Crawl Spaces: Vented vs. Encapsulated

Your crawl space needs to be dealt with. It is musty, dingy, and dirty. The floors of your house are cold, and your energy bills are just too high. What options do you have for fixing your crawl space, and which method is best for your home and budget?

South Central Services has insulated hundreds of homes with spray foam insulation. In our service area, there are two common methods of dealing with crawl spaces. Many homeowners with crawl spaces in and around Gettysburg have to chose between these options. While we recommend one method over the other, this article will compare the methods so you can come to your own conclusion.

By the end of this article, you will understand:

• The building science behind crawl space venting and encapsulation
• The products involved in crawl space venting and encapsulation
• The costs of crawl space venting and encapsulation
• The results of crawl space venting and encapsulation

Building Science: Vented vs. Encapsulated

In southern Pennsylvania, vented and encapsulation are the two most common methods for handling crawl spaces. Each method tackles the problems of crawl spaces in different ways.

The Science Behind Vented Crawl Spaces

Vented crawl spaces operate on the principle that the ground will secrete moisture and that air movement will dry it out. With enough air movement, the humidity in the crawl space can be offset. Using air to dry out the crawl space, any insulation in the rafters does not have to be concerned with vapor transfer.

These crawl spaces have vent holes around the foundation to facilitate air movement. The vent holes allow air in at will. Sometimes, plastic sheathing is placed on the ground to prevent excess moisture from entering the crawl space air. The ceiling of the crawl space is insulated to slow air exchange and create a separate climate between the vented crawl space and the living space.

Unfortunately, there is not enough air movement to offset the moisture in the crawl space. External factors like moisture from the ground, ventilation, and outside temperature and humidity dictate the climate in these crawl spaces.

The Science Behind Encapsulated Crawl Spaces

Encapsulation operates from the idea that crawl spaces cannot address excess moisture, no matter how much air circulates through them. Rather than allowing air to circulate randomly through the crawl space and eventually into your living space, encapsulation seals the crawl space from outside elements.

Encapsulated crawl spaces use spray foam and plastic sheathing to create a seamless air and vapor barrier. The ceiling of the crawl space is left open so the conditioned crawl space air can be exchanged with the rest of the home.

Even though encapsulation adds cubic feet to the home's conditioned space, the net energy usage is lower because conditioned air does not escape through the crawl space.

Products: Vented vs. Encapsulated

On the surface, the products used for venting and encapsulation look remarkably similar: an insulation product and a plastic sheathing product. However, the details of the features of these products make these applications quite different.

Products For Vented Crawl Spaces

The insulation product of choice in a vented crawl space is a fiberglass batt. This batt insulation is used to fill the ceiling cavities of the crawl space and provide some thermal barrier between the home's living space and the crawl space. Since the crawl space is open to the circulation of outside air, this insulation layer is essential.

Vented crawl spaces usually have 2 to 6 mil plastic sheathing placed on the floor to act as a vapor barrier. However, the sheathing cannot serve as a vapor barrier if it is not sealed. Additionally, 6 mil plastic is not thick enough to prevent vapor transfer. At best, thin plastic sheathing sealed around the crawl space edges can act as a vapor retarder.

Products For Encapsulated Crawl Spaces

An encapsulated crawl space could use closed cell spray foam, rigid foam board, tape, plastic sheathing, and dimple mat. Which products are used depends on the crawl space and who completes the encapsulation.

DIY encapsulations classically use rigid foam boards on the walls of the crawl space. Foam board creates an effective thermal barrier, especially if the crawl space walls are flat. However, foam board cannot offer a vapor barrier like closed cell spray foam can. An encapsulation completed by a professional will use closed cell on the walls to ensure both a thermal and a vapor barrier.

