Crawl Space Radon Mitigation: Ultimate Guide

A crawl space is a space or compartmentalized space within a building or other structure. Crawl spaces are often found beneath buildings and can be accessed using doors, hatches, or sometimes via an egress window.

Why is crawl space mitigation important

As you know, radon gas enters a home through the soil beneath it. Since a crawlspace is located below the house, it is the first place where the radon gas enters. This means that the concentration of the radon gas is much higher in a crawl space.

A crawl space

As radon is a heavy gas,  most of it won’t enter the house’s living areas. However, as the concentration of the radon gas in the crawl space increases, the gas needs someplace to go, and it will slowly seep into the lower levels of your home. This can result in cancer-causing health hazards, and so this gas should be mitigated.

Should you test for radon in the crawl space?

Radon is present in all the houses in the US, and one out of fifteen of them has unsafe radon levels. EPA recommends that the home should be fixed if the levels exceed 4pCi/L. Therefore, it is important to test for radon in the house to ensure that they are taken care of as soon as you find high levels.

However, no one tests the radon levels in the crawl space. The testing is done in the room above the crawl space, not inside the crawl space.

For testing, a long-term or short-term test kit is placed inside the room just above the crawl space. If the tested levels are below 2 pCi/L, you don’t need to do any mitigation. If the levels exceed 4, the house should be fixed, and if it is between 2 to 4 pCi/L, further reduction is recommended.

How to mitigate radon in crawl space

There are mainly five ways to reduce radon levels in crawl spaces. They are;

Natural ventilation

The easiest way to minimize radon exposure in a crawl space is to ensure proper natural ventilation. This can be easily achieved by opening the windows of the crawl space. However, this is only a temporary fix as windows cannot be kept open at all times, especially during the winter months. In addition, radon levels get higher in winter, so this method is not very practical. Besides, many homes don’t have crawl pace windows. Keeping the windows can also lead to mold growth and other related problems.

Seal the ground

Another method of reducing radon levels in a crawl space is by sealing it with a material that reduces the air exchange with the outside atmosphere. Materials like concrete make perfect encapsulation as it has almost zero air exchange. Even though radon gas can seep into the house through the cracks on the floor, a concrete floor can reduce radon levels if they weren’t high to start with.

If your crawl space already has a concrete floor, try to seal its cracks and holes as much as possible. This will limit the number of paths for the radon to seep into the crawl space.

Crawlspace depressurization

Crawl space depressurization is another method used to lower radon levels in the crawl space. This system works by actively venting the crawlspace with the help of a fan. This system removes the radon gas in the space as soon as it forms. However, this is not as efficient as the other methods and has some drawbacks. The main drawback of the system is that it uses electricity. Another is that the negative pressure created by the fan sucks in more radon gas into the crawl space. This system only works if the crawl space and the house’s living areas are perfectly sealed off.

Crawl space encapsulation

This is the most popular radon reduction technique used in crawl spaces. In this method, a thick plastic sheet, aka vapor barrier, is used to cover the crawl space floor, this making it air-tight. The ends of the sheet are sealed to the walls of the crawl space. This prevents radon gas from entering the crawl space. Even though the sheet is not 100% impermeable, it offers resistance, so the radon gas chooses other easy paths to escape outside.

This method is very effective in radon reduction and costs less than an active mitigation system. If your house had radon levels lower than 4pCi/L, this is a good method to implement for further reduction.

Crawl space encapsulation is also effective in reducing the moisture problems in your home. It prevents any soil moisture from passing into the house. In addition, the encapsulation also prevents pests and insects from coming into the house.

Sub-membrane depressurization system

If the radon levels in the house are very high, an active mitigation system is recommended. A sub-membrane depressurization system involves encapsulating the crawl space and then using a radon fan to suck the air out from beneath it.

working of Sub-membrane suction radon system for crawl spaces
Sub-membrane suction radon system for crawl spaces

In this system, the floor and the crawl space walls are sealed air-tight using a thick vapor barrier. Then an intake pipe connected to a radon fan is inserted through this vapor barrier. The pipe should end just below the vapor barrier, and the plastic sheet should be secured around it to prevent any air from leaking into the crawl space. The other end of the radon fan is connected to a vent pipe that ends above the house’s roofline.

When the fan is run, it creates a negative pressure zone under the vapor barrier. This zone acts as a collection point of radon gas. The gas is then sucked by the fan and vented through the radon pipes that reach above the house’s roof.

This system is very effective in removing radon levels and works well in homes that had high levels of radon before. However, it is not needed if the house’s level of radon was lower than 4pCi/L.

Charles John

A novice DIYer who learns about home ventilation. I am a mechanical engineer and have a basic knowledge of HVAC systems but I learn continuously to make myself the best blogger in that space.

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