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14TH CANAD IAN CONFERENCE ON BU I LD ING S C I ENCE AND T E CHNOLOGY

RADON - SOIL GAS INFULTRATION CONTROL: A COMPREHENSIVE

REVIEW OF RADON RESISTANT CONSTRUCTION, MITIGATION

REQUIREMENTS AND OPTIONS IN ONTARIO

B. Decker and B. Wood

ABSTRACT

Radiation exposure from radon impacts the health of all types of building occupants across the country and

is the largest contributor to an individual’s annual radiation exposure (Canadian Nuclear Safety Commission,

2012). Contrary to previous conventional thinking, its distribution is not isolated to “designated” geographic

areas, and all buildings will be affected to some degree. Evidence shows typical building methods do not

adequately control its ingress and that additional measures to mitigate its infiltration are warranted. There

are many challenges and potential short comings with the minimum building code requirements that could

result in elevated radon in buildings. More importantly, the designers, constructors, authorities, building

owners and occupants may assume that because a prescriptive code requirement was met, the occupants are

safe. This paper explores the pitfalls within current construction codes and methods and emphasizes where

passive design and diligent quality control can mitigate the impacts of radon ingress and reduce the

requirement for active (energy consuming) control systems. In our goal to build green by conserving energy,

we must ensure that our efforts do not increase the burden of illness by drawing radon in through earth tube

systems or increasing air tightness without purpose built ventilation. In situations where active mitigation

systems must be implemented to adequately control radon levels, extensive energy savings can be realized

by favouring sub-slab depressurization (SSD) methods to general dilution ventilation. In large scale

buildings, dynamic monitoring and ventilation systems can control radon and further reduce energy

expenditure requirements of SSD by up to 94%.

INTRODUCTION

In a focused national radon program, Health Canada is addressing the serious cancer risks associated with

radon exposure. “Recent efforts to investigate the direct association between indoor radon and lung cancer

have provided convincing evidence of increased lung cancer risk at levels commonly found in buildings.

Radon is now recognized as the second most important cause of lung cancer, after smoking, in the general

population” (Canadian Nuclear Safety Commission, 2012).

A radioactive, colourless and odourless gas, radon (and its radioactive progeny, polonium, bismuth and lead)

is the by-product of the radioactive decay of uranium which is distributed worldwide in rock and soil. Once

uranium decays to radon gas it is mobilized by pressure and concentration gradients and moves through

rock and soil pore spaces. Stack effect draws radon into buildings where it can accumulate and expose

occupants to elevated levels. In March 2012, Health Canada completed a random, cross-Canada survey of

radon concentrations in nearly 14,000 homes. “The results from this two-year study concluded that 6.9% of

Canadians are living in homes with radon levels above the current radon “actionable level” of 200 Becquerels

per cubic metre of air (Bq/m3)” (Canadian Nuclear Safety Commission, 2012). Subsequent efforts including,

risk communication strategies, public education and changes to building codes have been implemented to

protect Canadians from radon exposure.

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Sections and supplemental standards of the National Building Code (NBC) and Ontario Building Code

(OBC), primarily in residential construction, prescribe radon resistant construction measures. These measures

have become more stringent and less geographically localized. It is a common misconception that high risk

radon areas are limited to a few areas in the province. There is also an entrenched belief that simply extending

the continuity of the air barrier through the building foundation, as prescribed by the building code, is

sufficient by itself to control radon levels in Ontario. These views are contrary to the findings of Health

Canada and extensive evidence and experience from relevant agencies in the United States and Europe.

Sealing the building foundation against radon intrusion, although not completely effective, will aid in the

reduction of indoor radon concentrations but it is far from an infallible control. “The difficulties that arise

when using barrier techniques are numerous. Failure to seal a single opening may negate the entire effort”

(United States Environmental Protection Agency, 1991). This paper aims to address some of the

misconceptions about radon and its effective control in buildings as well as provide radon control options

available to designers and builders that are innovative, energy efficient and cost effective.

RADON STANDARDS

As with all exposure to cancer causing agents the principle of As Low As Reasonably Achievable (ALARA)

applies to radon. Regardless of the establishment of a maximum acceptable exposure value it is deemed

prudent to reduce exposures as much as practicable. The foundations for the measurement and control of

radon in Canada are embodied by the following documents: Guide for Radon Measurements in ResidentialDwellings (Homes), 2008 Health Canada; Guide for Radon Measurements in Public Buildings (Schools,Hospitals, Care Facilities, Detention Centres), 2008, Health Canada; and Reducing Radon Levels in ExistingHomes: A Canadian Guide for Professional Contractors, 2010, Health Canada.