The other non-negotiable products involved would be crawl space tape and thick plastic sheathing. The tape is necessary to seal the plastic sheathing and ensure it can act as a true vapor barrier. Also, to that end, the plastic sheathing must be at least 12 mil thick. For crawl spaces that experience more foot traffic, 20 mil may be more desirable. Any thinner and the plastic sheathing will only be a vapor retarder.

An optional product for an encapsulated crawl space is a dimple mat. Dimple mat is used for additional floor durability and extra drainage capability.

Encapsulated crawl space may also use a dehumidification system to maintain the humidity levels in the crawl space.

Costs: Vented vs. Encapsulated

How much will venting and encapsulation cost for your crawl space? One method is much less expensive than the other but may not offer reliable long-term results.

Cost Of Vented Crawl Spaces

Vented crawl spaces are inexpensive, which is why they are a predominant method in southern PA. Fiberglass batt insulation costs between $1.00 and $2.00 per square foot. If any plastic sheathing is placed on the ground, it would likely cost between $0.05 and $0.45 per square foot.

Cost Of Encapsulated Crawl Spaces

Encapsulated crawl spaces are comparatively more expensive than vented ones. To calculate the cost for your crawl space, all you need is the square footage of the crawl space floor.

Encapsulation costs between $4 and $8 per square foot in our service area. Which price you would pay depends on several factors, but you can estimate an average of $6 per square foot for basic calculations.

If you want to see some examples of the cost of encapsulation, check out our guide to estimating the cost of encapsulation.

Results: Vented vs. Encapsulated

Venting and encapsulation methods use different products, cost different amounts, and are based on different understandings of building science. What do these differences mean for performance?

Performance Of Vented Crawl Spaces

A vented crawl space has no effective vapor barrier. Even if plastic sheathing is placed on the floor, it is not sealed to create an actual barrier. Without a vapor barrier, the crawl space faces a lot of moisture and humidity.

When the batt insulation is exposed to excess humidity, it absorbs that moisture. Over time, batt insulation will fall out of the crawl space ceiling because it becomes too heavy with water to stay rooted in the ceiling. Once the insulation has fallen out, it is rendered ineffective.

Even in the best scenarios, vented crawl spaces cannot offer reliable performance. Batt insulation does not create an airtight seal, so any mold, mildew, or mustiness in the crawl space can infiltrate the air in your home. The cold air of the crawl space can also make your floors cold.

Performance Of Encapsulated Crawl Spaces

Encapsulated crawl spaces seek to solve the problems that venting could not solve. Rather than letting musty air leak between the crawl space and the living space, encapsulation invites clean air to exchange.

Encapsulation seals the crawl space off from the elements to stop the potential for mildew and mold. The air in the crawl space becomes cleaner. The excess humidity is dealt with and protects the home's structural integrity.

Since the conditioned air in the home cannot escape through the crawl space, energy bills are lowered. The HVAC system does not have to compensate for air leakage or random temperature shifts.

Encapsulation does not deteriorate over time. At most, the dehumidification system should be checked periodically for regular maintenance. The vapor barrier on the floor may need occasional repairs if any tears occur.

The Bottom Line About Vented And Encapsulated Crawl Spaces

Both venting and encapsulation are used for crawl spaces in southern Pennsylvania. Venting has long been a popular method due to its low investment cost. However, the venting method is based on a faulty understanding of air circulation.

In our climate zone, no amount of air circulation beneath the home will address excess moisture. And even if that were possible, the circulated air would impact the temperature and air quality of the house above.

Encapsulation has become a sought-after method to solve the issues that venting cannot solve. While encapsulation is an expensive investment for an area of your home that you do not live in, your crawl space does influence the quality of life in your home. By encapsulating it, you can improve your air quality, lower your energy bills, and have a more comfortable experience in your home.

Now that you understand the differences between vented and encapsulated crawl spaces, your next step is to:

• Calculate a rough estimate of encapsulating your crawl space
• Walk through the crawl space encapsulation process with South Central Services
• Learn whether encapsulation is really worth investing in