Joints

31.4.3.2.1 French Drains and Floor/Wall Cracks

The French drain (also called a channel drain or floating slab) is a construction feature that appears to provoke strong reaction from its defenders and detractors alike. French drains are only a concern in basement foundations. This slab detail is a standard feature in new houses in parts of the country as varied as New York and Colorado, but in other places it is virtually unknown. French drains are used in areas with expansive soils, such as parts of Colorado, to protect the slab from damage if the wall moves. In central New York State, the main function of the French drain is to drain away water that may seep down the walls. One national builder has discontinued and now prohibits the use of French drains in houses because of the potential for radon problems. This builder states that French drains also have been found to significantly increase indoor moisture levels.

Various treatments can be used to seal French drains against gas entry. Some of those treatments have crack-spanning capability in the case of structural movement. French drains can be sealed airtight and still preserve their water drainage function by caulking the channel to a level below the top of the slab and sloping the trough toward the sump. This assumes that the sump lid is inset below the surface of the slab and that a water-trapped drain in the sump lid drains water into the sump. Figure 31.14 shows a French drain treatment.

It is recommended that French drains be avoided if possible because of the difficulty in sealing them at the time of construction and the expense and difficulty of sealing them after construction.

31.4.3.2.2 Perimeter Crack

The perimeter crack is located between the edge of the floor slab and the foundation wall. This applies to slabs in basements, crawlspaces, and slab-on-grade foundations. As a cold joint, this perimeter crack is always a potential radon entry point. Contractors building radon-resistant houses

drainage channel

FIGURE 31.14 Sealing a French drain. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

drainage channel

FIGURE 31.14 Sealing a French drain. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

may deliberately create a significant floor/wall crack so that it will be easy to work with and seal. A perimeter expansion joint is made of a closed-cell, flexible foam strip. The expansion joint is presliced so that the top 1/2 in. can be pulled off to leave room for caulk. Another approach is to tool the floor/wall joint with an edging tool and seal it with caulk. Particular attention should be paid to sealing this crack in slab-on-grade houses because the joint is often inaccessible after the house walls are raised.

31.4.3.2.3 Control of Joints

When large areas of slab are poured, some cracks are unavoidable. There will be cold joints because the slab was poured in small sections to avoid cracks, or the slab will crack because the pours were too large. To direct the inevitable cracking that will occur in either case, a control joint can be made by grooving the surface of the slab. The groove should be large enough to seal with caulk. Cold joints can make use of the same expansion joint materials that have a zip-off top that was described for the slab edge crack.

31.4.3.3 Penetrations

Every house has some minimum penetration through the slab or foundation walls. The ones always present are water pipe entry and sewer pipe exit. Common additional penetrations are floor drains, sump holes, and air conditioner condensate drains.

31.4.3.3.1 Openings around Water Pipe Entries and Sewer Exits

Openings around water pipe entries and sewer exits that pass through concrete can be easily sealed using caulks. Many builders use plastic sleeves to protect metal pipes from corrosion when they pass through concrete. In this case, an effort can be made to leave a space around the pipe that can be sealed with caulk or backer rod and caulk. The same techniques can be used for pipes passing through block walls.

Depending on the details of a floor drain, a great deal of soil gas can enter through large openings to the drainage matrix. This is true not only of slop drains that are simply holes through slabs into the subslab area, but also of other types of drains. Even water-trapped drains with water in the traps can allow radon an entry passage where the dish-shaped bottom of the drain seats into the drain pipe. It is recommended that floor drains connect to pipe that drains to daylight using solid PVC pipe glued at the joints, or that water-trapped drains or mechanical traps be installed that do not have unsealed joints on the room side of the water trap.

31.4.3.3.2 Sump Holes

Sump holes are usually a collection point for the drainage system. Almost by definition, this is a terrifically good radon collection system. It must have access to large areas of soil beneath the

FIGURE 31.15 Sealing a slump hole to a shallow yet operable sump. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/ 2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

foundation, so it is easier for water to run into the sump than to penetrate the foundation. It is better if there is no open sump at all. A subslab drainage system that can drain by gravity to a daylight opening serves the same purpose as a sump hole but offers no fewer radon entry routes. If this is not possible then the sump hole must be sealed (a code item in some places to keep children from playing in them). Sumps can be sealed airtight and still function as a water collection and removal system by routing the interior and/or exterior drainage pipes or layer into the sump. The sump hole is then sealed with a corrosion-resistant lid that is recessed a few inches to create a shallow sump. The lid is fitted with a water-trapped drain, so water that flows across the floor will end up in the sump. Lastly, a low-profile sump pump is installed to eject water collected in the sump through a check valve to approved disposal. This detail is illustrated in Figure 31.15.

31.4.3.3.3 Air Conditioner Condensate

Air conditioner condensate lines are sometimes installed so that they penetrate the slab to dispose of the water in the subslab area. Even when water is trapped, this can be a problem because the traps often dry up during the heating season. At this point they become radon entry routes. It is recommended that air conditioning condensate lines run to a drain that will not dry out or that a condensate pump is installed that collects the condensate and disposes of it through a water trap. Often a washing machine drain is located in a basement near enough to use it.

31.4.3.3.4 Sealants for Cracks, Joints, and Penetrations

Masonry sealants for radon-resistant applications must have good adhesion and be durable and elastic. Polyurethane comes in gunnable grades, and one- and two-part self-leveling types. Self-leveling urethanes can be used only on level surfaces as they are very mobile. In fact, if there is even a small crack at the bottom of a joint being sealed, the self-leveling caulk may drain out. The popularity of polyurethane is based on a combination of good adhesion even under difficult conditions, long service life, good elasticity, and easy availability. Copolymer caulks have very similar properties as the polyurethanes. Recently, some copolymer caulks have been packaged as sealants specific to radon control. Silicone caulks have also been used in radon control but require more extensive surface preparation for good adhesion. Many radon mitigators have adopted the use of silicone caulks for sealing sump lids and access ports because they make a tight-fitting gasket that can be removed more easily than polyurethane at a future date. Butyl caulk is susceptible to attack by groundwater acids. Polysulfides have been largely supplanted by polyurethanes because the former are more chemically reactive with asphalts.