TARION HOME WARRANTY RADON CLAIMS

Tarion (the agency which administers the Ontario New Home Warranties Plan Act) warrants new home

construction against levels of radon exceeding 200 Bq/m³. The warranty period is for up to seven (7) years

after construction and is covered under, fit for habitation, OBC violations, OBC Health and Safety or Major

Structural Deficiencies for homes that do not comply with sections 9.1.17, 9.13.4.1or 9.13.4. of the OBC.

RADON RISK AREAS – CANADA AND ONTARIO

A common misconception is that problem radon areas in Ontario are limited to the Town of Elliot Lake in

the Territorial District of Algoma, The Township of Faraday in the County of Hastings, and The Township

of Hyman in the District of Sudbury which were historically listed as “designated areas” in OBC documents.

Previously the OBC prescribed that houses in the “designated areas” be designed and constructed to control

the annual average concentration for radon below 250 millibecquerels per litre of air (250 Bq/m³). The 2011

OBC changes reduced this value to 200 Bq/m³ to be consistent with the Health Canada actionable level.

Health Canada’s March 2012 Cross-Canada Survey of Radon Concentrations in Homes Final Reportdetermined the percentage of homes that tested above 200 Bq/m3, grouped by Health Region. For the Health

Regions of Algoma, Hastings and Prince Edward Counties, and Sudbury the percentage of homes that tested

above 200 Bq/m3 were 8.6%, 12.1% and 5.1% respectively. Of the 35 health regions in Ontario, 23 of them

(67%) fall within or exceed the percentages identified in the “designated areas”. Health Canada has also

concluded that there is a high degree of uncertainty about where radon might be an issue. Figures 1 and 2

illustrate the radon potential risks in Canada and Ontario, respectively, into three categories: Zone 1 – High,

Zone 2 – Elevated and Zone 3 – Guarded.


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“The testing of soil is not a reliable indicator to predict indoor concentrations of radon and other soil gases.

It is virtually impossible to demonstrate that soil gas does not constitute a problem before construction is

completed” (Canadian Commission on Building And Fire Codes, 2009). Many other factors including but

not limited to; construction methods, construction quality, basement depth, HVAC, wind pressure, heat

recovery ventilators and occupant activity all have an effect on indoor radon concentrations. It is for these

reasons that testing after occupancy is the only way to determine indoor radon levels.

FIGURE 1: RADON POTENTIAL MAP OF CANADA

(RADON ENVIRONMENTAL MANAGEMENT CORPORATION, 2011).


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BUILDING CODE REQUIREMENTS TO CONTROL RADON

“It is not possible to predict before construction whether or not a new home will have high radon levels.

Fortunately, preventive measures can be taken by the builder during the design and construction process to

reduce the amount of radon that gets into the home and make it easier to install a radon reduction system, if

required” (Health Canada, 2013). For these reasons changes in the NBC and OBC have occurred. The most

significant change “reverses the burden of proof (to demonstrate that radon is not a hazard) and links

additional measures for protection from radon ingress to actual risk established by an authority (Health

Canada) having jurisdiction” (Canadian Commission on Building And Fire Codes, 2009).

The 2010 National Building Code (NBC) includes requirements that address radon control. Parts 5 and 6 of

the code require that engineers and designers consider radon protection in their designs and ensure control

of air leakage and soil gas infiltration to minimize the level of radon entering a home through the foundation.

“Part nine of the code includes consolidating air barrier requirements such as a sealed plastic membrane

(with joints in the barrier lapped not less than 300 mm) under the foundation slab, and requiring that every

building have granular fill under the slab and a rough-in for a future radon reduction system should the need

later arise. Many provinces have adopted or are in the process of adopting these 2010 National Building

Codes” (Health Canada, 2013). Sections 9.25.3.2. & 9.25.3.3 of the OBC state, “where the foundation wall

and floor slab form the air barrier, all joints, intersections and penetrations shall be caulked and a floor-on-

ground shall be sealed around its perimeter to the inner surfaces of adjacent walls using flexible sealant. All

penetrations of a floor-on-ground by pipes or other objects shall be sealed against soil gas leakage. Sump

pit covers must also be sealed to maintain air barrier continuity”. Figures 4 & 5 show the code requirements

slab to foundation sealing, sub-slab barriers and granular placement.

FIGURE2: RADON POTENTIAL MAP OF ONTARIO

(RADON ENVIRONMENTAL MANAGEMENT CORPORATION, 2011)

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What is not illustrated by Figures 3 & 4 are the details required to prepare the seal at the cold joint and the

details ensuring polyethylene sealing at the wall. “Proper preparation of the surface area to be sealed is

extremely important to create an effective and long lasting seal” (Health Canada, 2013). Figures 5 & 6 show

the required preparation to obtain such a seal.

