What Is Crawl Space Encapsulation?

Crawl spaces are the area of the home no one wants to talk about. They're usually dirty, musty, and damp. Generally, we try to put them out of our minds. But ignoring your crawl space can cause a number of problems.

For most homes, the crawl space raises energy costs and makes the home uncomfortable. A dirty, musty, and damp crawl space can also lead to mold growth and structural damage. Encapsulation is the only method to address all of these concerns.

South Central Services has insulated hundreds of homes with spray foam insulation. For many of those homes, we've also encapsulated the crawl space. If you've never heard of crawl space encapsulation, you are not alone. This article will explain everything you need to know about crawl space encapsulation.

By the end of this article, you will understand:

• What crawl space encapsulation is
• How encapsulation works
• What problems encapsulation can solve
• Alternatives to crawl space encapsulation

What Is Crawl Space Encapsulation?

The crawl space and the home environment are supposed to be separate. The air you pay to heat and cool should only circulate in your living space. However, there is no effective barrier between these two climates. When air circulates in your home, crawl space air is pulled into your living space.

Crawl space air does not have controlled temperature or humidity. The crawl space climate is determined by external factors. Moisture from the ground, outside ventilation, and outside temperatures all influence the air in your crawl space.

Rather than creating an effective barrier between the living space and the crawl space, encapsulation isolates the crawl space climate from the external environment. The crawl space is intentionally added to the conditioned space of the home. When air is pulled from an encapsulated crawl space, it is temperature-controlled and clean.

Products Involved In Crawl Space Encapsulation

There are three key products related to crawl space encapsulation: vapor barriers, closed cell spray foam, and dimple mat. Let's examine these products in more detail.

Vapor Barriers

A vapor barrier is a crucial component of crawl space encapsulation. We use a barrier at least 12 mils thick to ensure durability and effectiveness. For some crawl spaces, the floor's vapor barrier is 20 mil. Heavy-duty vapor barrier material should withstand crawl space conditions and provide long-lasting protection.

The plastic sheathing must also be sealed to effectively act as a vapor barrier. No matter how thick your plastic sheathing is, the material cannot function as a vapor barrier if not properly sealed.

Closed Cell Spray Foam

Closed cell spray foam is ideal for crawl spaces because it provides a thermal barrier and a vapor barrier. The foam is applied to the crawl space walls to prevent the infiltration of outside air and moisture.

Closed cell spray foam is ideal for our climate zone, Climate Zone 5, where temperatures and humidity vary widely depending on the season. Homes in Pennsylvania, Maryland, Virginia, and West Virginia all have weather patterns that necessitate vapor barriers.

Dimple Mat

Dimple mat is an additional layer that can be added to the crawl space floor for enhanced drainage and durability. For crawl spaces that will see foot traffic, such as those housing HVAC equipment, a dimple mat is a valuable addition.

The dimple mat is a buffer layer between the stone or dirt substrate and the vapor barrier, allowing for better drainage and helping the area dry out underneath the vapor barrier. It typically adds about 3/4 to 1 inch of thickness overall to the membrane. The added cost of a dimple mat is calculated by square footage.

How Are Crawl Spaces Encapsulated?

After these materials are installed, the crawl space becomes a climate-controlled environment. It is sealed and insulated from the outside climate. The encapsulated crawl space can even be used for storage, as the conditions inside will be clean and dry.

But how do these materials create an encapsulated crawl space? Let's walk through the steps to arrive at an encapsulated crawl space.

Step 1: Prep the Crawl Space

Before encapsulating a crawl space, we must remove any existing insulation and debris. Most crawl spaces have pink fiberglass batts in the ceiling that must be removed. We also level the ground to ensure proper drainage and to create a smooth surface for the vapor barrier.

Step 2: Install a Vapor Barrier

After prepping the crawl space, we install a heavy-duty vapor barrier. As discussed earlier, this vapor barrier is typically made of 12 mil or 20 mil thick plastic. This barrier is laid across the entire floor of the crawl space. All seams and joints are meticulously sealed with special tape to ensure that no moisture can penetrate the barrier.

The vapor barrier serves as the primary line of defense against ground moisture. The floor’s vapor barrier effectively locks out moisture and creates a dry environment.

If the crawl space needs additional drainage or durability, we will install a dimple mat before the vapor barrier.

Step 3: Install Closed Cell Spray Foam

After the vapor barrier on the floor has been installed, the walls of the crawl space are insulated with closed cell spray foam.

This type of spray foam not only offers insulating power but also serves as a vapor barrier, helping to control the moisture content in the air within the crawl space.

In our climate zone, Climate Zone 5, closed cell spray foam is usually applied at a thickness of 2 to 3 inches.

Optional: Install Dehumidifier System

Some crawl spaces may need a dehumidifier to control humidity levels. We recommend a dehumidifier in every crawl space that doesn’t have HVAC ductwork running through it. For crawl spaces with HVAC ductwork, the ductwork can be tapped into to add some conditioned air into the crawl space.

