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Understanding What Makes a Radon Mitigation System Unique

Friday, March 18th by Samantha Walton


If you're considering installing a radon mitigation system in your home, but are unsure what makes your home different than all the rest-- it's all about the foundation.

Houses are generally categorized according to their foundation design. For example, there's the:

  • Basement
  • Slab-on-grade (concrete poured at ground level)
  • Crawl space (a shallow unfinished space under the first floor).

Not every house, however, has just one foundation design to worry about. It's quite common to have a basement under one part of the house and a slab-on-grade or crawl space under another part. In order to reduce the radon levels to a healthy level, a combination of radon abatement methods may be required.

Regardless of the foundation type, your local National Radon Defense contractor can help you! Contact us today for a free estimate for radon mitigation in your state!

Radon Reduction for Homes With Basements or Slab-on-Grade Foundations

Radon is usually reduced in houses that have a basement or a slab-on-grade foundation by using one of these four types of soil suction: subslab suction, drain tile suction, sump hole suction, or block wall suction. In some cases, radon levels can be lowered passively without the use of a fan or actively with the use of a fan.

Active subslab suction (also called subslab depressurization) is the most common and tends to be the most reliable radon reduction method. Insert one or more suction pipes through the floor slab into the crushed rock or soil underneath. Or, insert them below the concrete slab from outside the house. The number and location of suction pipes depends on how easily the air moves in the crushed rock or soil under the slab, and depends on the strength of the radon source. Usually, only a single suction point is needed.

Here's how it works: A radon vent fan connected to the suction pipe(s) draws the radon gas from below the house and releases it into the outdoor air simultaneously creating a negative pressure (vacuum) beneath the slab. Unconditioned spaces in houses or garages are perfect fan locations, especially the attic and exterior of the house.

Passive subslab suction is the same as active subslab suction relies on natural pressure differentials and air currents instead of a fan to redirect the radon from beneath the house. This technique is usually associated with radon-resistant features installed in newly constructed homes. Unfortunately, it’s not as effective in reducing high radon levels as active subslab suction.

Some houses have drain tiles or perforated pipes to direct water away from the foundation of the house. The suction on these tiles or pipes is often effective in reducing radon levels.

One variation of subslab and drain tile suction is sump hole suction.  Since Basements usually have a sump pump to remove unwanted water, it can also be used for a radon suction pipe. The sump is capped so that it can continue to drain water, but now it also lowers the radon levels.

Block wall suction can be used in basements with hollow block foundation walls. This method removes radon and depressurizes the block wall, similar to subslab suction. Oftentimes, it’s used in combination with subslab suction.

Reduce Radon in Homes with Crawl Spaces

Crawlspace ventilation may lower indoor radon levels by reducing the home's suction on the soil and by diluting the radon beneath the house.

Submembrane suction is the most effective radon reduction system being used in homes with crawl spaces. If your home has a crawl space, your radon mitigation system will cover the earth floor with a high-density plastic sheet. Then, a vent pipe will direct the radon from beneath the sheet and then a pushes it outside.

Active crawlspace depressurization is another, though less-favorable, option that directly draws air from the crawlspace using a fan. This technique requires special attention to several items: combustion appliance back-drafting, crawl space sealing, and the possible increase in energy costs-- due to loss of conditioned air from the house.

Radon levels can also be lowered in crawl spaces by passive ventilation or active ventilation. By opening the vents or by installing additional vents, you're actually passively ventilating the crawl space—without using a fan. However, active ventilation uses a fan to blow air through the crawlspace instead of relying on natural air circulation.

Ventilating a crawl space in the colder climates requires proper insulation for water pipes, sewer lines and appliances. Bear in mind, some of these methods could increase your home’s energy costs.

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