Section 9.16.2.1.(1) of the OBC states “a pipe not less than 100 mm in diameter shall be installed (roughed-

in) vertically through the floor, at or near its centre, such that: (a) its bottom end opens into the granular fill,

and (b) its top end will permit connection to depressurization equipment. The granular material at the rough-

in, shall be not less than 150 mm deep for a radius of not less than 300 mm centred on the pipe. The upper

end of the pipe shall be provided with a removable seal and shall be clearly labeled to indicate that it is

intended only for the removal of soil gas from below the floor-on-ground.” Figures 6a & 6b, illustrate the

rough-in requirements, with the exception of the 150 mm deep 300 mm radius centered on the pipe inlet.

FIGURE 3: DAMPPROOFING AND SOIL

GAS CONTROL AT FOUNDATION WALL/

FLOOR JUNCTIONS WITH SOLID WALLS.

(MMAH Supplementary Standard SB-9, 2012[Figure SB-9A] and OBC APPENDIX A – 2011,FIGURE A-9.25.3.4)

FIGURE 4: DAMPPROOFING AND SOIL GAS

CONTROL AT FOUNDATION WALL/FLOOR

JUNCTIONS WITH BLOCK/HOLLOW WALLS.

(MMAH Supplementary Standard SB-9, 2012, [Figure SB-9B] and OBC FIGURE9.25.3.6 APPENDIX A – 2011.)

FIGURE 5: SEALING FOUNDATION WALL

AND BASEMENT FLOOR JOINT. – Radon –Reduction Guide for Canadians _ Information forCanadians on How to Reduce Exposures to Radon,Health Canada 2013. p. 21

FIGURE 6: SEALING FOUNDATION WALL AND

FLOOR CRACKS. – Radon – Reduction Guide forCanadians _ Information for Canadians on How toReduce Exposures to Radon, Health Canada 2013. p. 23


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Section 3.2 (6) of the 2012 Ontario Ministry of Municipal Affairs and Housing (MMAH) Supplemental

Standard SB-9 under the OBC requires that when a building constructed in accordance with the provisions

for a sub-slab depressurization rough-in is complete, testing shall be conducted according to Health Canada’s

Guide for Radon Measurements in Residential Dwellings (Homes), 2008 to determine the radon

concentration in the building. Therefore, post construction radon testing is required where SB-9 is enforced.

PROVIDING FOR SUBFLOOR DEPRESSURIZATION

The depressurization stack may run indoors or outdoors. However if it is indoors it is advisable to acoustically

insulate the cavity in which the stack runs to control sound and vibration caused by the exhaust fan. Ideally

stacks should be located away from bedrooms and recreational spaces to ensure any noise from system

operation does not impair use of the building.

A passive vent system may prove to be adequate for the control of radon in buildings where the actionable

level is only marginally exceeded. In these cases a straight vertical stack is most desirable as any bend will

impede stack draw. Previous rationale lead designers to install the soil gas draw point rough-in near the

centre of the building to maximize radial pressure field extension. Experience and current mitigation

teachings place emphasis on locating the draw point near an exterior foundation wall. With a clean granular

base below the slab, pressure field extension is often readily achieved across the entire sub-slab regardless

of draw point location. A number of practical benefits can be realized with a draw point located along a

perimeter wall including: less piping, fewer bends, less head loss, a smaller fan, and more piping outdoors

which results in less noise complaints and less risk of radon leakage to the indoors and less refinish cost.

In general the proactive measures designed and built into a building to mitigate radon are very practical

given the most recent state of the science. Furthermore the prescribed “measures are low in cost, difficult to

retrofit, and desirable for other benefits they provide. The principal method of resisting the ingress of all

soil gases is to seal the interface between the soil and the occupied space, so far as is reasonably practicable.

However, the principal method of excluding radon is to ensure that the pressure difference across the

ground/space interface is positive (i.e., towards the outside) so that the inward flow of radon through any

remaining leaks will be minimized” (Ontario Ministry of Municipal Affairs and Housing, 2011a). This can

only be achieved by decoupling the sub-slab space from the building.

FIGURE 6a FIGURE 6b

SUB-SLAB DEPRESSUIZATION ROUGH-IN. – Radon – Reduction Guide for Canadians _ Information forCanadians on How to Reduce Exposures to Radon, Health Canada 2013. p. 29


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CHALLENGES AND LIMITATIONS OF FOUNDATION SEALING

A designer may very well design the perfect continuous air barrier; whether it can be built is another thing

entirely. Sealing “actions can help reduce the amount of radon that enters a home but do not guarantee that

annual average radon levels will be below 200 Bq/m3. Sealing off openings in a home where radon could

be entering may help to lower radon levels in the home. However, because it is difficult to identify access

and permanently seal all openings it is not a standalone technique for reducing radon levels” (Health Canada,2013).