For the homes that need the additional dehumidification system, a crawl space-specific dehumidifier can be installed after encapsulation. These dehumidifiers are designed to operate efficiently in confined spaces. Crawl space dehumidifiers maintain a specific humidity level.

Problems Crawl Space Encapsulation Solves

Encapsulation helps with four fundamental problems crawl spaces are known for causing. Let's examine these issues in more detail.

1. Uncomfortable Home Environment

Cold floors and a drafty house are often the result of a poorly insulated crawl space or basement. Most of the air leaking into a house comes from these places. If the crawl space is not insulated, there is no temperature control. When air leaks, it is cold and unpleasant.

Sealing off the crawl space from the outside temperature influences can significantly change the comfort of your home. If air is pulled from your crawl space, it should be conditioned like the rest of your living space.

2. Poor Air Quality

One of the most immediate benefits of crawl space encapsulation is improving indoor air quality. Crawl spaces are often breeding grounds for mold, mildew, and bacteria due to the high moisture levels. These allergens can easily make their way into the living areas of your home as air is pulled from the crawl space. For individuals with respiratory issues or allergies, crawl space air can pose serious health risks.

By sealing off the crawl space and controlling humidity, encapsulation eliminates these risks, leading to a healthier living environment. You'll notice fewer musty odors, reduced allergy symptoms, and a fresher feel to the air inside your home.

3. Energy Inefficiency

A poorly insulated and vented crawl space can be a significant drain on your home's energy efficiency. The HVAC system has to work harder to maintain a comfortable temperature, leading to higher energy bills.

Encapsulation addresses this by insulating the crawl space walls and sealing off external vents.

You may wonder how adding cubic feet to the conditioned space of your home can actually net a lower overall energy use. If your HVAC system is responsible for conditioning more air, would that not increase your energy usage?

The airtight seal of encapsulation significantly reduces air infiltration that comes through the crawl space and into the living space. The air barrier ensures a lower overall energy use. You will notice a difference in energy costs by your next billing cycle, even though you added the crawl space to your thermal envelope.

Additionally, if there is any HVAC in the crawl space, encapsulation moves this system into a conditioned space. When HVAC equipment no longer needs to compensate for heat loss in its ducts, the system runs more efficiently. Stabilizing the temperature in the crawl space reduces the load on your HVAC system.

4. Structural Issues

Over time, excess moisture can damage your home's structural integrity. In a damp crawl space, wooden beams and floor joists can rot and decay, while metal components may rust and weaken.

These issues can lead to sagging floors and cracked walls. In extreme cases, there could be significant structural damage requiring costly repairs. Encapsulation locks out ground and atmospheric moisture, preserving the integrity of critical structural components beneath your home.

Encapsulation itself will not solve existing structural problems, but a spray foam contractor could diagnose structural issues in your crawl space and recommend another professional to address them before encapsulating.

Alternative to Encapsulation: Vented Crawl Spaces

You may have heard about vented crawl spaces. Ventilation and encapsulation are two different approaches to the moisture in crawl spaces.

Vented crawl spaces are designed with the idea that outside air to flow will help keep the space dry. This design typically includes vent openings in the crawl space walls to facilitate air circulation. The vents are strategically placed around the foundation to maximize airflow. By moving enough air through the crawl space, moisture should be carried away to prevent dampness and mold growth.

Additionally, the floor of the crawl space is often covered with a thin layer of plastic, usually between 2 to 6 mils thick, to act as a rudimentary vapor barrier. However, this plastic is rarely sealed correctly, rendering it ineffective as a true vapor barrier.

Why We Don’t Recommend Vented Crawl Spaces

Despite the simplicity of the design, vented crawl spaces have several drawbacks.

First, the assumption that ventilation will dry out the crawl space is often incorrect. In humid climates like southern Pennsylvania, the incoming air can introduce more moisture.

Second, the vents provide an entry point for insects and rodents. The dark, damp environment of a vented crawl space is often an ideal nesting ground.

Vented crawl spaces generally insulate in the floor system of the house with batt insulation. Fiberglass batts are prone to moisture absorption, which not only makes them ineffective but can also lead to mold growth. Over time, the insulation often ends up sagging or falling.

Lastly, vented crawl spaces contribute to energy inefficiency. The outside air that enters through the vents can make it more challenging to maintain a consistent indoor temperature, putting extra strain on your HVAC system and increasing your energy bills.

While vented crawl spaces may seem like a more straightforward and less expensive option, they do not address all of the problems crawl spaces cause. A vented crawl space can lead to higher costs and health risks in the long run.

The Bottom Line About Crawl Space Encapsulation

Crawl space encapsulation makes your crawl space air clean and dry. Encapsulation is an effective way to control moisture, improve air quality, and increase energy efficiency in your home.

By installing vapor barriers on the floors and walls, external temperatures and humidity cannot influence your home environment. While there are alternatives for crawl spaces, encapsulation is a more comprehensive and effective method for managing temperature and moisture.

Now that you know what encapsulation is, your next step is to:

• Weigh the benefits and drawbacks of encapsulation
• Calculate a sample estimate for encapsulating your crawl space
• Discover if DIY crawl space encapsulation is a feasible option for you