Surfaces should be clean and dry when caulk is applied. Bear in mind that the idea is to get a flexible membrane to bridge between the two surfaces that the crack divides. It is a poor practice to simply fill every crack. Manufacturers usually specify appropriate dimensions for their caulks.

Often this is a minimum of 1/4 x 1/4 in. For small cracks, it may be necessary to grind them larger to meet the caulk manufacturers' specifications. For cracks much larger than 1/4 in., a backer rod should be used to support the caulk so that it can be applied correctly.

Caulks give off organic compounds. Some of these are carcinogenic. Users are reminded here that they should have the Manufacturers Data Sheets for any chemicals they use. These sheets identify hazardous aspects in the use of the products. OSHA requires that contractors have these sheets available for employees and that a safety training program be in effect for these products.

31.4.4 Crawlspaces

Crawlspaces are being treated here as a special case of using the foundation materials to make a mechanical barrier. In this subsection, isolating the living space from the crawlspace by sealing the floor between the two spaces will be discussed. A sheet of plywood is a relatively good barrier to radon-laden crawlspace air and, as with the other material barriers, it is the joints and penetrations that are the problems. The major entry points are through numerous electrical, heating, and plumbing penetrations in the house floor and via the return air duct often located in the crawlspace. Lower air pressure in the house and the return air duct than in the crawlspace draws radon-laden crawlspace air into the living space of the house.

During construction, all possible penetrations between the crawlspace and the house should be sealed to simply prevent the passage of radon up into the living areas. Attempts to seal penetrations can be made by using expandable closed-cell foam sealants and urethane caulk. Sealing these areas can be difficult because of limited access even during construction. Areas of particular concern include9

1. Openings in the subfloor for waste pipes including openings for tubs, toilets, and showers

2. Openings for water supply lines

3. Openings for electrical wiring

4. Openings for air ducting for the heating, ventilating, and air conditioning (HVAC) system

5. Openings around hot water heating pipes. Check on code requirements for clearance between hot water pipes and wood floors. These may require a special sealant

6. Joints between sheets of plywood.

Any sealing around plumbing traps must be done so that the trap can still be reached and serviced.

Return air for the HVAC system should not be supplied from the crawlspace. It is best to avoid routing return air ductwork through the crawlspace, but if it must be, then it should be thoroughly sealed with duct tape at a minimum. It should be understood, however, that duct tape may dry out and fall off. A better approach would be to use seamless ductwork in these areas. The use of floor joists and subflooring as three sides of a return air plenum should be avoided because of the difficulties encountered in sealing. If the space between the joists must be used, an alternative to ducts is to use a rectangular duct to fit the space.

If isolation of the crawlspace is the primary method of radon-resistant construction being used, the number and size of crawlspace vents should be maximized. The Florida's guideline for radon-resistant construction35 suggests vents of not less than 1 ft2 of vent for each 150 ft2 of crawlspace. The guideline also requires that vents be located to provide good circulation of air across the crawlspace and should not include registers or other provisions for closure. This requirement would be impractical in cold climates with water pipes in the crawlspace. If there were no water pipes to worry about, then the floor would need to be well insulated in order to ensure that a large energy and comfort penalty was not incurred.

Other radon-resistant alternatives besides simple isolation of the crawlspace should be considered because of the difficulties encountered in getting an adequate seal between the house and the crawlspace. These alternatives will be discussed in the next section.

TABLE 31.2

Results Using Vented Crawlspace Technique

Buried

Crawlspace Level Basement Level

TABLE 31.2

Results Using Vented Crawlspace Technique

Buried

Crawlspace Level Basement Level

1

Off

9.9

1.9

1

On 2 weeks

9.9

1.4

1

On 2 weeks

8.4

1.4

2

Off

27.8

1.8

2

On 1 week

18.6

1.2

2

On 1 week

16.7

0.9

3

On 1 day

26.4

1.3

3

On 1 day

15.5

0.9

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.

A NEWHEP builder in Denver uses an innovative foundation technique to simultaneously deal with problems of expansive soil and high soil radium and radon content. The foundation excavation is overdug to a depth of 10 ft. Caisson pilings are driven to support the 10-ft-tall reinforced poured concrete walls. Band joists are bolted to the walls 2 ft above the dirt floor, and a carefully sealed wood subfloor, supported by steel "I" beams and standard size floor joists, is installed. The 2-ft-high "buried crawlspace" is actively ventilated by installing a sheet metal inlet duct at one corner of the basement, drawing in outdoor air through an aboveground vent. A similar duct with an in-line fan is located at the opposite corner to exhaust air through an above-grade vent. Soil gas radon at levels from 3163 to 4647 pCi/L was measured at three of these building sites. Soil radium-226 content was measured at 1.05-1.62 pCi/g. Indoor radon measurements were then taken in the buried crawlspaces and in the basements. Measurements were made during summer with the exhaust fan off, and after 1 day, 1 week, and 2 weeks of operation. The results are shown in Table 31.2.36

31.4.5 Coatings

If waterproofing or dampproofing treatments that are effective gas barriers and that can be sealed at joints and penetrations could be identified, then walls could be made radon resistant. Acceptable dampproofing or waterproofing treatments are specifically listed in building codes in many areas of the United States; these lists are periodically amended as new materials come into use. These coatings apply primarily to basement walls.