There are several issues to consider with the prescribed code changes. It is highly unlikely that a 0.15 mm

polyethylene barrier will remain intact and un-perforated during its installation or the pouring of the concrete.

It is doubtful that conventional construction methods and diligence will result in the perfect sealing of all

foundation penetrations. There are several major hurdles with obtaining a perfect radon gas barrier. The

consequences of even the smallest failure can result in unacceptable radon levels. “The major limit on the

radon concentration in buildings is the resistance of the soil to air movement. To illustrate, if a house with

exposed soil in the basement (so there is no foundation resistance to soil gas entry) has an average radon

concentration of 400 Bq/m3, then the average radon supply rate is about 80,000 Bq per hour. (The natural

ventilation rate of a typical 2-storey house averages about 200 m3/h, so on average; radon supply = radon

loss by ventilation = 200 m3/h x 400 Bq/m3 = 80,000 Bq/h) This amount of radon is contained in

approximately 1 m3 of soil gas. A pressure differential of 10 Pascal (Pa) (comparable to the wintertime

inside-outside pressure differential) gives a flow rate of 1 m3/h through a 1 cm2 opening. Clearly, if soil gas

is to be excluded by using passive barriers and closing entry routes, the resistance of the foundation to gas

flow must be greater than that of the soil. This implies total openings in the foundation (floor and walls)

through to the soil must be less than 1 cm2 in area. Conventional building construction leads to much larger

foundation openings. To illustrate, in a house with poured concrete basement walls, there is a shrinkage gap

where the floor meets the wall, which totals about ~100 cm2. The gaps around the sanitary and water pipes

and house supports can add up to ~100 cm2 and penetrating shrinkage cracks in the concrete floor itself can

add another ~ 100 cm2 for a total of ~300 cm2. A ground water control drainpipe into a sump is a ~100 cm2

opening. Failure to seal 1% of just one of these entry points will render the entire effort ineffective. “The

cost of sealing entry routes is highly variable. It can range from a few hundred dollars to $2,000 or more.

Although the material cost is relatively low, it is very labour-intensive to do a comprehensive job. As the

house ages and settles, the seals can deteriorate, and new cracks or entry routes can appear. As a result, there

will be an ongoing cost to maintain the seals” or an increase in indoor radon levels” (Health Canada, 2013).

Another “practical difficulty is ensuring an effective bond between the sealant and the concrete. When the

wall was poured, the surface layer of the concrete mix was in contact with the form, and is composed of

cement paste and the smallest aggregate particles. The thickness of this layer is 3 to 5 mm, depending on

the mix and concrete placement practices. Most concrete mixtures have 1-2% volume of air in the cement

paste as 0.5 to 1 mm diameter bubbles to increase the fluidity, and these bubbles may link to form channels

in the surface layer. Water released while the concrete sets bleeds to the surface, and drains down between

the form and the bulk concrete, producing additional vertical channels in the surface layer. These channels

provide a bypass to any seal that is applied to a vertical concrete surface (foundation wall). Either the 3-5 mm

layer must be removed, to expose solid concrete, or the seal must have a large contact width (a few cm) to

bridge the channels” (Health Canada, 2010). Considering typical construction practice, it is highly unlikely

that the effort will be taken to chip out concrete along seams and cracks and it is equally unlikely that the

sealant applied along the cold joint will be of sufficient width.


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Alternatively, the application of 50 mm (2 inches) closed-cell spray foam over granular as under-slab

insulation will attain a continuous air barrier. The spray foam is very likely to survive the pouring of the

concrete intact and will outperform manual sealing measures increasing the efficacy of the gas barrier. The

addition of under-slab insulation gains considerable energy savings and with spray application, unlike using

rigid insulation sheets, does not require the labour and associated quality issues which accompany taping of

the seams. Adding 50 mm (2 inches) rigid under-slab insulating sheets, taping all seams and implementing

all other radon resistant construction requirements would cost $1900 to $2200 (2014 CDN dollars) for a

100 m2 footprint. The application of 50 mm (2 inches) of spray-foam would cost $2900 to $3200 (2014

CDN dollars). Other proprietary liquid applied sub-slab air barrier systems are available at similar cost.

