Radioactive gas seeping through porous building foundations and threatening residents’ health sounds like the stuff of science fiction, but it’s something that homeowners in many parts of North America should legitimately worry about.
The culprit is radon, a colorless, odorless, radioactive gas that occurs naturally in the soil and bedrock underlying huge swathes of the continent. According to the EPA, radon is responsible for about 21,000 lung cancer deaths per year. It’s the second most common cause of lung cancer overall (after smoking) and the leading cause of lung cancer in nonsmokers.
Fortunately, radon is easy to detect. Relative to the health risks and associated medical expenses, it’s also not particularly costly to mitigate. While it’s not possible to completely eradicate radon from the home, it is possible to reduce concentrations to levels deemed safe by federal health authorities and independent medical research.
What Is Radon?
Causes and Geography
Radon (atomic number: 86) is the heaviest of the noble gases, a class of elements characterized by minimal chemical bonding with other elements. It’s formed over time as uranium and thorium, naturally occurring metals found throughout the planet’s crust, decay into other elements and isotopes.
Due to its relatively low density and the immense weight of the bedrock in which it forms, radon is constantly being forced out of the ground – both into outdoor air, where it immediately dissipates, and into basements and lower levels of homes, where it presents a risk to human health.
Less commonly, dissolved radon can work its way into a home’s potable water supply. There is little evidence that ingesting radon-tainted water presents a serious health risk, though inhaling radon-tainted water droplets (most likely when showering) may have adverse effects over long periods.
Though radon is widespread, homes in the Northeast, Midwest, and Intermountain West are more likely to have elevated or unsafe radon levels than homes in the South and on the West Coast.
It’s important not to overstate the risk of radon. Under normal circumstances, including in homes with concentrations higher than recommended safe levels, short-term radon exposure isn’t something to worry about. Unlike other harmful gases that can occur in the home, such as carbon monoxide, radon takes years to affect the human body.
That said, long-term exposure to radon is not good for you. According to the EPA, exposure to indoor radon levels greater than 2 picocuries per liter of air (pCi/l) is abnormal and represents a long-term health risk. For reference, the average indoor radon level is 1.3 pCi/l.
According to the EPA, long-term (several years or longer) exposure to an average radon level of 2 pCi/l may result in lung cancer for 4 out of every 1,000 people who have never smoked (“never smokers”), on average, over the course of their lifetimes. (Since a cancer diagnosis can come years after exposure, absolute causation is difficult to prove, so the EPA qualifies all predictive statements.)
At 4 pCi/l, 8 out of every 1,000 people may develop lung cancer. At 20 pCi/l, 36 out of every 1,000 may get sick.
The long-term risks of radon exposure multiply for current smokers because radon readily binds to inhaled smoke particles and stays in the lungs for far longer, increasing exposure. At 2 pCi/l, 32 out of every 1,000 may develop cancer. At 4 pCi/l, 62 out of 1,000 may get sick. At 20 pCi/l, 260 out of 1,000 may fall ill. If you smoke, the single most cost-effective way to reduce the risk of radon exposure is to stop smoking.
Radon risks likely also increase for people who live in lower-level and partially underground rooms, such as basement apartments. However, there’s a dearth of medical studies on this point.
How to Detect & Evaluate Radon
There are two basic ways to detect radon in the home: purchasing a DIY home radon testing kit or hiring a qualified radon inspection company.
1. Home-Testing Kits
Home-testing kits are usually quite cheap – $15 to $30 in stores or online. Major home improvement stores, such as The Home Depot and Lowe’s, stock radon testing kits, as do many independent hardware stores. If you’d prefer to buy online, Amazon sells the First Alert RD1 Radon Gas Test Kit for under $12.
Some home-testing kits test short-term radon levels, typically over three to four days. Others test longer-term levels over periods as long as one year. In either case, most kits require you to send them (usually with a prepaid shipping label) to a lab for analysis after the testing period ends.
Home-testing kits are accurate enough to make a basic determination about whether mitigation is necessary, though they’re not ideal for precise measurements or ascertaining minute-to-minute fluctuations.