The terms "waterproofing" and "dampproofing" are often used interchangeably. Briefly, any waterproofing material can also be used for dampproofing; the converse is not true. Waterproofing materials must resist the penetration of water under a hydrostatic load. Dampproofing materials are not expected to keep out water under pressure, but do impede water entry and block diffusive movement of water through pores.

Any material that provides adequate protection against water should at least limit convective soil gas movement. Properly applied waterproofing materials should help block pressure-driven entry of soil gas.

The most common dampproofing treatment for residential foundation walls is a parge coat covered with bituminous asphalt. The parge coat is used for concrete masonry walls but is not necessary for poured concrete walls. This two-stage treatment has been replaced by surface bonding cement in some areas.

Oak Ridge National Laboratory indicates that bituminous asphalt may be attacked by soil and groundwater chemicals, specifically acids.37 Bituminous materials may also lose their elasticity at below-freezing temperatures. These features render bituminous asphalt an undependable waterproofing treatment; in fact, it is listed by code organizations such as Building Officials and Code Administrators International (BOCA), Council of American Building Officials (CABO), and Southern Building Code Congress International (SBCCI) only for dampproofing.

A number of dampproofing systems are better gas barriers than bituminous asphalt. Some are relatively new to the residential marketplace but have track records in industrial/commercial settings. Others have been introduced into the most expensive residential market or have found applications at problem sites. A common feature of these alternatives is that they are generally more expensive than bituminous dampproofing. However, a survey of 31,456 properties by Owens-Corning Corporation38 found that 59% of property owners with basements reported water leaks. As the supply of trouble-free building lots dwindles, home buyers may decide that investment is justified, and improved dampproofing systems may be developed to address radon and water problems simultaneously.

The following is a sampling of alternative waterproofing systems that are readily available to builders.

31.4.5.1 Coal Tar-Modified Polyurethane

Coal tar-modified polyurethane is a cold-applied liquid waterproofing system. The system by Sonneborn is an example of this approach to waterproofing. It is applied as a liquid at the rate of 10-15 mils/coat. The coating dries hard, but has some elasticity. This material may be attacked by acids in groundwater but can be defended by a protection board. The performance of any liquidapplied waterproofing systems is limited by the capabilities of the applicator (it is difficult to achieve even coats on vertical surfaces).

31.4.5.2 Polymer-Modified Asphalt

Polymer-modified asphalt is a cold-applied liquid waterproofing system. As with the Sonneborn system mentioned above, the quality of the installation depends on the applicator (it is difficult to achieve an even coating on a vertical surface). High-grade polymer-modified asphalt is superior to coal tar-modified polyurethane in elasticity, crack-spanning ability, and resealability, but inferior in its resistance to chemicals.

31.4.5.3 Membrane Waterproofing Systems

Waterproofing applied as a membrane has an advantage over liquid-applied systems in that quality control over thickness is ensured by the manufacturing process. Most membrane systems are also chemically stable and have good crack-spanning ability. On the other hand, effective waterproofing demands that seams be smooth so that the membrane is not punctured. Some masons apply parging to a half-height level and then return to finish the upper half of the wall. This tends to leave a rough section where the two applications overlap and means that the waterproofing crew has to grind the wall smooth before applying the waterproofing membrane. Thermoplastic membranes may be applied in various ways—affixed to walls or laid beneath slabs. Thermoplastic membranes are highly rated for resistance to chemicals and longevity. Rubberized asphalt polyethylene membranes have superior crack-bridging ability compared with fully adhered thermoplastic membranes. (Loosely hung thermoplastic membranes, by their nature, have obvious crack-bridging ability in that they are bonded to the walls.)

Seams and overlaps must be carefully and completely sealed in order for membranes to function as radon barriers. The choice of seam material varies with the type of sealant. Manufacturers' recommendations for sealant, procedure, and safety precautions should be followed.

31.4.5.4 Bentonite

Bentonite clay expands when moist to create a waterproof barrier. Bentonite is sold in various forms, including panels and mats. Bentonite is not as resistant to chemicals as the thermoplastic membranes, nor is it puncture resistant. The major flaw of bentonite as a radon barrier, however, is that it is only tightly expanded when wet. This is acceptable for a waterproofing material, but not for a gas barrier.

31.4.5.5 Surface Bonding Cement

Surface bonding mortar or cement is mentioned in some building codes as an approved dampproof-ing treatment, but not as a waterproofing treatment. A number of manufacturers produce cements and mortars impregnated with fibrous glass or other fibers. Some of these may be chemically unstable in the alkaline environment of Portland cement.

One technique of assembly using surface bonding cement is to dry stack blocks and apply the cement on both sides. As an alternative, the block wall is conventionally assembled with only an outside coating as a positive-side waterproofing.

31.4.5.6 Cementitious Waterproofing

A number of additives can be incorporated into concrete to create cementitious "waterproofing." This type of waterproofing is appropriate only for interior applications because it is inelastic, does not have good crack-spanning ability, and cannot resist hydrostatic pressure.

31.4.5.7 Interior Paint as a Barrier

A variety of interior applied masonry paints are available. Some of these have been tested by the AEERL laboratory at the U.S. EPA. Results of these tests are given in a paper presented at a Symposium on Radon Reduction Technology.39

31.4.6 Membranes

Membranes of plastics and rubbers that are used to control liquid water penetration and water vapor diffusion are effective in controlling air movement as well. If they can be adequately sealed at the joints and penetrations and installed intact, then they could also provide a mechanical barrier to radon entry.