(ANGELL, WILLIAM J ET AL, 2012) A REVIEW OF RADON CONTROL IN NEW HOMES: A META-ANALYSIS OF

25 YEARS OF RESEARCH

In 2012 (William Angell et al. 2012) prepared a review of radon control and studies in new homes over the

past 25 years. The international experience of this study identified the challenges and short comings of

foundation sealing alone to control indoor radon. Using tracer gas (Brennan, et al. 1990) “found that a very

small amount of below-grade leakage resulted in elevated indoor radon levels.” (Clark, 1993) determined

that “an opening of 65 cm2 (10 square inches) was associated with a radon concentration of 995 Bq/m3 (26.9

pCi/L). They conducted a series of experiments that demonstrated the extreme difficulty of sealing radon

out of a house.” A review of 40 houses was conducted by (Tappan, 1988) “where only sealing techniques

were applied. A year after sealing, 22 of the 40 homes exceeded the project's radon criteria, and thus it was

concluded that sealing was unreliable.” An assessment of 65 new houses (The City of Fort Collins, 2006)

found “improper sealing/caulking of slab penetrations and joints or no sealing or caulking.” It was discovered

by (Tyson et al. 1995) that “houses with unsealed pipe penetrations through the slab had 33 percent higher

indoor radon concentrations. The single factor that appeared to have the most direct relationship with indoor

radon concentrations was the air pressure difference across the slab.” A survey conducted by (Arvela et al.2008) “revealed in a questionnaire sent to 400 dwellings, the sealing recommendation became too tedious

and uncommon (for builders).” A study by (Brenmnet et al. 1988) concluded that “passive barriers may be

impractical with the ordinary amount of quality assurance found in house construction”. The National

Association of Home Builders Research Center (NAHB, 1991) discussed challenges with radon-control

systems in new houses and determined: “a) Complete sealing of the under-slab soil gas barrier is not feasible;

b) Maintaining construction quality control was one of the most deficient aspects of the recommended

construction methods; c) Many caulking and sealing details were overlooked by builders and site supervisors

since most are not sufficiently aware of radon control; and c) Low priority for labourers and tradesmen.

Many of the problems cited in NAHB (1991) were observed in later studies.”

Based on the body of research and experience it is clear that if sealing is to be the primary approach to radon

intrusion control in Ontario and Canada then extreme care in air barrier installation and sealing is required.

Even in circumstances where this may be achieved standalone air barriers as a radon intrusion control

measure appear to fail more often than they succeed.

GREEN BUILDING, ENERGY EFFICIENCY AND RADON

THE EFFECTS OF BUILDING FREEN ON RADON CONCENTRATIONS AND OCCUPANT RISK

In 2014 (Milner, et al. 2014) conducted a modelling study on the effects of air tightening retrofits to

residential dwellings, required by the 2008 Climate Change Act (in the United Kingdom), and the effects

on radon levels and related deaths. The results indicated “Increasing the air tightness of dwellings (without


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compensatory purpose-provided ventilation) increased mean indoor radon concentrations by an estimated

56.6%, from 21.2 to 33.2 Bq/m3” (Milner, et al. 2014). This would result in an additional 278 deaths (in the

UK) annually. Milner concluded that “leaving aside the use of mechanical ventilation and heat recovery,

ventilation related improvements in energy efficiency can be achieved only at the expense of additional

radon related lung cancer burdens unless there is widespread use of remediation. For radon at least, caution

is needed to ensure that the pursuit of energy efficiency does not precipitate an unwelcome increase in

disease burden in the population as a whole” (Milner, et al. 2014).

THE BENEFITS AND RISK WITH EARTH TUBE SYSTEMS AND RADON

Significant care must be taken when using earth tube ventilation systems to ensure radon does not enter the

building. Since earth tube systems take unconditioned outdoor or return air through ducts buried several

meters underground for conditioning and subsequent distribution to the building interior there is a risk of

radon ingress. These systems are also referred to as ground air heat exchange systems (GAHE) or earth air

heat exchange systems (EAHX). To the authors’ knowledge no study has been conducted assessing the

relative leakiness of earth tube systems and the resultant increase in indoor radon levels. One could theorize

that any minor leak in an air tube that would promote radon intrusion would be more than compensated for

by dilution of the sheer volume of fresh air being introduced. Alternatively one could theorize that if a strong

radon source existed and significant deficiencies in an earth tube system existed or developed over time

(due to settlement, material degradation etc.) and the make-up air rate was decreased post construction to

realize greater energy savings that an effective radon collection and dispersal system had been developed.

Until actual data is available and a study is conducted both stances remain purely theoretical.

An air quality assessment of 20 Passivehaus dwellings was conducted in the southern part Belgium, where

elevated indoor radon is a regular occurrence. Passivehaus designs typically have a high air tightness level

with respect to the ground. Approximately “45% of the houses were equipped with a GAHE, known as the

“Canadian well”, although many studies have indicated that in a moderate climate as in Belgium, the energy

saving by such a system is quite negligible.” (Poffijin et al.) One of the houses, which was not located in a

radon-prone area, was the only house in the study to report a radon concentration above 200 Bq/m3 at

approximately 750 Bq/m3. The cause of the high radon was theorized to be related to an installation problem

with the geothermal heating system. “It was clear that the ground-air-heat exchange system requires more

detailed investigation with regards to indoor radon concentrations.” (Poffijin et al.)