2. Professional Detection
If you want a more precise reading or are in the midst of a real estate transaction (either selling a house that hasn’t previously been tested for radon, or purchasing a house in an area known for indoor radon), invest in professional radon measurement services. Professional measurement is more accurate than DIY measurement and offers the added security of third-party certification, meaning the homeowner can’t claim that the home’s radon levels are safe when they’re actually not. Though most states and municipalities don’t require radon testing certification as a condition of title transfer, many private mortgage lenders do require it.
Many general contractors (and some home inspection companies) offer radon detection and measurement services. Most states’ environmental services agencies maintain lists of approved or licensed companies. Professional radon detection costs usually start at $150 and rise from there.
Paying for Radon Detection & Mitigation
If you’re buying a house in an area where radon is commonplace, request in your purchase offer that the seller pay for a radon inspection, preferably by a qualified radon inspector. Many sellers are willing to do so, even in seller’s markets.
If the inspection turns up elevated radon levels, don’t be shy about making your offer contingent on seller-paid radon mitigation. And if the seller balks at that stipulation, which can lengthen the escrow period, consider requesting that the seller cover a portion of the closing costs equal to the expected cost of the mitigation system, and then install the system after moving in.
Evaluating Radon Concentrations & Determining Whether to Mitigate
The EPA encourages radon mitigation for indoor concentrations greater than 2 pCi/l and strongly recommends it for concentrations greater than 4 pCi/l. Reducing radon levels below 2 pCi/l isn’t cost-effective with current mitigation technologies. If anyone in your household smokes, or there are small children present, the case for mitigating at levels between 2 and 4 pCi/l is much stronger.
It’s worth noting that many new construction homes in high-radon areas feature pre-installed radon mitigation systems. Though their cost is typically reflected in the purchase price of the home, pre-installed systems allow you to cross an important item off your post-purchase to-do list.
Radon Mitigation Options
Radon mitigation options come in many different forms. In general, professionally installed suction-based ventilation systems are more effective at reducing indoor radon concentrations to safe levels. However, they can be more costly than other systems – upwards of $3,000 in some cases.
Non-suction systems and DIY solutions require smaller upfront investments, sometimes no more than $100 or $200, but usually demand regular upkeep. Some, such as pressurization or ventilation systems that require closed windows and doors to work properly, also impose annoying restrictions on homeowners.
Soil Suction Systems
There are five main types of soil suction systems. Unless you’re a licensed contractor, all require professional installation. Those that involve the use of powered fans carry annual operating costs of $75 to as much as $400, depending on heaviness of use and local power costs.
In many cases, soil suction systems require some modification to the home, such as drilling into the foundation or the construction of vertical shafts for exhaust vents.
1. Active Sub-Slab Depressurization
Active sub-slab depressurization (ASSD) is the most common and effective radon mitigation technique. ASSD consists of one or more airtight suction vent pipes installed in the rock or soil below the home’s slab. These pipes typically vent up through the house, under the slab, or along an exterior wall. A fan installed in each pipe’s upper reaches creates a vacuum that draws radon from the soil, through the pipe, and out an outdoor opening (usually in the attic, at the roofline, or in a corner of the yard), where the gas dissipates harmlessly. Pipe openings must be at least 10 feet above the ground and 10 feet from any windows, doors, or openings.
ASSD costs depend on the number of vent pipes needed and the depth of the foundation. $1,500 to $3,000 is a typical range for a 2,000-square-foot home, though larger homes can cost more.
2. Passive Sub-Slab Depressurization
Passive sub-slab depressurization (PSSD) systems resemble ASSD systems, sans the suction fans. Instead of active suction, PSSD relies on natural airflow and the pressure differential between the open air and the top layer of bedrock.
PSSD systems cost at least $100 per pipe less than ASSD systems – roughly $1,200 to $2,500, depending on the number of pipes and size of the home. However, they’re not as effective at clearing radon from beneath the house. As a result, homes with PSSD systems tend to have higher indoor radon concentrations than nearby homes with ASSD systems, though the exact difference varies by geology and other factors.
3. Drain Tile Suction
Homes with drain tile installed on the outer foundation sometimes use localized mitigation systems that apply suction directly to the tile, effectively blowing radon away from the house and into the outside air. Since drain tile suction usually doesn’t require drilling beneath the foundation or installing vertical vent columns through the house, it’s generally cheaper to install than sub-slab systems. Total costs run anywhere from $500 to $1,500, depending on home size and pipe count.