Construction film is already in common use as a subslab vapor barrier in many areas of the country. The current prevalence and low cost of this material mean that it may be worthwhile to continue its use even though it is an imperfect barrier. It is possible to seal polyethylene vapor barriers at the overlapped edges, at penetrations, and at the footing; but it may be that the extra effort will not be rewarded with improved radon resistance.

In Sweden, subslab membranes are not required in high-radon areas and a tightly sealed slab is considered to be a more effective radon barrier. The difficulty of achieving a completely sealed, intact subslab membrane is widely acknowledged; however, a subslab barrier may be worthwhile even if it is imperfectly installed. Polyethylene construction film (6-mil) can serve as a backup radon barrier to the concrete slab, even though it is not a complete radon barrier by itself. The barrier may continue to function, even with punctures, if incidental cracks and holes in the slab are aligned with intact areas of polyethylene.

In summary, it is worthwhile to continue the installation of a vapor barrier that serves as the added valid function of moisture barrier. More comprehensive installation measures and more expensive materials may be merited in areas where the radon source is strong because of either high radon concentrations or high soil gas flow rates.

31.4.6.1 Polyethylene Film

A vapor barrier of polyethylene film is a typical subslab feature in many areas of the country. The intent of the vapor barrier is to prevent moisture entry from beneath the slab.

Installation of any subslab membrane is problematic because an effective barrier should be both well sealed and intact. Builders who use polyethylene under the slab indicate that achieving a complete seal at all laps and edges and around pipe penetrations is difficult. It is difficult to seal the polyethylene to the footing because the weight of the concrete tends to pull it away from the walls during the pour. There is also a high probability that the vapor barrier will be punctured during installation. It has been observed that even a 10-mil polyethylene in a heavy felt membrane is likely to be punctured during installation.

Another issue is the stability of polyethylene vapor barriers. Polyethylene is known to be harmed by ultraviolet (UV) exposure. One radon mitigator has found polyethylene under slabs in Florida that deteriorated in less than 15 years; more frequently, polyethylene of comparable age is in mint condition.

Polyethylene films are manufactured with an array of additives selected to support specific applications. Durability varies according to the additives employed, film thickness, length of UV exposure, temperature swings, and other factors. Resins used in polyethylene manufacturing have improved over time, so that the life expectancy of polyethylene film is longer than that of films used in the 1960s and 1970s. The durability of polyethylene films in current use depends on the contractor's selection and proper storage of appropriate film for the job.

On the other hand, there is no evidence to support the assertion that polyethylene vapor berries deteriorate with exposure to soil chemicals. Construction film is a low-density polyethylene. High-density polyethylenes are used for the storage and transportation of an array of chemicals. Polyethylene is chemically stable, but may be adversely affected by aliphatic hydrocarbons (such as hexane, octane. and butane) and chlorinated solvents. It does not appear to be reactive with the acids and salts likely to be encountered in soil and concrete.

Polyethylene-coated kraft paper vapor barrier is available in 8 x l25 ft rolls. Overlaps of 6 in. are marked on the paper with a printed line. They can be sealed with polyethylene tape. This material is attractive to contractors because it is more puncture resistant than a 6-mil polyethylene construction film, but less expensive than many alternative products.

Polyethylene-based membranes are manufactured for use in hazardous waste landfills, lagoons, and similar applications. Two of these products have been tested to determine their effectiveness as barriers against radon diffusion. (In most cases, diffusive flow is considered of little or no significance as a mechanism of radon entry compared with convective flow). A 20-mil high-density polyethylene tested 99.9% effective in blocking radon diffusion under neutral pressure conditions. A 30-mil low-density polyethylene tested 98% effective in blocking radon diffusion under neutral pressure conditions.

31.4.6.2 Double-Layered High-Strength Bubble-Pack with Aluminum Foil

A material composed of a double layer of high-strength bubble-pack with aluminum foil bonded on both sides is available. It has high compression strength and doubles as an insulator. Concern exists over its fragility and susceptibility to pinhole punctures. Both foil-faced membranes can be punctured, but the double bubble-pack offers some defense against complete penetration. Punctures are easily repaired with aluminum tape, which is also used at seams. A well-made seal is diffusion resistant; however, gas can migrate through wrinkles in the tape. The fragility of the material is believed to be a significant limiting factor in using it under the slab or as perimeter insulation.

31.4.6.3 Two-Faced Aluminum Foil over a Core of Glass Scrim Webbing

Another available product has two faces of aluminum foil over a core of glass scrim webbing; it is coated with asphalt. The membrane is 0.012 in. thick. This material has not been tested as a barrier against diffusive flow of radon, but its performance should be similar to that of other foil-faced products. Seams are sealed with aluminum tape.

31.4.6.4 PVC Membranes

PVC membranes have been used as a subslab membrane during radon mitigation work in existing houses. They are usually sealed with solvents and were developed as roofing membranes.

Another product EPDM™ is a rubber-like material. It comes in 60-mil thickness in 100 ft by 61-1/2 in. rolls. EPDM also comes in 45-mil thickness in 25 ft by 60 ft rolls. This product has gained popularity as a ground cover in crawlspaces because of its durability qualities.

31.4.7 Mechanical Barriers Applied to the Soil

It has been suggested that mechanical barriers could be applied to the soil beneath the foundation that would prevent the migration of radon into the building. This has the benefit of being less susceptible to occupant behavior, future remodeling activities, and mechanical failure of fans. Two approaches have been brought forward. One would use an injection of slurry composed of clay to dramatically reduce the permeability of the soil. This technique is used in the construction of lagoons, landfills, and dams. The second idea is to spray the soil surface with polymer-modified asphalt. This technique has been used to cap landfills to control the release of methane and other organic compounds.