In 2011, The Canada Mortgage and Housing (CMHC) conducted a study which evaluated the applicability

of earth tube systems in the Canadian Climate. Of the 27 system designs reviewed there is only one mention

of a potential radon concern from the use of perforated pipe on the exhaust earth tube. “The use of perforated

tubes presents a risk of infiltration by radon gas if for some reason the fan stops” (CMHC, 2011). At the

time of publication, approximately 50 of these systems had been built in Saskatchewan, an area now

confirmed to be in Zone 1 – High Radon Potential where 16.3% of the houses have indoor radon

concentrations above 200 Bq/m3. There is no mention of radon testing in any of the buildings where the

systems were installed.

“An alternative to earth tubes is the use of a brine or glycol loop with a heat exchanger located at the entrance

of the heat recovery unit and that such systems solve some of the risks associated with EAHX systems

(growth of moulds, infiltrations of radon). It is reported that they are as efficient as air-based systems in

heating mode, but less efficient in cooling mode” (CMHC, 2011). The efficacy of these systems combined

with the reduced risk on indoor air contamination from biological and radiological sources suggest that they

may be a better system than the EAHX. So much so that “Canadian and US Passive House Institutes, which


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promote the Passivehaus standard in North America, indicate a move away from EAHX in favour of brine

or glycol based loops” (CMHC, 2011). Considering “one also needs to be conscious of the redundancy with

the HRV, and be aware that the economics (of earth tube systems) are rarely favourable” (CMHC, 2011) it

is surprising they are used at all with the exception of “other non-monetary advantages, such as the possibility

to obtain LEED points” (CMHC, 2011). Since green building is as much about environmental leadership as

it is human health, green buildings should utilize systems that minimize the risk of coupling indoor air with

a radon laden subsurface. Designers should consider giving preference to those systems or more efficient

HRVs since ambient surface air will not be elevated in radon thereby improving occupant safety.

RADON MITIGATION

SUB-SLAB DEPRESSURIZATION

Since sealing radon out of a building is virtually impossible additional mitigation measures are necessary.

Decades of industry experience show the most effective, permanent and economical method for radon

mitigation is an Air Soil Depressurization (ASD) system, the most common of these is Sub-Slab

Depressurization (SSD). SSD in its simplest of forms is a piping system and in-line fan that connects to the

soil gas space to the atmosphere. A slight negative pressure is induced on the soil pores relative to the pressure

above the slab. This provides a preferential flow path for radon and greatly reduces indoor concentrations.

Where certified mitigators are locally available, it will cost between $2500 and $3500 (2014 CND dollars)

to retrofit an ASD in a typical residential dwelling with a 100 m2 footprint. Where a proper rough-in is

provided, a passive system will cost between $750 and $1000 to complete in a newly built home of the same

size. Electricity costs for ASD are between $3 and $5 per month for fan operation with a $400 to $600 fan

replacement every 15 years.

SPACE PRESSURIZATION

Some success has been realized in temperate climates with mechanically pressurizing the building space to

lower the neutral pressure plan or reduce the pressure delta across the foundation, thereby reducing the rate

of radon infiltration. This method may prove favourable in moderate climates but would likely be impractical

in Canada.

MECHANICAL DILUTION VENTILATION

Radon mitigation can be done successfully by increased ventilation of the occupied space. These systems

are attractive to mechanical designers due to their familiarity; however, significant energy penalties may be

realized. Others may alter the system performance to save energy, control comfort or reduce maintenance

requirements. Such alterations will likely occur with no regard to the effect on radon concentrations and

inadvertently defeat the radon mitigation system. More importantly these systems still place the occupant

in the path of the contaminant which is a poor hazard control from a health protection approach. Source

control of a contaminant (particularly a carcinogen) by local ventilation is preferred and more effective at

exposure control. The ASD system is a localized ventilation control system that controls radon at the

beginning of the exposure path rather just before the point of occupant exposure. In many cases the entire

building may not require mitigative measures and several small localized ASD systems may prove more

cost effective and demonstrate better control.

