a vapor barrier is meant to do.

A vapor barrier can’t stop all water vapor from getting through.

Why Use Moisture Barrier?

With a moisture barrier’s function, the barrier’s installation on your deck floor is recommended. Besides preventing mold and mildew, there are other benefits of installing the barriers. Check out some benefits of it in the following explanations.

1. Pest Control

The space under your deck floor can be the best place for many pests and wildlife to live in. Their existence somehow causes damage to the deck floor. However, a moisture barrier helps eliminate or minimize the pests and wildlife on your deck floor.

2. Structural Protection

The deck foundation is vital to its structure. The moisture on the deck floor can lead to wood rot and cause significant structural damage. The moisture barrier installation would reduce the moisture under the deck floor and protect the structure.

Different Types of Moisture Barrier

Vapor barriers can be made of many different things and used in many ways. Rigid foam insulation works as a vapor barrier pretty well. Most items are made of polyethylene plastic, which lets the least amount of water through.

Bricks are often painted and primed with vapor barrier paints and primers, which make a versatile vapor barrier. The aluminum foil keeps more water, but that isn’t always good.

Water vapor is measured by its permeability. In this case, there are three classes or categories of moisture barriers for flooring. You can choose the moisture barrier from class I to class III, depending on your need for the deck floor.

1. Class I

This class of moisture barrier is known as the strongest water vapor. As an impermeable barrier, there will not be any fluid passing through the material. Some examples of moisture barriers in this class are sheet metal, glass, rubber membranes, and plastic sheets.

2. Class II

The second category refers to semi-permeable materials so that some fluid can flow through them.

If you choose this class II moisture barrier, you will get plywood, extruded polystyrene, bitumen-coated kraft paper, and 30-pound asphalt-coated paper.

3. Class III

In Class III, the vapor barriers are permeable, meaning water can pass through. Some materials included in this category are gypsum board, brick, concrete block, 15-pound asphalt-coated paper, board lumber, and fiberglass insulation.

When Do You Need Moisture Barrier Over the Deck Floor?

Natural wood is hygroscopic, which means it can take in or give off moisture to its surroundings. It does this to find a balance between the wood’s humidity and its surroundings’ humidity.

So, wood tends to take in or let go of water based on the conditions in its environment, such as relative humidity and air temperature.

Each environmental condition corresponds to a certain level of humidity in the wood, called its moisture content. Balance of water and air.

Regarding the best time for moisture barrier installation, you need to consider three things here. Those are your deck’s climate, grade level, and subfloor material.

  • Climate

The climate becomes one of the considerations when you plan to install a moisture barrier over your deck. Moisture barriers are not as common when your place has a mild climate. Meanwhile, water vapor on the deck is necessary for the drastic climate change areas.

  • Grade Level of the Deck

Another consideration is the grade level of your deck. The deck on the first and second floors will have different types of moisture barriers. The lower level commonly needs an impermeable type of barrier.

  • Subfloor Material in the Deck

Your deck subfloor material will decide what your moisture barrier type is. When you have an easy-to-porous subfloor, it means that you need an impenetrable barrier. Meanwhile, you can skip the moisture barrier installation for the subfloor material, such as iron or steel.

How to Install Moisture Barrier on Deck Floor?

To get the best benefits of a moisture barrier for the deck floor, you must install it properly. The careless barrier installation will reduce the function and waste your money and time in preparing all the equipment and tools.

In addition, the installation can be done well after considering the size of the area and the barrier class or category.

Moreover, if you have no experience installing the barrier, it is better to ask a professional to do it.

However, those who want to learn to install the moisture barrier over the deck floor can see the steps on youtube or ask a professional to install them directly.