31.4.8 Drainage Boards for Soil Gas and Radon Control

Soil that has been excavated from the basement is commonly used as backfill against foundation walls. This should not be the case where the site material contains clays and silts, particularly organic clays and silts. If local soils are not appropriate, the builder may use gravel to backfill.

Drainage boards are a substitute to backfilling with gravel. Drainage boards have been used for a number of years, particularly in commercial projects and underground houses. Depending on the cost of hauling sand and gravel, a drainage board may be a cost-effective alternative.

It has been hypothesized that a drainage board that is laid up against a house wall might provide an air buffer that can break the pressure connection between the soil and the house interior. This is rather like having a hole in your straw when drinking through it.

31.4.9 Summary of Recommendations for Mechanical Barriers

31.4.9.1 Rules of Thumb for Foundation Walls

1. Use reinforcing to limit cracking.

2. Seal pipe penetrations.

3. Cap masonry walls with bond beam or solid blocks.

4. Dampproof walls (interior as well as exterior on masonry walls).

31.4.9.2 Rules of Thumb for Slab and Subslab Barriers:

1. Make a slab edge joint that is easy to seal (tooled joint or zip-off expansion joint material).

2. Caulk perimeter crack and control joints with polyurethane.

3. Reinforce slabs with wire mesh to help prevent large cracks and use control joints; caulk the control joint.

4. Drain to daylight if possible, or to a drywell or sewer. If you must use an interior sump pump, seal it.

FIGURE 31.16 Summary of mechanical barrier approach for basement foundations. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

5. As a precaution, use interior footing drains (in addition to exterior drains) and 4 in. of No. 2 stone below the slab that drains to the building exterior. In this way, subslab ventilation can be added easily in case a problem is discovered later.40

These suggestions are illustrated in Figures 31.16 through 31.18.

31.5 SITE EVALUATION

When siting new residential construction, builders would like to determine the potential for radon problems associated with each building site. Unfortunately, at present there are no reliable, easily

FIGURE 31.17 Summary of mechanical barrier approach for slab-on-grade foundations. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

Vented crawlspace Unvented crawlspace

FIGURE 31.18 Summary of-mechanical barrier approach for crawlspace foundations. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

Vented crawlspace Unvented crawlspace

FIGURE 31.18 Summary of-mechanical barrier approach for crawlspace foundations. (Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.)

applied methods for correlating the results of tests made at a building site with subsequent indoor radon levels contained in a house built on that site. Houses vary significantly in their ability to resist radon entry. Bedrock and soils interact in complex ways with dynamic house behavior and environmental factors. There are too many combinations of factors that cause elevated indoor radon concentrations for simple correlations to exist.

In an effort to evaluate the risk of an indoor radon problem occurring in a home built on a particular site, researchers have made many types of measurements. The measurements commonly made include9

1. Soil and bedrock radium concentrations.

2. Radon measurements in the interstitial soil and bedrock pores.

3. Permeability of the soil or bedrock.

4. Airborne radiation measurements.

In addition to the above measurements, indexes using soil concentrations in combination with permeability measurements have been suggested by some researchers.4142 As elaborated on later in this section, these methods have been successful in establishing relationships between some of the site measurements and indexes, and indoor radon concentrations for specific areas and regions.

Although substantial progress has been made by investigators using geologic, radiation, and other site data to predict areas of high radon risk, it still requires many site measurements to adequately assess a particular site. The judgment that needs to be made is whether or not it is more cost-effective to make the building radon resistant to begin with, or to put the money into site evaluation and possibly avoid the need for radon-resistant construction techniques.

31.5.1 Radon in the Soil

In buildings with indoor radon concentrations greater than 4pCi/L, the majority of the radon is produced in the soil and enters the building through foundation openings. The radon gas found in soils is a product of the decay of radium-226, a radioactive chemical element present in trace levels in many types of soils and rocks. Radium and radon are elements that are part of the uranium-238 (U-238) decay series. See Figure 31.1 for details. Uranium-238 decays through a chain of radioactive elements. Radiation is released as each element decays. Radon will move through the porous soil or shattered bedrock by convection and diffusion because it is a gas. The other elements in the U-238 series will not easily move through the soil because they are particles and not gases. The amount of radon that enters the house depends on the amount of radon gas or radon parent compounds found in the soil beneath the house. The permeability of the soil, the presence of faults and fissures in underlying and nearby rock, openings between the house and soil, and the driving forces that move soil gas along pathways into the house also contribute to the total radon levels. To have a radon problem requires9

1. Radium nearby.

2. A pathway for the gas to move through the soil or rock.

3. A driving force.

4. Openings in the foundation.

31.5.1.1 Attempted Correlations between Indoor Radon and Measurement Made at Sites

Several studies have been attempted to make simple correlations between radon or radium concentrations in the soil and indoor radon concentrations.43,44 No significant correlations were made between these variables.

The Florida Statewide Radiation Study performed by Geomet44 illustrates the variability of radon-resistant construction and the resulting problem of trying to correlate soil radon levels with indoor radon levels. The study reports over 3000 paired soil radon and indoor radon samples. A total of 77 soil radon readings were greater than 1000 pCi/L. The two highest soil radon values were 6587.0 and 6367.2 pCi/L. Interestingly, corresponding indoor radon levels for the two highest sites were 6.8 and 0.2 pCi/L, respectively. In addition, almost half of the houses with soil radon levels in excess of 1000 pCi/L had indoor radon levels of less than 4 pCi/L.

The Florida data reported by Geomet have been evaluated and the houses are listed in order of highest measured indoor radon levels. This analysis is shown in Table 31.3.4445

TABLE 31.3

Florida Survey Soil Radon and Corresponding Indoor Radon Concentrations

Indoor Radon Concentration

Soil Radon Concentration

32.4

25.0

1591.1 1846.9 786.9 555.9 200.1 353.9 439.7 3561.3 2144.5

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.