“A heat recovery ventilator (HRV) or energy recovery ventilator (ERV) can increase ventilation, which will

reduce radon levels in a home. The effectiveness of ventilation for radon reduction is limited and only

appropriate for situations where only moderate reductions are needed. In general, increased ventilation


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methods for radon reduction will be most successful in houses that are more airtight and have low natural

ventilation rates. In most houses, an HRV might reduce radon levels by 25 to 50 percent. An HRV will cost

between $1,500 and $3,500 (material and labour). There is also an operating cost for electricity for the HRV's

as well as an increase in heating and cooling costs due to greater ventilation of the home” (Health Canada,

2013.) Therefore, using dilution ventilation as a primary means of radon control may not be effective or

environmentally conscious.

ON-CALL RADON REDUCTION VENTILATION

There are circumstances where SSD may not prove practical, such as buildings where soil pore space

communication and pressure field extension is poor or virtually non-existent. These conditions occur less

often than one would think so it is advisable to consult a certified and experienced mitigation contractor

when considering radon control options. Some European countries are using continuous radon monitoring

coupled with dynamic ventilation controls on existing HVAC systems. This system calls for added ventilation

when radon concentrations reach a set-point. This method may prove favourable in temperate climates but

its practicality in Canada requires some consideration as the greatest demand for increased ventilation will

be in the coldest months.

DYNAMIC CONTROLS ON SUB-SLAB DEPRESSURIZATION SYSTEMS

Very promising results in radon control and energy conservation have been realized in a case study (Hatton,

Nuzzetti et al.) which utilized dynamic motor controls in conjunction with ASD to maintain radon levels at

a set point. Unlike current ASD systems which are designed to operate continually at full capacity, this

system increases ventilation rates only when indoor radon concentrations are above the set-point. The remote

monitoring and control capabilities of this system can be tied to a building automation system, providing

continual proof of system efficacy and can provide early notification to building operators when a system

has failed or is in need of maintenance. The cost and greater degree of sophistication of this system make it

most applicable to industrial, commercial and institutional (ICI) buildings or large multi-unit residential

dwellings as opposed to a single family dwelling. However with ever advancing technology such a system

may eventually become mainstream.

Significant energy savings can be realized with this system. “Previous studies have indicated that one of the

greatest costs associated with operating a soil depressurization system is the loss of conditioned building

air drawn into the subsurface. It has been demonstrated that installing a tightly sealed vapour barrier system

during new construction and optimizing the blower size can save up to $1,000 annually in heating, cooling

and electric costs per 10,000 square feet of floor space (2009 energy costs).” (Hatton et al. 2014) Applying

only the required vacuum to the sub-slab is an optimal way to control indoor radon concentrations, minimize

the loss of conditioned air and maximizing energy conservation.

Hatton et al. (2014) studied the efficacy of this system in a 2,400 square foot slab on grade ICI building in

Blairstown, New Jersey. Pre-mitigation radon levels were 192 to 289 Bq/m3 (5.2 and 7.8 pCi/L) in the

cooling season and 274 to 359 Bq/m3 (7.4 and 9.7 pCi/L) in the heating season. The initial sub-slab vacuum

set-point of -1.2 Pa (-0.0048 inches of water column [“ w.c.]), slightly above the New Jersey minimum

requirement of 1 Pa (-0.004 “w.c.), was maintained to within ±0.25 Pa (0.001 “ w.c.) from January to May

2013. The average daily mitigated radon concentration during the test period was 26 Bq/m3 (0.7 pCi/L).

The radon concentrations remained consistently within a narrow range and were well below the actionable

level of 150 Bq/m3 (4.0 pCi/L). To further assess the efficacy of the system the initial sub-slab vacuum set-

point was increased to -2 Pa (-0.0080 “ w.c.) This had no appreciable effect on the indoor radon


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concentrations however the power consumption increased at an exponential rate while continually diverging

from the increase of total static pressure. “The results show a 94% energy reduction is achievable when

running a system in the summer months at the minimum required sub-slab vacuum level as opposed to the

full static vacuum that was required to generate the same sub-slab pressure field during the initial startup

and winter months” (Hatton et al. 2014). This alteration represented an annual decrease in energy cost from

$337.51 to $19.89 (2013 US dollars).

The dynamic system readily controlled indoor radon concentrations at much lower vacuums than required

by State mitigation standards with much less energy expenditure. The benefits that can be realized from the

energy savings of a system like this are worth serious consideration. With more case study data it may prove

that sub-slab pressure requirements can be reduced even further while still maintaining acceptable indoor

radon concentrations leading to even greater energy savings.

SUMMARY

It is clear that radon is a national problem in Canada and it can no longer be assumed that control of its

ingress is unwarranted. There are many challenges and potential shortcomings with the minimum building

code requirements that could result in elevated radon in buildings. If post-construction testing or ongoing

monitoring for radon is not enforced there is a vast potential for continued overexposure of building

occupants to occur. More importantly the designers, constructors, authorities, building owners and occupants

are potentially under the false belief that since a prescriptive code requirement was met (without post-

construction testing) that the occupants are safe. Since Tarion warranty claims are possible up to seven years

after construction this presents a significant liability to builders. There are several cost effective and energy

efficient means to control radon ingress provided sufficient forethought is put into the design and proper

attention is paid to their installation and operation.