4. Block Wall Suction
Homes with hollow foundation walls (block walls) support soil suction systems installed directly into the foundation wall. Block wall systems create negative pressure inside the wall and vent captured radon to a higher, outdoor level. System cost is comparable to ASSD costs – roughly $1,500 to $3,000.
However, depending on a home’s size and layout, a block wall system might not be sufficient to reduce indoor radon to acceptable levels. In this case, you likely need to pair a block wall system with a smaller ASSD system – at substantial extra cost – or invest in a larger ASSD system.
5. Sump Hole Suction
Sump hole suction is most common in homes built on at-grade slabs with sump hole cutouts for active water drainage. Sump hole suction systems are similar to ASSD systems, with the major addition of an airtight, watertight cap on the sump hole to facilitate suction. System costs are roughly equivalent to ASSD systems – about $1,500 to $3,000.
DIY or Ad Hoc Systems
Unlike soil suction systems, these radon mitigation techniques don’t use a closed, negative pressure system that requires professional installation. Because they can be installed and removed with without professional help, they’re considered temporary and are often recommended for use as you consider a more permanent fix.
6. Heat Recovery Ventilator (Heat Exchanger)
A heat recovery ventilator (HRV), or heat exchanger, is a mechanical device that increases indoor ventilation by drawing outside air inside and removing indoor air through external vents. When used as a radon mitigation system, it effectively vents radon-tainted air and introduces radon-free air. Also, it has an added benefit: lower heating and cooling costs.
Heat exchangers work best in smaller, closed spaces with limited airflow, such as a basement. For best results, they need to be operated continuously. While new heat exchangers can cost $500 or more, users can recoup that investment through lower utility bills.
7. Crawlspace Ventilation
Crawlspace ventilation comes in two forms: active and passive.
Active ventilation involves setting up a fan at the main entrance to the space and allowing it to blow continuously, creating positive pressure that reduces the rate of radon leakage out of the surrounding soil. Vents connecting the crawlspace with the outdoor air reduce radon even further.
Active crawlspace ventilation works best if the home’s windows and doors remain closed at all times. The cost varies widely depending on the number of vents and the type of fan (industrial-strength floor or window fans typically cost at least $50). In cold climates, this method typically requires additional insulation for any pipes running through the crawlspace, possibly increasing the project’s cost.
Passive ventilation involves venting the crawlspace to the outside, again with windows and doors closed, without the added benefit of a fan. It’s less effective than active ventilation.
8. Lower Level Pressurization
This method is similar to crawlspace ventilation, but on a larger scale. It involves setting up a fan at entrances to the basement or lowest level (typically the basement stairs, a larger basement window, or a large window on the first floor) and blowing air into the space from outdoors or a higher floor. For larger homes or lower levels, it may require multiple fans.
For the best results, fans need to be kept on continuously, and all doors and windows not equipped with a fan must remain shut at all times. The cost varies based on the number of fans used (at a cost of at least $50 per fan) and whether any special vents are required.
9. Sealing and Patching
The cheapest and simplest radon mitigation technique involves sealing and patching major points of entry for radon gas. Use a high-quality, waterproof sealant to patch visible cracks in your basement walls, foundation, and/or grade slab – basically, any structural component between your home’s lowest level and the surrounding bedrock. Depending on the size of your foundation or slab and the number of visible cracks, a sealing project can cost anywhere from $50 to several hundred dollars.
To counter the ongoing effects of settling, water damage, and seismic activity, repeat the sealing process every year. The EPA recommends pairing sealing and patching with another radon mitigation technique – or at least with constant ventilation (open windows and screen doors) – due to limited evidence that sealing reduces indoor radon concentrations on a consistent basis.
I’ve been a tenant in several older houses in the Upper Midwest, where radon is quite common. In fact, in Minnesota, where I live now, radon is present in unsafe concentrations in about two in five homes. Statistically, it’s likely that I lived in a rental with unsafe radon levels at some point. But until I bought my own house, I didn’t give radon much thought.
While I’m not losing sleep over my probable past exposure, my wife and I have penciled in radon detection and mitigation near the top of our new-homeowner project list. If you’re a homeowner, new or otherwise, consider doing the same. And if you’re a renter, particularly if you have children, ask your landlord if he or she has ever conducted a radon inspection. Landlords have little incentive to do so without prompting, but it never hurts to ask.
Does your home have elevated radon levels?