TABLE 31.4

Swedish Soil Risk Classification Scheme and Building Restrictions

Soil Radon Concentration

Permeability of Soil

Very low permeability

(e.g., clay and silt) Average permeability

Risk Classification

Building Restrictions

<27G

Use conventional construction Use radon-protective construction

27G-135G

Normal

>135G

High permeability (e.g. gravel and coarse sand)

High

Use radon-safe construction

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.

It is clear from Table 31.3 that soil radon measurements that varied over an order of magnitude produced significantly less than a factor of 2 difference in the indoor radon levels. Predictions of radon potential based on soil radon measurements would be highly suspect based on these data.

In Sweden, soils have been classified as having high, normal, or low radon risk potential based on soil radon concentration and soil permeability. The soil radon values and permeability characteristics used to establish the soil classifications and the corresponding construction requirements are given in Table 31.4. Factors other than soil radon that are considered before classification in Sweden are permeability, ground humidity, and soil thickness. Clearly, Sweden has decided that a number of factors must be addressed to evaluate the radon problem potential of a site. Using the suggested soil radon concentrations but not the permeability guidelines included in the Swedish soil classification scheme, no building restrictions would have been required for many of the houses surveyed in Florida with indoor radon measurements greater than or equal to 4pCi/L.

Fifteen of the houses in the Florida study with measurements greater than or equal to 4pCi/L had soil radon concentrations less than or equal to 200pCi/L. This corresponds to 13.5% of the houses with soil gas less than 270pCi/L being above the U.S. EPA action level of 4 pCi/L. Nineteen of the 48 houses (39.6%) that had radon in the soil over 1350 pCi/L had radon levels in the house less than 4 pCi/L. This means that almost 40% of the houses that would have been required to be built "radon-safe" under the Swedish guidelines were already below 4 pCi/L using standard construction practices.

The Florida survey was an ideal opportunity to compare soil radon and corresponding indoor radon levels in slab-on-grade construction. By looking exclusively at slab-on-grade houses, additional variables, including depth below grade of basements, and height and ventilation rates of crawlspaces, are eliminated. These variables, which are inherent in common construction techniques used throughout much of the rest of the country, exaggerate the difficulty in correlating indoor air radon and soil radon levels.

The major drawback to using the Florida study to support the correlation between indoor and soil measurements was that the indoor measurements were obtained from 3-day closed-house charcoal measurements, and soil radon was obtained from 1-month alpha track measurements buried 1 ft beneath the soil surface. Comparisons of charcoal and alpha track data are generally not recommended since they are quite different measurement techniques, and represent radon levels over different time periods. However, the study was subjected to numerous quality control checks including deployment of alpha track detectors in 10% of the houses to obtain a check on indoor air measurements made by charcoal canisters. In spite of the measurement drawbacks, the study indicates that soil radon measurements taken alone are not a dependable predictor of potential indoor radon concentration.

TABLE 31.5

Geometric Means for Soil Gas Radon-222, Soil Radium-226, Permeability, RIN, and Indoor Radon-222

TABLE 31.5

Geometric Means for Soil Gas Radon-222, Soil Radium-226, Permeability, RIN, and Indoor Radon-222

Soil Gas

Basement

Rn-222

Soil Ra-226

Permeability

Rn-222

Study Area (Soil Type)

(pCi/L)

(pCi/g)

(cm2 x 10-6)

RINa

(pCi/L)

Cortland Co. (Gravel)

551

NA

12.0

19.0

17.2

Albany Co. (Gravel)

675

1.0

6.7

18.0

20.2

Rensselaer Co. (Gravel)

1003

1.0

1.1

11.0

9.4

State Wide (Gravel)

602

1.2

4.1

12.0

NA

Long Island (Sand)

164

0.4

0.22

0.8

1.0

Onondaga Co.

1671

2.8

0.12

9.0

6.1

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical

Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991. a RIN = 10[soil gas radon (pCi/L)] (permeability) 0.5.

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical

Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991. a RIN = 10[soil gas radon (pCi/L)] (permeability) 0.5.

31.5.1.2 I ndexes Using Permeability and Soil Radon Concentrations

By making an index from the product of soil radon concentrations and soil permeabilities, a better assessment can be made of the risk of a problem on a given site. A radon index number (RIN) has been applied to three areas in New York State that have sandy, gravelly soils, and it predicted with some confidence the geometric mean of indoor radon concentrations using the geometric mean of the soil radon concentrations and the geometric mean of the square root of the soil permeability.41 The results of this effort are summarized in Table 31.5. This research also points out the barriers to applying this technique more widely without a substantial amount of additional work. First, the index must be modified by a depth factor when the soil depth to an impermeable layer (water table, some bedrock, and clay) is less than 10 ft. Second, the soil radon concentrations in all three areas were typical of most soils in New York State only. They ranged from slightly below to slightly above the statewide average for radon levels in gravel.

Using the permeability and soil radon measurements for the gravel soils in New York State to compare with the Swedish guidelines would result in a recommendation for radon-resistant techniques to be used in a large fraction of new houses in all the areas listed, except Long Island.

In U.S. EPA Office of Radiation Program's New House Evaluation Program (NEWHEP), two builders in the Denver area, two in Colorado Springs, and one in Southfield, Michigan, installed various radon-resistant features in houses during construction. A sampling of subsequent measurements of indoor radon, adjacent soil gas radon, and soil radium content is summarized in Table 31.6.36

The major difference between these data and the Florida survey data in Table 31.3 is that this portion of the NEWHEP data was collected from newly constructed houses where passive radon-resistant construction features were being tested. There are no data on control houses in the same area that did not have those built-in features, making it difficult to compare soil radon measurements with indoor radon concentrations. It appears, however, that passive-only building techniques do not consistently result in indoor radon levels below 4 pCi/L.

