A passive radon system, which is basically the guts of a mitigation system without a fan, can be activated by adding a radon fan in the attic to create suction under the home. It is important that all cracks and openings in the concrete floor are sealed to limit conditioned air (air from the house that you are paying to heat and cool) from being drawn into the mitigation system. This will reduce energy costs and make the mitigation system work better.

These photos are of passive radon systems. Passive systems are installed on all MN homes that were built after June 1, 2009 (if the building permit was pulled after that date). These homes typically have 4″ of washed rock, perforated pipe and six mil poly under the concrete floor. There is a 3″ PVC pipe tied into the perforated pipe that extends from the lowest level of the home, up through interior walls, into the attic and out through the roof. There is a label on the pipe identifying it as part of a radon reduction system. There is an outlet and a light in the attic so that a radon fan can be added at a later date. Passive radon systems reduce radon by about 50%.

 

Drain tile depressurization (DTD) is achieved by sealing the sump basket cover and installing a 4″ vent pipe through the sump basket cover or by coring through the concrete, removing 5 to 30 gallons of material and tieing into the drain tile pipe below the concrete floor. DTD systems are typically very effective at reducing radon concentrations and often the easiest and least expensive systems to install. One drawback to a home with drain tile is there are often a lot of air leaks that should be sealed. These leaks are usually found where the concrete floor meets the foundation wall and at the tops of concrete block walls. If the basement is finished it makes it hard to seal air leaks and a radon fan that is able to move a lot of air may be needed. These high flow systems come at a price, including the extra cost to run a bigger radon fan, the loss of conditioned air (air you are paying to heat and cool) that is drawn into the radon system through leaks in the floor and walls.

Sub-slab depressurization (SSD) is achieved by creating one or more suction pits under the concrete slab. A suction pit is a bowl-shaped pit under the concrete floor created by coring a hole through the concrete and removing 5 to 40 gallons of material from the pit. If there are tight soil conditions under the slab like clay or fine sand a bigger pit needs to be created. This allows for better pressure field extension (PFE) meaning the vacuum created by the radon fan will have a bigger influence under the slab. Some homes will require more than one suction point.

Crawlspaces that are dirt pose an issue when it comes to radon mitigation. They are an easy pathway for radon to enter a home. The room above a dirt floor crawlspace will sometimes test higher for radon then the basement. Mitigating crawlspaces properly is no easy task. They are often dark, dirty, mouse infested areas with limited access and headroom. The first thing to do is layout a grid system of Vapormatt that will allow airflow after the crawlspace is sealed. Next a vapor barrier is added to the foundation walls and floor. It is important to make this as airtight as possible to limit the loss of conditioned air. Next the vent pipe and a valve are added and tied into the rest of the mitigation system. The valve is used to control the airflow underneath the vapor barrier. Concrete can also be pumped into a crawlspace and is recommended if you plan to use it for storage or have a rodent problem that might result in holes in the vapor barrier.

The vent pipe is a PVC pipe routed from the suction point(s) to the outdoors. Code requires the vent pipe must exhaust at least 10 feet above the ground and one foot above the roof. It must also be two feet above any window within 10 feet to prevent radon from reentering the home through a window.

The vent pipe can be routed several different ways.

1. From the suction point(s), to the garage, into the attic and out through the roof.

2. From the suction point(s), up through a closet, into the house attic and out through the roof.

3. From the suction point(s), out through an exterior wall, around the soffit and facia and up past the roof. Exterior pipe routes are usually less expensive to install, but are not recommended in cold climates due to the possibility of the system freeze up. Other drawbacks include a shorter fan life and an ugly appearance on the home.

Radon fans are inline fans mounted to the vent pipe. The fan provides the suction necessary to draw soil gasses from the suction point(s) and must be located in an unconditioned area such as an attic or outdoors. Fans must be wired by a licensed electrician. Fans located in the attic must have an outlet within six feet. Fans outside need to be hardwired into a weatherproof switchable box. American Radon Mitigation does not wire fans. Beware of any radon contractor insisting they can wire radon fans on their own – they are radon mitigators not licenced electricians. We can arrange for a licensed electrician to wire the fan the same day American Radon Mitigation installs your system.

Sealing Benefits Include:

• Sealing cracks or openings in the concrete floor and block walls can improve radon mitigation results.
• Better pressure field extension, making the radon fan reach further for the air it’s pulling under the slab.
• Enables the use of a more energy efficient fan.
• Saves energy by reducing the amount of conditioned air loss.
• Most importantly, it can prevent a dangerous backdrafting situation. Backdrafting is caused when the hazardous exhaust gases from combustion appliances (such as fireplaces, furnaces and water heaters) are drawn down the flue and into the home.

In our opinion, diagnostics is the key to getting radon levels as low as possible. This is really what sets American Radon Mitigation apart from its competitors. Most contractors don’t do this because it takes a lot of time or they simply don’t understand it.  Now there are other factors like sealing air leaks and choosing the correct fan and pipe size, but diagnostics is the key. So how does it work? Several 1/4″ holes are drilled in different areas of the concrete floor, tubing is then run from each hole into a digital micromanometer. This instrument allows us to measure how much, if any vacuum the radon system has in each area of the home. We can even take this one step further to determine which location will give us the best pressure field extension (PFE) for the suction point. If there is an area that is still under positive pressure then it is still an entry point for radon gas. The key is to get vacuum under the entire home. If we are not achieving it in an area we need to do additional sealing, look to a different radon fan or add another suction point. If we can get the desired vacuum under every area of the home that contacts the ground we can usually expect the post mitigation radon levels to be around 0.5 pCi/L. Many contractors take the poke and hope approach. We like to be sure that a system will work before we leave the job. This eliminates the need for multiple visits and mediocre post mitigation radon results.