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Health Canada, Guide for Radon Measurements in Residential Dwellings (Homes), 2008 Health Canada;p. 14.Health Canada - Radon – Reduction Guide for Canadians- Information for Canadians on How to ReduceExposures to Radon, 2013. P.20, 24, 27-29Health Canada, Reducing Radon Levels in Existing Homes: A Canadian Guide for ProfessionalContractors, 2010, p 41.Lowe, S. and Pettenato,”Reduction of Indoor Radon by Air Cleaning—Case Study.” J. Environ. Eng.,126(12), 1125–1130. R. (2000). TECHNICAL PAPERShttp://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9372%282000%29126%3A12%281125%29February 9, 2014James Milner, lecturer1, Clive Shrubsole, research associate2, Payel Das, research associate2, BenjaminJones, lecturer23, Ian Ridley, senior research fellow24, Zaid Chalabi, senior lecturer1, Ian Hamilton,lecturer5, Ben Armstrong, professor in epidemiological statistics1, Michael Davies, professor of buildingphysics and the environment2, Paul Wilkinson, professor in environmental epidemiology1, Home energyefficiency and radon related risk of lung cancer: modelling study, January 10, 2014,http://www.bmj.com/content/348/bmj.f7493, February 9, 2014. P. 1, 4 & 5Ontario, 2010, Code and Construction Guide – Soil Gas Control, 2010, Section 2 P. 45-46Ontario Ministry of Municipal Affairs and Housing, Best Practice Guide – Full Height BasementInsulation, 2008, http://www.mah.gov.on.ca/Asset8275.aspx?method=1, p.23, 24.Ontario Ministry of Municipal Affairs and Housing, Ontario’ Building Code – Proposed Change to the2006 Building Code, Change Number R-B-09-13-01 Code Reference, Div. B 9.13.4.1. & 9.13.4.1.,January 2011, p. 2-4.Ontario Ministry of Municipal Affairs and Housing, Ontario Building Code – Proposed Change to the2006 Building Code, Change Number R-B-06-02-01 Code Reference, Div. B 6.2.1.1.(1), January 2011, p.2.Ontario Ministry of Municipal Affairs and Housing, Ontario Building Code – Proposed Change to the2006 Building Code, Change Number R-B-09-32-01 Code Reference, Div. B 9.32.3.8.(3), January 2011,p.1.Ontario Ministry of Municipal Affairs and Housing, Appendix A: Enhancing Radon Protection, February16, 2011, http://www.mah.gov.on.ca/AssetFactory.aspx?did=8787Ontario Ministry of Municipal Affairs and Housing, Potential Changes for the Next Edition of theBuilding Code: Second Round of Consultation, February-April 2011,http://www.mah.gov.on.ca/AssetFactory.aspx?did=9064, p.33, 34Ontario Ministry of Municipal Affairs and Housing, Ontario Building Code – Division B, Part 9 (OntarioRegulation 332/12), 2012Ontario Ministry of Municipal Affairs and Housing (MMAH), MMAH Supplementary Standard SB-9Requirements for Soil Gas Control, 2012, p. 1-3.Ontario Ministry of Municipal Affairs and Housing, Ontario’ Building Code – Proposed Change to the2006 Building Code, Change Number R-B-09-25-01 Code Reference, Div. B 9.25.3 January 2012, p.1-12A Poffijnl, 0. Tone~, B. Dehandschutter\ M. Rogd and C. Bouland, Federal Agency fur Nuclear Contro~ FANC, Brussels, Belgium, Free UniversityofBrussels, ULB, Brussels, Belgium, Hainaut Health Vigilance,HVS, Mons, Belgium, A PILOT STUDY ON THE AIR QUALITY IN PASSIVE HOUSES WITHPARTICULAR ATTENTION TO RADON, p. 107, 109, 110


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Radon Environmental Management Corporation, Radon Potential Map of Canada & Radon PotentialMap of Ontario, 2011.

Thomas E. Hatton, Daniel J. Nuzzetti, Applying Dynamic Controls And Remote Monitoring To RadonMitigation Systems To Advance Energy Conservation And The Stabilization Of Indoor RadonConcentrations,http://www.aarst.org/proceedings/2013/04_APPLYING_DYNAMIC_CONTROLS_AND_REMOTE_MONITORING.pdf, January 28, 2014, p. 32, 40.

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