31.5.1.3 Variations in Spatial and Temporal Soil Gas Concentrations

Aside from the difficulty in correlating soil radon measurements with indoor radon measurements, various field studies have also shown that obtaining a representative soil gas measurement is difficult. Soil gas radon measurements were made with a permeameter in seven central Florida houses.42

TABLE 31.6

Indoor Radon and Soil Radon Measurements in Colorado and Michigan

TABLE 31.6

Indoor Radon and Soil Radon Measurements in Colorado and Michigan

Indoor Radon in

Basement

Soil Gas Radon

Radium-226 in S

House No.

(pCi/L)

(pCi/L)

(pCi/g)

HECO 7300

5.9

-

1.3 (90 cm)

HECO 7395

14.5

-

1.3 (surface)

HECO 7395

16.7

-

1.9 (90 cm)

HECO 7419

5.7

710

-

HECO 7423

7.9

1002

1.3 (90 cm)

HECO 7423

-

1779

1.4 (90 cm)

HECO 7425

1.5

620

1.3 (surface)

HECO 7425

-

-

0.7 (90 cm)

HECO 7427

3.0

1430

1.1 (surface)

HECO 7427

-

1316

1.4 (90 cm)

HECO 7448

11.8

930-

HECO 7455

0.7

1240

0.4 (surface)

HECO 7456

2.3

996

0.6 (90 cm)

HECO 7458

7.2

2030

-

HECO 7458

3.5

388

-

HECO 7459

0.9

1095

1.0 (surface)

HECO 7459

-

1014

1.9 (30 cm)

HEMI 30001

1.8

-

*

HEMI 30002

0.9

-

*

HEMI 30003

4.2

-

*

HEMI 30004

1.7

-

*

HEMI 30005

3.6

-

*

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.

Source: Adapted from U.S. EPA, Radon-Resistant Construction Techniques for New Residential Construction—Technical Guidance, EPA/625/2-91/032, U.S. Environmental Protection Agency, Washington, DC, February 1991.

A permeameter is a soil gas and permeability measurement device that allows soil gas to be sampled at various depths. In this study, the radon concentration was the average of samples collected at depths of 60, 90, and 120 cm. Four to six samples were collected from the yard of each house at distances of 0.5-4.5 m from the house foundation. Soil radon concentration measurements in each of the seven yards varied by factors of 1.3-6.4, with an average variation of 3.1. In another study in the Piedmont area of New Jersey,46 soil radon was measured in the front, side, and backyards of seven houses. Grab samples and 3-month alpha track samples were obtained from a depth of about 1 m. The grab sample radon measurements varied by a factor of 50 between houses and by as much as a factor of 46 between test sites at a single house. The average variation for each of the seven houses was 12.9. The alpha track results showed seasonal variations of approximately an order of magnitude difference between fall and winter/spring soil gas levels. The soil alpha track results did not compare in general with the results obtained by grab sampling. For example, a factor of 30 increase in radon from the front to backyard was observed in one house by grab sample data, while alpha tracks taken in the front and backyards were similar. In a second house, the opposite was observed: grab samples collected in the front and backyards varied by less than a factor of two, while alpha track measurements in the same yards varied by a factor of 14.46 In another seven-home study in the Piedmont area,11 a large variability in permeability measurements and soil gas radon concentrations was seen. Spatial variation in soil permeability at individual homes ranges from a factor of 10-10,000. Temporal variations in soil permeability at a given test hole ranged from a factor of 2 to a factor of 90. Spatial variations in soil gas radon ranged from less than a factor of 2 to a factor of 200 in a given site. Temporal variations in soil gas radon ranged from less than a factor of 3 to a factor of 40 for a given test hole.

As indicated from the data, indoor radon concentrations cannot yet be predicted from soil radon values. The possibilities are not promising for designing a device and/or technique that builders can rely on to exclude building sites as potential indoor radon problems. As shown by the Florida and New Jersey data, multiple measurements would be required at each building site, and even those measurements can vary by orders of magnitude. Until the lot has been cleared, rough grading completed, and the foundation hole dug, access to the soil that actually produces the radon gas in the house is difficult, if not impossible. Few builders would decide not to build on a lot after they have incurred the costs of purchasing the lot and digging the foundation. In addition, many houses use fill dirt brought in from other locations. Unless the fill dirt is also characterized, additional radon potential may be missed or, on the other hand, the actual potential for radon entry may be overstated.

In summary, at present, individual building lots cannot be characterized reliably for radon potential, and because of the inherent problems that have been identified, builders should not expect to be able to make these measurements or pay someone else to make them reliable. Work to enhance the accurate prediction of radon-prone areas is continuing within U.S. EPA and among other research organizations.

31.5.2 Radon Observed in Nearby Buildings

Another approach for estimating the risk of a radon prob1em on a particular site is to examine measurements from nearby existing buildings. In U.S. EPA's Radon Reduction Demonstration Program for existing buildings, those with elevated radon levels generally have been identified through prior high-radon measurements in other buildings in the neighborhood. Although it is possible to have isolated pockets of radon gas in the soil beneath a single building, most radon-prone buildings are located in a geological setting common to most other buildings in the general vicinity or region. Because of the many variables that affect radon entry into a building, buildings with elevated radon can be found adjacent to buildings with very little radon. However, statistically, the presence of an elevated radon building in a neighborhood or a significant number of elevated buildings in an area as large as a county increases the likelihood of other elevated-radon buildings in the same area.

A classic example of one elevated radon building leading to the discovery of other elevated-radon buildings in the area occurred in Clinton, New Jersey. A property owner in the Clinton Knolls subdivision read about the radon problem in the Reading Prong area of Pennsylvania and decided to obtain a charcoal canister and measure the radon level in his own house. When he received a very high radon reading, he notified the New Jersey Department of Environmental Protection (NJ DEP). The NJ DEP surveyed the neighborhood, making charcoal canisters available to property owners who were willing to have the radon level checked in their buildings. A survey showed that 101 of 103 properties tested had radon levels above the U.S. EPA action level and over half of the properties had more than 25 times the action level.47

The Clinton experience can be contrasted with radon observations in Boyertown, Pennsylvania, where buildings with radon concentrations over 500 times the U.S. EPA action level were found adjacent to buildings below the action level.48 Therefore, the presence of elevated-radon buildings in a neighborhood is at best only an indication that the probability of having a radon problem has increased.

31.5.3 Airborne Measurements

The State of New Jersey has been able to correlate airborne radiation measurements to clusters of buildings with elevated indoor radon.49 In this study, researchers compared airborne y-ray spectrometer data with indoor radon data to see if any trends emerged. For the conditions in New Jersey, it was found that areas with airborne anomalies of 6 mg/L equivalent uranium or greater were likely to have clusters of homes with elevated radon. This could be a valuable tool for health officials who are trying to make the greatest public health impact for the most reasonable cost. Inasmuch as it alerts a region to be wary, it is helpful, but it is probably not of much benefit in the assessment of an individual site.

31.5.4 Radon in Water

Between 2% and 5% of the radon problems found in the United States can be attributed to radon in water.50 The most significant radon-in-water problems observed so far in the United States have occurred in the New England states. Houses with individual or community wells seem to have the greatest potential for a problem since the water in those systems is usually not well aerated.

Radon dissolves into groundwater from rocks or soils. When the water is exposed to the atmosphere, some of the dissolved radon is released. As a rule of thumb, there is an increase of about 1 pCi/L in the air inside a house for every 10,000 pCi/L of radon in the household water.50 Higher radon levels have been observed in individual rooms when water is heated or agitated, such as during shower use.51 Builders should be aware that houses require groundwater as the house water supply could have a radon problem. The only way to be certain that the groundwater is not a potential radon source is to have the water from the well tested. Some states and private companies provide test kits for this purpose. It should also be noted that radon concentrations in water, like radon concentrations in the air, can vary significantly.

If a well has not been drilled, a nearby well may be an indicator of potential radon problems. Identifying potential radon-in-water problems by using the results from adjacent wells is subject to the same problems that were mentioned earlier. There is no guarantee that the neighbor's well is producing water with the same characteristics as the new well will produce since it may not be from the same stratum. The limited data available on houses with radon-in-water problems indicate that adjacent houses with similar wells sometimes produce similar radon-in-water problems and sometimes do not. However, few isolated radon-in-water problem houses have been observed.

In summary, because of the small percentage of houses with radon-in-water problems, few builders will have to deal with this issue. However, if a house is being built in an area known to have many houses with radon-in-water problems, drilling the well and testing the water supply prior to construction are advised. If a house is built prior to identifying a radon-in-water problem, resolving the problem can be more difficult since space will not have been allowed for the radon-in-water mitigation techniques available.

31.5.5 Radon in Building Materials

A small percentage of the buildings in the United States with indoor radon concentrations in excess of 4 pCi/L can be attributed to building materials. Most of the building material problems have arisen from the use of known radium- or uranium-rich wastes such as aggregate in block or as backfill around houses. None of the houses studied in the U.S. EPA Radon Reduction Demonstration program have had any identifiable problem associated with radon from building materials.

Builders should be aware that this is a potential problem but, unless building materials have been identified as radium- or uranium-rich, the chances of obtaining radon from building materials are very slim.

31.6 PLANNED VENTILATION: MECHANICAL SYSTEMS

New construction offers the opportunity to plan and install mechanical equipment so that fresh outdoor air is supplied to the living space and the air pressure relationships between the inside of the building and the outside reduce the influx of soil gas. This approach requires a better understanding of moisture and airflow building dynamics than the others covered in this chapter. For example, it is important to understand what effect manipulating interzonal air pressure differences will have on the risk of condensation in the building shell, the entry rate of soil gas, the comfort of the occupants or the risk of increased spillage, and downdrafting of combustion devices. By careful planning, the risk of these and other potential problems can be reduced; however, no systematic research has been carried out to evaluate this approach for radon control. Many variables come into play in trying to design a mechanical system and a building shell that interact with the environment in the ways that are best for the health of the occupant and the building itself.

31.6.1 I nterdependence of Mechanical Systems and Climate

Traditionally, residential mechanical equipment has been treated as independent devices that have little or no impact on the rest of the building other than the obvious stated purpose. Bath fans, dryers, and kitchen ranges are assumed to exhaust moisture, lint, and cooking by-products, but to have no impact on the performance of chimneys. Instances have been reported that show that this is not the case in some houses where the fireplaces and other combustion appliances backdraft52 when one or more of the exhaust fans are in operation. Houses have been reported in which the operation of exhaust devices increases the radon concentration.53 Houses have been found in which pressure differences between different rooms of the house caused by HVAC distribution fans have increased energy costs,54 occupant discomfort,54,55 condensation of the building shell,55 and radon concentrations in parts of the houses.29,56 All of these effects are the result of air pressure relationships created by the interaction of equipment, indoor/outdoor temperature differences, wind velocity, and moisture and radon availability.

To a large extent, wind, temperature, moisture, and radon are beyond the control of the residential designer or builder. True, good drainage practice and the techniques outlined earlier in this chapter can divert moisture and radon from a building, but the amount of rainfall or radon produced is independent of

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